list-objects: pass full pathname to callbacks
[gitweb.git] / refs.c
diff --git a/refs.c b/refs.c
index e2b760d0baffd6db6b49e6014a58efa062f1a119..305bb54169b41cfb53c2eff260cb6cd80f1810c4 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -1,13 +1,73 @@
 #include "cache.h"
+#include "lockfile.h"
 #include "refs.h"
 #include "object.h"
 #include "tag.h"
 #include "dir.h"
 #include "string-list.h"
 
+struct ref_lock {
+       char *ref_name;
+       char *orig_ref_name;
+       struct lock_file *lk;
+       unsigned char old_sha1[20];
+       int lock_fd;
+};
+
+/*
+ * How to handle various characters in refnames:
+ * 0: An acceptable character for refs
+ * 1: End-of-component
+ * 2: ., look for a preceding . to reject .. in refs
+ * 3: {, look for a preceding @ to reject @{ in refs
+ * 4: A bad character: ASCII control characters, "~", "^", ":" or SP
+ */
+static unsigned char refname_disposition[256] = {
+       1, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+       4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+       4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 2, 1,
+       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 4,
+       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 4, 0, 4, 0,
+       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 4, 4
+};
+
+/*
+ * Flag passed to lock_ref_sha1_basic() telling it to tolerate broken
+ * refs (i.e., because the reference is about to be deleted anyway).
+ */
+#define REF_DELETING   0x02
+
+/*
+ * Used as a flag in ref_update::flags when a loose ref is being
+ * pruned.
+ */
+#define REF_ISPRUNING  0x04
+
+/*
+ * Used as a flag in ref_update::flags when the reference should be
+ * updated to new_sha1.
+ */
+#define REF_HAVE_NEW   0x08
+
+/*
+ * Used as a flag in ref_update::flags when old_sha1 should be
+ * checked.
+ */
+#define REF_HAVE_OLD   0x10
+
+/*
+ * Used as a flag in ref_update::flags when the lockfile needs to be
+ * committed.
+ */
+#define REF_NEEDS_COMMIT 0x20
+
 /*
- * Make sure "ref" is something reasonable to have under ".git/refs/";
- * We do not like it if:
+ * Try to read one refname component from the front of refname.
+ * Return the length of the component found, or -1 if the component is
+ * not legal.  It is legal if it is something reasonable to have under
+ * ".git/refs/"; We do not like it if:
  *
  * - any path component of it begins with ".", or
  * - it has double dots "..", or
  * - it ends with ".lock"
  * - it contains a "\" (backslash)
  */
-
-/* Return true iff ch is not allowed in reference names. */
-static inline int bad_ref_char(int ch)
-{
-       if (((unsigned) ch) <= ' ' || ch == 0x7f ||
-           ch == '~' || ch == '^' || ch == ':' || ch == '\\')
-               return 1;
-       /* 2.13 Pattern Matching Notation */
-       if (ch == '*' || ch == '?' || ch == '[') /* Unsupported */
-               return 1;
-       return 0;
-}
-
-/*
- * Try to read one refname component from the front of refname.  Return
- * the length of the component found, or -1 if the component is not
- * legal.
- */
 static int check_refname_component(const char *refname, int flags)
 {
        const char *cp;
        char last = '\0';
 
        for (cp = refname; ; cp++) {
-               char ch = *cp;
-               if (ch == '\0' || ch == '/')
+               int ch = *cp & 255;
+               unsigned char disp = refname_disposition[ch];
+               switch (disp) {
+               case 1:
+                       goto out;
+               case 2:
+                       if (last == '.')
+                               return -1; /* Refname contains "..". */
                        break;
-               if (bad_ref_char(ch))
-                       return -1; /* Illegal character in refname. */
-               if (last == '.' && ch == '.')
-                       return -1; /* Refname contains "..". */
-               if (last == '@' && ch == '{')
-                       return -1; /* Refname contains "@{". */
+               case 3:
+                       if (last == '@')
+                               return -1; /* Refname contains "@{". */
+                       break;
+               case 4:
+                       return -1;
+               }
                last = ch;
        }
+out:
        if (cp == refname)
                return 0; /* Component has zero length. */
-       if (refname[0] == '.') {
-               if (!(flags & REFNAME_DOT_COMPONENT))
-                       return -1; /* Component starts with '.'. */
-               /*
-                * Even if leading dots are allowed, don't allow "."
-                * as a component (".." is prevented by a rule above).
-                */
-               if (refname[1] == '\0')
-                       return -1; /* Component equals ".". */
-       }
-       if (cp - refname >= 5 && !memcmp(cp - 5, ".lock", 5))
+       if (refname[0] == '.')
+               return -1; /* Component starts with '.'. */
+       if (cp - refname >= LOCK_SUFFIX_LEN &&
+           !memcmp(cp - LOCK_SUFFIX_LEN, LOCK_SUFFIX, LOCK_SUFFIX_LEN))
                return -1; /* Refname ends with ".lock". */
        return cp - refname;
 }
@@ -72,6 +115,10 @@ int check_refname_format(const char *refname, int flags)
 {
        int component_len, component_count = 0;
 
+       if (!strcmp(refname, "@"))
+               /* Refname is a single character '@'. */
+               return -1;
+
        while (1) {
                /* We are at the start of a path component. */
                component_len = check_refname_component(refname, flags);
@@ -109,7 +156,20 @@ struct ref_entry;
  * (ref_entry->flag & REF_DIR) is zero.
  */
 struct ref_value {
+       /*
+        * The name of the object to which this reference resolves
+        * (which may be a tag object).  If REF_ISBROKEN, this is
+        * null.  If REF_ISSYMREF, then this is the name of the object
+        * referred to by the last reference in the symlink chain.
+        */
        unsigned char sha1[20];
+
+       /*
+        * If REF_KNOWS_PEELED, then this field holds the peeled value
+        * of this reference, or null if the reference is known not to
+        * be peelable.  See the documentation for peel_ref() for an
+        * exact definition of "peelable".
+        */
        unsigned char peeled[20];
 };
 
@@ -158,17 +218,27 @@ struct ref_dir {
        struct ref_entry **entries;
 };
 
-/* ISSYMREF=0x01, ISPACKED=0x02, and ISBROKEN=0x04 are public interfaces */
-#define REF_KNOWS_PEELED 0x08
+/*
+ * Bit values for ref_entry::flag.  REF_ISSYMREF=0x01,
+ * REF_ISPACKED=0x02, REF_ISBROKEN=0x04 and REF_BAD_NAME=0x08 are
+ * public values; see refs.h.
+ */
+
+/*
+ * The field ref_entry->u.value.peeled of this value entry contains
+ * the correct peeled value for the reference, which might be
+ * null_sha1 if the reference is not a tag or if it is broken.
+ */
+#define REF_KNOWS_PEELED 0x10
 
 /* ref_entry represents a directory of references */
-#define REF_DIR 0x10
+#define REF_DIR 0x20
 
 /*
  * Entry has not yet been read from disk (used only for REF_DIR
  * entries representing loose references)
  */
-#define REF_INCOMPLETE 0x20
+#define REF_INCOMPLETE 0x40
 
 /*
  * A ref_entry represents either a reference or a "subdirectory" of
@@ -199,7 +269,7 @@ struct ref_dir {
  * presence of an empty subdirectory does not block the creation of a
  * similarly-named reference.  (The fact that reference names with the
  * same leading components can conflict *with each other* is a
- * separate issue that is regulated by is_refname_available().)
+ * separate issue that is regulated by verify_refname_available().)
  *
  * Please note that the name field contains the fully-qualified
  * reference (or subdirectory) name.  Space could be saved by only
@@ -237,6 +307,39 @@ static struct ref_dir *get_ref_dir(struct ref_entry *entry)
        return dir;
 }
 
+/*
+ * Check if a refname is safe.
+ * For refs that start with "refs/" we consider it safe as long they do
+ * not try to resolve to outside of refs/.
+ *
+ * For all other refs we only consider them safe iff they only contain
+ * upper case characters and '_' (like "HEAD" AND "MERGE_HEAD", and not like
+ * "config").
+ */
+static int refname_is_safe(const char *refname)
+{
+       if (starts_with(refname, "refs/")) {
+               char *buf;
+               int result;
+
+               buf = xmalloc(strlen(refname) + 1);
+               /*
+                * Does the refname try to escape refs/?
+                * For example: refs/foo/../bar is safe but refs/foo/../../bar
+                * is not.
+                */
+               result = !normalize_path_copy(buf, refname + strlen("refs/"));
+               free(buf);
+               return result;
+       }
+       while (*refname) {
+               if (!isupper(*refname) && *refname != '_')
+                       return 0;
+               refname++;
+       }
+       return 1;
+}
+
 static struct ref_entry *create_ref_entry(const char *refname,
                                          const unsigned char *sha1, int flag,
                                          int check_name)
@@ -245,8 +348,10 @@ static struct ref_entry *create_ref_entry(const char *refname,
        struct ref_entry *ref;
 
        if (check_name &&
-           check_refname_format(refname, REFNAME_ALLOW_ONELEVEL|REFNAME_DOT_COMPONENT))
+           check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
                die("Reference has invalid format: '%s'", refname);
+       if (!check_name && !refname_is_safe(refname))
+               die("Reference has invalid name: '%s'", refname);
        len = strlen(refname) + 1;
        ref = xmalloc(sizeof(struct ref_entry) + len);
        hashcpy(ref->u.value.sha1, sha1);
@@ -343,18 +448,17 @@ static int ref_entry_cmp_sslice(const void *key_, const void *ent_)
 }
 
 /*
- * Return the entry with the given refname from the ref_dir
- * (non-recursively), sorting dir if necessary.  Return NULL if no
- * such entry is found.  dir must already be complete.
+ * Return the index of the entry with the given refname from the
+ * ref_dir (non-recursively), sorting dir if necessary.  Return -1 if
+ * no such entry is found.  dir must already be complete.
  */
-static struct ref_entry *search_ref_dir(struct ref_dir *dir,
-                                       const char *refname, size_t len)
+static int search_ref_dir(struct ref_dir *dir, const char *refname, size_t len)
 {
        struct ref_entry **r;
        struct string_slice key;
 
        if (refname == NULL || !dir->nr)
-               return NULL;
+               return -1;
 
        sort_ref_dir(dir);
        key.len = len;
@@ -363,9 +467,9 @@ static struct ref_entry *search_ref_dir(struct ref_dir *dir,
                    ref_entry_cmp_sslice);
 
        if (r == NULL)
-               return NULL;
+               return -1;
 
-       return *r;
+       return r - dir->entries;
 }
 
 /*
@@ -379,8 +483,9 @@ static struct ref_dir *search_for_subdir(struct ref_dir *dir,
                                         const char *subdirname, size_t len,
                                         int mkdir)
 {
-       struct ref_entry *entry = search_ref_dir(dir, subdirname, len);
-       if (!entry) {
+       int entry_index = search_ref_dir(dir, subdirname, len);
+       struct ref_entry *entry;
+       if (entry_index == -1) {
                if (!mkdir)
                        return NULL;
                /*
@@ -391,6 +496,8 @@ static struct ref_dir *search_for_subdir(struct ref_dir *dir,
                 */
                entry = create_dir_entry(dir->ref_cache, subdirname, len, 0);
                add_entry_to_dir(dir, entry);
+       } else {
+               entry = dir->entries[entry_index];
        }
        return get_ref_dir(entry);
 }
@@ -429,12 +536,67 @@ static struct ref_dir *find_containing_dir(struct ref_dir *dir,
  */
 static struct ref_entry *find_ref(struct ref_dir *dir, const char *refname)
 {
+       int entry_index;
        struct ref_entry *entry;
        dir = find_containing_dir(dir, refname, 0);
        if (!dir)
                return NULL;
-       entry = search_ref_dir(dir, refname, strlen(refname));
-       return (entry && !(entry->flag & REF_DIR)) ? entry : NULL;
+       entry_index = search_ref_dir(dir, refname, strlen(refname));
+       if (entry_index == -1)
+               return NULL;
+       entry = dir->entries[entry_index];
+       return (entry->flag & REF_DIR) ? NULL : entry;
+}
+
+/*
+ * Remove the entry with the given name from dir, recursing into
+ * subdirectories as necessary.  If refname is the name of a directory
+ * (i.e., ends with '/'), then remove the directory and its contents.
+ * If the removal was successful, return the number of entries
+ * remaining in the directory entry that contained the deleted entry.
+ * If the name was not found, return -1.  Please note that this
+ * function only deletes the entry from the cache; it does not delete
+ * it from the filesystem or ensure that other cache entries (which
+ * might be symbolic references to the removed entry) are updated.
+ * Nor does it remove any containing dir entries that might be made
+ * empty by the removal.  dir must represent the top-level directory
+ * and must already be complete.
+ */
+static int remove_entry(struct ref_dir *dir, const char *refname)
+{
+       int refname_len = strlen(refname);
+       int entry_index;
+       struct ref_entry *entry;
+       int is_dir = refname[refname_len - 1] == '/';
+       if (is_dir) {
+               /*
+                * refname represents a reference directory.  Remove
+                * the trailing slash; otherwise we will get the
+                * directory *representing* refname rather than the
+                * one *containing* it.
+                */
+               char *dirname = xmemdupz(refname, refname_len - 1);
+               dir = find_containing_dir(dir, dirname, 0);
+               free(dirname);
+       } else {
+               dir = find_containing_dir(dir, refname, 0);
+       }
+       if (!dir)
+               return -1;
+       entry_index = search_ref_dir(dir, refname, refname_len);
+       if (entry_index == -1)
+               return -1;
+       entry = dir->entries[entry_index];
+
+       memmove(&dir->entries[entry_index],
+               &dir->entries[entry_index + 1],
+               (dir->nr - entry_index - 1) * sizeof(*dir->entries)
+               );
+       dir->nr--;
+       if (dir->sorted > entry_index)
+               dir->sorted--;
+       free_ref_entry(entry);
+       return dir->nr;
 }
 
 /*
@@ -503,28 +665,69 @@ static void sort_ref_dir(struct ref_dir *dir)
        dir->sorted = dir->nr = i;
 }
 
-#define DO_FOR_EACH_INCLUDE_BROKEN 01
+/* Include broken references in a do_for_each_ref*() iteration: */
+#define DO_FOR_EACH_INCLUDE_BROKEN 0x01
+
+/*
+ * Return true iff the reference described by entry can be resolved to
+ * an object in the database.  Emit a warning if the referred-to
+ * object does not exist.
+ */
+static int ref_resolves_to_object(struct ref_entry *entry)
+{
+       if (entry->flag & REF_ISBROKEN)
+               return 0;
+       if (!has_sha1_file(entry->u.value.sha1)) {
+               error("%s does not point to a valid object!", entry->name);
+               return 0;
+       }
+       return 1;
+}
 
+/*
+ * current_ref is a performance hack: when iterating over references
+ * using the for_each_ref*() functions, current_ref is set to the
+ * current reference's entry before calling the callback function.  If
+ * the callback function calls peel_ref(), then peel_ref() first
+ * checks whether the reference to be peeled is the current reference
+ * (it usually is) and if so, returns that reference's peeled version
+ * if it is available.  This avoids a refname lookup in a common case.
+ */
 static struct ref_entry *current_ref;
 
-static int do_one_ref(const char *base, each_ref_fn fn, int trim,
-                     int flags, void *cb_data, struct ref_entry *entry)
+typedef int each_ref_entry_fn(struct ref_entry *entry, void *cb_data);
+
+struct ref_entry_cb {
+       const char *base;
+       int trim;
+       int flags;
+       each_ref_fn *fn;
+       void *cb_data;
+};
+
+/*
+ * Handle one reference in a do_for_each_ref*()-style iteration,
+ * calling an each_ref_fn for each entry.
+ */
+static int do_one_ref(struct ref_entry *entry, void *cb_data)
 {
+       struct ref_entry_cb *data = cb_data;
+       struct ref_entry *old_current_ref;
        int retval;
-       if (prefixcmp(entry->name, base))
+
+       if (!starts_with(entry->name, data->base))
                return 0;
 
-       if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN)) {
-               if (entry->flag & REF_ISBROKEN)
-                       return 0; /* ignore broken refs e.g. dangling symref */
-               if (!has_sha1_file(entry->u.value.sha1)) {
-                       error("%s does not point to a valid object!", entry->name);
-                       return 0;
-               }
-       }
+       if (!(data->flags & DO_FOR_EACH_INCLUDE_BROKEN) &&
+             !ref_resolves_to_object(entry))
+               return 0;
+
+       /* Store the old value, in case this is a recursive call: */
+       old_current_ref = current_ref;
        current_ref = entry;
-       retval = fn(entry->name + trim, entry->u.value.sha1, entry->flag, cb_data);
-       current_ref = NULL;
+       retval = data->fn(entry->name + data->trim, entry->u.value.sha1,
+                         entry->flag, data->cb_data);
+       current_ref = old_current_ref;
        return retval;
 }
 
