git fetch-pack: add --diag-url
[gitweb.git] / refs.c
diff --git a/refs.c b/refs.c
index e264f7a9f493671db652599172b472b3ef4a00b6..5e5a3824b992132aaac8d86698feebcb773e13c6 100644 (file)
--- a/refs.c
+++ b/refs.c
 #include "object.h"
 #include "tag.h"
 #include "dir.h"
+#include "string-list.h"
 
-/* ISSYMREF=01 and ISPACKED=02 are public interfaces */
-#define REF_KNOWS_PEELED 04
+/*
+ * Make sure "ref" 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 has ASCII control character, "~", "^", ":" or SP, anywhere, or
+ * - it ends with a "/".
+ * - it ends with ".lock"
+ * - it contains a "\" (backslash)
+ */
 
-struct ref_list {
-       struct ref_list *next;
-       unsigned char flag; /* ISSYMREF? ISPACKED? */
+/* 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 == '/')
+                       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 "@{". */
+               last = ch;
+       }
+       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))
+               return -1; /* Refname ends with ".lock". */
+       return cp - refname;
+}
+
+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);
+               if (component_len <= 0) {
+                       if ((flags & REFNAME_REFSPEC_PATTERN) &&
+                                       refname[0] == '*' &&
+                                       (refname[1] == '\0' || refname[1] == '/')) {
+                               /* Accept one wildcard as a full refname component. */
+                               flags &= ~REFNAME_REFSPEC_PATTERN;
+                               component_len = 1;
+                       } else {
+                               return -1;
+                       }
+               }
+               component_count++;
+               if (refname[component_len] == '\0')
+                       break;
+               /* Skip to next component. */
+               refname += component_len + 1;
+       }
+
+       if (refname[component_len - 1] == '.')
+               return -1; /* Refname ends with '.'. */
+       if (!(flags & REFNAME_ALLOW_ONELEVEL) && component_count < 2)
+               return -1; /* Refname has only one component. */
+       return 0;
+}
+
+struct ref_entry;
+
+/*
+ * Information used (along with the information in ref_entry) to
+ * describe a single cached reference.  This data structure only
+ * occurs embedded in a union in struct ref_entry, and only when
+ * (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];
+};
+
+struct ref_cache;
+
+/*
+ * Information used (along with the information in ref_entry) to
+ * describe a level in the hierarchy of references.  This data
+ * structure only occurs embedded in a union in struct ref_entry, and
+ * only when (ref_entry.flag & REF_DIR) is set.  In that case,
+ * (ref_entry.flag & REF_INCOMPLETE) determines whether the references
+ * in the directory have already been read:
+ *
+ *     (ref_entry.flag & REF_INCOMPLETE) unset -- a directory of loose
+ *         or packed references, already read.
+ *
+ *     (ref_entry.flag & REF_INCOMPLETE) set -- a directory of loose
+ *         references that hasn't been read yet (nor has any of its
+ *         subdirectories).
+ *
+ * Entries within a directory are stored within a growable array of
+ * pointers to ref_entries (entries, nr, alloc).  Entries 0 <= i <
+ * sorted are sorted by their component name in strcmp() order and the
+ * remaining entries are unsorted.
+ *
+ * Loose references are read lazily, one directory at a time.  When a
+ * directory of loose references is read, then all of the references
+ * in that directory are stored, and REF_INCOMPLETE stubs are created
+ * for any subdirectories, but the subdirectories themselves are not
+ * read.  The reading is triggered by get_ref_dir().
+ */
+struct ref_dir {
+       int nr, alloc;
+
+       /*
+        * Entries with index 0 <= i < sorted are sorted by name.  New
+        * entries are appended to the list unsorted, and are sorted
+        * only when required; thus we avoid the need to sort the list
+        * after the addition of every reference.
+        */
+       int sorted;
+
+       /* A pointer to the ref_cache that contains this ref_dir. */
+       struct ref_cache *ref_cache;
+
+       struct ref_entry **entries;
+};
+
+/*
+ * Bit values for ref_entry::flag.  REF_ISSYMREF=0x01,
+ * REF_ISPACKED=0x02, and REF_ISBROKEN=0x04 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 0x08
+
+/* ref_entry represents a directory of references */
+#define REF_DIR 0x10
+
+/*
+ * Entry has not yet been read from disk (used only for REF_DIR
+ * entries representing loose references)
+ */
+#define REF_INCOMPLETE 0x20
+
+/*
+ * A ref_entry represents either a reference or a "subdirectory" of
+ * references.
+ *
+ * Each directory in the reference namespace is represented by a
+ * ref_entry with (flags & REF_DIR) set and containing a subdir member
+ * that holds the entries in that directory that have been read so
+ * far.  If (flags & REF_INCOMPLETE) is set, then the directory and
+ * its subdirectories haven't been read yet.  REF_INCOMPLETE is only
+ * used for loose reference directories.
+ *
+ * References are represented by a ref_entry with (flags & REF_DIR)
+ * unset and a value member that describes the reference's value.  The
+ * flag member is at the ref_entry level, but it is also needed to
+ * interpret the contents of the value field (in other words, a
+ * ref_value object is not very much use without the enclosing
+ * ref_entry).
+ *
+ * Reference names cannot end with slash and directories' names are
+ * always stored with a trailing slash (except for the top-level
+ * directory, which is always denoted by "").  This has two nice
+ * consequences: (1) when the entries in each subdir are sorted
+ * lexicographically by name (as they usually are), the references in
+ * a whole tree can be generated in lexicographic order by traversing
+ * the tree in left-to-right, depth-first order; (2) the names of
+ * references and subdirectories cannot conflict, and therefore the
+ * 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().)
+ *
+ * Please note that the name field contains the fully-qualified
+ * reference (or subdirectory) name.  Space could be saved by only
+ * storing the relative names.  But that would require the full names
+ * to be generated on the fly when iterating in do_for_each_ref(), and
+ * would break callback functions, who have always been able to assume
+ * that the name strings that they are passed will not be freed during
+ * the iteration.
+ */
+struct ref_entry {
+       unsigned char flag; /* ISSYMREF? ISPACKED? */
+       union {
+               struct ref_value value; /* if not (flags&REF_DIR) */
+               struct ref_dir subdir; /* if (flags&REF_DIR) */
+       } u;
+       /*
+        * The full name of the reference (e.g., "refs/heads/master")
+        * or the full name of the directory with a trailing slash
+        * (e.g., "refs/heads/"):
+        */
        char name[FLEX_ARRAY];
 };
 