@@ -532,11 +735,11 @@ static int do_one_ref(const char *base, each_ref_fn fn, int trim,
  * Call fn for each reference in dir that has index in the range
  * offset <= index < dir->nr.  Recurse into subdirectories that are in
  * that index range, sorting them before iterating.  This function
- * does not sort dir itself; it should be sorted beforehand.
+ * does not sort dir itself; it should be sorted beforehand.  fn is
+ * called for all references, including broken ones.
  */
-static int do_for_each_ref_in_dir(struct ref_dir *dir, int offset,
-                                 const char *base,
-                                 each_ref_fn fn, int trim, int flags, void *cb_data)
+static int do_for_each_entry_in_dir(struct ref_dir *dir, int offset,
+                                   each_ref_entry_fn fn, void *cb_data)
 {
        int i;
        assert(dir->sorted == dir->nr);
@@ -546,10 +749,9 @@ static int do_for_each_ref_in_dir(struct ref_dir *dir, int offset,
                if (entry->flag & REF_DIR) {
                        struct ref_dir *subdir = get_ref_dir(entry);
                        sort_ref_dir(subdir);
-                       retval = do_for_each_ref_in_dir(subdir, 0,
-                                                       base, fn, trim, flags, cb_data);
+                       retval = do_for_each_entry_in_dir(subdir, 0, fn, cb_data);
                } else {
-                       retval = do_one_ref(base, fn, trim, flags, cb_data, entry);
+                       retval = fn(entry, cb_data);
                }
                if (retval)
                        return retval;
@@ -562,12 +764,12 @@ static int do_for_each_ref_in_dir(struct ref_dir *dir, int offset,
  * by refname.  Recurse into subdirectories.  If a value entry appears
  * in both dir1 and dir2, then only process the version that is in
  * dir2.  The input dirs must already be sorted, but subdirs will be
- * sorted as needed.
+ * sorted as needed.  fn is called for all references, including
+ * broken ones.
  */
-static int do_for_each_ref_in_dirs(struct ref_dir *dir1,
-                                  struct ref_dir *dir2,
-                                  const char *base, each_ref_fn fn, int trim,
-                                  int flags, void *cb_data)
+static int do_for_each_entry_in_dirs(struct ref_dir *dir1,
+                                    struct ref_dir *dir2,
+                                    each_ref_entry_fn fn, void *cb_data)
 {
        int retval;
        int i1 = 0, i2 = 0;
@@ -578,12 +780,10 @@ static int do_for_each_ref_in_dirs(struct ref_dir *dir1,
                struct ref_entry *e1, *e2;
                int cmp;
                if (i1 == dir1->nr) {
-                       return do_for_each_ref_in_dir(dir2, i2,
-                                                     base, fn, trim, flags, cb_data);
+                       return do_for_each_entry_in_dir(dir2, i2, fn, cb_data);
                }
                if (i2 == dir2->nr) {
-                       return do_for_each_ref_in_dir(dir1, i1,
-                                                     base, fn, trim, flags, cb_data);
+                       return do_for_each_entry_in_dir(dir1, i1, fn, cb_data);
                }
                e1 = dir1->entries[i1];
                e2 = dir2->entries[i2];
@@ -595,14 +795,13 @@ static int do_for_each_ref_in_dirs(struct ref_dir *dir1,
                                struct ref_dir *subdir2 = get_ref_dir(e2);
                                sort_ref_dir(subdir1);
                                sort_ref_dir(subdir2);
-                               retval = do_for_each_ref_in_dirs(
-                                               subdir1, subdir2,
-                                               base, fn, trim, flags, cb_data);
+                               retval = do_for_each_entry_in_dirs(
+                                               subdir1, subdir2, fn, cb_data);
                                i1++;
                                i2++;
                        } else if (!(e1->flag & REF_DIR) && !(e2->flag & REF_DIR)) {
                                /* Both are references; ignore the one from dir1. */
-                               retval = do_one_ref(base, fn, trim, flags, cb_data, e2);
+                               retval = fn(e2, cb_data);
                                i1++;
                                i2++;
                        } else {
@@ -621,85 +820,234 @@ static int do_for_each_ref_in_dirs(struct ref_dir *dir1,
                        if (e->flag & REF_DIR) {
                                struct ref_dir *subdir = get_ref_dir(e);
                                sort_ref_dir(subdir);
-                               retval = do_for_each_ref_in_dir(
-                                               subdir, 0,
-                                               base, fn, trim, flags, cb_data);
+                               retval = do_for_each_entry_in_dir(
+                                               subdir, 0, fn, cb_data);
                        } else {
-                               retval = do_one_ref(base, fn, trim, flags, cb_data, e);
+                               retval = fn(e, cb_data);
                        }
                }
                if (retval)
                        return retval;
        }
-       if (i1 < dir1->nr)
-               return do_for_each_ref_in_dir(dir1, i1,
-                                             base, fn, trim, flags, cb_data);
-       if (i2 < dir2->nr)
-               return do_for_each_ref_in_dir(dir2, i2,
-                                             base, fn, trim, flags, cb_data);
-       return 0;
 }
 
 /*
- * Return true iff refname1 and refname2 conflict with each other.
- * Two reference names conflict if one of them exactly matches the
- * leading components of the other; e.g., "foo/bar" conflicts with
- * both "foo" and with "foo/bar/baz" but not with "foo/bar" or
- * "foo/barbados".
+ * Load all of the refs from the dir into our in-memory cache. The hard work
+ * of loading loose refs is done by get_ref_dir(), so we just need to recurse
+ * through all of the sub-directories. We do not even need to care about
+ * sorting, as traversal order does not matter to us.
  */
-static int names_conflict(const char *refname1, const char *refname2)
+static void prime_ref_dir(struct ref_dir *dir)
 {
-       for (; *refname1 && *refname1 == *refname2; refname1++, refname2++)
-               ;
-       return (*refname1 == '\0' && *refname2 == '/')
-               || (*refname1 == '/' && *refname2 == '\0');
+       int i;
+       for (i = 0; i < dir->nr; i++) {
+               struct ref_entry *entry = dir->entries[i];
+               if (entry->flag & REF_DIR)
+                       prime_ref_dir(get_ref_dir(entry));
+       }
 }
 
-struct name_conflict_cb {
-       const char *refname;
-       const char *oldrefname;
+struct nonmatching_ref_data {
+       const struct string_list *skip;
        const char *conflicting_refname;
 };
 
-static int name_conflict_fn(const char *existingrefname, const unsigned char *sha1,
-                           int flags, void *cb_data)
+static int nonmatching_ref_fn(struct ref_entry *entry, void *vdata)
 {
-       struct name_conflict_cb *data = (struct name_conflict_cb *)cb_data;
-       if (data->oldrefname && !strcmp(data->oldrefname, existingrefname))
+       struct nonmatching_ref_data *data = vdata;
+
+       if (data->skip && string_list_has_string(data->skip, entry->name))
                return 0;
-       if (names_conflict(data->refname, existingrefname)) {
-               data->conflicting_refname = existingrefname;
-               return 1;
-       }
-       return 0;
+
+       data->conflicting_refname = entry->name;
+       return 1;
 }
 
 /*
- * Return true iff a reference named refname could be created without
- * conflicting with the name of an existing reference in array.  If
- * oldrefname is non-NULL, ignore potential conflicts with oldrefname
- * (e.g., because oldrefname is scheduled for deletion in the same
- * operation).
+ * Return 0 if a reference named refname could be created without
+ * conflicting with the name of an existing reference in dir.
+ * Otherwise, return a negative value and write an explanation to err.
+ * If extras is non-NULL, it is a list of additional refnames with
+ * which refname is not allowed to conflict. If skip is non-NULL,
+ * ignore potential conflicts with refs in skip (e.g., because they
+ * are scheduled for deletion in the same operation). Behavior is
+ * undefined if the same name is listed in both extras and skip.
+ *
+ * Two reference names conflict if one of them exactly matches the
+ * leading components of the other; e.g., "refs/foo/bar" conflicts
+ * with both "refs/foo" and with "refs/foo/bar/baz" but not with
+ * "refs/foo/bar" or "refs/foo/barbados".
+ *
+ * extras and skip must be sorted.
  */
-static int is_refname_available(const char *refname, const char *oldrefname,
-                               struct ref_dir *dir)
+static int verify_refname_available(const char *refname,
+                                   const struct string_list *extras,
+                                   const struct string_list *skip,
+                                   struct ref_dir *dir,
+                                   struct strbuf *err)
 {
-       struct name_conflict_cb data;
-       data.refname = refname;
-       data.oldrefname = oldrefname;
-       data.conflicting_refname = NULL;
+       const char *slash;
+       int pos;
+       struct strbuf dirname = STRBUF_INIT;
+       int ret = -1;
 
-       sort_ref_dir(dir);
-       if (do_for_each_ref_in_dir(dir, 0, "", name_conflict_fn,
-                                  0, DO_FOR_EACH_INCLUDE_BROKEN,
-                                  &data)) {
-               error("'%s' exists; cannot create '%s'",
-                     data.conflicting_refname, refname);
-               return 0;
+       /*
+        * For the sake of comments in this function, suppose that
+        * refname is "refs/foo/bar".
+        */
+
+       assert(err);
+
+       strbuf_grow(&dirname, strlen(refname) + 1);
+       for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
+               /* Expand dirname to the new prefix, not including the trailing slash: */
+               strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);
+
+               /*
+                * We are still at a leading dir of the refname (e.g.,
+                * "refs/foo"; if there is a reference with that name,
+                * it is a conflict, *unless* it is in skip.
+                */
+               if (dir) {
+                       pos = search_ref_dir(dir, dirname.buf, dirname.len);
+                       if (pos >= 0 &&
+                           (!skip || !string_list_has_string(skip, dirname.buf))) {
+                               /*
+                                * We found a reference whose name is
+                                * a proper prefix of refname; e.g.,
+                                * "refs/foo", and is not in skip.
+                                */
+                               strbuf_addf(err, "'%s' exists; cannot create '%s'",
+                                           dirname.buf, refname);
+                               goto cleanup;
+                       }
+               }
+
+               if (extras && string_list_has_string(extras, dirname.buf) &&
+                   (!skip || !string_list_has_string(skip, dirname.buf))) {
+                       strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
+                                   refname, dirname.buf);
+                       goto cleanup;
+               }
+
+               /*
+                * Otherwise, we can try to continue our search with
+                * the next component. So try to look up the
+                * directory, e.g., "refs/foo/". If we come up empty,
+                * we know there is nothing under this whole prefix,
+                * but even in that case we still have to continue the
+                * search for conflicts with extras.
+                */
+               strbuf_addch(&dirname, '/');
+               if (dir) {
+                       pos = search_ref_dir(dir, dirname.buf, dirname.len);
+                       if (pos < 0) {
+                               /*
+                                * There was no directory "refs/foo/",
+                                * so there is nothing under this
+                                * whole prefix. So there is no need
+                                * to continue looking for conflicting
+                                * references. But we need to continue
+                                * looking for conflicting extras.
+                                */
+                               dir = NULL;
+                       } else {
+                               dir = get_ref_dir(dir->entries[pos]);
+                       }
+               }
        }
-       return 1;
+
+       /*
+        * We are at the leaf of our refname (e.g., "refs/foo/bar").
+        * There is no point in searching for a reference with that
+        * name, because a refname isn't considered to conflict with
+        * itself. But we still need to check for references whose
+        * names are in the "refs/foo/bar/" namespace, because they
+        * *do* conflict.
+        */
+       strbuf_addstr(&dirname, refname + dirname.len);
+       strbuf_addch(&dirname, '/');
+
+       if (dir) {
+               pos = search_ref_dir(dir, dirname.buf, dirname.len);
+
+               if (pos >= 0) {
+                       /*
+                        * We found a directory named "$refname/"
+                        * (e.g., "refs/foo/bar/"). It is a problem
+                        * iff it contains any ref that is not in
+                        * "skip".
+                        */
+                       struct nonmatching_ref_data data;
+
+                       data.skip = skip;
+                       data.conflicting_refname = NULL;
+                       dir = get_ref_dir(dir->entries[pos]);
+                       sort_ref_dir(dir);
+                       if (do_for_each_entry_in_dir(dir, 0, nonmatching_ref_fn, &data)) {
+                               strbuf_addf(err, "'%s' exists; cannot create '%s'",
+                                           data.conflicting_refname, refname);
+                               goto cleanup;
+                       }
+               }
+       }
+
+       if (extras) {
+               /*
+                * Check for entries in extras that start with
+                * "$refname/". We do that by looking for the place
+                * where "$refname/" would be inserted in extras. If
+                * there is an entry at that position that starts with
+                * "$refname/" and is not in skip, then we have a
+                * conflict.
+                */
+               for (pos = string_list_find_insert_index(extras, dirname.buf, 0);
+                    pos < extras->nr; pos++) {
+                       const char *extra_refname = extras->items[pos].string;
+
+                       if (!starts_with(extra_refname, dirname.buf))
+                               break;
+
+                       if (!skip || !string_list_has_string(skip, extra_refname)) {
+                               strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
+                                           refname, extra_refname);
+                               goto cleanup;
+                       }
+               }
+       }
+
+       /* No conflicts were found */
+       ret = 0;
+
+cleanup:
+       strbuf_release(&dirname);
+       return ret;
 }
 
+struct packed_ref_cache {
+       struct ref_entry *root;
+
+       /*
+        * Count of references to the data structure in this instance,
+        * including the pointer from ref_cache::packed if any.  The
+        * data will not be freed as long as the reference count is
+        * nonzero.
+        */
+       unsigned int referrers;
+
+       /*
+        * Iff the packed-refs file associated with this instance is
+        * currently locked for writing, this points at the associated
+        * lock (which is owned by somebody else).  The referrer count
+        * is also incremented when the file is locked and decremented
+        * when it is unlocked.
+        */
+       struct lock_file *lock;
+
+       /* The metadata from when this packed-refs cache was read */
+       struct stat_validity validity;
+};
+
 /*
  * Future: need to be in "struct repository"
  * when doing a full libification.
@@ -707,16 +1055,51 @@ static int is_refname_available(const char *refname, const char *oldrefname,
 static struct ref_cache {
        struct ref_cache *next;
        struct ref_entry *loose;
-       struct ref_entry *packed;
-       /* The submodule name, or "" for the main repo. */
-       char name[FLEX_ARRAY];
-} *ref_cache;
+       struct packed_ref_cache *packed;
+       /*
+        * The submodule name, or "" for the main repo.  We allocate
+        * length 1 rather than FLEX_ARRAY so that the main ref_cache
+        * is initialized correctly.
+        */
+       char name[1];
+} ref_cache, *submodule_ref_caches;
+
+/* Lock used for the main packed-refs file: */
+static struct lock_file packlock;
+
+/*
+ * Increment the reference count of *packed_refs.
+ */
+static void acquire_packed_ref_cache(struct packed_ref_cache *packed_refs)
+{
+       packed_refs->referrers++;
+}
+
+/*
+ * Decrease the reference count of *packed_refs.  If it goes to zero,
+ * free *packed_refs and return true; otherwise return false.
+ */
+static int release_packed_ref_cache(struct packed_ref_cache *packed_refs)
+{
+       if (!--packed_refs->referrers) {
+               free_ref_entry(packed_refs->root);
+               stat_validity_clear(&packed_refs->validity);
+               free(packed_refs);
+               return 1;
+       } else {
+               return 0;
+       }
+}
 
 static void clear_packed_ref_cache(struct ref_cache *refs)
 {
        if (refs->packed) {
-               free_ref_entry(refs->packed);
+               struct packed_ref_cache *packed_refs = refs->packed;
+
+               if (packed_refs->lock)
+                       die("internal error: packed-ref cache cleared while locked");
                refs->packed = NULL;
+               release_packed_ref_cache(packed_refs);
        }
 }
 
@@ -748,35 +1131,40 @@ static struct ref_cache *create_ref_cache(const char *submodule)
  */
 static struct ref_cache *get_ref_cache(const char *submodule)
 {
-       struct ref_cache *refs = ref_cache;
-       if (!submodule)
-               submodule = "";
-       while (refs) {
+       struct ref_cache *refs;
+
+       if (!submodule || !*submodule)
+               return &ref_cache;
+
+       for (refs = submodule_ref_caches; refs; refs = refs->next)
                if (!strcmp(submodule, refs->name))
                        return refs;
-               refs = refs->next;
-       }
 
        refs = create_ref_cache(submodule);
-       refs->next = ref_cache;
-       ref_cache = refs;
+       refs->next = submodule_ref_caches;
+       submodule_ref_caches = refs;
        return refs;
 }
 
-void invalidate_ref_cache(const char *submodule)
-{
-       struct ref_cache *refs = get_ref_cache(submodule);
-       clear_packed_ref_cache(refs);
-       clear_loose_ref_cache(refs);
-}
+/* The length of a peeled reference line in packed-refs, including EOL: */
+#define PEELED_LINE_LENGTH 42
+
+/*
+ * The packed-refs header line that we write out.  Perhaps other
+ * traits will be added later.  The trailing space is required.
+ */
+static const char PACKED_REFS_HEADER[] =
+       "# pack-refs with: peeled fully-peeled \n";
 
 /*
  * Parse one line from a packed-refs file.  Write the SHA1 to sha1.
  * Return a pointer to the refname within the line (null-terminated),
  * or NULL if there was a problem.
  */
-static const char *parse_ref_line(char *line, unsigned char *sha1)
+static const char *parse_ref_line(struct strbuf *line, unsigned char *sha1)
 {
+       const char *ref;
+
        /*
         * 42: the answer to everything.
         *
@@ -785,22 +1173,23 @@ static const char *parse_ref_line(char *line, unsigned char *sha1)
         *  +1 (space in between hex and name)
         *  +1 (newline at the end of the line)
         */
-       int len = strlen(line) - 42;
-
-       if (len <= 0)
+       if (line->len <= 42)
                return NULL;
-       if (get_sha1_hex(line, sha1) < 0)
+
+       if (get_sha1_hex(line->buf, sha1) < 0)
                return NULL;
-       if (!isspace(line[40]))
+       if (!isspace(line->buf[40]))
                return NULL;
-       line += 41;
-       if (isspace(*line))
+
+       ref = line->buf + 41;
+       if (isspace(*ref))
                return NULL;
-       if (line[len] != '\n')
+
+       if (line->buf[line->len - 1] != '\n')
                return NULL;
-       line[len] = 0;
+       line->buf[--line->len] = 0;
 
-       return line;
+       return ref;
 }
 
 /*
@@ -833,16 +1222,15 @@ static const char *parse_ref_line(char *line, unsigned char *sha1)
 static void read_packed_refs(FILE *f, struct ref_dir *dir)
 {
        struct ref_entry *last = NULL;
-       char refline[PATH_MAX];
+       struct strbuf line = STRBUF_INIT;
        enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE;
 
-       while (fgets(refline, sizeof(refline), f)) {
+       while (strbuf_getwholeline(&line, f, '\n') != EOF) {
                unsigned char sha1[20];
                const char *refname;
-               static const char header[] = "# pack-refs with:";
+               const char *traits;
 
-               if (!strncmp(refline, header, sizeof(header)-1)) {
-                       const char *traits = refline + sizeof(header) - 1;
+               if (skip_prefix(line.buf, "# pack-refs with:", &traits)) {
                        if (strstr(traits, " fully-peeled "))
                                peeled = PEELED_FULLY;
                        else if (strstr(traits, " peeled "))
@@ -851,20 +1239,26 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
                        continue;
                }
 