+static void read_loose_refs(const char *dirname, struct ref_dir *dir);
+
+static struct ref_dir *get_ref_dir(struct ref_entry *entry)
+{
+       struct ref_dir *dir;
+       assert(entry->flag & REF_DIR);
+       dir = &entry->u.subdir;
+       if (entry->flag & REF_INCOMPLETE) {
+               read_loose_refs(entry->name, dir);
+               entry->flag &= ~REF_INCOMPLETE;
+       }
+       return dir;
+}
+
+static struct ref_entry *create_ref_entry(const char *refname,
+                                         const unsigned char *sha1, int flag,
+                                         int check_name)
+{
+       int len;
+       struct ref_entry *ref;
+
+       if (check_name &&
+           check_refname_format(refname, REFNAME_ALLOW_ONELEVEL|REFNAME_DOT_COMPONENT))
+               die("Reference has invalid format: '%s'", refname);
+       len = strlen(refname) + 1;
+       ref = xmalloc(sizeof(struct ref_entry) + len);
+       hashcpy(ref->u.value.sha1, sha1);
+       hashclr(ref->u.value.peeled);
+       memcpy(ref->name, refname, len);
+       ref->flag = flag;
+       return ref;
+}
+
+static void clear_ref_dir(struct ref_dir *dir);
+
+static void free_ref_entry(struct ref_entry *entry)
+{
+       if (entry->flag & REF_DIR) {
+               /*
+                * Do not use get_ref_dir() here, as that might
+                * trigger the reading of loose refs.
+                */
+               clear_ref_dir(&entry->u.subdir);
+       }
+       free(entry);
+}
+
+/*
+ * Add a ref_entry to the end of dir (unsorted).  Entry is always
+ * stored directly in dir; no recursion into subdirectories is
+ * done.
+ */
+static void add_entry_to_dir(struct ref_dir *dir, struct ref_entry *entry)
+{
+       ALLOC_GROW(dir->entries, dir->nr + 1, dir->alloc);
+       dir->entries[dir->nr++] = entry;
+       /* optimize for the case that entries are added in order */
+       if (dir->nr == 1 ||
+           (dir->nr == dir->sorted + 1 &&
+            strcmp(dir->entries[dir->nr - 2]->name,
+                   dir->entries[dir->nr - 1]->name) < 0))
+               dir->sorted = dir->nr;
+}
+
+/*
+ * Clear and free all entries in dir, recursively.
+ */
+static void clear_ref_dir(struct ref_dir *dir)
+{
+       int i;
+       for (i = 0; i < dir->nr; i++)
+               free_ref_entry(dir->entries[i]);
+       free(dir->entries);
+       dir->sorted = dir->nr = dir->alloc = 0;
+       dir->entries = NULL;
+}
+
+/*
+ * Create a struct ref_entry object for the specified dirname.
+ * dirname is the name of the directory with a trailing slash (e.g.,
+ * "refs/heads/") or "" for the top-level directory.
+ */
+static struct ref_entry *create_dir_entry(struct ref_cache *ref_cache,
+                                         const char *dirname, size_t len,
+                                         int incomplete)
+{
+       struct ref_entry *direntry;
+       direntry = xcalloc(1, sizeof(struct ref_entry) + len + 1);
+       memcpy(direntry->name, dirname, len);
+       direntry->name[len] = '\0';
+       direntry->u.subdir.ref_cache = ref_cache;
+       direntry->flag = REF_DIR | (incomplete ? REF_INCOMPLETE : 0);
+       return direntry;
+}
+
+static int ref_entry_cmp(const void *a, const void *b)
+{
+       struct ref_entry *one = *(struct ref_entry **)a;
+       struct ref_entry *two = *(struct ref_entry **)b;
+       return strcmp(one->name, two->name);
+}
+
+static void sort_ref_dir(struct ref_dir *dir);
+
+struct string_slice {
+       size_t len;
+       const char *str;
+};
+
+static int ref_entry_cmp_sslice(const void *key_, const void *ent_)
+{
+       const struct string_slice *key = key_;
+       const struct ref_entry *ent = *(const struct ref_entry * const *)ent_;
+       int cmp = strncmp(key->str, ent->name, key->len);
+       if (cmp)
+               return cmp;
+       return '\0' - (unsigned char)ent->name[key->len];
+}
+
+/*
+ * 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 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 -1;
+
+       sort_ref_dir(dir);
+       key.len = len;
+       key.str = refname;
+       r = bsearch(&key, dir->entries, dir->nr, sizeof(*dir->entries),
+                   ref_entry_cmp_sslice);
+
+       if (r == NULL)
+               return -1;
+
+       return r - dir->entries;
+}
+
+/*
+ * Search for a directory entry directly within dir (without
+ * recursing).  Sort dir if necessary.  subdirname must be a directory
+ * name (i.e., end in '/').  If mkdir is set, then create the
+ * directory if it is missing; otherwise, return NULL if the desired
+ * directory cannot be found.  dir must already be complete.
+ */
+static struct ref_dir *search_for_subdir(struct ref_dir *dir,
+                                        const char *subdirname, size_t len,
+                                        int mkdir)
+{
+       int entry_index = search_ref_dir(dir, subdirname, len);
+       struct ref_entry *entry;
+       if (entry_index == -1) {
+               if (!mkdir)
+                       return NULL;
+               /*
+                * Since dir is complete, the absence of a subdir
+                * means that the subdir really doesn't exist;
+                * therefore, create an empty record for it but mark
+                * the record complete.
+                */
+               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);
+}
+
+/*
+ * If refname is a reference name, find the ref_dir within the dir
+ * tree that should hold refname.  If refname is a directory name
+ * (i.e., ends in '/'), then return that ref_dir itself.  dir must
+ * represent the top-level directory and must already be complete.
+ * Sort ref_dirs and recurse into subdirectories as necessary.  If
+ * mkdir is set, then create any missing directories; otherwise,
+ * return NULL if the desired directory cannot be found.
+ */
+static struct ref_dir *find_containing_dir(struct ref_dir *dir,
+                                          const char *refname, int mkdir)
+{
+       const char *slash;
+       for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
+               size_t dirnamelen = slash - refname + 1;
+               struct ref_dir *subdir;
+               subdir = search_for_subdir(dir, refname, dirnamelen, mkdir);
+               if (!subdir) {
+                       dir = NULL;
+                       break;
+               }
+               dir = subdir;
+       }
+
+       return dir;
+}
+
+/*
+ * Find the value entry with the given name in dir, sorting ref_dirs
+ * and recursing into subdirectories as necessary.  If the name is not
+ * found or it corresponds to a directory entry, return NULL.
+ */
+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_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;
+}
+
+/*
+ * Add a ref_entry to the ref_dir (unsorted), recursing into
+ * subdirectories as necessary.  dir must represent the top-level
+ * directory.  Return 0 on success.
+ */
+static int add_ref(struct ref_dir *dir, struct ref_entry *ref)
+{
+       dir = find_containing_dir(dir, ref->name, 1);
+       if (!dir)
+               return -1;
+       add_entry_to_dir(dir, ref);
+       return 0;
+}
+
+/*
+ * Emit a warning and return true iff ref1 and ref2 have the same name
+ * and the same sha1.  Die if they have the same name but different
+ * sha1s.
+ */
+static int is_dup_ref(const struct ref_entry *ref1, const struct ref_entry *ref2)
+{
+       if (strcmp(ref1->name, ref2->name))
+               return 0;
+
+       /* Duplicate name; make sure that they don't conflict: */
+
+       if ((ref1->flag & REF_DIR) || (ref2->flag & REF_DIR))
+               /* This is impossible by construction */
+               die("Reference directory conflict: %s", ref1->name);
+
+       if (hashcmp(ref1->u.value.sha1, ref2->u.value.sha1))
+               die("Duplicated ref, and SHA1s don't match: %s", ref1->name);
+
+       warning("Duplicated ref: %s", ref1->name);
+       return 1;
+}
+
+/*
+ * Sort the entries in dir non-recursively (if they are not already
+ * sorted) and remove any duplicate entries.
+ */
+static void sort_ref_dir(struct ref_dir *dir)
+{
+       int i, j;
+       struct ref_entry *last = NULL;
+
+       /*
+        * This check also prevents passing a zero-length array to qsort(),
+        * which is a problem on some platforms.
+        */
+       if (dir->sorted == dir->nr)
+               return;
+
+       qsort(dir->entries, dir->nr, sizeof(*dir->entries), ref_entry_cmp);
+
+       /* Remove any duplicates: */
+       for (i = 0, j = 0; j < dir->nr; j++) {
+               struct ref_entry *entry = dir->entries[j];
+               if (last && is_dup_ref(last, entry))
+                       free_ref_entry(entry);
+               else
+                       last = dir->entries[i++] = entry;
+       }
+       dir->sorted = dir->nr = i;
+}
+
+/* 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;
+
+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, data->base))
+               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 = data->fn(entry->name + data->trim, entry->u.value.sha1,
+                         entry->flag, data->cb_data);
+       current_ref = old_current_ref;
+       return retval;
+}
+
+/*
+ * 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.  fn is
+ * called for all references, including broken ones.
+ */
+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);
+       for (i = offset; i < dir->nr; i++) {
+               struct ref_entry *entry = dir->entries[i];
+               int retval;
+               if (entry->flag & REF_DIR) {
+                       struct ref_dir *subdir = get_ref_dir(entry);
+                       sort_ref_dir(subdir);
+                       retval = do_for_each_entry_in_dir(subdir, 0, fn, cb_data);
+               } else {
+                       retval = fn(entry, cb_data);
+               }
+               if (retval)
+                       return retval;
+       }
+       return 0;
+}
+
+/*
+ * Call fn for each reference in the union of dir1 and dir2, in order
+ * 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.  fn is called for all references, including
+ * broken ones.
+ */
+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;
+
+       assert(dir1->sorted == dir1->nr);
+       assert(dir2->sorted == dir2->nr);
+       while (1) {
+               struct ref_entry *e1, *e2;
+               int cmp;
+               if (i1 == dir1->nr) {
+                       return do_for_each_entry_in_dir(dir2, i2, fn, cb_data);
+               }
+               if (i2 == dir2->nr) {
+                       return do_for_each_entry_in_dir(dir1, i1, fn, cb_data);
+               }
+               e1 = dir1->entries[i1];
+               e2 = dir2->entries[i2];
+               cmp = strcmp(e1->name, e2->name);
+               if (cmp == 0) {
+                       if ((e1->flag & REF_DIR) && (e2->flag & REF_DIR)) {
+                               /* Both are directories; descend them in parallel. */
+                               struct ref_dir *subdir1 = get_ref_dir(e1);
+                               struct ref_dir *subdir2 = get_ref_dir(e2);
+                               sort_ref_dir(subdir1);
+                               sort_ref_dir(subdir2);
+                               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 = fn(e2, cb_data);
+                               i1++;
+                               i2++;
+                       } else {
+                               die("conflict between reference and directory: %s",
+                                   e1->name);
+                       }
+               } else {
+                       struct ref_entry *e;
+                       if (cmp < 0) {
+                               e = e1;
+                               i1++;
+                       } else {
+                               e = e2;
+                               i2++;
+                       }
+                       if (e->flag & REF_DIR) {
+                               struct ref_dir *subdir = get_ref_dir(e);
+                               sort_ref_dir(subdir);
+                               retval = do_for_each_entry_in_dir(
+                                               subdir, 0, fn, cb_data);
+                       } else {
+                               retval = fn(e, cb_data);
+                       }
+               }
+               if (retval)
+                       return retval;
+       }
+}
+
+/*
+ * 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 void prime_ref_dir(struct ref_dir *dir)
+{
+       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));
+       }
+}
+/*
+ * 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".
+ */
+static int names_conflict(const char *refname1, const char *refname2)
+{
+       for (; *refname1 && *refname1 == *refname2; refname1++, refname2++)
+               ;
+       return (*refname1 == '\0' && *refname2 == '/')
+               || (*refname1 == '/' && *refname2 == '\0');
+}
+
+struct name_conflict_cb {
+       const char *refname;
+       const char *oldrefname;
+       const char *conflicting_refname;
+};
+
+static int name_conflict_fn(struct ref_entry *entry, void *cb_data)
+{
+       struct name_conflict_cb *data = (struct name_conflict_cb *)cb_data;
+       if (data->oldrefname && !strcmp(data->oldrefname, entry->name))
+               return 0;
+       if (names_conflict(data->refname, entry->name)) {
+               data->conflicting_refname = entry->name;
+               return 1;
+       }
+       return 0;
+}
+
+/*
+ * Return true iff a reference named refname could be created without
+ * conflicting with the name of an existing reference in dir.  If
+ * oldrefname is non-NULL, ignore potential conflicts with oldrefname
+ * (e.g., because oldrefname is scheduled for deletion in the same
+ * operation).
+ */
+static int is_refname_available(const char *refname, const char *oldrefname,
+                               struct ref_dir *dir)
+{
+       struct name_conflict_cb data;
+       data.refname = refname;
+       data.oldrefname = oldrefname;
+       data.conflicting_refname = NULL;
+
+       sort_ref_dir(dir);
+       if (do_for_each_entry_in_dir(dir, 0, name_conflict_fn, &data)) {
+               error("'%s' exists; cannot create '%s'",
+                     data.conflicting_refname, refname);
+               return 0;
+       }
+       return 1;
+}
+
+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.
+ */
+static struct ref_cache {
+       struct ref_cache *next;
+       struct ref_entry *loose;
+       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) {
+               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);
+       }
+}
+
+static void clear_loose_ref_cache(struct ref_cache *refs)
+{
+       if (refs->loose) {
+               free_ref_entry(refs->loose);
+               refs->loose = NULL;
+       }
+}
+
+static struct ref_cache *create_ref_cache(const char *submodule)
+{
+       int len;
+       struct ref_cache *refs;
+       if (!submodule)
+               submodule = "";
+       len = strlen(submodule) + 1;
+       refs = xcalloc(1, sizeof(struct ref_cache) + len);
+       memcpy(refs->name, submodule, len);
+       return refs;
+}
+
+/*
+ * Return a pointer to a ref_cache for the specified submodule. For
+ * the main repository, use submodule==NULL. The returned structure
+ * will be allocated and initialized but not necessarily populated; it
+ * should not be freed.
+ */
+static struct ref_cache *get_ref_cache(const char *submodule)
+{
+       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 = create_ref_cache(submodule);
+       refs->next = submodule_ref_caches;
+       submodule_ref_caches = refs;
+       return 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)
 {
        /*
@@ -30,341 +977,271 @@ static const char *parse_ref_line(char *line, unsigned char *sha1)
        if (len <= 0)
                return NULL;
        if (get_sha1_hex(line, sha1) < 0)
-               return NULL;
-       if (!isspace(line[40]))
-               return NULL;
-       line += 41;
-       if (isspace(*line))
-               return NULL;
-       if (line[len] != '\n')
-               return NULL;
-       line[len] = 0;
-
-       return line;
-}
-
-static struct ref_list *add_ref(const char *name, const unsigned char *sha1,
-                               int flag, struct ref_list *list,
-                               struct ref_list **new_entry)
-{
-       int len;
-       struct ref_list *entry;
-
-       /* Allocate it and add it in.. */
-       len = strlen(name) + 1;
-       entry = xmalloc(sizeof(struct ref_list) + len);
-       hashcpy(entry->sha1, sha1);
-       hashclr(entry->peeled);
-       memcpy(entry->name, name, len);
-       entry->flag = flag;
-       entry->next = list;
-       if (new_entry)
-               *new_entry = entry;
-       return entry;
-}
-
-/* merge sort the ref list */
-static struct ref_list *sort_ref_list(struct ref_list *list)
-{
-       int psize, qsize, last_merge_count, cmp;
-       struct ref_list *p, *q, *l, *e;
-       struct ref_list *new_list = list;
-       int k = 1;
-       int merge_count = 0;
-
-       if (!list)
-               return list;
-
-       do {
-               last_merge_count = merge_count;
-               merge_count = 0;
-
-               psize = 0;
-
-               p = new_list;
-               q = new_list;
-               new_list = NULL;
-               l = NULL;
-
-               while (p) {
-                       merge_count++;
-
-                       while (psize < k && q->next) {
-                               q = q->next;
-                               psize++;
-                       }
-                       qsize = k;
-
-                       while ((psize > 0) || (qsize > 0 && q)) {
-                               if (qsize == 0 || !q) {
-                                       e = p;
-                                       p = p->next;
-                                       psize--;
-                               } else if (psize == 0) {
-                                       e = q;
-                                       q = q->next;
-                                       qsize--;
-                               } else {
-                                       cmp = strcmp(q->name, p->name);
-                                       if (cmp < 0) {
-                                               e = q;
-                                               q = q->next;
-                                               qsize--;
-                                       } else if (cmp > 0) {
-                                               e = p;
-                                               p = p->next;
-                                               psize--;
-                                       } else {
-                                               if (hashcmp(q->sha1, p->sha1))
-                                                       die("Duplicated ref, and SHA1s don't match: %s",
-                                                           q->name);
-                                               warning("Duplicated ref: %s", q->name);
-                                               e = q;
-                                               q = q->next;
-                                               qsize--;
-                                               free(e);
-                                               e = p;
-                                               p = p->next;
-                                               psize--;
-                                       }
-                               }
-
-                               e->next = NULL;
-
-                               if (l)
-                                       l->next = e;
-                               if (!new_list)
-                                       new_list = e;
-                               l = e;
-                       }
-
-                       p = q;
-               };
-
-               k = k * 2;
-       } while ((last_merge_count != merge_count) || (last_merge_count != 1));
+               return NULL;
+       if (!isspace(line[40]))
+               return NULL;
+       line += 41;
+       if (isspace(*line))
+               return NULL;
+       if (line[len] != '\n')
+               return NULL;
+       line[len] = 0;
 
-       return new_list;
+       return line;
 }
 
 /*
- * Future: need to be in "struct repository"
- * when doing a full libification.
+ * Read f, which is a packed-refs file, into dir.
+ *
+ * A comment line of the form "# pack-refs with: " may contain zero or
+ * more traits. We interpret the traits as follows:
+ *
+ *   No traits:
+ *
+ *      Probably no references are peeled. But if the file contains a
+ *      peeled value for a reference, we will use it.
+ *
+ *   peeled:
+ *
+ *      References under "refs/tags/", if they *can* be peeled, *are*
+ *      peeled in this file. References outside of "refs/tags/" are
+ *      probably not peeled even if they could have been, but if we find
+ *      a peeled value for such a reference we will use it.
+ *
+ *   fully-peeled:
+ *
+ *      All references in the file that can be peeled are peeled.
+ *      Inversely (and this is more important), any references in the
+ *      file for which no peeled value is recorded is not peelable. This
+ *      trait should typically be written alongside "peeled" for
+ *      compatibility with older clients, but we do not require it
+ *      (i.e., "peeled" is a no-op if "fully-peeled" is set).
  */
-static struct cached_refs {
-       char did_loose;
-       char did_packed;
-       struct ref_list *loose;
-       struct ref_list *packed;
-} cached_refs;
-static struct ref_list *current_ref;
-
-static struct ref_list *extra_refs;
-
-static void free_ref_list(struct ref_list *list)
-{
-       struct ref_list *next;
-       for ( ; list; list = next) {
-               next = list->next;
-               free(list);
-       }
-}
-
-static void invalidate_cached_refs(void)
-{
-       struct cached_refs *ca = &cached_refs;
-
-       if (ca->did_loose && ca->loose)
-               free_ref_list(ca->loose);
-       if (ca->did_packed && ca->packed)
-               free_ref_list(ca->packed);
-       ca->loose = ca->packed = NULL;
-       ca->did_loose = ca->did_packed = 0;
-}
-
-static void read_packed_refs(FILE *f, struct cached_refs *cached_refs)
+static void read_packed_refs(FILE *f, struct ref_dir *dir)
 {
-       struct ref_list *list = NULL;
-       struct ref_list *last = NULL;
+       struct ref_entry *last = NULL;
        char refline[PATH_MAX];
-       int flag = REF_ISPACKED;
+       enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE;
 
        while (fgets(refline, sizeof(refline), f)) {
                unsigned char sha1[20];
-               const char *name;
+               const char *refname;
                static const char header[] = "# pack-refs with:";
 
                if (!strncmp(refline, header, sizeof(header)-1)) {
                        const char *traits = refline + sizeof(header) - 1;
-                       if (strstr(traits, " peeled "))
-                               flag |= REF_KNOWS_PEELED;
+                       if (strstr(traits, " fully-peeled "))
+                               peeled = PEELED_FULLY;
+                       else if (strstr(traits, " peeled "))
+                               peeled = PEELED_TAGS;
                        /* perhaps other traits later as well */
                        continue;
                }
 
-               name = parse_ref_line(refline, sha1);
-               if (name) {
-                       list = add_ref(name, sha1, flag, list, &last);
+               refname = parse_ref_line(refline, sha1);
+               if (refname) {
+                       last = create_ref_entry(refname, sha1, REF_ISPACKED, 1);
+                       if (peeled == PEELED_FULLY ||
+                           (peeled == PEELED_TAGS && !prefixcmp(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))
-                       hashcpy(last->peeled, sha1);
+                   strlen(refline) == PEELED_LINE_LENGTH &&
+                   refline[PEELED_LINE_LENGTH - 1] == '\n' &&
+                   !get_sha1_hex(refline + 1, sha1)) {
+                       hashcpy(last->u.value.peeled, sha1);
+                       /*
+                        * Regardless of what the file header said,
+                        * we definitely know the value of *this*
+                        * reference:
+                        */
+                       last->flag |= REF_KNOWS_PEELED;
+               }
        }
-       cached_refs->packed = sort_ref_list(list);
 }
 
-void add_extra_ref(const char *name, const unsigned char *sha1, int flag)
+/*
+ * 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)
 {
-       extra_refs = add_ref(name, sha1, flag, extra_refs, NULL);
-}
+       const char *packed_refs_file;
 
-void clear_extra_refs(void)
-{
-       free_ref_list(extra_refs);
-       extra_refs = NULL;
-}
+       if (*refs->name)
+               packed_refs_file = git_path_submodule(refs->name, "packed-refs");
+       else
+               packed_refs_file = git_path("packed-refs");
 
-static struct ref_list *get_packed_refs(void)
-{
-       if (!cached_refs.did_packed) {
-               FILE *f = fopen(git_path("packed-refs"), "r");
-               cached_refs.packed = NULL;
+       if (refs->packed &&
+           !stat_validity_check(&refs->packed->validity, packed_refs_file))
+               clear_packed_ref_cache(refs);
+
+       if (!refs->packed) {
+               FILE *f;
+
+               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, &cached_refs);
+                       stat_validity_update(&refs->packed->validity, fileno(f));
+                       read_packed_refs(f, get_ref_dir(refs->packed->root));
                        fclose(f);
                }
-               cached_refs.did_packed = 1;
        }
-       return cached_refs.packed;
+       return refs->packed;
 }
 
-static struct ref_list *get_ref_dir(const char *base, struct ref_list *list)
+static struct ref_dir *get_packed_ref_dir(struct packed_ref_cache *packed_ref_cache)
 {
-       DIR *dir = opendir(git_path("%s", base));
-
-       if (dir) {
-               struct dirent *de;
-               int baselen = strlen(base);
-               char *ref = xmalloc(baselen + 257);
-
-               memcpy(ref, base, baselen);
-               if (baselen && base[baselen-1] != '/')
-                       ref[baselen++] = '/';
-
-               while ((de = readdir(dir)) != NULL) {
-                       unsigned char sha1[20];
-                       struct stat st;
-                       int flag;
-                       int namelen;
-
-                       if (de->d_name[0] == '.')
-                               continue;
-                       namelen = strlen(de->d_name);
-                       if (namelen > 255)
-                               continue;
-                       if (has_extension(de->d_name, ".lock"))
-                               continue;
-                       memcpy(ref + baselen, de->d_name, namelen+1);
-                       if (stat(git_path("%s", ref), &st) < 0)
-                               continue;
-                       if (S_ISDIR(st.st_mode)) {
-                               list = get_ref_dir(ref, list);
-                               continue;
-                       }
-                       if (!resolve_ref(ref, sha1, 1, &flag))
-                               hashclr(sha1);
-                       list = add_ref(ref, sha1, flag, list, NULL);
-               }
-               free(ref);
-               closedir(dir);
-       }
-       return sort_ref_list(list);
+       return get_ref_dir(packed_ref_cache->root);
 }
 
-struct warn_if_dangling_data {
-       const char *refname;
-       const char *msg_fmt;
-};
-
-static int warn_if_dangling_symref(const char *refname, const unsigned char *sha1,
-                                  int flags, void *cb_data)
+static struct ref_dir *get_packed_refs(struct ref_cache *refs)
 {
-       struct warn_if_dangling_data *d = cb_data;
-       const char *resolves_to;
-       unsigned char junk[20];
-
-       if (!(flags & REF_ISSYMREF))
-               return 0;
+       return get_packed_ref_dir(get_packed_ref_cache(refs));
+}
 
-       resolves_to = resolve_ref(refname, junk, 0, NULL);
-       if (!resolves_to || strcmp(resolves_to, d->refname))
-               return 0;
+void add_packed_ref(const char *refname, const unsigned char *sha1)
+{
+       struct packed_ref_cache *packed_ref_cache =
+               get_packed_ref_cache(&ref_cache);
 
-       printf(d->msg_fmt, refname);
-       return 0;
+       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));
 }
 
-void warn_dangling_symref(const char *msg_fmt, const char *refname)
+/*
+ * Read the loose references from the namespace dirname into dir
+ * (without recursing).  dirname must end with '/'.  dir must be the
+ * directory entry corresponding to dirname.
+ */
+static void read_loose_refs(const char *dirname, struct ref_dir *dir)
 {
-       struct warn_if_dangling_data data = { refname, msg_fmt };
-       for_each_rawref(warn_if_dangling_symref, &data);
+       struct ref_cache *refs = dir->ref_cache;
+       DIR *d;
+       const char *path;
+       struct dirent *de;
+       int dirnamelen = strlen(dirname);
+       struct strbuf refname;
+
+       if (*refs->name)
+               path = git_path_submodule(refs->name, "%s", dirname);
+       else
+               path = git_path("%s", dirname);
+
+       d = opendir(path);
+       if (!d)
+               return;
+
+       strbuf_init(&refname, dirnamelen + 257);
+       strbuf_add(&refname, dirname, dirnamelen);
+
+       while ((de = readdir(d)) != NULL) {
+               unsigned char sha1[20];
+               struct stat st;
+               int flag;
+               const char *refdir;
+
+               if (de->d_name[0] == '.')
+                       continue;
+               if (has_extension(de->d_name, ".lock"))
+                       continue;
+               strbuf_addstr(&refname, de->d_name);
+               refdir = *refs->name
+                       ? git_path_submodule(refs->name, "%s", refname.buf)
+                       : git_path("%s", refname.buf);
+               if (stat(refdir, &st) < 0) {
+                       ; /* silently ignore */
+               } else if (S_ISDIR(st.st_mode)) {
+                       strbuf_addch(&refname, '/');
+                       add_entry_to_dir(dir,
+                                        create_dir_entry(refs, refname.buf,
+                                                         refname.len, 1));
+               } else {
+                       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)) {
+                               hashclr(sha1);
+                               flag |= REF_ISBROKEN;
+                       }
+                       add_entry_to_dir(dir,
+                                        create_ref_entry(refname.buf, sha1, flag, 1));
+               }
+               strbuf_setlen(&refname, dirnamelen);
+       }
+       strbuf_release(&refname);
+       closedir(d);
 }
 