-               refname = parse_ref_line(refline, sha1);
+               refname = parse_ref_line(&line, sha1);
                if (refname) {
-                       last = create_ref_entry(refname, sha1, REF_ISPACKED, 1);
+                       int flag = REF_ISPACKED;
+
+                       if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
+                               hashclr(sha1);
+                               flag |= REF_BAD_NAME | REF_ISBROKEN;
+                       }
+                       last = create_ref_entry(refname, sha1, flag, 0);
                        if (peeled == PEELED_FULLY ||
-                           (peeled == PEELED_TAGS && !prefixcmp(refname, "refs/tags/")))
+                           (peeled == PEELED_TAGS && starts_with(refname, "refs/tags/")))
                                last->flag |= REF_KNOWS_PEELED;
                        add_ref(dir, last);
                        continue;
                }
                if (last &&
-                   refline[0] == '^' &&
-                   strlen(refline) == 42 &&
-                   refline[41] == '\n' &&
-                   !get_sha1_hex(refline + 1, sha1)) {
+                   line.buf[0] == '^' &&
+                   line.len == PEELED_LINE_LENGTH &&
+                   line.buf[PEELED_LINE_LENGTH - 1] == '\n' &&
+                   !get_sha1_hex(line.buf + 1, sha1)) {
                        hashcpy(last->u.value.peeled, sha1);
                        /*
                         * Regardless of what the file header said,
@@ -874,32 +1268,62 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
                        last->flag |= REF_KNOWS_PEELED;
                }
        }
+
+       strbuf_release(&line);
 }
 
-static struct ref_dir *get_packed_refs(struct ref_cache *refs)
+/*
+ * Get the packed_ref_cache for the specified ref_cache, creating it
+ * if necessary.
+ */
+static struct packed_ref_cache *get_packed_ref_cache(struct ref_cache *refs)
 {
+       const char *packed_refs_file;
+
+       if (*refs->name)
+               packed_refs_file = git_path_submodule(refs->name, "packed-refs");
+       else
+               packed_refs_file = git_path("packed-refs");
+
+       if (refs->packed &&
+           !stat_validity_check(&refs->packed->validity, packed_refs_file))
+               clear_packed_ref_cache(refs);
+
        if (!refs->packed) {
-               const char *packed_refs_file;
                FILE *f;
 
-               refs->packed = create_dir_entry(refs, "", 0, 0);
-               if (*refs->name)
-                       packed_refs_file = git_path_submodule(refs->name, "packed-refs");
-               else
-                       packed_refs_file = git_path("packed-refs");
+               refs->packed = xcalloc(1, sizeof(*refs->packed));
+               acquire_packed_ref_cache(refs->packed);
+               refs->packed->root = create_dir_entry(refs, "", 0, 0);
                f = fopen(packed_refs_file, "r");
                if (f) {
-                       read_packed_refs(f, get_ref_dir(refs->packed));
+                       stat_validity_update(&refs->packed->validity, fileno(f));
+                       read_packed_refs(f, get_ref_dir(refs->packed->root));
                        fclose(f);
                }
        }
-       return get_ref_dir(refs->packed);
+       return refs->packed;
+}
+
+static struct ref_dir *get_packed_ref_dir(struct packed_ref_cache *packed_ref_cache)
+{
+       return get_ref_dir(packed_ref_cache->root);
+}
+
+static struct ref_dir *get_packed_refs(struct ref_cache *refs)
+{
+       return get_packed_ref_dir(get_packed_ref_cache(refs));
 }
 
 void add_packed_ref(const char *refname, const unsigned char *sha1)
 {
-       add_ref(get_packed_refs(get_ref_cache(NULL)),
-                       create_ref_entry(refname, sha1, REF_ISPACKED, 1));
+       struct packed_ref_cache *packed_ref_cache =
+               get_packed_ref_cache(&ref_cache);
+
+       if (!packed_ref_cache->lock)
+               die("internal error: packed refs not locked");
+       add_ref(get_packed_ref_dir(packed_ref_cache),
+               create_ref_entry(refname, sha1, REF_ISPACKED, 1));
 }
 
 /*
@@ -936,7 +1360,7 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
 
                if (de->d_name[0] == '.')
                        continue;
-               if (has_extension(de->d_name, ".lock"))
+               if (ends_with(de->d_name, ".lock"))
                        continue;
                strbuf_addstr(&refname, de->d_name);
                refdir = *refs->name
@@ -950,19 +1374,41 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
                                         create_dir_entry(refs, refname.buf,
                                                          refname.len, 1));
                } else {
+                       int read_ok;
+
                        if (*refs->name) {
                                hashclr(sha1);
                                flag = 0;
-                               if (resolve_gitlink_ref(refs->name, refname.buf, sha1) < 0) {
-                                       hashclr(sha1);
-                                       flag |= REF_ISBROKEN;
-                               }
-                       } else if (read_ref_full(refname.buf, sha1, 1, &flag)) {
+                               read_ok = !resolve_gitlink_ref(refs->name,
+                                                              refname.buf, sha1);
+                       } else {
+                               read_ok = !read_ref_full(refname.buf,
+                                                        RESOLVE_REF_READING,
+                                                        sha1, &flag);
+                       }
+
+                       if (!read_ok) {
                                hashclr(sha1);
                                flag |= REF_ISBROKEN;
+                       } else if (is_null_sha1(sha1)) {
+                               /*
+                                * It is so astronomically unlikely
+                                * that NULL_SHA1 is the SHA-1 of an
+                                * actual object that we consider its
+                                * appearance in a loose reference
+                                * file to be repo corruption
+                                * (probably due to a software bug).
+                                */
+                               flag |= REF_ISBROKEN;
+                       }
+
+                       if (check_refname_format(refname.buf,
+                                                REFNAME_ALLOW_ONELEVEL)) {
+                               hashclr(sha1);
+                               flag |= REF_BAD_NAME | REF_ISBROKEN;
                        }
                        add_entry_to_dir(dir,
-                                        create_ref_entry(refname.buf, sha1, flag, 1));
+                                        create_ref_entry(refname.buf, sha1, flag, 0));
                }
                strbuf_setlen(&refname, dirnamelen);
        }
@@ -1007,7 +1453,7 @@ static int resolve_gitlink_packed_ref(struct ref_cache *refs,
        if (ref == NULL)
                return -1;
 
-       memcpy(sha1, ref->u.value.sha1, 20);
+       hashcpy(sha1, ref->u.value.sha1);
        return 0;
 }
 
@@ -1069,77 +1515,135 @@ int resolve_gitlink_ref(const char *path, const char *refname, unsigned char *sh
 }
 
 /*
- * Try to read ref from the packed references.  On success, set sha1
- * and return 0; otherwise, return -1.
+ * Return the ref_entry for the given refname from the packed
+ * references.  If it does not exist, return NULL.
+ */
+static struct ref_entry *get_packed_ref(const char *refname)
+{
+       return find_ref(get_packed_refs(&ref_cache), refname);
+}
+
+/*
+ * A loose ref file doesn't exist; check for a packed ref.  The
+ * options are forwarded from resolve_safe_unsafe().
  */
-static int get_packed_ref(const char *refname, unsigned char *sha1)
+static int resolve_missing_loose_ref(const char *refname,
+                                    int resolve_flags,
+                                    unsigned char *sha1,
+                                    int *flags)
 {
-       struct ref_dir *packed = get_packed_refs(get_ref_cache(NULL));
-       struct ref_entry *entry = find_ref(packed, refname);
+       struct ref_entry *entry;
+
+       /*
+        * The loose reference file does not exist; check for a packed
+        * reference.
+        */
+       entry = get_packed_ref(refname);
        if (entry) {
                hashcpy(sha1, entry->u.value.sha1);
+               if (flags)
+                       *flags |= REF_ISPACKED;
+               return 0;
+       }
+       /* The reference is not a packed reference, either. */
+       if (resolve_flags & RESOLVE_REF_READING) {
+               errno = ENOENT;
+               return -1;
+       } else {
+               hashclr(sha1);
                return 0;
        }
-       return -1;
 }
 
-const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int reading, int *flag)
+/* This function needs to return a meaningful errno on failure */
+const char *resolve_ref_unsafe(const char *refname, int resolve_flags, unsigned char *sha1, int *flags)
 {
        int depth = MAXDEPTH;
        ssize_t len;
        char buffer[256];
        static char refname_buffer[256];
+       int bad_name = 0;
 
-       if (flag)
-               *flag = 0;
+       if (flags)
+               *flags = 0;
 
-       if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
-               return NULL;
+       if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
+               if (flags)
+                       *flags |= REF_BAD_NAME;
 
+               if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
+                   !refname_is_safe(refname)) {
+                       errno = EINVAL;
+                       return NULL;
+               }
+               /*
+                * dwim_ref() uses REF_ISBROKEN to distinguish between
+                * missing refs and refs that were present but invalid,
+                * to complain about the latter to stderr.
+                *
+                * We don't know whether the ref exists, so don't set
+                * REF_ISBROKEN yet.
+                */
+               bad_name = 1;
+       }
        for (;;) {
                char path[PATH_MAX];
                struct stat st;
                char *buf;
                int fd;
 
-               if (--depth < 0)
+               if (--depth < 0) {
+                       errno = ELOOP;
                        return NULL;
+               }
 
                git_snpath(path, sizeof(path), "%s", refname);
 
+               /*
+                * We might have to loop back here to avoid a race
+                * condition: first we lstat() the file, then we try
+                * to read it as a link or as a file.  But if somebody
+                * changes the type of the file (file <-> directory
+                * <-> symlink) between the lstat() and reading, then
+                * we don't want to report that as an error but rather
+                * try again starting with the lstat().
+                */
+       stat_ref:
                if (lstat(path, &st) < 0) {
                        if (errno != ENOENT)
                                return NULL;
-                       /*
-                        * The loose reference file does not exist;
-                        * check for a packed reference.
-                        */
-                       if (!get_packed_ref(refname, sha1)) {
-                               if (flag)
-                                       *flag |= REF_ISPACKED;
-                               return refname;
-                       }
-                       /* The reference is not a packed reference, either. */
-                       if (reading) {
+                       if (resolve_missing_loose_ref(refname, resolve_flags,
+                                                     sha1, flags))
                                return NULL;
-                       } else {
+                       if (bad_name) {
                                hashclr(sha1);
-                               return refname;
+                               if (flags)
+                                       *flags |= REF_ISBROKEN;
                        }
+                       return refname;
                }
 
                /* Follow "normalized" - ie "refs/.." symlinks by hand */
                if (S_ISLNK(st.st_mode)) {
                        len = readlink(path, buffer, sizeof(buffer)-1);
-                       if (len < 0)
-                               return NULL;
+                       if (len < 0) {
+                               if (errno == ENOENT || errno == EINVAL)
+                                       /* inconsistent with lstat; retry */
+                                       goto stat_ref;
+                               else
+                                       return NULL;
+                       }
                        buffer[len] = 0;
-                       if (!prefixcmp(buffer, "refs/") &&
+                       if (starts_with(buffer, "refs/") &&
                                        !check_refname_format(buffer, 0)) {
                                strcpy(refname_buffer, buffer);
                                refname = refname_buffer;
-                               if (flag)
-                                       *flag |= REF_ISSYMREF;
+                               if (flags)
+                                       *flags |= REF_ISSYMREF;
+                               if (resolve_flags & RESOLVE_REF_NO_RECURSE) {
+                                       hashclr(sha1);
+                                       return refname;
+                               }
                                continue;
                        }
                }
@@ -1155,12 +1659,21 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
                 * a ref
                 */
                fd = open(path, O_RDONLY);
-               if (fd < 0)
-                       return NULL;
+               if (fd < 0) {
+                       if (errno == ENOENT)
+                               /* inconsistent with lstat; retry */
+                               goto stat_ref;
+                       else
+                               return NULL;
+               }
                len = read_in_full(fd, buffer, sizeof(buffer)-1);
-               close(fd);
-               if (len < 0)
+               if (len < 0) {
+                       int save_errno = errno;
+                       close(fd);
+                       errno = save_errno;
                        return NULL;
+               }
+               close(fd);
                while (len && isspace(buffer[len-1]))
                        len--;
                buffer[len] = '\0';
@@ -1168,33 +1681,52 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
                /*
                 * Is it a symbolic ref?
                 */
-               if (prefixcmp(buffer, "ref:"))
-                       break;
-               if (flag)
-                       *flag |= REF_ISSYMREF;
+               if (!starts_with(buffer, "ref:")) {
+                       /*
+                        * Please note that FETCH_HEAD has a second
+                        * line containing other data.
+                        */
+                       if (get_sha1_hex(buffer, sha1) ||
+                           (buffer[40] != '\0' && !isspace(buffer[40]))) {
+                               if (flags)
+                                       *flags |= REF_ISBROKEN;
+                               errno = EINVAL;
+                               return NULL;
+                       }
+                       if (bad_name) {
+                               hashclr(sha1);
+                               if (flags)
+                                       *flags |= REF_ISBROKEN;
+                       }
+                       return refname;
+               }
+               if (flags)
+                       *flags |= REF_ISSYMREF;
                buf = buffer + 4;
                while (isspace(*buf))
                        buf++;
+               refname = strcpy(refname_buffer, buf);
+               if (resolve_flags & RESOLVE_REF_NO_RECURSE) {
+                       hashclr(sha1);
+                       return refname;
+               }
                if (check_refname_format(buf, REFNAME_ALLOW_ONELEVEL)) {
-                       if (flag)
-                               *flag |= REF_ISBROKEN;
-                       return NULL;
+                       if (flags)
+                               *flags |= REF_ISBROKEN;
+
+                       if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
+                           !refname_is_safe(buf)) {
+                               errno = EINVAL;
+                               return NULL;
+                       }
+                       bad_name = 1;
                }
-               refname = strcpy(refname_buffer, buf);
-       }
-       /* Please note that FETCH_HEAD has a second line containing other data. */
-       if (get_sha1_hex(buffer, sha1) || (buffer[40] != '\0' && !isspace(buffer[40]))) {
-               if (flag)
-                       *flag |= REF_ISBROKEN;
-               return NULL;
        }
-       return refname;
 }
 
-char *resolve_refdup(const char *ref, unsigned char *sha1, int reading, int *flag)
+char *resolve_refdup(const char *ref, int resolve_flags, unsigned char *sha1, int *flags)
 {
-       const char *ret = resolve_ref_unsafe(ref, sha1, reading, flag);
-       return ret ? xstrdup(ret) : NULL;
+       return xstrdup_or_null(resolve_ref_unsafe(ref, resolve_flags, sha1, flags));
 }
 
 /* The argument to filter_refs */
@@ -1204,86 +1736,162 @@ struct ref_filter {
        void *cb_data;
 };
 
-int read_ref_full(const char *refname, unsigned char *sha1, int reading, int *flags)
+int read_ref_full(const char *refname, int resolve_flags, unsigned char *sha1, int *flags)
 {
-       if (resolve_ref_unsafe(refname, sha1, reading, flags))
+       if (resolve_ref_unsafe(refname, resolve_flags, sha1, flags))
                return 0;
        return -1;
 }
 
 int read_ref(const char *refname, unsigned char *sha1)
 {
-       return read_ref_full(refname, sha1, 1, NULL);
+       return read_ref_full(refname, RESOLVE_REF_READING, sha1, NULL);
 }
 
 int ref_exists(const char *refname)
 {
        unsigned char sha1[20];
-       return !!resolve_ref_unsafe(refname, sha1, 1, NULL);
+       return !!resolve_ref_unsafe(refname, RESOLVE_REF_READING, sha1, NULL);
 }
 
 static int filter_refs(const char *refname, const unsigned char *sha1, int flags,
                       void *data)
 {
        struct ref_filter *filter = (struct ref_filter *)data;
-       if (fnmatch(filter->pattern, refname, 0))
+       if (wildmatch(filter->pattern, refname, 0, NULL))
                return 0;
        return filter->fn(refname, sha1, flags, filter->cb_data);
 }
 
-int peel_ref(const char *refname, unsigned char *sha1)
+enum peel_status {
+       /* object was peeled successfully: */
+       PEEL_PEELED = 0,
+
+       /*
+        * object cannot be peeled because the named object (or an
+        * object referred to by a tag in the peel chain), does not
+        * exist.
+        */
+       PEEL_INVALID = -1,
+
+       /* object cannot be peeled because it is not a tag: */
+       PEEL_NON_TAG = -2,
+
+       /* ref_entry contains no peeled value because it is a symref: */
+       PEEL_IS_SYMREF = -3,
+
+       /*
+        * ref_entry cannot be peeled because it is broken (i.e., the
+        * symbolic reference cannot even be resolved to an object
+        * name):
+        */
+       PEEL_BROKEN = -4
+};
+
+/*
+ * Peel the named object; i.e., if the object is a tag, resolve the
+ * tag recursively until a non-tag is found.  If successful, store the
+ * result to sha1 and return PEEL_PEELED.  If the object is not a tag
+ * or is not valid, return PEEL_NON_TAG or PEEL_INVALID, respectively,
+ * and leave sha1 unchanged.
+ */
+static enum peel_status peel_object(const unsigned char *name, unsigned char *sha1)
 {
-       int flag;
-       unsigned char base[20];
-       struct object *o;
+       struct object *o = lookup_unknown_object(name);
 
-       if (current_ref && (current_ref->name == refname
-               || !strcmp(current_ref->name, refname))) {
-               if (current_ref->flag & REF_KNOWS_PEELED) {
-                       if (is_null_sha1(current_ref->u.value.peeled))
-                           return -1;
-                       hashcpy(sha1, current_ref->u.value.peeled);
-                       return 0;
-               }
-               hashcpy(base, current_ref->u.value.sha1);
-               goto fallback;
+       if (o->type == OBJ_NONE) {
+               int type = sha1_object_info(name, NULL);
+               if (type < 0 || !object_as_type(o, type, 0))
+                       return PEEL_INVALID;
        }
 
-       if (read_ref_full(refname, base, 1, &flag))
-               return -1;
+       if (o->type != OBJ_TAG)
+               return PEEL_NON_TAG;
 
-       if ((flag & REF_ISPACKED)) {
-               struct ref_dir *dir = get_packed_refs(get_ref_cache(NULL));
-               struct ref_entry *r = find_ref(dir, refname);
+       o = deref_tag_noverify(o);
+       if (!o)
+               return PEEL_INVALID;
 
-               if (r != NULL && r->flag & REF_KNOWS_PEELED) {
-                       hashcpy(sha1, r->u.value.peeled);
-                       return 0;
+       hashcpy(sha1, o->sha1);
+       return PEEL_PEELED;
+}
+
+/*
+ * Peel the entry (if possible) and return its new peel_status.  If
+ * repeel is true, re-peel the entry even if there is an old peeled
+ * value that is already stored in it.
+ *
+ * It is OK to call this function with a packed reference entry that
+ * might be stale and might even refer to an object that has since
+ * been garbage-collected.  In such a case, if the entry has
+ * REF_KNOWS_PEELED then leave the status unchanged and return
+ * PEEL_PEELED or PEEL_NON_TAG; otherwise, return PEEL_INVALID.
+ */
+static enum peel_status peel_entry(struct ref_entry *entry, int repeel)
+{
+       enum peel_status status;
+
+       if (entry->flag & REF_KNOWS_PEELED) {
+               if (repeel) {
+                       entry->flag &= ~REF_KNOWS_PEELED;
+                       hashclr(entry->u.value.peeled);
+               } else {
+                       return is_null_sha1(entry->u.value.peeled) ?
+                               PEEL_NON_TAG : PEEL_PEELED;
                }
        }
+       if (entry->flag & REF_ISBROKEN)
+               return PEEL_BROKEN;
+       if (entry->flag & REF_ISSYMREF)
+               return PEEL_IS_SYMREF;
+
+       status = peel_object(entry->u.value.sha1, entry->u.value.peeled);
+       if (status == PEEL_PEELED || status == PEEL_NON_TAG)
+               entry->flag |= REF_KNOWS_PEELED;
+       return status;
+}
 
-fallback:
-       o = lookup_unknown_object(base);
-       if (o->type == OBJ_NONE) {
-               int type = sha1_object_info(base, NULL);
-               if (type < 0)
+int peel_ref(const char *refname, unsigned char *sha1)
+{
+       int flag;
+       unsigned char base[20];
+
+       if (current_ref && (current_ref->name == refname
+                           || !strcmp(current_ref->name, refname))) {
+               if (peel_entry(current_ref, 0))
                        return -1;
-               o->type = type;
+               hashcpy(sha1, current_ref->u.value.peeled);
+               return 0;
        }
 
-       if (o->type == OBJ_TAG) {
-               o = deref_tag_noverify(o);
-               if (o) {
-                       hashcpy(sha1, o->sha1);
+       if (read_ref_full(refname, RESOLVE_REF_READING, base, &flag))
+               return -1;
+
+       /*
+        * If the reference is packed, read its ref_entry from the
+        * cache in the hope that we already know its peeled value.
+        * We only try this optimization on packed references because
+        * (a) forcing the filling of the loose reference cache could
+        * be expensive and (b) loose references anyway usually do not
+        * have REF_KNOWS_PEELED.
+        */
+       if (flag & REF_ISPACKED) {
+               struct ref_entry *r = get_packed_ref(refname);
+               if (r) {
+                       if (peel_entry(r, 0))
+                               return -1;
+                       hashcpy(sha1, r->u.value.peeled);
                        return 0;
                }
        }
-       return -1;
+
+       return peel_object(base, sha1);
 }
 
 struct warn_if_dangling_data {
        FILE *fp;
        const char *refname;
+       const struct string_list *refnames;
        const char *msg_fmt;
 };
 
@@ -1297,9 +1905,13 @@ static int warn_if_dangling_symref(const char *refname, const unsigned char *sha
        if (!(flags & REF_ISSYMREF))
                return 0;
 
-       resolves_to = resolve_ref_unsafe(refname, junk, 0, NULL);
-       if (!resolves_to || strcmp(resolves_to, d->refname))
+       resolves_to = resolve_ref_unsafe(refname, 0, junk, NULL);
+       if (!resolves_to
+           || (d->refname
+               ? strcmp(resolves_to, d->refname)
+               : !string_list_has_string(d->refnames, resolves_to))) {
                return 0;
+       }
 
        fprintf(d->fp, d->msg_fmt, refname);
        fputc('\n', d->fp);
@@ -1312,44 +1924,105 @@ void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char *refname)
 
        data.fp = fp;
        data.refname = refname;
+       data.refnames = NULL;
+       data.msg_fmt = msg_fmt;
+       for_each_rawref(warn_if_dangling_symref, &data);
+}
+
+void warn_dangling_symrefs(FILE *fp, const char *msg_fmt, const struct string_list *refnames)
+{
+       struct warn_if_dangling_data data;
+
+       data.fp = fp;
+       data.refname = NULL;
+       data.refnames = refnames;
        data.msg_fmt = msg_fmt;
        for_each_rawref(warn_if_dangling_symref, &data);
 }
 
-static int do_for_each_ref(const char *submodule, const char *base, each_ref_fn fn,
-                          int trim, int flags, void *cb_data)
+/*
+ * Call fn for each reference in the specified ref_cache, omitting
+ * references not in the containing_dir of base.  fn is called for all
+ * references, including broken ones.  If fn ever returns a non-zero
+ * value, stop the iteration and return that value; otherwise, return
+ * 0.
+ */
+static int do_for_each_entry(struct ref_cache *refs, const char *base,
+                            each_ref_entry_fn fn, void *cb_data)
 {
-       struct ref_cache *refs = get_ref_cache(submodule);
-       struct ref_dir *packed_dir = get_packed_refs(refs);
-       struct ref_dir *loose_dir = get_loose_refs(refs);
+       struct packed_ref_cache *packed_ref_cache;
+       struct ref_dir *loose_dir;
+       struct ref_dir *packed_dir;
        int retval = 0;
 
+       /*
+        * We must make sure that all loose refs are read before accessing the
+        * packed-refs file; this avoids a race condition in which loose refs
+        * are migrated to the packed-refs file by a simultaneous process, but
+        * our in-memory view is from before the migration. get_packed_ref_cache()
+        * takes care of making sure our view is up to date with what is on
+        * disk.
+        */
+       loose_dir = get_loose_refs(refs);
        if (base && *base) {
-               packed_dir = find_containing_dir(packed_dir, base, 0);
                loose_dir = find_containing_dir(loose_dir, base, 0);
        }
+       if (loose_dir)
+               prime_ref_dir(loose_dir);
+
+       packed_ref_cache = get_packed_ref_cache(refs);
+       acquire_packed_ref_cache(packed_ref_cache);
+       packed_dir = get_packed_ref_dir(packed_ref_cache);
+       if (base && *base) {
+               packed_dir = find_containing_dir(packed_dir, base, 0);
+       }
 
        if (packed_dir && loose_dir) {
                sort_ref_dir(packed_dir);
                sort_ref_dir(loose_dir);
-               retval = do_for_each_ref_in_dirs(
-                               packed_dir, loose_dir,
-                               base, fn, trim, flags, cb_data);
+               retval = do_for_each_entry_in_dirs(
+                               packed_dir, loose_dir, fn, cb_data);
        } else if (packed_dir) {
                sort_ref_dir(packed_dir);
-               retval = do_for_each_ref_in_dir(
-                               packed_dir, 0,
-                               base, fn, trim, flags, cb_data);
+               retval = do_for_each_entry_in_dir(
+                               packed_dir, 0, fn, cb_data);
        } else if (loose_dir) {
                sort_ref_dir(loose_dir);
-               retval = do_for_each_ref_in_dir(
-                               loose_dir, 0,
-                               base, fn, trim, flags, cb_data);
+               retval = do_for_each_entry_in_dir(
+                               loose_dir, 0, fn, cb_data);
        }
 
+       release_packed_ref_cache(packed_ref_cache);
        return retval;
 }
 
+/*
+ * Call fn for each reference in the specified ref_cache for which the
+ * refname begins with base.  If trim is non-zero, then trim that many
+ * characters off the beginning of each refname before passing the
+ * refname to fn.  flags can be DO_FOR_EACH_INCLUDE_BROKEN to include
+ * broken references in the iteration.  If fn ever returns a non-zero
+ * value, stop the iteration and return that value; otherwise, return
+ * 0.
+ */
+static int do_for_each_ref(struct ref_cache *refs, const char *base,
+                          each_ref_fn fn, int trim, int flags, void *cb_data)
+{
+       struct ref_entry_cb data;
+       data.base = base;
+       data.trim = trim;
+       data.flags = flags;
+       data.fn = fn;
+       data.cb_data = cb_data;
+
+       if (ref_paranoia < 0)
+               ref_paranoia = git_env_bool("GIT_REF_PARANOIA", 0);
+       if (ref_paranoia)
+               data.flags |= DO_FOR_EACH_INCLUDE_BROKEN;
+
+       return do_for_each_entry(refs, base, do_one_ref, &data);
+}
+
 static int do_head_ref(const char *submodule, each_ref_fn fn, void *cb_data)
 {
        unsigned char sha1[20];
@@ -1362,7 +2035,7 @@ static int do_head_ref(const char *submodule, each_ref_fn fn, void *cb_data)
                return 0;
        }
 
-       if (!read_ref_full("HEAD", sha1, 1, &flag))
+       if (!read_ref_full("HEAD", RESOLVE_REF_READING, sha1, &flag))
                return fn("HEAD", sha1, flag, cb_data);
 
        return 0;
@@ -1380,23 +2053,23 @@ int head_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
 
 int for_each_ref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(NULL, "", fn, 0, 0, cb_data);
+       return do_for_each_ref(&ref_cache, "", fn, 0, 0, cb_data);
 }
 
 int for_each_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(submodule, "", fn, 0, 0, cb_data);
+       return do_for_each_ref(get_ref_cache(submodule), "", fn, 0, 0, cb_data);
 }
 
 int for_each_ref_in(const char *prefix, each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(NULL, prefix, fn, strlen(prefix), 0, cb_data);
+       return do_for_each_ref(&ref_cache, prefix, fn, strlen(prefix), 0, cb_data);
 }
 
 int for_each_ref_in_submodule(const char *submodule, const char *prefix,
                each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(submodule, prefix, fn, strlen(prefix), 0, cb_data);
+       return do_for_each_ref(get_ref_cache(submodule), prefix, fn, strlen(prefix), 0, cb_data);
 }
 
 int for_each_tag_ref(each_ref_fn fn, void *cb_data)
@@ -1431,7 +2104,7 @@ int for_each_remote_ref_submodule(const char *submodule, each_ref_fn fn, void *c
 
 int for_each_replace_ref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(NULL, "refs/replace/", fn, 13, 0, cb_data);
+       return do_for_each_ref(&ref_cache, "refs/replace/", fn, 13, 0, cb_data);
 }
 
 int head_ref_namespaced(each_ref_fn fn, void *cb_data)
@@ -1442,7 +2115,7 @@ int head_ref_namespaced(each_ref_fn fn, void *cb_data)
        int flag;
 
        strbuf_addf(&buf, "%sHEAD", get_git_namespace());
-       if (!read_ref_full(buf.buf, sha1, 1, &flag))
+       if (!read_ref_full(buf.buf, RESOLVE_REF_READING, sha1, &flag))
                ret = fn(buf.buf, sha1, flag, cb_data);
        strbuf_release(&buf);
 
@@ -1454,7 +2127,7 @@ int for_each_namespaced_ref(each_ref_fn fn, void *cb_data)
        struct strbuf buf = STRBUF_INIT;
        int ret;
        strbuf_addf(&buf, "%srefs/", get_git_namespace());
-       ret = do_for_each_ref(NULL, buf.buf, fn, 0, 0, cb_data);
+       ret = do_for_each_ref(&ref_cache, buf.buf, fn, 0, 0, cb_data);
        strbuf_release(&buf);
        return ret;
 }
@@ -1466,7 +2139,7 @@ int for_each_glob_ref_in(each_ref_fn fn, const char *pattern,
        struct ref_filter filter;
        int ret;
 
-       if (!prefix && prefixcmp(pattern, "refs/"))
+       if (!prefix && !starts_with(pattern, "refs/"))
                strbuf_addstr(&real_pattern, "refs/");
        else if (prefix)
                strbuf_addstr(&real_pattern, prefix);
@@ -1496,20 +2169,20 @@ int for_each_glob_ref(each_ref_fn fn, const char *pattern, void *cb_data)
 
 int for_each_rawref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref(NULL, "", fn, 0,
+       return do_for_each_ref(&ref_cache, "", fn, 0,
                               DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
 }
 
 const char *prettify_refname(const char *name)
 {
        return name + (
-               !prefixcmp(name, "refs/heads/") ? 11 :
-               !prefixcmp(name, "refs/tags/") ? 10 :
-               !prefixcmp(name, "refs/remotes/") ? 13 :
+               starts_with(name, "refs/heads/") ? 11 :
+               starts_with(name, "refs/tags/") ? 10 :
+               starts_with(name, "refs/remotes/") ? 13 :
                0);
 }
 
-const char *ref_rev_parse_rules[] = {
+static const char *ref_rev_parse_rules[] = {
        "%.*s",
        "refs/%.*s",
        "refs/tags/%.*s",
@@ -1519,12 +2192,12 @@ const char *ref_rev_parse_rules[] = {
        NULL
 };
 
-int refname_match(const char *abbrev_name, const char *full_name, const char **rules)
+int refname_match(const char *abbrev_name, const char *full_name)
 {
        const char **p;
        const int abbrev_name_len = strlen(abbrev_name);
 
-       for (p = rules; *p; p++) {
+       for (p = ref_rev_parse_rules; *p; p++) {
                if (!strcmp(full_name, mkpath(*p, abbrev_name_len, abbrev_name))) {
                        return 1;
                }
@@ -1533,18 +2206,34 @@ int refname_match(const char *abbrev_name, const char *full_name, const char **r
        return 0;
 }
 
+static void unlock_ref(struct ref_lock *lock)
+{
+       /* Do not free lock->lk -- atexit() still looks at them */
+       if (lock->lk)
+               rollback_lock_file(lock->lk);
+       free(lock->ref_name);
+       free(lock->orig_ref_name);
+       free(lock);
+}
+
+/* This function should make sure errno is meaningful on error */
 static struct ref_lock *verify_lock(struct ref_lock *lock,
        const unsigned char *old_sha1, int mustexist)
 {
-       if (read_ref_full(lock->ref_name, lock->old_sha1, mustexist, NULL)) {
+       if (read_ref_full(lock->ref_name,
+                         mustexist ? RESOLVE_REF_READING : 0,
+                         lock->old_sha1, NULL)) {
+               int save_errno = errno;
                error("Can't verify ref %s", lock->ref_name);
                unlock_ref(lock);
+               errno = save_errno;
                return NULL;
        }
        if (hashcmp(lock->old_sha1, old_sha1)) {
                error("Ref %s is at %s but expected %s", lock->ref_name,
                        sha1_to_hex(lock->old_sha1), sha1_to_hex(old_sha1));
                unlock_ref(lock);
+               errno = EBUSY;
                return NULL;
        }
        return lock;
@@ -1557,14 +2246,16 @@ static int remove_empty_directories(const char *file)
         * only empty directories), remove them.
         */
        struct strbuf path;
-       int result;
+       int result, save_errno;
 
        strbuf_init(&path, 20);
        strbuf_addstr(&path, file);
 
        result = remove_dir_recursively(&path, REMOVE_DIR_EMPTY_ONLY);
+       save_errno = errno;
 
        strbuf_release(&path);
+       errno = save_errno;
 
        return result;
 }
@@ -1577,7 +2268,7 @@ static int remove_empty_directories(const char *file)
 static char *substitute_branch_name(const char **string, int *len)
 {
        struct strbuf buf = STRBUF_INIT;
-       int ret = interpret_branch_name(*string, &buf);
+       int ret = interpret_branch_name(*string, *len, &buf);
 
        if (ret == *len) {
                size_t size;
@@ -1604,7 +2295,8 @@ int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 
                this_result = refs_found ? sha1_from_ref : sha1;
                mksnpath(fullref, sizeof(fullref), *p, len, str);
-               r = resolve_ref_unsafe(fullref, this_result, 1, &flag);
+               r = resolve_ref_unsafe(fullref, RESOLVE_REF_READING,
+                                      this_result, &flag);
                if (r) {
                        if (!refs_found++)
                                *ref = xstrdup(r);
@@ -1628,21 +2320,18 @@ int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
 
        *log = NULL;
        for (p = ref_rev_parse_rules; *p; p++) {
-               struct stat st;
                unsigned char hash[20];
                char path[PATH_MAX];
                const char *ref, *it;
 
                mksnpath(path, sizeof(path), *p, len, str);
-               ref = resolve_ref_unsafe(path, hash, 1, NULL);
+               ref = resolve_ref_unsafe(path, RESOLVE_REF_READING,
+                                        hash, NULL);
                if (!ref)
                        continue;
-               if (!stat(git_path("logs/%s", path), &st) &&
-                   S_ISREG(st.st_mode))
+               if (reflog_exists(path))
                        it = path;
-               else if (strcmp(ref, path) &&
-                        !stat(git_path("logs/%s", ref), &st) &&
-                        S_ISREG(st.st_mode))
+               else if (strcmp(ref, path) && reflog_exists(ref))
                        it = ref;
                else
                        continue;
@@ -1657,9 +2346,16 @@ int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
        return logs_found;
 }
 
+/*
+ * Locks a ref returning the lock on success and NULL on failure.
+ * On failure errno is set to something meaningful.
+ */
 static struct ref_lock *lock_ref_sha1_basic(const char *refname,
                                            const unsigned char *old_sha1,
-                                           int flags, int *type_p)
+                                           const struct string_list *extras,
+                                           const struct string_list *skip,
+                                           unsigned int flags, int *type_p,
+                                           struct strbuf *err)
 {
        char *ref_file;
        const char *orig_refname = refname;
@@ -1667,12 +2363,24 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
        int last_errno = 0;
        int type, lflags;
        int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
-       int missing = 0;
+       int resolve_flags = 0;
+       int attempts_remaining = 3;
+
+       assert(err);
 
        lock = xcalloc(1, sizeof(struct ref_lock));
        lock->lock_fd = -1;
 