-static struct ref_list *get_loose_refs(void)
+static struct ref_dir *get_loose_refs(struct ref_cache *refs)
 {
-       if (!cached_refs.did_loose) {
-               cached_refs.loose = get_ref_dir("refs", NULL);
-               cached_refs.did_loose = 1;
+       if (!refs->loose) {
+               /*
+                * Mark the top-level directory complete because we
+                * are about to read the only subdirectory that can
+                * hold references:
+                */
+               refs->loose = create_dir_entry(refs, "", 0, 0);
+               /*
+                * Create an incomplete entry for "refs/":
+                */
+               add_entry_to_dir(get_ref_dir(refs->loose),
+                                create_dir_entry(refs, "refs/", 5, 1));
        }
-       return cached_refs.loose;
+       return get_ref_dir(refs->loose);
 }
 
 /* We allow "recursive" symbolic refs. Only within reason, though */
 #define MAXDEPTH 5
 #define MAXREFLEN (1024)
 
-static int resolve_gitlink_packed_ref(char *name, int pathlen, const char *refname, unsigned char *result)
+/*
+ * Called by resolve_gitlink_ref_recursive() after it failed to read
+ * from the loose refs in ref_cache refs. Find <refname> in the
+ * packed-refs file for the submodule.
+ */
+static int resolve_gitlink_packed_ref(struct ref_cache *refs,
+                                     const char *refname, unsigned char *sha1)
 {
-       FILE *f;
-       struct cached_refs refs;
-       struct ref_list *ref;
-       int retval;
+       struct ref_entry *ref;
+       struct ref_dir *dir = get_packed_refs(refs);
 
-       strcpy(name + pathlen, "packed-refs");
-       f = fopen(name, "r");
-       if (!f)
+       ref = find_ref(dir, refname);
+       if (ref == NULL)
                return -1;
-       read_packed_refs(f, &refs);
-       fclose(f);
-       ref = refs.packed;
-       retval = -1;
-       while (ref) {
-               if (!strcmp(ref->name, refname)) {
-                       retval = 0;
-                       memcpy(result, ref->sha1, 20);
-                       break;
-               }
-               ref = ref->next;
-       }
-       free_ref_list(refs.packed);
-       return retval;
+
+       memcpy(sha1, ref->u.value.sha1, 20);
+       return 0;
 }
 
-static int resolve_gitlink_ref_recursive(char *name, int pathlen, const char *refname, unsigned char *result, int recursion)
+static int resolve_gitlink_ref_recursive(struct ref_cache *refs,
+                                        const char *refname, unsigned char *sha1,
+                                        int recursion)
 {
-       int fd, len = strlen(refname);
+       int fd, len;
        char buffer[128], *p;
+       char *path;
 
-       if (recursion > MAXDEPTH || len > MAXREFLEN)
+       if (recursion > MAXDEPTH || strlen(refname) > MAXREFLEN)
                return -1;
-       memcpy(name + pathlen, refname, len+1);
-       fd = open(name, O_RDONLY);
+       path = *refs->name
+               ? git_path_submodule(refs->name, "%s", refname)
+               : git_path("%s", refname);
+       fd = open(path, O_RDONLY);
        if (fd < 0)
-               return resolve_gitlink_packed_ref(name, pathlen, refname, result);
+               return resolve_gitlink_packed_ref(refs, refname, sha1);
 
        len = read(fd, buffer, sizeof(buffer)-1);
        close(fd);
@@ -375,7 +1252,7 @@ static int resolve_gitlink_ref_recursive(char *name, int pathlen, const char *re
        buffer[len] = 0;
 
        /* Was it a detached head or an old-fashioned symlink? */
-       if (!get_sha1_hex(buffer, result))
+       if (!get_sha1_hex(buffer, sha1))
                return 0;
 
        /* Symref? */
@@ -385,60 +1262,80 @@ static int resolve_gitlink_ref_recursive(char *name, int pathlen, const char *re
        while (isspace(*p))
                p++;
 
-       return resolve_gitlink_ref_recursive(name, pathlen, p, result, recursion+1);
+       return resolve_gitlink_ref_recursive(refs, p, sha1, recursion+1);
 }
 
-int resolve_gitlink_ref(const char *path, const char *refname, unsigned char *result)
+int resolve_gitlink_ref(const char *path, const char *refname, unsigned char *sha1)
 {
        int len = strlen(path), retval;
-       char *gitdir;
-       const char *tmp;
+       char *submodule;
+       struct ref_cache *refs;
 
        while (len && path[len-1] == '/')
                len--;
        if (!len)
                return -1;
-       gitdir = xmalloc(len + MAXREFLEN + 8);
-       memcpy(gitdir, path, len);
-       memcpy(gitdir + len, "/.git", 6);
-       len += 5;
-
-       tmp = read_gitfile_gently(gitdir);
-       if (tmp) {
-               free(gitdir);
-               len = strlen(tmp);
-               gitdir = xmalloc(len + MAXREFLEN + 3);
-               memcpy(gitdir, tmp, len);
-       }
-       gitdir[len] = '/';
-       gitdir[++len] = '\0';
-       retval = resolve_gitlink_ref_recursive(gitdir, len, refname, result, 0);
-       free(gitdir);
+       submodule = xstrndup(path, len);
+       refs = get_ref_cache(submodule);
+       free(submodule);
+
+       retval = resolve_gitlink_ref_recursive(refs, refname, sha1, 0);
        return retval;
 }
 
 /*
- * If the "reading" argument is set, this function finds out what _object_
- * the ref points at by "reading" the ref.  The ref, if it is not symbolic,
- * has to exist, and if it is symbolic, it has to point at an existing ref,
- * because the "read" goes through the symref to the ref it points at.
- *
- * The access that is not "reading" may often be "writing", but does not
- * have to; it can be merely checking _where it leads to_. If it is a
- * prelude to "writing" to the ref, a write to a symref that points at
- * yet-to-be-born ref will create the real ref pointed by the symref.
- * reading=0 allows the caller to check where such a symref leads to.
+ * 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().
  */
-const char *resolve_ref(const char *ref, unsigned char *sha1, int reading, int *flag)
+static const char *handle_missing_loose_ref(const char *refname,
+                                           unsigned char *sha1,
+                                           int reading,
+                                           int *flag)
+{
+       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 (flag)
+                       *flag |= REF_ISPACKED;
+               return refname;
+       }
+       /* The reference is not a packed reference, either. */
+       if (reading) {
+               return NULL;
+       } else {
+               hashclr(sha1);
+               return refname;
+       }
+}
+
+const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int reading, int *flag)
 {
        int depth = MAXDEPTH;
        ssize_t len;
        char buffer[256];
-       static char ref_buffer[256];
+       static char refname_buffer[256];
 
        if (flag)
                *flag = 0;
 
+       if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
+               return NULL;
+
        for (;;) {
                char path[PATH_MAX];
                struct stat st;
@@ -448,32 +1345,41 @@ const char *resolve_ref(const char *ref, unsigned char *sha1, int reading, int *
                if (--depth < 0)
                        return NULL;
 
-               git_snpath(path, sizeof(path), "%s", ref);
-               /* Special case: non-existing file. */
+               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) {
-                       struct ref_list *list = get_packed_refs();
-                       while (list) {
-                               if (!strcmp(ref, list->name)) {
-                                       hashcpy(sha1, list->sha1);
-                                       if (flag)
-                                               *flag |= REF_ISPACKED;
-                                       return ref;
-                               }
-                               list = list->next;
-                       }
-                       if (reading || errno != ENOENT)
+                       if (errno == ENOENT)
+                               return handle_missing_loose_ref(refname, sha1,
+                                                               reading, flag);
+                       else
                                return NULL;
-                       hashclr(sha1);
-                       return ref;
                }
 
                /* Follow "normalized" - ie "refs/.." symlinks by hand */
                if (S_ISLNK(st.st_mode)) {
                        len = readlink(path, buffer, sizeof(buffer)-1);
-                       if (len >= 5 && !memcmp("refs/", buffer, 5)) {
-                               buffer[len] = 0;
-                               strcpy(ref_buffer, buffer);
-                               ref = ref_buffer;
+                       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/") &&
+                                       !check_refname_format(buffer, 0)) {
+                               strcpy(refname_buffer, buffer);
+                               refname = refname_buffer;
                                if (flag)
                                        *flag |= REF_ISSYMREF;
                                continue;
@@ -491,263 +1397,482 @@ const char *resolve_ref(const char *ref, unsigned char *sha1, int reading, int *
                 * 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)
+                       return NULL;
+               while (len && isspace(buffer[len-1]))
+                       len--;
+               buffer[len] = '\0';
 
                /*
                 * Is it a symbolic ref?
                 */
-               if (len < 4 || memcmp("ref:", buffer, 4))
-                       break;
-               buf = buffer + 4;
-               len -= 4;
-               while (len && isspace(*buf))
-                       buf++, len--;
-               while (len && isspace(buf[len-1]))
-                       len--;
-               buf[len] = 0;
-               memcpy(ref_buffer, buf, len + 1);
-               ref = ref_buffer;
+               if (prefixcmp(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 (flag)
+                                       *flag |= REF_ISBROKEN;
+                               return NULL;
+                       }
+                       return refname;
+               }
                if (flag)
                        *flag |= REF_ISSYMREF;
+               buf = buffer + 4;
+               while (isspace(*buf))
+                       buf++;
+               if (check_refname_format(buf, REFNAME_ALLOW_ONELEVEL)) {
+                       if (flag)
+                               *flag |= REF_ISBROKEN;
+                       return NULL;
+               }
+               refname = strcpy(refname_buffer, buf);
        }
-       if (len < 40 || get_sha1_hex(buffer, sha1))
-               return NULL;
-       return ref;
 }
 
-int read_ref(const char *ref, unsigned char *sha1)
+char *resolve_refdup(const char *ref, unsigned char *sha1, int reading, int *flag)
+{
+       const char *ret = resolve_ref_unsafe(ref, sha1, reading, flag);
+       return ret ? xstrdup(ret) : NULL;
+}
+
+/* The argument to filter_refs */
+struct ref_filter {
+       const char *pattern;
+       each_ref_fn *fn;
+       void *cb_data;
+};
+
+int read_ref_full(const char *refname, unsigned char *sha1, int reading, int *flags)
 {
-       if (resolve_ref(ref, sha1, 1, NULL))
+       if (resolve_ref_unsafe(refname, sha1, reading, flags))
                return 0;
        return -1;
 }
 
-#define DO_FOR_EACH_INCLUDE_BROKEN 01
-static int do_one_ref(const char *base, each_ref_fn fn, int trim,
-                     int flags, void *cb_data, struct ref_list *entry)
+int read_ref(const char *refname, unsigned char *sha1)
 {
-       if (strncmp(base, entry->name, trim))
+       return read_ref_full(refname, sha1, 1, NULL);
+}
+
+int ref_exists(const char *refname)
+{
+       unsigned char sha1[20];
+       return !!resolve_ref_unsafe(refname, sha1, 1, 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))
                return 0;
-       if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN)) {
-               if (is_null_sha1(entry->sha1))
-                       return 0;
-               if (!has_sha1_file(entry->sha1)) {
-                       error("%s does not point to a valid object!", entry->name);
-                       return 0;
+       return filter->fn(refname, sha1, flags, filter->cb_data);
+}
+
+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)
+{
+       struct object *o = lookup_unknown_object(name);
+
+       if (o->type == OBJ_NONE) {
+               int type = sha1_object_info(name, NULL);
+               if (type < 0)
+                       return PEEL_INVALID;
+               o->type = type;
+       }
+
+       if (o->type != OBJ_TAG)
+               return PEEL_NON_TAG;
+
+       o = deref_tag_noverify(o);
+       if (!o)
+               return PEEL_INVALID;
+
+       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;
                }
        }
-       current_ref = entry;
-       return fn(entry->name + trim, entry->sha1, entry->flag, cb_data);
+       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;
 }
 
-int peel_ref(const char *ref, unsigned char *sha1)
+int peel_ref(const char *refname, unsigned char *sha1)
 {
        int flag;
        unsigned char base[20];
-       struct object *o;
 
-       if (current_ref && (current_ref->name == ref
-               || !strcmp(current_ref->name, ref))) {
-               if (current_ref->flag & REF_KNOWS_PEELED) {
-                       hashcpy(sha1, current_ref->peeled);
+       if (current_ref && (current_ref->name == refname
+                           || !strcmp(current_ref->name, refname))) {
+               if (peel_entry(current_ref, 0))
+                       return -1;
+               hashcpy(sha1, current_ref->u.value.peeled);
+               return 0;
+       }
+
+       if (read_ref_full(refname, base, 1, &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;
                }
-               hashcpy(base, current_ref->sha1);
-               goto fallback;
        }
 
-       if (!resolve_ref(ref, base, 1, &flag))
-               return -1;
+       return peel_object(base, sha1);
+}
 
-       if ((flag & REF_ISPACKED)) {
-               struct ref_list *list = get_packed_refs();
+struct warn_if_dangling_data {
+       FILE *fp;
+       const char *refname;
+       const char *msg_fmt;
+};
 
-               while (list) {
-                       if (!strcmp(list->name, ref)) {
-                               if (list->flag & REF_KNOWS_PEELED) {
-                                       hashcpy(sha1, list->peeled);
-                                       return 0;
-                               }
-                               /* older pack-refs did not leave peeled ones */
-                               break;
-                       }
-                       list = list->next;
-               }
+static int warn_if_dangling_symref(const char *refname, const unsigned char *sha1,
+                                  int flags, void *cb_data)
+{
+       struct warn_if_dangling_data *d = cb_data;
+       const char *resolves_to;
+       unsigned char junk[20];
+
+       if (!(flags & REF_ISSYMREF))
+               return 0;
+
+       resolves_to = resolve_ref_unsafe(refname, junk, 0, NULL);
+       if (!resolves_to || strcmp(resolves_to, d->refname))
+               return 0;
+
+       fprintf(d->fp, d->msg_fmt, refname);
+       fputc('\n', d->fp);
+       return 0;
+}
+
+void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char *refname)
+{
+       struct warn_if_dangling_data data;
+
+       data.fp = fp;
+       data.refname = refname;
+       data.msg_fmt = msg_fmt;
+       for_each_rawref(warn_if_dangling_symref, &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 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) {
+               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);
        }
 
-fallback:
-       o = parse_object(base);
-       if (o && o->type == OBJ_TAG) {
-               o = deref_tag(o, ref, 0);
-               if (o) {
-                       hashcpy(sha1, o->sha1);
-                       return 0;
-               }
+       if (packed_dir && loose_dir) {
+               sort_ref_dir(packed_dir);
+               sort_ref_dir(loose_dir);
+               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_entry_in_dir(
+                               packed_dir, 0, fn, cb_data);
+       } else if (loose_dir) {
+               sort_ref_dir(loose_dir);
+               retval = do_for_each_entry_in_dir(
+                               loose_dir, 0, fn, cb_data);
        }
-       return -1;
+
+       release_packed_ref_cache(packed_ref_cache);
+       return retval;
 }
 
-static int do_for_each_ref(const char *base, each_ref_fn fn, int trim,
-                          int flags, void *cb_data)
+/*
+ * 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)
 {
-       int retval = 0;
-       struct ref_list *packed = get_packed_refs();
-       struct ref_list *loose = get_loose_refs();
+       struct ref_entry_cb data;
+       data.base = base;
+       data.trim = trim;
+       data.flags = flags;
+       data.fn = fn;
+       data.cb_data = cb_data;
+
+       return do_for_each_entry(refs, base, do_one_ref, &data);
+}
 
-       struct ref_list *extra;
+static int do_head_ref(const char *submodule, each_ref_fn fn, void *cb_data)
+{
+       unsigned char sha1[20];
+       int flag;
 
-       for (extra = extra_refs; extra; extra = extra->next)
-               retval = do_one_ref(base, fn, trim, flags, cb_data, extra);
+       if (submodule) {
+               if (resolve_gitlink_ref(submodule, "HEAD", sha1) == 0)
+                       return fn("HEAD", sha1, 0, cb_data);
 
-       while (packed && loose) {
-               struct ref_list *entry;
-               int cmp = strcmp(packed->name, loose->name);
-               if (!cmp) {
-                       packed = packed->next;
-                       continue;
-               }
-               if (cmp > 0) {
-                       entry = loose;
-                       loose = loose->next;
-               } else {
-                       entry = packed;
-                       packed = packed->next;
-               }
-               retval = do_one_ref(base, fn, trim, flags, cb_data, entry);
-               if (retval)
-                       goto end_each;
+               return 0;
        }
 
-       for (packed = packed ? packed : loose; packed; packed = packed->next) {
-               retval = do_one_ref(base, fn, trim, flags, cb_data, packed);
-               if (retval)
-                       goto end_each;
-       }
+       if (!read_ref_full("HEAD", sha1, 1, &flag))
+               return fn("HEAD", sha1, flag, cb_data);
 
-end_each:
-       current_ref = NULL;
-       return retval;
+       return 0;
 }
 
 int head_ref(each_ref_fn fn, void *cb_data)
 {
-       unsigned char sha1[20];
-       int flag;
+       return do_head_ref(NULL, fn, cb_data);
+}
 
-       if (resolve_ref("HEAD", sha1, 1, &flag))
-               return fn("HEAD", sha1, flag, cb_data);
-       return 0;
+int head_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
+{
+       return do_head_ref(submodule, fn, cb_data);
 }
 
 int for_each_ref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref("refs/", 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(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(&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(get_ref_cache(submodule), prefix, fn, strlen(prefix), 0, cb_data);
 }
 
 int for_each_tag_ref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref("refs/tags/", fn, 10, 0, cb_data);
+       return for_each_ref_in("refs/tags/", fn, cb_data);
+}
+
+int for_each_tag_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
+{
+       return for_each_ref_in_submodule(submodule, "refs/tags/", fn, cb_data);
 }
 
 int for_each_branch_ref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref("refs/heads/", fn, 11, 0, cb_data);
+       return for_each_ref_in("refs/heads/", fn, cb_data);
 }
 
-int for_each_remote_ref(each_ref_fn fn, void *cb_data)
+int for_each_branch_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref("refs/remotes/", fn, 13, 0, cb_data);
+       return for_each_ref_in_submodule(submodule, "refs/heads/", fn, cb_data);
 }
 
-int for_each_rawref(each_ref_fn fn, void *cb_data)
+int for_each_remote_ref(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_ref("refs/", fn, 0,
-                              DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
+       return for_each_ref_in("refs/remotes/", fn, cb_data);
 }
 
-/*
- * Make sure "ref" 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 has ASCII control character, "~", "^", ":" or SP, anywhere, or
- * - it ends with a "/".
- * - it ends with ".lock"
- */
+int for_each_remote_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
+{
+       return for_each_ref_in_submodule(submodule, "refs/remotes/", fn, cb_data);
+}
 
-static inline int bad_ref_char(int ch)
+int for_each_replace_ref(each_ref_fn fn, void *cb_data)
 {
-       if (((unsigned) ch) <= ' ' ||
-           ch == '~' || ch == '^' || ch == ':')
-               return 1;
-       /* 2.13 Pattern Matching Notation */
-       if (ch == '?' || ch == '[') /* Unsupported */
-               return 1;
-       if (ch == '*') /* Supported at the end */
-               return 2;
-       return 0;
+       return do_for_each_ref(&ref_cache, "refs/replace/", fn, 13, 0, cb_data);
 }
 
-int check_ref_format(const char *ref)
+int head_ref_namespaced(each_ref_fn fn, void *cb_data)
 {
-       int ch, level, bad_type, last;
-       int ret = CHECK_REF_FORMAT_OK;
-       const char *cp = ref;
+       struct strbuf buf = STRBUF_INIT;
+       int ret = 0;
+       unsigned char sha1[20];
+       int flag;
 
-       level = 0;
-       while (1) {
-               while ((ch = *cp++) == '/')
-                       ; /* tolerate duplicated slashes */
-               if (!ch)
-                       /* should not end with slashes */
-                       return CHECK_REF_FORMAT_ERROR;
-
-               /* we are at the beginning of the path component */
-               if (ch == '.')
-                       return CHECK_REF_FORMAT_ERROR;
-               bad_type = bad_ref_char(ch);
-               if (bad_type) {
-                       if (bad_type == 2 && (!*cp || *cp == '/') &&
-                           ret == CHECK_REF_FORMAT_OK)
-                               ret = CHECK_REF_FORMAT_WILDCARD;
-                       else
-                               return CHECK_REF_FORMAT_ERROR;
-               }
+       strbuf_addf(&buf, "%sHEAD", get_git_namespace());
+       if (!read_ref_full(buf.buf, sha1, 1, &flag))
+               ret = fn(buf.buf, sha1, flag, cb_data);
+       strbuf_release(&buf);
 
-               last = ch;
-               /* scan the rest of the path component */
-               while ((ch = *cp++) != 0) {
-                       bad_type = bad_ref_char(ch);
-                       if (bad_type)
-                               return CHECK_REF_FORMAT_ERROR;
-                       if (ch == '/')
-                               break;
-                       if (last == '.' && ch == '.')
-                               return CHECK_REF_FORMAT_ERROR;
-                       if (last == '@' && ch == '{')
-                               return CHECK_REF_FORMAT_ERROR;
-                       last = ch;
-               }
-               level++;
-               if (!ch) {
-                       if (ref <= cp - 2 && cp[-2] == '.')
-                               return CHECK_REF_FORMAT_ERROR;
-                       if (level < 2)
-                               return CHECK_REF_FORMAT_ONELEVEL;
-                       if (has_extension(ref, ".lock"))
-                               return CHECK_REF_FORMAT_ERROR;
-                       return ret;
-               }
+       return ret;
+}
+
+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(&ref_cache, buf.buf, fn, 0, 0, cb_data);
+       strbuf_release(&buf);
+       return ret;
+}
+
+int for_each_glob_ref_in(each_ref_fn fn, const char *pattern,
+       const char *prefix, void *cb_data)
+{
+       struct strbuf real_pattern = STRBUF_INIT;
+       struct ref_filter filter;
+       int ret;
+
+       if (!prefix && prefixcmp(pattern, "refs/"))
+               strbuf_addstr(&real_pattern, "refs/");
+       else if (prefix)
+               strbuf_addstr(&real_pattern, prefix);
+       strbuf_addstr(&real_pattern, pattern);
+
+       if (!has_glob_specials(pattern)) {
+               /* Append implied '/' '*' if not present. */
+               if (real_pattern.buf[real_pattern.len - 1] != '/')
+                       strbuf_addch(&real_pattern, '/');
+               /* No need to check for '*', there is none. */
+               strbuf_addch(&real_pattern, '*');
        }
+
+       filter.pattern = real_pattern.buf;
+       filter.fn = fn;
+       filter.cb_data = cb_data;
+       ret = for_each_ref(filter_refs, &filter);
+
+       strbuf_release(&real_pattern);
+       return ret;
+}
+
+int for_each_glob_ref(each_ref_fn fn, const char *pattern, void *cb_data)
+{
+       return for_each_glob_ref_in(fn, pattern, NULL, cb_data);
+}
+
+int for_each_rawref(each_ref_fn fn, void *cb_data)
+{
+       return do_for_each_ref(&ref_cache, "", fn, 0,
+                              DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
 }
 