-       refname = resolve_ref_unsafe(refname, lock->old_sha1, mustexist, &type);
+       if (mustexist)
+               resolve_flags |= RESOLVE_REF_READING;
+       if (flags & REF_DELETING) {
+               resolve_flags |= RESOLVE_REF_ALLOW_BAD_NAME;
+               if (flags & REF_NODEREF)
+                       resolve_flags |= RESOLVE_REF_NO_RECURSE;
+       }
+
+       refname = resolve_ref_unsafe(refname, resolve_flags,
+                                    lock->old_sha1, &type);
        if (!refname && errno == EISDIR) {
                /* we are trying to lock foo but we used to
                 * have foo/bar which now does not exist;
@@ -1682,53 +2390,82 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
                ref_file = git_path("%s", orig_refname);
                if (remove_empty_directories(ref_file)) {
                        last_errno = errno;
-                       error("there are still refs under '%s'", orig_refname);
+
+                       if (!verify_refname_available(orig_refname, extras, skip,
+                                                     get_loose_refs(&ref_cache), err))
+                               strbuf_addf(err, "there are still refs under '%s'",
+                                           orig_refname);
+
                        goto error_return;
                }
-               refname = resolve_ref_unsafe(orig_refname, lock->old_sha1, mustexist, &type);
+               refname = resolve_ref_unsafe(orig_refname, resolve_flags,
+                                            lock->old_sha1, &type);
        }
        if (type_p)
            *type_p = type;
        if (!refname) {
                last_errno = errno;
-               error("unable to resolve reference %s: %s",
-                       orig_refname, strerror(errno));
+               if (last_errno != ENOTDIR ||
+                   !verify_refname_available(orig_refname, extras, skip,
+                                             get_loose_refs(&ref_cache), err))
+                       strbuf_addf(err, "unable to resolve reference %s: %s",
+                                   orig_refname, strerror(last_errno));
+
                goto error_return;
        }
-       missing = is_null_sha1(lock->old_sha1);
-       /* When the ref did not exist and we are creating it,
-        * make sure there is no existing ref that is packed
-        * whose name begins with our refname, nor a ref whose
-        * name is a proper prefix of our refname.
+       /*
+        * If the ref did not exist and we are creating it, make sure
+        * there is no existing packed ref whose name begins with our
+        * refname, nor a packed ref whose name is a proper prefix of
+        * our refname.
         */
-       if (missing &&
-            !is_refname_available(refname, NULL, get_packed_refs(get_ref_cache(NULL)))) {
+       if (is_null_sha1(lock->old_sha1) &&
+           verify_refname_available(refname, extras, skip,
+                                    get_packed_refs(&ref_cache), err)) {
                last_errno = ENOTDIR;
                goto error_return;
        }
 
        lock->lk = xcalloc(1, sizeof(struct lock_file));
 
-       lflags = LOCK_DIE_ON_ERROR;
+       lflags = 0;
        if (flags & REF_NODEREF) {
                refname = orig_refname;
-               lflags |= LOCK_NODEREF;
+               lflags |= LOCK_NO_DEREF;
        }
        lock->ref_name = xstrdup(refname);
        lock->orig_ref_name = xstrdup(orig_refname);
        ref_file = git_path("%s", refname);
-       if (missing)
-               lock->force_write = 1;
-       if ((flags & REF_NODEREF) && (type & REF_ISSYMREF))
-               lock->force_write = 1;
 
-       if (safe_create_leading_directories(ref_file)) {
+ retry:
+       switch (safe_create_leading_directories(ref_file)) {
+       case SCLD_OK:
+               break; /* success */
+       case SCLD_VANISHED:
+               if (--attempts_remaining > 0)
+                       goto retry;
+               /* fall through */
+       default:
                last_errno = errno;
-               error("unable to create directory for %s", ref_file);
+               strbuf_addf(err, "unable to create directory for %s", ref_file);
                goto error_return;
        }
 
        lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, lflags);
+       if (lock->lock_fd < 0) {
+               last_errno = errno;
+               if (errno == ENOENT && --attempts_remaining > 0)
+                       /*
+                        * Maybe somebody just deleted one of the
+                        * directories leading to ref_file.  Try
+                        * again:
+                        */
+                       goto retry;
+               else {
+                       unable_to_lock_message(ref_file, errno, err);
+                       goto error_return;
+               }
+       }
        return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;
 
  error_return:
@@ -1737,95 +2474,329 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
        return NULL;
 }
 
-struct ref_lock *lock_ref_sha1(const char *refname, const unsigned char *old_sha1)
+/*
+ * Write an entry to the packed-refs file for the specified refname.
+ * If peeled is non-NULL, write it as the entry's peeled value.
+ */
+static void write_packed_entry(FILE *fh, char *refname, unsigned char *sha1,
+                              unsigned char *peeled)
+{
+       fprintf_or_die(fh, "%s %s\n", sha1_to_hex(sha1), refname);
+       if (peeled)
+               fprintf_or_die(fh, "^%s\n", sha1_to_hex(peeled));
+}
+
+/*
+ * An each_ref_entry_fn that writes the entry to a packed-refs file.
+ */
+static int write_packed_entry_fn(struct ref_entry *entry, void *cb_data)
 {
-       char refpath[PATH_MAX];
-       if (check_refname_format(refname, 0))
-               return NULL;
-       strcpy(refpath, mkpath("refs/%s", refname));
-       return lock_ref_sha1_basic(refpath, old_sha1, 0, NULL);
+       enum peel_status peel_status = peel_entry(entry, 0);
+
+       if (peel_status != PEEL_PEELED && peel_status != PEEL_NON_TAG)
+               error("internal error: %s is not a valid packed reference!",
+                     entry->name);
+       write_packed_entry(cb_data, entry->name, entry->u.value.sha1,
+                          peel_status == PEEL_PEELED ?
+                          entry->u.value.peeled : NULL);
+       return 0;
 }
 
-struct ref_lock *lock_any_ref_for_update(const char *refname,
-                                        const unsigned char *old_sha1, int flags)
+/* This should return a meaningful errno on failure */
+int lock_packed_refs(int flags)
 {
-       if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
-               return NULL;
-       return lock_ref_sha1_basic(refname, old_sha1, flags, NULL);
+       struct packed_ref_cache *packed_ref_cache;
+
+       if (hold_lock_file_for_update(&packlock, git_path("packed-refs"), flags) < 0)
+               return -1;
+       /*
+        * Get the current packed-refs while holding the lock.  If the
+        * packed-refs file has been modified since we last read it,
+        * this will automatically invalidate the cache and re-read
+        * the packed-refs file.
+        */
+       packed_ref_cache = get_packed_ref_cache(&ref_cache);
+       packed_ref_cache->lock = &packlock;
+       /* Increment the reference count to prevent it from being freed: */
+       acquire_packed_ref_cache(packed_ref_cache);
+       return 0;
 }
 
-struct repack_without_ref_sb {
-       const char *refname;
-       int fd;
+/*
+ * Commit the packed refs changes.
+ * On error we must make sure that errno contains a meaningful value.
+ */
+int commit_packed_refs(void)
+{
+       struct packed_ref_cache *packed_ref_cache =
+               get_packed_ref_cache(&ref_cache);
+       int error = 0;
+       int save_errno = 0;
+       FILE *out;
+
+       if (!packed_ref_cache->lock)
+               die("internal error: packed-refs not locked");
+
+       out = fdopen_lock_file(packed_ref_cache->lock, "w");
+       if (!out)
+               die_errno("unable to fdopen packed-refs descriptor");
+
+       fprintf_or_die(out, "%s", PACKED_REFS_HEADER);
+       do_for_each_entry_in_dir(get_packed_ref_dir(packed_ref_cache),
+                                0, write_packed_entry_fn, out);
+
+       if (commit_lock_file(packed_ref_cache->lock)) {
+               save_errno = errno;
+               error = -1;
+       }
+       packed_ref_cache->lock = NULL;
+       release_packed_ref_cache(packed_ref_cache);
+       errno = save_errno;
+       return error;
+}
+
+void rollback_packed_refs(void)
+{
+       struct packed_ref_cache *packed_ref_cache =
+               get_packed_ref_cache(&ref_cache);
+
+       if (!packed_ref_cache->lock)
+               die("internal error: packed-refs not locked");
+       rollback_lock_file(packed_ref_cache->lock);
+       packed_ref_cache->lock = NULL;
+       release_packed_ref_cache(packed_ref_cache);
+       clear_packed_ref_cache(&ref_cache);
+}
+
+struct ref_to_prune {
+       struct ref_to_prune *next;
+       unsigned char sha1[20];
+       char name[FLEX_ARRAY];
+};
+
+struct pack_refs_cb_data {
+       unsigned int flags;
+       struct ref_dir *packed_refs;
+       struct ref_to_prune *ref_to_prune;
 };
 
-static int repack_without_ref_fn(const char *refname, const unsigned char *sha1,
-                                int flags, void *cb_data)
+/*
+ * An each_ref_entry_fn that is run over loose references only.  If
+ * the loose reference can be packed, add an entry in the packed ref
+ * cache.  If the reference should be pruned, also add it to
+ * ref_to_prune in the pack_refs_cb_data.
+ */
+static int pack_if_possible_fn(struct ref_entry *entry, void *cb_data)
 {
-       struct repack_without_ref_sb *data = cb_data;
-       char line[PATH_MAX + 100];
-       int len;
+       struct pack_refs_cb_data *cb = cb_data;
+       enum peel_status peel_status;
+       struct ref_entry *packed_entry;
+       int is_tag_ref = starts_with(entry->name, "refs/tags/");
+
+       /* ALWAYS pack tags */
+       if (!(cb->flags & PACK_REFS_ALL) && !is_tag_ref)
+               return 0;
 
-       if (!strcmp(data->refname, refname))
+       /* Do not pack symbolic or broken refs: */
+       if ((entry->flag & REF_ISSYMREF) || !ref_resolves_to_object(entry))
                return 0;
-       len = snprintf(line, sizeof(line), "%s %s\n",
-                      sha1_to_hex(sha1), refname);
-       /* this should not happen but just being defensive */
-       if (len > sizeof(line))
-               die("too long a refname '%s'", refname);
-       write_or_die(data->fd, line, len);
+
+       /* Add a packed ref cache entry equivalent to the loose entry. */
+       peel_status = peel_entry(entry, 1);
+       if (peel_status != PEEL_PEELED && peel_status != PEEL_NON_TAG)
+               die("internal error peeling reference %s (%s)",
+                   entry->name, sha1_to_hex(entry->u.value.sha1));
+       packed_entry = find_ref(cb->packed_refs, entry->name);
+       if (packed_entry) {
+               /* Overwrite existing packed entry with info from loose entry */
+               packed_entry->flag = REF_ISPACKED | REF_KNOWS_PEELED;
+               hashcpy(packed_entry->u.value.sha1, entry->u.value.sha1);
+       } else {
+               packed_entry = create_ref_entry(entry->name, entry->u.value.sha1,
+                                               REF_ISPACKED | REF_KNOWS_PEELED, 0);
+               add_ref(cb->packed_refs, packed_entry);
+       }
+       hashcpy(packed_entry->u.value.peeled, entry->u.value.peeled);
+
+       /* Schedule the loose reference for pruning if requested. */
+       if ((cb->flags & PACK_REFS_PRUNE)) {
+               int namelen = strlen(entry->name) + 1;
+               struct ref_to_prune *n = xcalloc(1, sizeof(*n) + namelen);
+               hashcpy(n->sha1, entry->u.value.sha1);
+               strcpy(n->name, entry->name);
+               n->next = cb->ref_to_prune;
+               cb->ref_to_prune = n;
+       }
        return 0;
 }
 
-static struct lock_file packlock;
+/*
+ * Remove empty parents, but spare refs/ and immediate subdirs.
+ * Note: munges *name.
+ */
+static void try_remove_empty_parents(char *name)
+{
+       char *p, *q;
+       int i;
+       p = name;
+       for (i = 0; i < 2; i++) { /* refs/{heads,tags,...}/ */
+               while (*p && *p != '/')
+                       p++;
+               /* tolerate duplicate slashes; see check_refname_format() */
+               while (*p == '/')
+                       p++;
+       }
+       for (q = p; *q; q++)
+               ;
+       while (1) {
+               while (q > p && *q != '/')
+                       q--;
+               while (q > p && *(q-1) == '/')
+                       q--;
+               if (q == p)
+                       break;
+               *q = '\0';
+               if (rmdir(git_path("%s", name)))
+                       break;
+       }
+}
+
+/* make sure nobody touched the ref, and unlink */
+static void prune_ref(struct ref_to_prune *r)
+{
+       struct ref_transaction *transaction;
+       struct strbuf err = STRBUF_INIT;
+
+       if (check_refname_format(r->name, 0))
+               return;
+
+       transaction = ref_transaction_begin(&err);
+       if (!transaction ||
+           ref_transaction_delete(transaction, r->name, r->sha1,
+                                  REF_ISPRUNING, NULL, &err) ||
+           ref_transaction_commit(transaction, &err)) {
+               ref_transaction_free(transaction);
+               error("%s", err.buf);
+               strbuf_release(&err);
+               return;
+       }
+       ref_transaction_free(transaction);
+       strbuf_release(&err);
+       try_remove_empty_parents(r->name);
+}
+
+static void prune_refs(struct ref_to_prune *r)
+{
+       while (r) {
+               prune_ref(r);
+               r = r->next;
+       }
+}
+
+int pack_refs(unsigned int flags)
+{
+       struct pack_refs_cb_data cbdata;
+
+       memset(&cbdata, 0, sizeof(cbdata));
+       cbdata.flags = flags;
+
+       lock_packed_refs(LOCK_DIE_ON_ERROR);
+       cbdata.packed_refs = get_packed_refs(&ref_cache);
+
+       do_for_each_entry_in_dir(get_loose_refs(&ref_cache), 0,
+                                pack_if_possible_fn, &cbdata);
 
-static int repack_without_ref(const char *refname)
+       if (commit_packed_refs())
+               die_errno("unable to overwrite old ref-pack file");
+
+       prune_refs(cbdata.ref_to_prune);
+       return 0;
+}
+
+int repack_without_refs(struct string_list *refnames, struct strbuf *err)
 {
-       struct repack_without_ref_sb data;
-       struct ref_cache *refs = get_ref_cache(NULL);
-       struct ref_dir *packed = get_packed_refs(refs);
-       if (find_ref(packed, refname) == NULL)
+       struct ref_dir *packed;
+       struct string_list_item *refname;
+       int ret, needs_repacking = 0, removed = 0;
+
+       assert(err);
+
+       /* Look for a packed ref */
+       for_each_string_list_item(refname, refnames) {
+               if (get_packed_ref(refname->string)) {
+                       needs_repacking = 1;
+                       break;
+               }
+       }
+
+       /* Avoid locking if we have nothing to do */
+       if (!needs_repacking)
+               return 0; /* no refname exists in packed refs */
+
+       if (lock_packed_refs(0)) {
+               unable_to_lock_message(git_path("packed-refs"), errno, err);
+               return -1;
+       }
+       packed = get_packed_refs(&ref_cache);
+
+       /* Remove refnames from the cache */
+       for_each_string_list_item(refname, refnames)
+               if (remove_entry(packed, refname->string) != -1)
+                       removed = 1;
+       if (!removed) {
+               /*
+                * All packed entries disappeared while we were
+                * acquiring the lock.
+                */
+               rollback_packed_refs();
                return 0;
-       data.refname = refname;
-       data.fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
-       if (data.fd < 0) {
-               unable_to_lock_error(git_path("packed-refs"), errno);
-               return error("cannot delete '%s' from packed refs", refname);
        }
-       clear_packed_ref_cache(refs);
-       packed = get_packed_refs(refs);
-       do_for_each_ref_in_dir(packed, 0, "", repack_without_ref_fn, 0, 0, &data);
-       return commit_lock_file(&packlock);
+
+       /* Write what remains */
+       ret = commit_packed_refs();
+       if (ret)
+               strbuf_addf(err, "unable to overwrite old ref-pack file: %s",
+                           strerror(errno));
+       return ret;
 }
 
-int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
+static int delete_ref_loose(struct ref_lock *lock, int flag, struct strbuf *err)
 {
-       struct ref_lock *lock;
-       int err, i = 0, ret = 0, flag = 0;
+       assert(err);
 
-       lock = lock_ref_sha1_basic(refname, sha1, delopt, &flag);
-       if (!lock)
-               return 1;
        if (!(flag & REF_ISPACKED) || flag & REF_ISSYMREF) {
-               /* loose */
-               i = strlen(lock->lk->filename) - 5; /* .lock */
-               lock->lk->filename[i] = 0;
-               err = unlink_or_warn(lock->lk->filename);
-               if (err && errno != ENOENT)
-                       ret = 1;
-
-               lock->lk->filename[i] = '.';
-       }
-       /* removing the loose one could have resurrected an earlier
-        * packed one.  Also, if it was not loose we need to repack
-        * without it.
-        */
-       ret |= repack_without_ref(lock->ref_name);
+               /*
+                * loose.  The loose file name is the same as the
+                * lockfile name, minus ".lock":
+                */
+               char *loose_filename = get_locked_file_path(lock->lk);
+               int res = unlink_or_msg(loose_filename, err);
+               free(loose_filename);
+               if (res)
+                       return 1;
+       }
+       return 0;
+}
 
-       unlink_or_warn(git_path("logs/%s", lock->ref_name));
-       invalidate_ref_cache(NULL);
-       unlock_ref(lock);
-       return ret;
+int delete_ref(const char *refname, const unsigned char *sha1, unsigned int flags)
+{
+       struct ref_transaction *transaction;
+       struct strbuf err = STRBUF_INIT;
+
+       transaction = ref_transaction_begin(&err);
+       if (!transaction ||
+           ref_transaction_delete(transaction, refname,
+                                  (sha1 && !is_null_sha1(sha1)) ? sha1 : NULL,
+                                  flags, NULL, &err) ||
+           ref_transaction_commit(transaction, &err)) {
+               error("%s", err.buf);
+               ref_transaction_free(transaction);
+               strbuf_release(&err);
+               return 1;
+       }
+       ref_transaction_free(transaction);
+       strbuf_release(&err);
+       return 0;
 }
 
 /*
@@ -1837,30 +2808,96 @@ int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
  */
 #define TMP_RENAMED_LOG  "logs/refs/.tmp-renamed-log"
 
-int rename_ref(const char *oldrefname, const char *newrefname, const char *logmsg)
+static int rename_tmp_log(const char *newrefname)
 {
-       unsigned char sha1[20], orig_sha1[20];
-       int flag = 0, logmoved = 0;
-       struct ref_lock *lock;
-       struct stat loginfo;
-       int log = !lstat(git_path("logs/%s", oldrefname), &loginfo);
-       const char *symref = NULL;
-       struct ref_cache *refs = get_ref_cache(NULL);
+       int attempts_remaining = 4;
 
-       if (log && S_ISLNK(loginfo.st_mode))
-               return error("reflog for %s is a symlink", oldrefname);
+ retry:
+       switch (safe_create_leading_directories(git_path("logs/%s", newrefname))) {
+       case SCLD_OK:
+               break; /* success */
+       case SCLD_VANISHED:
+               if (--attempts_remaining > 0)
+                       goto retry;
+               /* fall through */
+       default:
+               error("unable to create directory for %s", newrefname);
+               return -1;
+       }
 