-const char *prettify_ref(const struct ref *ref)
+const char *prettify_refname(const char *name)
 {
-       const char *name = ref->name;
        return name + (
                !prefixcmp(name, "refs/heads/") ? 11 :
                !prefixcmp(name, "refs/tags/") ? 10 :
@@ -765,13 +1890,6 @@ const char *ref_rev_parse_rules[] = {
        NULL
 };
 
-const char *ref_fetch_rules[] = {
-       "%.*s",
-       "refs/%.*s",
-       "refs/heads/%.*s",
-       NULL
-};
-
 int refname_match(const char *abbrev_name, const char *full_name, const char **rules)
 {
        const char **p;
@@ -789,7 +1907,7 @@ int refname_match(const char *abbrev_name, const char *full_name, const char **r
 static struct ref_lock *verify_lock(struct ref_lock *lock,
        const unsigned char *old_sha1, int mustexist)
 {
-       if (!resolve_ref(lock->ref_name, lock->old_sha1, mustexist, NULL)) {
+       if (read_ref_full(lock->ref_name, lock->old_sha1, mustexist, NULL)) {
                error("Can't verify ref %s", lock->ref_name);
                unlock_ref(lock);
                return NULL;
@@ -812,313 +1930,675 @@ static int remove_empty_directories(const char *file)
        struct strbuf path;
        int result;
 
-       strbuf_init(&path, 20);
-       strbuf_addstr(&path, file);
+       strbuf_init(&path, 20);
+       strbuf_addstr(&path, file);
+
+       result = remove_dir_recursively(&path, REMOVE_DIR_EMPTY_ONLY);
+
+       strbuf_release(&path);
+
+       return result;
+}
+
+/*
+ * *string and *len will only be substituted, and *string returned (for
+ * later free()ing) if the string passed in is a magic short-hand form
+ * to name a branch.
+ */
+static char *substitute_branch_name(const char **string, int *len)
+{
+       struct strbuf buf = STRBUF_INIT;
+       int ret = interpret_branch_name(*string, *len, &buf);
+
+       if (ret == *len) {
+               size_t size;
+               *string = strbuf_detach(&buf, &size);
+               *len = size;
+               return (char *)*string;
+       }
+
+       return NULL;
+}
+
+int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
+{
+       char *last_branch = substitute_branch_name(&str, &len);
+       const char **p, *r;
+       int refs_found = 0;
+
+       *ref = NULL;
+       for (p = ref_rev_parse_rules; *p; p++) {
+               char fullref[PATH_MAX];
+               unsigned char sha1_from_ref[20];
+               unsigned char *this_result;
+               int flag;
+
+               this_result = refs_found ? sha1_from_ref : sha1;
+               mksnpath(fullref, sizeof(fullref), *p, len, str);
+               r = resolve_ref_unsafe(fullref, this_result, 1, &flag);
+               if (r) {
+                       if (!refs_found++)
+                               *ref = xstrdup(r);
+                       if (!warn_ambiguous_refs)
+                               break;
+               } else if ((flag & REF_ISSYMREF) && strcmp(fullref, "HEAD")) {
+                       warning("ignoring dangling symref %s.", fullref);
+               } else if ((flag & REF_ISBROKEN) && strchr(fullref, '/')) {
+                       warning("ignoring broken ref %s.", fullref);
+               }
+       }
+       free(last_branch);
+       return refs_found;
+}
+
+int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
+{
+       char *last_branch = substitute_branch_name(&str, &len);
+       const char **p;
+       int logs_found = 0;
+
+       *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);
+               if (!ref)
+                       continue;
+               if (!stat(git_path("logs/%s", path), &st) &&
+                   S_ISREG(st.st_mode))
+                       it = path;
+               else if (strcmp(ref, path) &&
+                        !stat(git_path("logs/%s", ref), &st) &&
+                        S_ISREG(st.st_mode))
+                       it = ref;
+               else
+                       continue;
+               if (!logs_found++) {
+                       *log = xstrdup(it);
+                       hashcpy(sha1, hash);
+               }
+               if (!warn_ambiguous_refs)
+                       break;
+       }
+       free(last_branch);
+       return logs_found;
+}
+
+static struct ref_lock *lock_ref_sha1_basic(const char *refname,
+                                           const unsigned char *old_sha1,
+                                           int flags, int *type_p)
+{
+       char *ref_file;
+       const char *orig_refname = refname;
+       struct ref_lock *lock;
+       int last_errno = 0;
+       int type, lflags;
+       int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
+       int missing = 0;
+
+       lock = xcalloc(1, sizeof(struct ref_lock));
+       lock->lock_fd = -1;
+
+       refname = resolve_ref_unsafe(refname, lock->old_sha1, mustexist, &type);
+       if (!refname && errno == EISDIR) {
+               /* we are trying to lock foo but we used to
+                * have foo/bar which now does not exist;
+                * it is normal for the empty directory 'foo'
+                * to remain.
+                */
+               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);
+                       goto error_return;
+               }
+               refname = resolve_ref_unsafe(orig_refname, lock->old_sha1, mustexist, &type);
+       }
+       if (type_p)
+           *type_p = type;
+       if (!refname) {
+               last_errno = errno;
+               error("unable to resolve reference %s: %s",
+                       orig_refname, strerror(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 (missing &&
+            !is_refname_available(refname, NULL, get_packed_refs(&ref_cache))) {
+               last_errno = ENOTDIR;
+               goto error_return;
+       }
+
+       lock->lk = xcalloc(1, sizeof(struct lock_file));
+
+       lflags = LOCK_DIE_ON_ERROR;
+       if (flags & REF_NODEREF) {
+               refname = orig_refname;
+               lflags |= LOCK_NODEREF;
+       }
+       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)) {
+               last_errno = errno;
+               error("unable to create directory for %s", ref_file);
+               goto error_return;
+       }
+
+       lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, lflags);
+       return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;
+
+ error_return:
+       unlock_ref(lock);
+       errno = last_errno;
+       return NULL;
+}
+
+struct ref_lock *lock_ref_sha1(const char *refname, const unsigned char *old_sha1)
+{
+       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);
+}
+
+struct ref_lock *lock_any_ref_for_update(const char *refname,
+                                        const unsigned char *old_sha1,
+                                        int flags, int *type_p)
+{
+       if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
+               return NULL;
+       return lock_ref_sha1_basic(refname, old_sha1, flags, type_p);
+}
+
+/*
+ * 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(int fd, char *refname, unsigned char *sha1,
+                              unsigned char *peeled)
+{
+       char line[PATH_MAX + 100];
+       int len;
+
+       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(fd, line, len);
+
+       if (peeled) {
+               if (snprintf(line, sizeof(line), "^%s\n",
+                            sha1_to_hex(peeled)) != PEELED_LINE_LENGTH)
+                       die("internal error");
+               write_or_die(fd, line, PEELED_LINE_LENGTH);
+       }
+}
+
+/*
+ * 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)
+{
+       int *fd = cb_data;
+       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(*fd, entry->name, entry->u.value.sha1,
+                          peel_status == PEEL_PEELED ?
+                          entry->u.value.peeled : NULL);
+       return 0;
+}
+
+int lock_packed_refs(int flags)
+{
+       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;
+}
+
+int commit_packed_refs(void)
+{
+       struct packed_ref_cache *packed_ref_cache =
+               get_packed_ref_cache(&ref_cache);
+       int error = 0;
+
+       if (!packed_ref_cache->lock)
+               die("internal error: packed-refs not locked");
+       write_or_die(packed_ref_cache->lock->fd,
+                    PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
+
+       do_for_each_entry_in_dir(get_packed_ref_dir(packed_ref_cache),
+                                0, write_packed_entry_fn,
+                                &packed_ref_cache->lock->fd);
+       if (commit_lock_file(packed_ref_cache->lock))
+               error = -1;
+       packed_ref_cache->lock = NULL;
+       release_packed_ref_cache(packed_ref_cache);
+       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;
+};
+
+/*
+ * 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 pack_refs_cb_data *cb = cb_data;
+       enum peel_status peel_status;
+       struct ref_entry *packed_entry;
+       int is_tag_ref = !prefixcmp(entry->name, "refs/tags/");
+
+       /* ALWAYS pack tags */
+       if (!(cb->flags & PACK_REFS_ALL) && !is_tag_ref)
+               return 0;
+
+       /* Do not pack symbolic or broken refs: */
+       if ((entry->flag & REF_ISSYMREF) || !ref_resolves_to_object(entry))
+               return 0;
+
+       /* 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;
+}
+
+/*
+ * 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_lock *lock = lock_ref_sha1(r->name + 5, r->sha1);
+
+       if (lock) {
+               unlink_or_warn(git_path("%s", r->name));
+               unlock_ref(lock);
+               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;
 
-       result = remove_dir_recursively(&path, 1);
+       memset(&cbdata, 0, sizeof(cbdata));
+       cbdata.flags = flags;
 
-       strbuf_release(&path);
+       lock_packed_refs(LOCK_DIE_ON_ERROR);
+       cbdata.packed_refs = get_packed_refs(&ref_cache);
 
-       return result;
-}
+       do_for_each_entry_in_dir(get_loose_refs(&ref_cache), 0,
+                                pack_if_possible_fn, &cbdata);
 
-static int is_refname_available(const char *ref, const char *oldref,
-                               struct ref_list *list, int quiet)
-{
-       int namlen = strlen(ref); /* e.g. 'foo/bar' */
-       while (list) {
-               /* list->name could be 'foo' or 'foo/bar/baz' */
-               if (!oldref || strcmp(oldref, list->name)) {
-                       int len = strlen(list->name);
-                       int cmplen = (namlen < len) ? namlen : len;
-                       const char *lead = (namlen < len) ? list->name : ref;
-                       if (!strncmp(ref, list->name, cmplen) &&
-                           lead[cmplen] == '/') {
-                               if (!quiet)
-                                       error("'%s' exists; cannot create '%s'",
-                                             list->name, ref);
-                               return 0;
-                       }
-               }
-               list = list->next;
-       }
-       return 1;
+       if (commit_packed_refs())
+               die_errno("unable to overwrite old ref-pack file");
+
+       prune_refs(cbdata.ref_to_prune);
+       return 0;
 }
 
-static struct ref_lock *lock_ref_sha1_basic(const char *ref, const unsigned char *old_sha1, int flags, int *type_p)
+/*
+ * If entry is no longer needed in packed-refs, add it to the string
+ * list pointed to by cb_data.  Reasons for deleting entries:
+ *
+ * - Entry is broken.
+ * - Entry is overridden by a loose ref.
+ * - Entry does not point at a valid object.
+ *
+ * In the first and third cases, also emit an error message because these
+ * are indications of repository corruption.
+ */
+static int curate_packed_ref_fn(struct ref_entry *entry, void *cb_data)
 {
-       char *ref_file;
-       const char *orig_ref = ref;
-       struct ref_lock *lock;
-       int last_errno = 0;
-       int type, lflags;
-       int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
-       int missing = 0;
+       struct string_list *refs_to_delete = cb_data;
 
-       lock = xcalloc(1, sizeof(struct ref_lock));
-       lock->lock_fd = -1;
+       if (entry->flag & REF_ISBROKEN) {
+               /* This shouldn't happen to packed refs. */
+               error("%s is broken!", entry->name);
+               string_list_append(refs_to_delete, entry->name);
+               return 0;
+       }
+       if (!has_sha1_file(entry->u.value.sha1)) {
+               unsigned char sha1[20];
+               int flags;
 