-       symref = resolve_ref_unsafe(oldrefname, orig_sha1, 1, &flag);
+       if (rename(git_path(TMP_RENAMED_LOG), git_path("logs/%s", newrefname))) {
+               if ((errno==EISDIR || errno==ENOTDIR) && --attempts_remaining > 0) {
+                       /*
+                        * rename(a, b) when b is an existing
+                        * directory ought to result in ISDIR, but
+                        * Solaris 5.8 gives ENOTDIR.  Sheesh.
+                        */
+                       if (remove_empty_directories(git_path("logs/%s", newrefname))) {
+                               error("Directory not empty: logs/%s", newrefname);
+                               return -1;
+                       }
+                       goto retry;
+               } else if (errno == ENOENT && --attempts_remaining > 0) {
+                       /*
+                        * Maybe another process just deleted one of
+                        * the directories in the path to newrefname.
+                        * Try again from the beginning.
+                        */
+                       goto retry;
+               } else {
+                       error("unable to move logfile "TMP_RENAMED_LOG" to logs/%s: %s",
+                               newrefname, strerror(errno));
+                       return -1;
+               }
+       }
+       return 0;
+}
+
+static int rename_ref_available(const char *oldname, const char *newname)
+{
+       struct string_list skip = STRING_LIST_INIT_NODUP;
+       struct strbuf err = STRBUF_INIT;
+       int ret;
+
+       string_list_insert(&skip, oldname);
+       ret = !verify_refname_available(newname, NULL, &skip,
+                                       get_packed_refs(&ref_cache), &err)
+               && !verify_refname_available(newname, NULL, &skip,
+                                            get_loose_refs(&ref_cache), &err);
+       if (!ret)
+               error("%s", err.buf);
+
+       string_list_clear(&skip, 0);
+       strbuf_release(&err);
+       return ret;
+}
+
+static int write_ref_to_lockfile(struct ref_lock *lock, const unsigned char *sha1);
+static int commit_ref_update(struct ref_lock *lock,
+                            const unsigned char *sha1, const char *logmsg);
+
+int rename_ref(const char *oldrefname, const char *newrefname, const char *logmsg)
+{
+       unsigned char sha1[20], orig_sha1[20];
+       int flag = 0, logmoved = 0;
+       struct ref_lock *lock;
+       struct stat loginfo;
+       int log = !lstat(git_path("logs/%s", oldrefname), &loginfo);
+       const char *symref = NULL;
+       struct strbuf err = STRBUF_INIT;
+
+       if (log && S_ISLNK(loginfo.st_mode))
+               return error("reflog for %s is a symlink", oldrefname);
+
+       symref = resolve_ref_unsafe(oldrefname, RESOLVE_REF_READING,
+                                   orig_sha1, &flag);
        if (flag & REF_ISSYMREF)
                return error("refname %s is a symbolic ref, renaming it is not supported",
                        oldrefname);
        if (!symref)
                return error("refname %s not found", oldrefname);
 
-       if (!is_refname_available(newrefname, oldrefname, get_packed_refs(refs)))
-               return 1;
-
-       if (!is_refname_available(newrefname, oldrefname, get_loose_refs(refs)))
+       if (!rename_ref_available(oldrefname, newrefname))
                return 1;
 
        if (log && rename(git_path("logs/%s", oldrefname), git_path(TMP_RENAMED_LOG)))
@@ -1872,7 +2909,7 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
                goto rollback;
        }
 
-       if (!read_ref_full(newrefname, sha1, 1, &flag) &&
+       if (!read_ref_full(newrefname, RESOLVE_REF_READING, sha1, NULL) &&
            delete_ref(newrefname, sha1, REF_NODEREF)) {
                if (errno==EISDIR) {
                        if (remove_empty_directories(git_path("%s", newrefname))) {
@@ -1885,40 +2922,21 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
                }
        }
 
-       if (log && safe_create_leading_directories(git_path("logs/%s", newrefname))) {
-               error("unable to create directory for %s", newrefname);
+       if (log && rename_tmp_log(newrefname))
                goto rollback;
-       }
 
- retry:
-       if (log && rename(git_path(TMP_RENAMED_LOG), git_path("logs/%s", newrefname))) {
-               if (errno==EISDIR || errno==ENOTDIR) {
-                       /*
-                        * rename(a, b) when b is an existing
-                        * directory ought to result in ISDIR, but
-                        * Solaris 5.8 gives ENOTDIR.  Sheesh.
-                        */
-                       if (remove_empty_directories(git_path("logs/%s", newrefname))) {
-                               error("Directory not empty: logs/%s", newrefname);
-                               goto rollback;
-                       }
-                       goto retry;
-               } else {
-                       error("unable to move logfile "TMP_RENAMED_LOG" to logs/%s: %s",
-                               newrefname, strerror(errno));
-                       goto rollback;
-               }
-       }
        logmoved = log;
 
-       lock = lock_ref_sha1_basic(newrefname, NULL, 0, NULL);
+       lock = lock_ref_sha1_basic(newrefname, NULL, NULL, NULL, 0, NULL, &err);
        if (!lock) {
-               error("unable to lock %s for update", newrefname);
+               error("unable to rename '%s' to '%s': %s", oldrefname, newrefname, err.buf);
+               strbuf_release(&err);
                goto rollback;
        }
-       lock->force_write = 1;
        hashcpy(lock->old_sha1, orig_sha1);
-       if (write_ref_sha1(lock, orig_sha1, logmsg)) {
+
+       if (write_ref_to_lockfile(lock, orig_sha1) ||
+           commit_ref_update(lock, orig_sha1, logmsg)) {
                error("unable to write current sha1 into %s", newrefname);
                goto rollback;
        }
@@ -1926,16 +2944,17 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
        return 0;
 
  rollback:
-       lock = lock_ref_sha1_basic(oldrefname, NULL, 0, NULL);
+       lock = lock_ref_sha1_basic(oldrefname, NULL, NULL, NULL, 0, NULL, &err);
        if (!lock) {
-               error("unable to lock %s for rollback", oldrefname);
+               error("unable to lock %s for rollback: %s", oldrefname, err.buf);
+               strbuf_release(&err);
                goto rollbacklog;
        }
 
-       lock->force_write = 1;
        flag = log_all_ref_updates;
        log_all_ref_updates = 0;
-       if (write_ref_sha1(lock, orig_sha1, NULL))
+       if (write_ref_to_lockfile(lock, orig_sha1) ||
+           commit_ref_update(lock, orig_sha1, NULL))
                error("unable to write current sha1 into %s", oldrefname);
        log_all_ref_updates = flag;
 
@@ -1951,7 +2970,7 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
        return 1;
 }
 
-int close_ref(struct ref_lock *lock)
+static int close_ref(struct ref_lock *lock)
 {
        if (close_lock_file(lock->lk))
                return -1;
@@ -1959,7 +2978,7 @@ int close_ref(struct ref_lock *lock)
        return 0;
 }
 
-int commit_ref(struct ref_lock *lock)
+static int commit_ref(struct ref_lock *lock)
 {
        if (commit_lock_file(lock->lk))
                return -1;
@@ -1967,16 +2986,6 @@ int commit_ref(struct ref_lock *lock)
        return 0;
 }
 
-void unlock_ref(struct ref_lock *lock)
-{
-       /* Do not free lock->lk -- atexit() still looks at them */
-       if (lock->lk)
-               rollback_lock_file(lock->lk);
-       free(lock->ref_name);
-       free(lock->orig_ref_name);
-       free(lock);
-}
-
 /*
  * copy the reflog message msg to buf, which has been allocated sufficiently
  * large, while cleaning up the whitespaces.  Especially, convert LF to space,
@@ -2003,38 +3012,49 @@ static int copy_msg(char *buf, const char *msg)
        return cp - buf;
 }
 
+/* This function must set a meaningful errno on failure */
 int log_ref_setup(const char *refname, char *logfile, int bufsize)
 {
        int logfd, oflags = O_APPEND | O_WRONLY;
 
        git_snpath(logfile, bufsize, "logs/%s", refname);
        if (log_all_ref_updates &&
-           (!prefixcmp(refname, "refs/heads/") ||
-            !prefixcmp(refname, "refs/remotes/") ||
-            !prefixcmp(refname, "refs/notes/") ||
+           (starts_with(refname, "refs/heads/") ||
+            starts_with(refname, "refs/remotes/") ||
+            starts_with(refname, "refs/notes/") ||
             !strcmp(refname, "HEAD"))) {
-               if (safe_create_leading_directories(logfile) < 0)
-                       return error("unable to create directory for %s",
-                                    logfile);
+               if (safe_create_leading_directories(logfile) < 0) {
+                       int save_errno = errno;
+                       error("unable to create directory for %s", logfile);
+                       errno = save_errno;
+                       return -1;
+               }
                oflags |= O_CREAT;
        }
 
        logfd = open(logfile, oflags, 0666);
        if (logfd < 0) {
-               if (!(oflags & O_CREAT) && errno == ENOENT)
+               if (!(oflags & O_CREAT) && (errno == ENOENT || errno == EISDIR))
                        return 0;
 
-               if ((oflags & O_CREAT) && errno == EISDIR) {
+               if (errno == EISDIR) {
                        if (remove_empty_directories(logfile)) {
-                               return error("There are still logs under '%s'",
-                                            logfile);
+                               int save_errno = errno;
+                               error("There are still logs under '%s'",
+                                     logfile);
+                               errno = save_errno;
+                               return -1;
                        }
                        logfd = open(logfile, oflags, 0666);
                }
 
-               if (logfd < 0)
-                       return error("Unable to append to %s: %s",
-                                    logfile, strerror(errno));
+               if (logfd < 0) {
+                       int save_errno = errno;
+                       error("Unable to append to %s: %s", logfile,
+                             strerror(errno));
+                       errno = save_errno;
+                       return -1;
+               }
        }
 
        adjust_shared_perm(logfile);
@@ -2042,15 +3062,37 @@ int log_ref_setup(const char *refname, char *logfile, int bufsize)
        return 0;
 }
 
+static int log_ref_write_fd(int fd, const unsigned char *old_sha1,
+                           const unsigned char *new_sha1,
+                           const char *committer, const char *msg)
+{
+       int msglen, written;
+       unsigned maxlen, len;
+       char *logrec;
+
+       msglen = msg ? strlen(msg) : 0;
+       maxlen = strlen(committer) + msglen + 100;
+       logrec = xmalloc(maxlen);
+       len = sprintf(logrec, "%s %s %s\n",
+                     sha1_to_hex(old_sha1),
+                     sha1_to_hex(new_sha1),
+                     committer);
+       if (msglen)
+               len += copy_msg(logrec + len - 1, msg) - 1;
+
+       written = len <= maxlen ? write_in_full(fd, logrec, len) : -1;
+       free(logrec);
+       if (written != len)
+               return -1;
+
+       return 0;
+}
+
 static int log_ref_write(const char *refname, const unsigned char *old_sha1,
                         const unsigned char *new_sha1, const char *msg)
 {
-       int logfd, result, written, oflags = O_APPEND | O_WRONLY;
-       unsigned maxlen, len;
-       int msglen;
+       int logfd, result, oflags = O_APPEND | O_WRONLY;
        char log_file[PATH_MAX];
-       char *logrec;
-       const char *committer;
 
        if (log_all_ref_updates < 0)
                log_all_ref_updates = !is_bare_repository();
@@ -2062,61 +3104,75 @@ static int log_ref_write(const char *refname, const unsigned char *old_sha1,
        logfd = open(log_file, oflags);
        if (logfd < 0)
                return 0;
-       msglen = msg ? strlen(msg) : 0;
-       committer = git_committer_info(0);
-       maxlen = strlen(committer) + msglen + 100;
-       logrec = xmalloc(maxlen);
-       len = sprintf(logrec, "%s %s %s\n",
-                     sha1_to_hex(old_sha1),
-                     sha1_to_hex(new_sha1),
-                     committer);
-       if (msglen)
-               len += copy_msg(logrec + len - 1, msg) - 1;
-       written = len <= maxlen ? write_in_full(logfd, logrec, len) : -1;
-       free(logrec);
-       if (close(logfd) != 0 || written != len)
-               return error("Unable to append to %s", log_file);
+       result = log_ref_write_fd(logfd, old_sha1, new_sha1,
+                                 git_committer_info(0), msg);
+       if (result) {
+               int save_errno = errno;
+               close(logfd);
+               error("Unable to append to %s", log_file);
+               errno = save_errno;
+               return -1;
+       }
+       if (close(logfd)) {
+               int save_errno = errno;
+               error("Unable to append to %s", log_file);
+               errno = save_errno;
+               return -1;
+       }
        return 0;
 }
 
-static int is_branch(const char *refname)
+int is_branch(const char *refname)
 {
-       return !strcmp(refname, "HEAD") || !prefixcmp(refname, "refs/heads/");
+       return !strcmp(refname, "HEAD") || starts_with(refname, "refs/heads/");
 }
 
-int write_ref_sha1(struct ref_lock *lock,
-       const unsigned char *sha1, const char *logmsg)
+/*
+ * Write sha1 into the open lockfile, then close the lockfile. On
+ * errors, rollback the lockfile and set errno to reflect the problem.
+ */
+static int write_ref_to_lockfile(struct ref_lock *lock,
+                                const unsigned char *sha1)
 {
        static char term = '\n';
        struct object *o;
 
-       if (!lock)
-               return -1;
-       if (!lock->force_write && !hashcmp(lock->old_sha1, sha1)) {
-               unlock_ref(lock);
-               return 0;
-       }
        o = parse_object(sha1);
        if (!o) {
                error("Trying to write ref %s with nonexistent object %s",
                        lock->ref_name, sha1_to_hex(sha1));
                unlock_ref(lock);
+               errno = EINVAL;
                return -1;
        }
        if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
                error("Trying to write non-commit object %s to branch %s",
                        sha1_to_hex(sha1), lock->ref_name);
                unlock_ref(lock);
+               errno = EINVAL;
                return -1;
        }
        if (write_in_full(lock->lock_fd, sha1_to_hex(sha1), 40) != 40 ||
-           write_in_full(lock->lock_fd, &term, 1) != 1
-               || close_ref(lock) < 0) {
-               error("Couldn't write %s", lock->lk->filename);
+           write_in_full(lock->lock_fd, &term, 1) != 1 ||
+           close_ref(lock) < 0) {
+               int save_errno = errno;
+               error("Couldn't write %s", lock->lk->filename.buf);
                unlock_ref(lock);
+               errno = save_errno;
                return -1;
        }
-       clear_loose_ref_cache(get_ref_cache(NULL));
+       return 0;
+}
+
+/*
+ * Commit a change to a loose reference that has already been written
+ * to the loose reference lockfile. Also update the reflogs if
+ * necessary, using the specified lockmsg (which can be NULL).
+ */
+static int commit_ref_update(struct ref_lock *lock,
+                            const unsigned char *sha1, const char *logmsg)
+{
+       clear_loose_ref_cache(&ref_cache);
        if (log_ref_write(lock->ref_name, lock->old_sha1, sha1, logmsg) < 0 ||
            (strcmp(lock->ref_name, lock->orig_ref_name) &&
             log_ref_write(lock->orig_ref_name, lock->old_sha1, sha1, logmsg) < 0)) {
@@ -2139,7 +3195,8 @@ int write_ref_sha1(struct ref_lock *lock,
                unsigned char head_sha1[20];
                int head_flag;
                const char *head_ref;
-               head_ref = resolve_ref_unsafe("HEAD", head_sha1, 1, &head_flag);
+               head_ref = resolve_ref_unsafe("HEAD", RESOLVE_REF_READING,
+                                             head_sha1, &head_flag);
                if (head_ref && (head_flag & REF_ISSYMREF) &&
                    !strcmp(head_ref, lock->ref_name))
                        log_ref_write("HEAD", lock->old_sha1, sha1, logmsg);
@@ -2216,175 +3273,273 @@ int create_symref(const char *ref_target, const char *refs_heads_master,
        return 0;
 }
 
-static char *ref_msg(const char *line, const char *endp)
+struct read_ref_at_cb {
+       const char *refname;
+       unsigned long at_time;
+       int cnt;
+       int reccnt;
+       unsigned char *sha1;
+       int found_it;
+
+       unsigned char osha1[20];
+       unsigned char nsha1[20];
+       int tz;
+       unsigned long date;
+       char **msg;
+       unsigned long *cutoff_time;
+       int *cutoff_tz;
+       int *cutoff_cnt;
+};
+
+static int read_ref_at_ent(unsigned char *osha1, unsigned char *nsha1,
+               const char *email, unsigned long timestamp, int tz,
+               const char *message, void *cb_data)
 {
-       const char *ep;
-       line += 82;
-       ep = memchr(line, '\n', endp - line);
-       if (!ep)
-               ep = endp;
-       return xmemdupz(line, ep - line);
+       struct read_ref_at_cb *cb = cb_data;
+
+       cb->reccnt++;
+       cb->tz = tz;
+       cb->date = timestamp;
+
+       if (timestamp <= cb->at_time || cb->cnt == 0) {
+               if (cb->msg)
+                       *cb->msg = xstrdup(message);
+               if (cb->cutoff_time)
+                       *cb->cutoff_time = timestamp;
+               if (cb->cutoff_tz)
+                       *cb->cutoff_tz = tz;
+               if (cb->cutoff_cnt)
+                       *cb->cutoff_cnt = cb->reccnt - 1;
+               /*
+                * we have not yet updated cb->[n|o]sha1 so they still
+                * hold the values for the previous record.
+                */
+               if (!is_null_sha1(cb->osha1)) {
+                       hashcpy(cb->sha1, nsha1);
+                       if (hashcmp(cb->osha1, nsha1))
+                               warning("Log for ref %s has gap after %s.",
+                                       cb->refname, show_date(cb->date, cb->tz, DATE_RFC2822));
+               }
+               else if (cb->date == cb->at_time)
+                       hashcpy(cb->sha1, nsha1);
+               else if (hashcmp(nsha1, cb->sha1))
+                       warning("Log for ref %s unexpectedly ended on %s.",
+                               cb->refname, show_date(cb->date, cb->tz,
+                                                  DATE_RFC2822));
+               hashcpy(cb->osha1, osha1);
+               hashcpy(cb->nsha1, nsha1);
+               cb->found_it = 1;
+               return 1;
+       }
+       hashcpy(cb->osha1, osha1);
+       hashcpy(cb->nsha1, nsha1);
+       if (cb->cnt > 0)
+               cb->cnt--;
+       return 0;
+}
+
+static int read_ref_at_ent_oldest(unsigned char *osha1, unsigned char *nsha1,
+                                 const char *email, unsigned long timestamp,
+                                 int tz, const char *message, void *cb_data)
+{
+       struct read_ref_at_cb *cb = cb_data;
+
+       if (cb->msg)
+               *cb->msg = xstrdup(message);
+       if (cb->cutoff_time)
+               *cb->cutoff_time = timestamp;
+       if (cb->cutoff_tz)
+               *cb->cutoff_tz = tz;
+       if (cb->cutoff_cnt)
+               *cb->cutoff_cnt = cb->reccnt;
+       hashcpy(cb->sha1, osha1);
+       if (is_null_sha1(cb->sha1))
+               hashcpy(cb->sha1, nsha1);
+       /* We just want the first entry */
+       return 1;
 }
 