-       ref = resolve_ref(ref, lock->old_sha1, mustexist, &type);
-       if (!ref && errno == EISDIR) {
-               /* we are trying to lock foo but we used to
-                * have foo/bar which now does not exist;
-                * it is normal for the empty directory 'foo'
-                * to remain.
-                */
-               ref_file = git_path("%s", orig_ref);
-               if (remove_empty_directories(ref_file)) {
-                       last_errno = errno;
-                       error("there are still refs under '%s'", orig_ref);
-                       goto error_return;
+               if (read_ref_full(entry->name, sha1, 0, &flags))
+                       /* We should at least have found the packed ref. */
+                       die("Internal error");
+               if ((flags & REF_ISSYMREF) || !(flags & REF_ISPACKED)) {
+                       /*
+                        * This packed reference is overridden by a
+                        * loose reference, so it is OK that its value
+                        * is no longer valid; for example, it might
+                        * refer to an object that has been garbage
+                        * collected.  For this purpose we don't even
+                        * care whether the loose reference itself is
+                        * invalid, broken, symbolic, etc.  Silently
+                        * remove the packed reference.
+                        */
+                       string_list_append(refs_to_delete, entry->name);
+                       return 0;
                }
-               ref = resolve_ref(orig_ref, lock->old_sha1, mustexist, &type);
-       }
-       if (type_p)
-           *type_p = type;
-       if (!ref) {
-               last_errno = errno;
-               error("unable to resolve reference %s: %s",
-                       orig_ref, strerror(errno));
-               goto error_return;
+               /*
+                * There is no overriding loose reference, so the fact
+                * that this reference doesn't refer to a valid object
+                * indicates some kind of repository corruption.
+                * Report the problem, then omit the reference from
+                * the output.
+                */
+               error("%s does not point to a valid object!", entry->name);
+               string_list_append(refs_to_delete, entry->name);
+               return 0;
        }
-       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 (missing &&
-            !is_refname_available(ref, NULL, get_packed_refs(), 0))
-               goto error_return;
 
-       lock->lk = xcalloc(1, sizeof(struct lock_file));
+       return 0;
+}
 
-       lflags = LOCK_DIE_ON_ERROR;
-       if (flags & REF_NODEREF) {
-               ref = orig_ref;
-               lflags |= LOCK_NODEREF;
-       }
-       lock->ref_name = xstrdup(ref);
-       lock->orig_ref_name = xstrdup(orig_ref);
-       ref_file = git_path("%s", ref);
-       if (missing)
-               lock->force_write = 1;
-       if ((flags & REF_NODEREF) && (type & REF_ISSYMREF))
-               lock->force_write = 1;
+static int repack_without_refs(const char **refnames, int n)
+{
+       struct ref_dir *packed;
+       struct string_list refs_to_delete = STRING_LIST_INIT_DUP;
+       struct string_list_item *ref_to_delete;
+       int i, removed = 0;
+
+       /* Look for a packed ref */
+       for (i = 0; i < n; i++)
+               if (get_packed_ref(refnames[i]))
+                       break;
 
-       if (safe_create_leading_directories(ref_file)) {
-               last_errno = errno;
-               error("unable to create directory for %s", ref_file);
-               goto error_return;
+       /* Avoid locking if we have nothing to do */
+       if (i == n)
+               return 0; /* no refname exists in packed refs */
+
+       if (lock_packed_refs(0)) {
+               unable_to_lock_error(git_path("packed-refs"), errno);
+               return error("cannot delete '%s' from packed refs", refnames[i]);
        }
+       packed = get_packed_refs(&ref_cache);
 
-       lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, lflags);
-       return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;
+       /* Remove refnames from the cache */
+       for (i = 0; i < n; i++)
+               if (remove_entry(packed, refnames[i]) != -1)
+                       removed = 1;
+       if (!removed) {
+               /*
+                * All packed entries disappeared while we were
+                * acquiring the lock.
+                */
+               rollback_packed_refs();
+               return 0;
+       }
 
- error_return:
-       unlock_ref(lock);
-       errno = last_errno;
-       return NULL;
-}
+       /* Remove any other accumulated cruft */
+       do_for_each_entry_in_dir(packed, 0, curate_packed_ref_fn, &refs_to_delete);
+       for_each_string_list_item(ref_to_delete, &refs_to_delete) {
+               if (remove_entry(packed, ref_to_delete->string) == -1)
+                       die("internal error");
+       }
 
-struct ref_lock *lock_ref_sha1(const char *ref, const unsigned char *old_sha1)
-{
-       char refpath[PATH_MAX];
-       if (check_ref_format(ref))
-               return NULL;
-       strcpy(refpath, mkpath("refs/%s", ref));
-       return lock_ref_sha1_basic(refpath, old_sha1, 0, NULL);
+       /* Write what remains */
+       return commit_packed_refs();
 }
 
-struct ref_lock *lock_any_ref_for_update(const char *ref, const unsigned char *old_sha1, int flags)
+static int repack_without_ref(const char *refname)
 {
-       switch (check_ref_format(ref)) {
-       default:
-               return NULL;
-       case 0:
-       case CHECK_REF_FORMAT_ONELEVEL:
-               return lock_ref_sha1_basic(ref, old_sha1, flags, NULL);
-       }
+       return repack_without_refs(&refname, 1);
 }
 
-static struct lock_file packlock;
-
-static int repack_without_ref(const char *refname)
+static int delete_ref_loose(struct ref_lock *lock, int flag)
 {
-       struct ref_list *list, *packed_ref_list;
-       int fd;
-       int found = 0;
-
-       packed_ref_list = get_packed_refs();
-       for (list = packed_ref_list; list; list = list->next) {
-               if (!strcmp(refname, list->name)) {
-                       found = 1;
-                       break;
-               }
-       }
-       if (!found)
-               return 0;
-       fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
-       if (fd < 0)
-               return error("cannot delete '%s' from packed refs", refname);
-
-       for (list = packed_ref_list; list; list = list->next) {
-               char line[PATH_MAX + 100];
-               int len;
+       if (!(flag & REF_ISPACKED) || flag & REF_ISSYMREF) {
+               /* loose */
+               int err, i = strlen(lock->lk->filename) - 5; /* .lock */
 
-               if (!strcmp(refname, list->name))
-                       continue;
-               len = snprintf(line, sizeof(line), "%s %s\n",
-                              sha1_to_hex(list->sha1), list->name);
-               /* this should not happen but just being defensive */
-               if (len > sizeof(line))
-                       die("too long a refname '%s'", list->name);
-               write_or_die(fd, line, len);
+               lock->lk->filename[i] = 0;
+               err = unlink_or_warn(lock->lk->filename);
+               lock->lk->filename[i] = '.';
+               if (err && errno != ENOENT)
+                       return 1;
        }
-       return commit_lock_file(&packlock);
+       return 0;
 }
 
 int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
 {
        struct ref_lock *lock;
-       int err, i = 0, ret = 0, flag = 0;
+       int ret = 0, flag = 0;
 
-       lock = lock_ref_sha1_basic(refname, sha1, 0, &flag);
+       lock = lock_ref_sha1_basic(refname, sha1, delopt, &flag);
        if (!lock)
                return 1;
-       if (!(flag & REF_ISPACKED) || flag & REF_ISSYMREF) {
-               /* loose */
-               const char *path;
+       ret |= delete_ref_loose(lock, flag);
 
-               if (!(delopt & REF_NODEREF)) {
-                       i = strlen(lock->lk->filename) - 5; /* .lock */
-                       lock->lk->filename[i] = 0;
-                       path = lock->lk->filename;
-               } else {
-                       path = git_path("%s", refname);
-               }
-               err = unlink(path);
-               if (err && errno != ENOENT) {
-                       ret = 1;
-                       error("unlink(%s) failed: %s",
-                             path, strerror(errno));
-               }
-               if (!(delopt & REF_NODEREF))
-                       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(refname);
+       ret |= repack_without_ref(lock->ref_name);
 
-       err = unlink(git_path("logs/%s", lock->ref_name));
-       if (err && errno != ENOENT)
-               warning("unlink(%s) failed: %s",
-                       git_path("logs/%s", lock->ref_name), strerror(errno));
-       invalidate_cached_refs();
+       unlink_or_warn(git_path("logs/%s", lock->ref_name));
+       clear_loose_ref_cache(&ref_cache);
        unlock_ref(lock);
        return ret;
 }
 
-int rename_ref(const char *oldref, const char *newref, const char *logmsg)
+/*
+ * People using contrib's git-new-workdir have .git/logs/refs ->
+ * /some/other/path/.git/logs/refs, and that may live on another device.
+ *
+ * IOW, to avoid cross device rename errors, the temporary renamed log must
+ * live into logs/refs.
+ */
+#define TMP_RENAMED_LOG  "logs/refs/.tmp-renamed-log"
+
+int rename_ref(const char *oldrefname, const char *newrefname, const char *logmsg)
 {
-       static const char renamed_ref[] = "RENAMED-REF";
        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", oldref), &loginfo);
+       int log = !lstat(git_path("logs/%s", oldrefname), &loginfo);
        const char *symref = NULL;
 
        if (log && S_ISLNK(loginfo.st_mode))
-               return error("reflog for %s is a symlink", oldref);
+               return error("reflog for %s is a symlink", oldrefname);
 
-       symref = resolve_ref(oldref, orig_sha1, 1, &flag);
+       symref = resolve_ref_unsafe(oldrefname, orig_sha1, 1, &flag);
        if (flag & REF_ISSYMREF)
                return error("refname %s is a symbolic ref, renaming it is not supported",
-                       oldref);
+                       oldrefname);
        if (!symref)
-               return error("refname %s not found", oldref);
+               return error("refname %s not found", oldrefname);
 
-       if (!is_refname_available(newref, oldref, get_packed_refs(), 0))
+       if (!is_refname_available(newrefname, oldrefname, get_packed_refs(&ref_cache)))
                return 1;
 
-       if (!is_refname_available(newref, oldref, get_loose_refs(), 0))
+       if (!is_refname_available(newrefname, oldrefname, get_loose_refs(&ref_cache)))
                return 1;
 
-       lock = lock_ref_sha1_basic(renamed_ref, NULL, 0, NULL);
-       if (!lock)
-               return error("unable to lock %s", renamed_ref);
-       lock->force_write = 1;
-       if (write_ref_sha1(lock, orig_sha1, logmsg))
-               return error("unable to save current sha1 in %s", renamed_ref);
+       if (log && rename(git_path("logs/%s", oldrefname), git_path(TMP_RENAMED_LOG)))
+               return error("unable to move logfile logs/%s to "TMP_RENAMED_LOG": %s",
+                       oldrefname, strerror(errno));
 
-       if (log && rename(git_path("logs/%s", oldref), git_path("tmp-renamed-log")))
-               return error("unable to move logfile logs/%s to tmp-renamed-log: %s",
-                       oldref, strerror(errno));
-
-       if (delete_ref(oldref, orig_sha1, REF_NODEREF)) {
-               error("unable to delete old %s", oldref);
+       if (delete_ref(oldrefname, orig_sha1, REF_NODEREF)) {
+               error("unable to delete old %s", oldrefname);
                goto rollback;
        }
 