-int read_ref_at(const char *refname, unsigned long at_time, int cnt,
+int read_ref_at(const char *refname, unsigned int flags, unsigned long at_time, int cnt,
                unsigned char *sha1, char **msg,
                unsigned long *cutoff_time, int *cutoff_tz, int *cutoff_cnt)
 {
-       const char *logfile, *logdata, *logend, *rec, *lastgt, *lastrec;
-       char *tz_c;
-       int logfd, tz, reccnt = 0;
-       struct stat st;
-       unsigned long date;
-       unsigned char logged_sha1[20];
-       void *log_mapped;
-       size_t mapsz;
+       struct read_ref_at_cb cb;
+
+       memset(&cb, 0, sizeof(cb));
+       cb.refname = refname;
+       cb.at_time = at_time;
+       cb.cnt = cnt;
+       cb.msg = msg;
+       cb.cutoff_time = cutoff_time;
+       cb.cutoff_tz = cutoff_tz;
+       cb.cutoff_cnt = cutoff_cnt;
+       cb.sha1 = sha1;
+
+       for_each_reflog_ent_reverse(refname, read_ref_at_ent, &cb);
+
+       if (!cb.reccnt) {
+               if (flags & GET_SHA1_QUIETLY)
+                       exit(128);
+               else
+                       die("Log for %s is empty.", refname);
+       }
+       if (cb.found_it)
+               return 0;
 
-       logfile = git_path("logs/%s", refname);
-       logfd = open(logfile, O_RDONLY, 0);
-       if (logfd < 0)
-               die_errno("Unable to read log '%s'", logfile);
-       fstat(logfd, &st);
-       if (!st.st_size)
-               die("Log %s is empty.", logfile);
-       mapsz = xsize_t(st.st_size);
-       log_mapped = xmmap(NULL, mapsz, PROT_READ, MAP_PRIVATE, logfd, 0);
-       logdata = log_mapped;
-       close(logfd);
+       for_each_reflog_ent(refname, read_ref_at_ent_oldest, &cb);
 
-       lastrec = NULL;
-       rec = logend = logdata + st.st_size;
-       while (logdata < rec) {
-               reccnt++;
-               if (logdata < rec && *(rec-1) == '\n')
-                       rec--;
-               lastgt = NULL;
-               while (logdata < rec && *(rec-1) != '\n') {
-                       rec--;
-                       if (*rec == '>')
-                               lastgt = rec;
-               }
-               if (!lastgt)
-                       die("Log %s is corrupt.", logfile);
-               date = strtoul(lastgt + 1, &tz_c, 10);
-               if (date <= at_time || cnt == 0) {
-                       tz = strtoul(tz_c, NULL, 10);
-                       if (msg)
-                               *msg = ref_msg(rec, logend);
-                       if (cutoff_time)
-                               *cutoff_time = date;
-                       if (cutoff_tz)
-                               *cutoff_tz = tz;
-                       if (cutoff_cnt)
-                               *cutoff_cnt = reccnt - 1;
-                       if (lastrec) {
-                               if (get_sha1_hex(lastrec, logged_sha1))
-                                       die("Log %s is corrupt.", logfile);
-                               if (get_sha1_hex(rec + 41, sha1))
-                                       die("Log %s is corrupt.", logfile);
-                               if (hashcmp(logged_sha1, sha1)) {
-                                       warning("Log %s has gap after %s.",
-                                               logfile, show_date(date, tz, DATE_RFC2822));
-                               }
-                       }
-                       else if (date == at_time) {
-                               if (get_sha1_hex(rec + 41, sha1))
-                                       die("Log %s is corrupt.", logfile);
-                       }
-                       else {
-                               if (get_sha1_hex(rec + 41, logged_sha1))
-                                       die("Log %s is corrupt.", logfile);
-                               if (hashcmp(logged_sha1, sha1)) {
-                                       warning("Log %s unexpectedly ended on %s.",
-                                               logfile, show_date(date, tz, DATE_RFC2822));
-                               }
-                       }
-                       munmap(log_mapped, mapsz);
-                       return 0;
-               }
-               lastrec = rec;
-               if (cnt > 0)
-                       cnt--;
-       }
-
-       rec = logdata;
-       while (rec < logend && *rec != '>' && *rec != '\n')
-               rec++;
-       if (rec == logend || *rec == '\n')
-               die("Log %s is corrupt.", logfile);
-       date = strtoul(rec + 1, &tz_c, 10);
-       tz = strtoul(tz_c, NULL, 10);
-       if (get_sha1_hex(logdata, sha1))
-               die("Log %s is corrupt.", logfile);
-       if (is_null_sha1(sha1)) {
-               if (get_sha1_hex(logdata + 41, sha1))
-                       die("Log %s is corrupt.", logfile);
-       }
-       if (msg)
-               *msg = ref_msg(logdata, logend);
-       munmap(log_mapped, mapsz);
-
-       if (cutoff_time)
-               *cutoff_time = date;
-       if (cutoff_tz)
-               *cutoff_tz = tz;
-       if (cutoff_cnt)
-               *cutoff_cnt = reccnt;
        return 1;
 }
 
-int for_each_recent_reflog_ent(const char *refname, each_reflog_ent_fn fn, long ofs, void *cb_data)
+int reflog_exists(const char *refname)
+{
+       struct stat st;
+
+       return !lstat(git_path("logs/%s", refname), &st) &&
+               S_ISREG(st.st_mode);
+}
+
+int delete_reflog(const char *refname)
+{
+       return remove_path(git_path("logs/%s", refname));
+}
+
+static int show_one_reflog_ent(struct strbuf *sb, each_reflog_ent_fn fn, void *cb_data)
+{
+       unsigned char osha1[20], nsha1[20];
+       char *email_end, *message;
+       unsigned long timestamp;
+       int tz;
+
+       /* old SP new SP name <email> SP time TAB msg LF */
+       if (sb->len < 83 || sb->buf[sb->len - 1] != '\n' ||
+           get_sha1_hex(sb->buf, osha1) || sb->buf[40] != ' ' ||
+           get_sha1_hex(sb->buf + 41, nsha1) || sb->buf[81] != ' ' ||
+           !(email_end = strchr(sb->buf + 82, '>')) ||
+           email_end[1] != ' ' ||
+           !(timestamp = strtoul(email_end + 2, &message, 10)) ||
+           !message || message[0] != ' ' ||
+           (message[1] != '+' && message[1] != '-') ||
+           !isdigit(message[2]) || !isdigit(message[3]) ||
+           !isdigit(message[4]) || !isdigit(message[5]))
+               return 0; /* corrupt? */
+       email_end[1] = '\0';
+       tz = strtol(message + 1, NULL, 10);
+       if (message[6] != '\t')
+               message += 6;
+       else
+               message += 7;
+       return fn(osha1, nsha1, sb->buf + 82, timestamp, tz, message, cb_data);
+}
+
+static char *find_beginning_of_line(char *bob, char *scan)
+{
+       while (bob < scan && *(--scan) != '\n')
+               ; /* keep scanning backwards */
+       /*
+        * Return either beginning of the buffer, or LF at the end of
+        * the previous line.
+        */
+       return scan;
+}
+
+int for_each_reflog_ent_reverse(const char *refname, each_reflog_ent_fn fn, void *cb_data)
 {
-       const char *logfile;
-       FILE *logfp;
        struct strbuf sb = STRBUF_INIT;
-       int ret = 0;
+       FILE *logfp;
+       long pos;
+       int ret = 0, at_tail = 1;
 
-       logfile = git_path("logs/%s", refname);
-       logfp = fopen(logfile, "r");
+       logfp = fopen(git_path("logs/%s", refname), "r");
        if (!logfp)
                return -1;
 
-       if (ofs) {
-               struct stat statbuf;
-               if (fstat(fileno(logfp), &statbuf) ||
-                   statbuf.st_size < ofs ||
-                   fseek(logfp, -ofs, SEEK_END) ||
-                   strbuf_getwholeline(&sb, logfp, '\n')) {
-                       fclose(logfp);
-                       strbuf_release(&sb);
-                       return -1;
+       /* Jump to the end */
+       if (fseek(logfp, 0, SEEK_END) < 0)
+               return error("cannot seek back reflog for %s: %s",
+                            refname, strerror(errno));
+       pos = ftell(logfp);
+       while (!ret && 0 < pos) {
+               int cnt;
+               size_t nread;
+               char buf[BUFSIZ];
+               char *endp, *scanp;
+
+               /* Fill next block from the end */
+               cnt = (sizeof(buf) < pos) ? sizeof(buf) : pos;
+               if (fseek(logfp, pos - cnt, SEEK_SET))
+                       return error("cannot seek back reflog for %s: %s",
+                                    refname, strerror(errno));
+               nread = fread(buf, cnt, 1, logfp);
+               if (nread != 1)
+                       return error("cannot read %d bytes from reflog for %s: %s",
+                                    cnt, refname, strerror(errno));
+               pos -= cnt;
+
+               scanp = endp = buf + cnt;
+               if (at_tail && scanp[-1] == '\n')
+                       /* Looking at the final LF at the end of the file */
+                       scanp--;
+               at_tail = 0;
+
+               while (buf < scanp) {
+                       /*
+                        * terminating LF of the previous line, or the beginning
+                        * of the buffer.
+                        */
+                       char *bp;
+
+                       bp = find_beginning_of_line(buf, scanp);
+
+                       if (*bp == '\n') {
+                               /*
+                                * The newline is the end of the previous line,
+                                * so we know we have complete line starting
+                                * at (bp + 1). Prefix it onto any prior data
+                                * we collected for the line and process it.
+                                */
+                               strbuf_splice(&sb, 0, 0, bp + 1, endp - (bp + 1));
+                               scanp = bp;
+                               endp = bp + 1;
+                               ret = show_one_reflog_ent(&sb, fn, cb_data);
+                               strbuf_reset(&sb);
+                               if (ret)
+                                       break;
+                       } else if (!pos) {
+                               /*
+                                * We are at the start of the buffer, and the
+                                * start of the file; there is no previous
+                                * line, and we have everything for this one.
+                                * Process it, and we can end the loop.
+                                */
+                               strbuf_splice(&sb, 0, 0, buf, endp - buf);
+                               ret = show_one_reflog_ent(&sb, fn, cb_data);
+                               strbuf_reset(&sb);
+                               break;
+                       }
+
+                       if (bp == buf) {
+                               /*
+                                * We are at the start of the buffer, and there
+                                * is more file to read backwards. Which means
+                                * we are in the middle of a line. Note that we
+                                * may get here even if *bp was a newline; that
+                                * just means we are at the exact end of the
+                                * previous line, rather than some spot in the
+                                * middle.
+                                *
+                                * Save away what we have to be combined with
+                                * the data from the next read.
+                                */
+                               strbuf_splice(&sb, 0, 0, buf, endp - buf);
+                               break;
+                       }
                }
-       }
 
-       while (!strbuf_getwholeline(&sb, logfp, '\n')) {
-               unsigned char osha1[20], nsha1[20];
-               char *email_end, *message;
-               unsigned long timestamp;
-               int tz;
-
-               /* old SP new SP name <email> SP time TAB msg LF */
-               if (sb.len < 83 || sb.buf[sb.len - 1] != '\n' ||
-                   get_sha1_hex(sb.buf, osha1) || sb.buf[40] != ' ' ||
-                   get_sha1_hex(sb.buf + 41, nsha1) || sb.buf[81] != ' ' ||
-                   !(email_end = strchr(sb.buf + 82, '>')) ||
-                   email_end[1] != ' ' ||
-                   !(timestamp = strtoul(email_end + 2, &message, 10)) ||
-                   !message || message[0] != ' ' ||
-                   (message[1] != '+' && message[1] != '-') ||
-                   !isdigit(message[2]) || !isdigit(message[3]) ||
-                   !isdigit(message[4]) || !isdigit(message[5]))
-                       continue; /* corrupt? */
-               email_end[1] = '\0';
-               tz = strtol(message + 1, NULL, 10);
-               if (message[6] != '\t')
-                       message += 6;
-               else
-                       message += 7;
-               ret = fn(osha1, nsha1, sb.buf + 82, timestamp, tz, message,
-                        cb_data);
-               if (ret)
-                       break;
        }
+       if (!ret && sb.len)
+               die("BUG: reverse reflog parser had leftover data");
+
        fclose(logfp);
        strbuf_release(&sb);
        return ret;
@@ -2392,9 +3547,20 @@ int for_each_recent_reflog_ent(const char *refname, each_reflog_ent_fn fn, long
 
 int for_each_reflog_ent(const char *refname, each_reflog_ent_fn fn, void *cb_data)
 {
-       return for_each_recent_reflog_ent(refname, fn, 0, cb_data);
-}
+       FILE *logfp;
+       struct strbuf sb = STRBUF_INIT;
+       int ret = 0;
 
+       logfp = fopen(git_path("logs/%s", refname), "r");
+       if (!logfp)
+               return -1;
+
+       while (!ret && !strbuf_getwholeline(&sb, logfp, '\n'))
+               ret = show_one_reflog_ent(&sb, fn, cb_data);
+       fclose(logfp);
+       strbuf_release(&sb);
+       return ret;
+}
 /*
  * Call fn for each reflog in the namespace indicated by name.  name
  * must be empty or end with '/'.  Name will be used as a scratch
@@ -2415,7 +3581,7 @@ static int do_for_each_reflog(struct strbuf *name, each_ref_fn fn, void *cb_data
 
                if (de->d_name[0] == '.')
                        continue;
-               if (has_extension(de->d_name, ".lock"))
+               if (ends_with(de->d_name, ".lock"))
                        continue;
                strbuf_addstr(name, de->d_name);
                if (stat(git_path("logs/%s", name->buf), &st) < 0) {
@@ -2426,7 +3592,7 @@ static int do_for_each_reflog(struct strbuf *name, each_ref_fn fn, void *cb_data
                                retval = do_for_each_reflog(name, fn, cb_data);
                        } else {
                                unsigned char sha1[20];
-                               if (read_ref_full(name->buf, sha1, 0, NULL))
+                               if (read_ref_full(name->buf, 0, sha1, NULL))
                                        retval = error("bad ref for %s", name->buf);
                                else
                                        retval = fn(name->buf, sha1, 0, cb_data);
@@ -2450,62 +3616,372 @@ int for_each_reflog(each_ref_fn fn, void *cb_data)
        return retval;
 }
 
-int update_ref(const char *action, const char *refname,
-               const unsigned char *sha1, const unsigned char *oldval,
-               int flags, enum action_on_err onerr)
+/**
+ * Information needed for a single ref update. Set new_sha1 to the new
+ * value or to null_sha1 to delete the ref. To check the old value
+ * while the ref is locked, set (flags & REF_HAVE_OLD) and set
+ * old_sha1 to the old value, or to null_sha1 to ensure the ref does
+ * not exist before update.
+ */
+struct ref_update {
+       /*
+        * If (flags & REF_HAVE_NEW), set the reference to this value:
+        */
+       unsigned char new_sha1[20];
+       /*
+        * If (flags & REF_HAVE_OLD), check that the reference
+        * previously had this value:
+        */
+       unsigned char old_sha1[20];
+       /*
+        * One or more of REF_HAVE_NEW, REF_HAVE_OLD, REF_NODEREF,
+        * REF_DELETING, and REF_ISPRUNING:
+        */
+       unsigned int flags;
+       struct ref_lock *lock;
+       int type;
+       char *msg;
+       const char refname[FLEX_ARRAY];
+};
+
+/*
+ * Transaction states.
+ * OPEN:   The transaction is in a valid state and can accept new updates.
+ *         An OPEN transaction can be committed.
+ * CLOSED: A closed transaction is no longer active and no other operations
+ *         than free can be used on it in this state.
+ *         A transaction can either become closed by successfully committing
+ *         an active transaction or if there is a failure while building
+ *         the transaction thus rendering it failed/inactive.
+ */
+enum ref_transaction_state {
+       REF_TRANSACTION_OPEN   = 0,
+       REF_TRANSACTION_CLOSED = 1
+};
+
+/*
+ * Data structure for holding a reference transaction, which can
+ * consist of checks and updates to multiple references, carried out
+ * as atomically as possible.  This structure is opaque to callers.
+ */
+struct ref_transaction {
+       struct ref_update **updates;
+       size_t alloc;
+       size_t nr;
+       enum ref_transaction_state state;
+};
+
+struct ref_transaction *ref_transaction_begin(struct strbuf *err)
+{
+       assert(err);
+
+       return xcalloc(1, sizeof(struct ref_transaction));
+}
+
+void ref_transaction_free(struct ref_transaction *transaction)
 {
-       static struct ref_lock *lock;
-       lock = lock_any_ref_for_update(refname, oldval, flags);
-       if (!lock) {
-               const char *str = "Cannot lock the ref '%s'.";
-               switch (onerr) {
-               case MSG_ON_ERR: error(str, refname); break;
-               case DIE_ON_ERR: die(str, refname); break;
-               case QUIET_ON_ERR: break;
-               }
-               return 1;
+       int i;
+
+       if (!transaction)
+               return;
+
+       for (i = 0; i < transaction->nr; i++) {
+               free(transaction->updates[i]->msg);
+               free(transaction->updates[i]);
        }
-       if (write_ref_sha1(lock, sha1, action) < 0) {
-               const char *str = "Cannot update the ref '%s'.";
+       free(transaction->updates);
+       free(transaction);
+}
+
+static struct ref_update *add_update(struct ref_transaction *transaction,
+                                    const char *refname)
+{
+       size_t len = strlen(refname);
+       struct ref_update *update = xcalloc(1, sizeof(*update) + len + 1);
+
+       strcpy((char *)update->refname, refname);
+       ALLOC_GROW(transaction->updates, transaction->nr + 1, transaction->alloc);
+       transaction->updates[transaction->nr++] = update;
+       return update;
+}
+
+int ref_transaction_update(struct ref_transaction *transaction,
+                          const char *refname,
+                          const unsigned char *new_sha1,
+                          const unsigned char *old_sha1,
+                          unsigned int flags, const char *msg,
+                          struct strbuf *err)
+{
+       struct ref_update *update;
+
+       assert(err);
+
+       if (transaction->state != REF_TRANSACTION_OPEN)
+               die("BUG: update called for transaction that is not open");
+
+       if (new_sha1 && !is_null_sha1(new_sha1) &&
+           check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
+               strbuf_addf(err, "refusing to update ref with bad name %s",
+                           refname);
+               return -1;
+       }
+
+       update = add_update(transaction, refname);
+       if (new_sha1) {
+               hashcpy(update->new_sha1, new_sha1);
+               flags |= REF_HAVE_NEW;
+       }
+       if (old_sha1) {
+               hashcpy(update->old_sha1, old_sha1);
+               flags |= REF_HAVE_OLD;
+       }
+       update->flags = flags;
+       if (msg)
+               update->msg = xstrdup(msg);
+       return 0;
+}
+
+int ref_transaction_create(struct ref_transaction *transaction,
+                          const char *refname,
+                          const unsigned char *new_sha1,
+                          unsigned int flags, const char *msg,
+                          struct strbuf *err)
+{
+       if (!new_sha1 || is_null_sha1(new_sha1))
+               die("BUG: create called without valid new_sha1");
+       return ref_transaction_update(transaction, refname, new_sha1,
+                                     null_sha1, flags, msg, err);
+}
+
+int ref_transaction_delete(struct ref_transaction *transaction,
+                          const char *refname,
+                          const unsigned char *old_sha1,
+                          unsigned int flags, const char *msg,
+                          struct strbuf *err)
+{
+       if (old_sha1 && is_null_sha1(old_sha1))
+               die("BUG: delete called with old_sha1 set to zeros");
+       return ref_transaction_update(transaction, refname,
+                                     null_sha1, old_sha1,
+                                     flags, msg, err);
+}
+
+int ref_transaction_verify(struct ref_transaction *transaction,
+                          const char *refname,
+                          const unsigned char *old_sha1,
+                          unsigned int flags,
+                          struct strbuf *err)
+{
+       if (!old_sha1)
+               die("BUG: verify called with old_sha1 set to NULL");
+       return ref_transaction_update(transaction, refname,
+                                     NULL, old_sha1,
+                                     flags, NULL, err);
+}
+
+int update_ref(const char *msg, const char *refname,
+              const unsigned char *new_sha1, const unsigned char *old_sha1,
+              unsigned int flags, enum action_on_err onerr)
+{
+       struct ref_transaction *t;
+       struct strbuf err = STRBUF_INIT;
+
+       t = ref_transaction_begin(&err);
+       if (!t ||
+           ref_transaction_update(t, refname, new_sha1, old_sha1,
+                                  flags, msg, &err) ||
+           ref_transaction_commit(t, &err)) {
+               const char *str = "update_ref failed for ref '%s': %s";
+
+               ref_transaction_free(t);
                switch (onerr) {
-               case MSG_ON_ERR: error(str, refname); break;
-               case DIE_ON_ERR: die(str, refname); break;
-               case QUIET_ON_ERR: break;
+               case UPDATE_REFS_MSG_ON_ERR:
+                       error(str, refname, err.buf);
+                       break;
+               case UPDATE_REFS_DIE_ON_ERR:
+                       die(str, refname, err.buf);
+                       break;
+               case UPDATE_REFS_QUIET_ON_ERR:
+                       break;
                }
+               strbuf_release(&err);
                return 1;
        }
+       strbuf_release(&err);
+       ref_transaction_free(t);
        return 0;
 }
 
-struct ref *find_ref_by_name(const struct ref *list, const char *name)
+static int ref_update_reject_duplicates(struct string_list *refnames,
+                                       struct strbuf *err)
 {
-       for ( ; list; list = list->next)
-               if (!strcmp(list->name, name))
-                       return (struct ref *)list;
-       return NULL;
+       int i, n = refnames->nr;
+
+       assert(err);
+
+       for (i = 1; i < n; i++)
+               if (!strcmp(refnames->items[i - 1].string, refnames->items[i].string)) {
+                       strbuf_addf(err,
+                                   "Multiple updates for ref '%s' not allowed.",
+                                   refnames->items[i].string);
+                       return 1;
+               }
+       return 0;
 }
 
-/*
- * generate a format suitable for scanf from a ref_rev_parse_rules
- * rule, that is replace the "%.*s" spec with a "%s" spec
- */
-static void gen_scanf_fmt(char *scanf_fmt, const char *rule)
+int ref_transaction_commit(struct ref_transaction *transaction,
+                          struct strbuf *err)
 {
-       char *spec;
+       int ret = 0, i;
+       int n = transaction->nr;
+       struct ref_update **updates = transaction->updates;
+       struct string_list refs_to_delete = STRING_LIST_INIT_NODUP;
+       struct string_list_item *ref_to_delete;
+       struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+
+       assert(err);
 
-       spec = strstr(rule, "%.*s");
-       if (!spec || strstr(spec + 4, "%.*s"))
-               die("invalid rule in ref_rev_parse_rules: %s", rule);
+       if (transaction->state != REF_TRANSACTION_OPEN)
+               die("BUG: commit called for transaction that is not open");
 
-       /* copy all until spec */
-       strncpy(scanf_fmt, rule, spec - rule);
-       scanf_fmt[spec - rule] = '\0';
-       /* copy new spec */
-       strcat(scanf_fmt, "%s");
-       /* copy remaining rule */
-       strcat(scanf_fmt, spec + 4);
+       if (!n) {
+               transaction->state = REF_TRANSACTION_CLOSED;
+               return 0;
+       }
+
+       /* Fail if a refname appears more than once in the transaction: */
+       for (i = 0; i < n; i++)
+               string_list_append(&affected_refnames, updates[i]->refname);
+       string_list_sort(&affected_refnames);
+       if (ref_update_reject_duplicates(&affected_refnames, err)) {
+               ret = TRANSACTION_GENERIC_ERROR;
+               goto cleanup;
+       }
+
+       /*
+        * Acquire all locks, verify old values if provided, check
+        * that new values are valid, and write new values to the
+        * lockfiles, ready to be activated. Only keep one lockfile
+        * open at a time to avoid running out of file descriptors.
+        */
+       for (i = 0; i < n; i++) {
+               struct ref_update *update = updates[i];
+
+               if ((update->flags & REF_HAVE_NEW) &&
+                   is_null_sha1(update->new_sha1))
+                       update->flags |= REF_DELETING;
+               update->lock = lock_ref_sha1_basic(
+                               update->refname,
+                               ((update->flags & REF_HAVE_OLD) ?
+                                update->old_sha1 : NULL),
+                               &affected_refnames, NULL,
+                               update->flags,
+                               &update->type,
+                               err);
+               if (!update->lock) {
+                       char *reason;
+
+                       ret = (errno == ENOTDIR)
+                               ? TRANSACTION_NAME_CONFLICT
+                               : TRANSACTION_GENERIC_ERROR;
+                       reason = strbuf_detach(err, NULL);
+                       strbuf_addf(err, "Cannot lock ref '%s': %s",
+                                   update->refname, reason);
+                       free(reason);
+                       goto cleanup;
+               }
+               if ((update->flags & REF_HAVE_NEW) &&
+                   !(update->flags & REF_DELETING)) {
+                       int overwriting_symref = ((update->type & REF_ISSYMREF) &&
+                                                 (update->flags & REF_NODEREF));
+
+                       if (!overwriting_symref &&
+                           !hashcmp(update->lock->old_sha1, update->new_sha1)) {
+                               /*
+                                * The reference already has the desired
+                                * value, so we don't need to write it.
+                                */
+                       } else if (write_ref_to_lockfile(update->lock,
+                                                        update->new_sha1)) {
+                               /*
+                                * The lock was freed upon failure of
+                                * write_ref_to_lockfile():
+                                */
+                               update->lock = NULL;
+                               strbuf_addf(err, "Cannot update the ref '%s'.",
+                                           update->refname);
+                               ret = TRANSACTION_GENERIC_ERROR;
+                               goto cleanup;
+                       } else {
+                               update->flags |= REF_NEEDS_COMMIT;
+                       }
+               }
+               if (!(update->flags & REF_NEEDS_COMMIT)) {
+                       /*
+                        * We didn't have to write anything to the lockfile.
+                        * Close it to free up the file descriptor:
+                        */
+                       if (close_ref(update->lock)) {
+                               strbuf_addf(err, "Couldn't close %s.lock",
+                                           update->refname);
+                               goto cleanup;
+                       }
+               }
+       }
+
+       /* Perform updates first so live commits remain referenced */
+       for (i = 0; i < n; i++) {
+               struct ref_update *update = updates[i];
+
+               if (update->flags & REF_NEEDS_COMMIT) {
+                       if (commit_ref_update(update->lock,
+                                             update->new_sha1, update->msg)) {
+                               /* freed by commit_ref_update(): */
+                               update->lock = NULL;
+                               strbuf_addf(err, "Cannot update the ref '%s'.",
+                                           update->refname);
+                               ret = TRANSACTION_GENERIC_ERROR;
+                               goto cleanup;
+                       } else {
+                               /* freed by commit_ref_update(): */
+                               update->lock = NULL;
+                       }
+               }
+       }
+
+       /* Perform deletes now that updates are safely completed */
+       for (i = 0; i < n; i++) {
+               struct ref_update *update = updates[i];
+
+               if (update->flags & REF_DELETING) {
+                       if (delete_ref_loose(update->lock, update->type, err)) {
+                               ret = TRANSACTION_GENERIC_ERROR;
+                               goto cleanup;
+                       }
+
+                       if (!(update->flags & REF_ISPRUNING))
+                               string_list_append(&refs_to_delete,
+                                                  update->lock->ref_name);
+               }
+       }
 
-       return;
+       if (repack_without_refs(&refs_to_delete, err)) {
+               ret = TRANSACTION_GENERIC_ERROR;
+               goto cleanup;
+       }
+       for_each_string_list_item(ref_to_delete, &refs_to_delete)
+               unlink_or_warn(git_path("logs/%s", ref_to_delete->string));
+       clear_loose_ref_cache(&ref_cache);
+
+cleanup:
+       transaction->state = REF_TRANSACTION_CLOSED;
+
+       for (i = 0; i < n; i++)
+               if (updates[i]->lock)
+                       unlock_ref(updates[i]->lock);
+       string_list_clear(&refs_to_delete, 0);
+       string_list_clear(&affected_refnames, 0);
+       return ret;
 }
 
 char *shorten_unambiguous_ref(const char *refname, int strict)
@@ -2515,23 +3991,29 @@ char *shorten_unambiguous_ref(const char *refname, int strict)
        static int nr_rules;
        char *short_name;
 
-       /* pre generate scanf formats from ref_rev_parse_rules[] */
        if (!nr_rules) {
+               /*
+                * Pre-generate scanf formats from ref_rev_parse_rules[].
+                * Generate a format suitable for scanf from a
+                * ref_rev_parse_rules rule by interpolating "%s" at the
+                * location of the "%.*s".
+                */
                size_t total_len = 0;
+               size_t offset = 0;
 
                /* the rule list is NULL terminated, count them first */
-               for (; ref_rev_parse_rules[nr_rules]; nr_rules++)
-                       /* no +1 because strlen("%s") < strlen("%.*s") */
-                       total_len += strlen(ref_rev_parse_rules[nr_rules]);
+               for (nr_rules = 0; ref_rev_parse_rules[nr_rules]; nr_rules++)
+                       /* -2 for strlen("%.*s") - strlen("%s"); +1 for NUL */
+                       total_len += strlen(ref_rev_parse_rules[nr_rules]) - 2 + 1;
 
                scanf_fmts = xmalloc(nr_rules * sizeof(char *) + total_len);
 
-               total_len = 0;
+               offset = 0;
                for (i = 0; i < nr_rules; i++) {
-                       scanf_fmts[i] = (char *)&scanf_fmts[nr_rules]
-                                       + total_len;
-                       gen_scanf_fmt(scanf_fmts[i], ref_rev_parse_rules[i]);
-                       total_len += strlen(ref_rev_parse_rules[i]);
+                       assert(offset < total_len);
+                       scanf_fmts[i] = (char *)&scanf_fmts[nr_rules] + offset;
+                       offset += snprintf(scanf_fmts[i], total_len - offset,
+                                          ref_rev_parse_rules[i], 2, "%s") + 1;
                }
        }
 
@@ -2601,7 +4083,7 @@ int parse_hide_refs_config(const char *var, const char *value, const char *secti
 {
        if (!strcmp("transfer.hiderefs", var) ||
            /* NEEDSWORK: use parse_config_key() once both are merged */
-           (!prefixcmp(var, section) && var[strlen(section)] == '.' &&
+           (starts_with(var, section) && var[strlen(section)] == '.' &&
             !strcmp(var + strlen(section), ".hiderefs"))) {
                char *ref;
                int len;
@@ -2629,7 +4111,7 @@ int ref_is_hidden(const char *refname)
                return 0;
        for_each_string_list_item(item, hide_refs) {
                int len;
-               if (prefixcmp(refname, item->string))
+               if (!starts_with(refname, item->string))
                        continue;
                len = strlen(item->string);
                if (!refname[len] || refname[len] == '/')
@@ -2637,3 +4119,145 @@ int ref_is_hidden(const char *refname)
        }
        return 0;
 }
+
+struct expire_reflog_cb {
+       unsigned int flags;
+       reflog_expiry_should_prune_fn *should_prune_fn;
+       void *policy_cb;
+       FILE *newlog;
+       unsigned char last_kept_sha1[20];
+};
+
+static int expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
+                            const char *email, unsigned long timestamp, int tz,
+                            const char *message, void *cb_data)
+{
+       struct expire_reflog_cb *cb = cb_data;
+       struct expire_reflog_policy_cb *policy_cb = cb->policy_cb;
+
+       if (cb->flags & EXPIRE_REFLOGS_REWRITE)
+               osha1 = cb->last_kept_sha1;
+
+       if ((*cb->should_prune_fn)(osha1, nsha1, email, timestamp, tz,
+                                  message, policy_cb)) {
+               if (!cb->newlog)
+                       printf("would prune %s", message);
+               else if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
+                       printf("prune %s", message);
+       } else {
+               if (cb->newlog) {
+                       fprintf(cb->newlog, "%s %s %s %lu %+05d\t%s",
+                               sha1_to_hex(osha1), sha1_to_hex(nsha1),
+                               email, timestamp, tz, message);
+                       hashcpy(cb->last_kept_sha1, nsha1);
+               }
+               if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
+                       printf("keep %s", message);
+       }
+       return 0;
+}
+
+int reflog_expire(const char *refname, const unsigned char *sha1,
+                unsigned int flags,
+                reflog_expiry_prepare_fn prepare_fn,
+                reflog_expiry_should_prune_fn should_prune_fn,
+                reflog_expiry_cleanup_fn cleanup_fn,
+                void *policy_cb_data)
+{
+       static struct lock_file reflog_lock;
+       struct expire_reflog_cb cb;
+       struct ref_lock *lock;
+       char *log_file;
+       int status = 0;
+       int type;
+       struct strbuf err = STRBUF_INIT;
+
+       memset(&cb, 0, sizeof(cb));
+       cb.flags = flags;
+       cb.policy_cb = policy_cb_data;
+       cb.should_prune_fn = should_prune_fn;
+
+       /*
+        * The reflog file is locked by holding the lock on the
+        * reference itself, plus we might need to update the
+        * reference if --updateref was specified:
+        */
+       lock = lock_ref_sha1_basic(refname, sha1, NULL, NULL, 0, &type, &err);
+       if (!lock) {
+               error("cannot lock ref '%s': %s", refname, err.buf);
+               strbuf_release(&err);
+               return -1;
+       }
+       if (!reflog_exists(refname)) {
+               unlock_ref(lock);
+               return 0;
+       }
+
+       log_file = git_pathdup("logs/%s", refname);
+       if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
+               /*
+                * Even though holding $GIT_DIR/logs/$reflog.lock has
+                * no locking implications, we use the lock_file
+                * machinery here anyway because it does a lot of the
+                * work we need, including cleaning up if the program
+                * exits unexpectedly.
+                */
+               if (hold_lock_file_for_update(&reflog_lock, log_file, 0) < 0) {
+                       struct strbuf err = STRBUF_INIT;
+                       unable_to_lock_message(log_file, errno, &err);
+                       error("%s", err.buf);
+                       strbuf_release(&err);
+                       goto failure;
+               }
+               cb.newlog = fdopen_lock_file(&reflog_lock, "w");
+               if (!cb.newlog) {
+                       error("cannot fdopen %s (%s)",
+                             reflog_lock.filename.buf, strerror(errno));
+                       goto failure;
+               }
+       }
+
+       (*prepare_fn)(refname, sha1, cb.policy_cb);
+       for_each_reflog_ent(refname, expire_reflog_ent, &cb);
+       (*cleanup_fn)(cb.policy_cb);
+
+       if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
+               /*
+                * It doesn't make sense to adjust a reference pointed
+                * to by a symbolic ref based on expiring entries in
+                * the symbolic reference's reflog. Nor can we update
+                * a reference if there are no remaining reflog
+                * entries.
+                */
+               int update = (flags & EXPIRE_REFLOGS_UPDATE_REF) &&
+                       !(type & REF_ISSYMREF) &&
+                       !is_null_sha1(cb.last_kept_sha1);
+
+               if (close_lock_file(&reflog_lock)) {
+                       status |= error("couldn't write %s: %s", log_file,
+                                       strerror(errno));
+               } else if (update &&
+                       (write_in_full(lock->lock_fd,
+                               sha1_to_hex(cb.last_kept_sha1), 40) != 40 ||
+                        write_str_in_full(lock->lock_fd, "\n") != 1 ||
+                        close_ref(lock) < 0)) {
+                       status |= error("couldn't write %s",
+                                       lock->lk->filename.buf);
+                       rollback_lock_file(&reflog_lock);
+               } else if (commit_lock_file(&reflog_lock)) {
+                       status |= error("unable to commit reflog '%s' (%s)",
+                                       log_file, strerror(errno));
+               } else if (update && commit_ref(lock)) {
+                       status |= error("couldn't set %s", lock->ref_name);
+               }
+       }
+       free(log_file);
+       unlock_ref(lock);
+       return status;
+
+ failure:
+       rollback_lock_file(&reflog_lock);
+       free(log_file);
+       unlock_ref(lock);
+       return -1;
+}