-       if (resolve_ref(newref, sha1, 1, &flag) && delete_ref(newref, sha1, REF_NODEREF)) {
+       if (!read_ref_full(newrefname, sha1, 1, &flag) &&
+           delete_ref(newrefname, sha1, REF_NODEREF)) {
                if (errno==EISDIR) {
-                       if (remove_empty_directories(git_path("%s", newref))) {
-                               error("Directory not empty: %s", newref);
+                       if (remove_empty_directories(git_path("%s", newrefname))) {
+                               error("Directory not empty: %s", newrefname);
                                goto rollback;
                        }
                } else {
-                       error("unable to delete existing %s", newref);
+                       error("unable to delete existing %s", newrefname);
                        goto rollback;
                }
        }
 
-       if (log && safe_create_leading_directories(git_path("logs/%s", newref))) {
-               error("unable to create directory for %s", newref);
+       if (log && safe_create_leading_directories(git_path("logs/%s", newrefname))) {
+               error("unable to create directory for %s", newrefname);
                goto rollback;
        }
 
  retry:
-       if (log && rename(git_path("tmp-renamed-log"), git_path("logs/%s", newref))) {
+       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", newref))) {
-                               error("Directory not empty: logs/%s", newref);
+                       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",
-                               newref, strerror(errno));
+                       error("unable to move logfile "TMP_RENAMED_LOG" to logs/%s: %s",
+                               newrefname, strerror(errno));
                        goto rollback;
                }
        }
        logmoved = log;
 
-       lock = lock_ref_sha1_basic(newref, NULL, 0, NULL);
+       lock = lock_ref_sha1_basic(newrefname, NULL, 0, NULL);
        if (!lock) {
-               error("unable to lock %s for update", newref);
+               error("unable to lock %s for update", newrefname);
                goto rollback;
        }
        lock->force_write = 1;
        hashcpy(lock->old_sha1, orig_sha1);
        if (write_ref_sha1(lock, orig_sha1, logmsg)) {
-               error("unable to write current sha1 into %s", newref);
+               error("unable to write current sha1 into %s", newrefname);
                goto rollback;
        }
 
        return 0;
 
  rollback:
-       lock = lock_ref_sha1_basic(oldref, NULL, 0, NULL);
+       lock = lock_ref_sha1_basic(oldrefname, NULL, 0, NULL);
        if (!lock) {
-               error("unable to lock %s for rollback", oldref);
+               error("unable to lock %s for rollback", oldrefname);
                goto rollbacklog;
        }
 
@@ -1126,17 +2606,17 @@ int rename_ref(const char *oldref, const char *newref, const char *logmsg)
        flag = log_all_ref_updates;
        log_all_ref_updates = 0;
        if (write_ref_sha1(lock, orig_sha1, NULL))
-               error("unable to write current sha1 into %s", oldref);
+               error("unable to write current sha1 into %s", oldrefname);
        log_all_ref_updates = flag;
 
  rollbacklog:
-       if (logmoved && rename(git_path("logs/%s", newref), git_path("logs/%s", oldref)))
+       if (logmoved && rename(git_path("logs/%s", newrefname), git_path("logs/%s", oldrefname)))
                error("unable to restore logfile %s from %s: %s",
-                       oldref, newref, strerror(errno));
+                       oldrefname, newrefname, strerror(errno));
        if (!logmoved && log &&
-           rename(git_path("tmp-renamed-log"), git_path("logs/%s", oldref)))
-               error("unable to restore logfile %s from tmp-renamed-log: %s",
-                       oldref, strerror(errno));
+           rename(git_path(TMP_RENAMED_LOG), git_path("logs/%s", oldrefname)))
+               error("unable to restore logfile %s from "TMP_RENAMED_LOG": %s",
+                       oldrefname, strerror(errno));
 
        return 1;
 }
@@ -1193,51 +2673,65 @@ static int copy_msg(char *buf, const char *msg)
        return cp - buf;
 }
 
-static int log_ref_write(const char *ref_name, const unsigned char *old_sha1,
-                        const unsigned char *new_sha1, const char *msg)
+int log_ref_setup(const char *refname, char *logfile, int bufsize)
 {
-       int logfd, written, oflags = O_APPEND | O_WRONLY;
-       unsigned maxlen, len;
-       int msglen;
-       char log_file[PATH_MAX];
-       char *logrec;
-       const char *committer;
-
-       if (log_all_ref_updates < 0)
-               log_all_ref_updates = !is_bare_repository();
-
-       git_snpath(log_file, sizeof(log_file), "logs/%s", ref_name);
+       int logfd, oflags = O_APPEND | O_WRONLY;
 
+       git_snpath(logfile, bufsize, "logs/%s", refname);
        if (log_all_ref_updates &&
-           (!prefixcmp(ref_name, "refs/heads/") ||
-            !prefixcmp(ref_name, "refs/remotes/") ||
-            !strcmp(ref_name, "HEAD"))) {
-               if (safe_create_leading_directories(log_file) < 0)
+           (!prefixcmp(refname, "refs/heads/") ||
+            !prefixcmp(refname, "refs/remotes/") ||
+            !prefixcmp(refname, "refs/notes/") ||
+            !strcmp(refname, "HEAD"))) {
+               if (safe_create_leading_directories(logfile) < 0)
                        return error("unable to create directory for %s",
-                                    log_file);
+                                    logfile);
                oflags |= O_CREAT;
        }
 
-       logfd = open(log_file, oflags, 0666);
+       logfd = open(logfile, oflags, 0666);
        if (logfd < 0) {
                if (!(oflags & O_CREAT) && errno == ENOENT)
                        return 0;
 
                if ((oflags & O_CREAT) && errno == EISDIR) {
-                       if (remove_empty_directories(log_file)) {
+                       if (remove_empty_directories(logfile)) {
                                return error("There are still logs under '%s'",
-                                            log_file);
+                                            logfile);
                        }
-                       logfd = open(log_file, oflags, 0666);
+                       logfd = open(logfile, oflags, 0666);
                }
 
                if (logfd < 0)
                        return error("Unable to append to %s: %s",
-                                    log_file, strerror(errno));
+                                    logfile, strerror(errno));
        }
 
-       adjust_shared_perm(log_file);
+       adjust_shared_perm(logfile);
+       close(logfd);
+       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;
+       char log_file[PATH_MAX];
+       char *logrec;
+       const char *committer;
+
+       if (log_all_ref_updates < 0)
+               log_all_ref_updates = !is_bare_repository();
+
+       result = log_ref_setup(refname, log_file, sizeof(log_file));
+       if (result)
+               return result;
 
+       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;
@@ -1274,7 +2768,7 @@ int write_ref_sha1(struct ref_lock *lock,
        }
        o = parse_object(sha1);
        if (!o) {
-               error("Trying to write ref %s with nonexistant object %s",
+               error("Trying to write ref %s with nonexistent object %s",
                        lock->ref_name, sha1_to_hex(sha1));
                unlock_ref(lock);
                return -1;
@@ -1292,7 +2786,7 @@ int write_ref_sha1(struct ref_lock *lock,
                unlock_ref(lock);
                return -1;
        }
-       invalidate_cached_refs();
+       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)) {
@@ -1315,7 +2809,7 @@ int write_ref_sha1(struct ref_lock *lock,
                unsigned char head_sha1[20];
                int head_flag;
                const char *head_ref;
-               head_ref = resolve_ref("HEAD", head_sha1, 1, &head_flag);
+               head_ref = resolve_ref_unsafe("HEAD", head_sha1, 1, &head_flag);
                if (head_ref && (head_flag & REF_ISSYMREF) &&
                    !strcmp(head_ref, lock->ref_name))
                        log_ref_write("HEAD", lock->old_sha1, sha1, logmsg);
@@ -1376,7 +2870,7 @@ int create_symref(const char *ref_target, const char *refs_heads_master,
        if (adjust_shared_perm(git_HEAD)) {
                error("Unable to fix permissions on %s", lockpath);
        error_unlink_return:
-               unlink(lockpath);
+               unlink_or_warn(lockpath);
        error_free_return:
                free(git_HEAD);
                return -1;
@@ -1402,7 +2896,9 @@ static char *ref_msg(const char *line, const char *endp)
        return xmemdupz(line, ep - line);
 }
 
-int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *sha1, char **msg, unsigned long *cutoff_time, int *cutoff_tz, int *cutoff_cnt)
+int read_ref_at(const char *refname, 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;
@@ -1413,10 +2909,10 @@ int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *
        void *log_mapped;
        size_t mapsz;
 
-       logfile = git_path("logs/%s", ref);
+       logfile = git_path("logs/%s", refname);
        logfd = open(logfile, O_RDONLY, 0);
        if (logfd < 0)
-               die("Unable to read log %s: %s", logfile, strerror(errno));
+               die_errno("Unable to read log '%s'", logfile);
        fstat(logfd, &st);
        if (!st.st_size)
                die("Log %s is empty.", logfile);
@@ -1506,124 +3002,200 @@ int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *
        return 1;
 }
 
-int for_each_recent_reflog_ent(const char *ref, each_reflog_ent_fn fn, long ofs, void *cb_data)
+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;
+       struct strbuf sb = STRBUF_INIT;
        FILE *logfp;
-       char buf[1024];
-       int ret = 0;
+       long pos;
+       int ret = 0, at_tail = 1;
 
-       logfile = git_path("logs/%s", ref);
-       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) ||
-                   fgets(buf, sizeof(buf), logfp))
-                       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') {
+                               strbuf_splice(&sb, 0, 0, buf, endp - buf);
+                               if (pos)
+                                       break; /* need to fill another block */
+                               scanp = buf - 1; /* leave loop */
+                       } else {
+                               /*
+                                * (bp + 1) thru endp is the beginning of the
+                                * current line we have in sb
+                                */
+                               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;
+               }
 
-       while (fgets(buf, sizeof(buf), logfp)) {
-               unsigned char osha1[20], nsha1[20];
-               char *email_end, *message;
-               unsigned long timestamp;
-               int len, tz;
-
-               /* old SP new SP name <email> SP time TAB msg LF */
-               len = strlen(buf);
-               if (len < 83 || buf[len-1] != '\n' ||
-                   get_sha1_hex(buf, osha1) || buf[40] != ' ' ||
-                   get_sha1_hex(buf + 41, nsha1) || buf[81] != ' ' ||
-                   !(email_end = strchr(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, buf+82, timestamp, tz, message, cb_data);
-               if (ret)
-                       break;
        }
+       if (!ret && sb.len)
+               ret = show_one_reflog_ent(&sb, fn, cb_data);
+
        fclose(logfp);
+       strbuf_release(&sb);
        return ret;
 }
 
-int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
+int for_each_reflog_ent(const char *refname, each_reflog_ent_fn fn, void *cb_data)
 {
-       return for_each_recent_reflog_ent(ref, 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;
 
-static int do_for_each_reflog(const char *base, each_ref_fn fn, void *cb_data)
+       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
+ * space, but its contents will be restored before return.
+ */
+static int do_for_each_reflog(struct strbuf *name, each_ref_fn fn, void *cb_data)
 {
-       DIR *dir = opendir(git_path("logs/%s", base));
+       DIR *d = opendir(git_path("logs/%s", name->buf));
        int retval = 0;
+       struct dirent *de;
+       int oldlen = name->len;
 
-       if (dir) {
-               struct dirent *de;
-               int baselen = strlen(base);
-               char *log = xmalloc(baselen + 257);
-
-               memcpy(log, base, baselen);
-               if (baselen && base[baselen-1] != '/')
-                       log[baselen++] = '/';
+       if (!d)
+               return name->len ? errno : 0;
 
-               while ((de = readdir(dir)) != NULL) {
-                       struct stat st;
-                       int namelen;
+       while ((de = readdir(d)) != NULL) {
+               struct stat st;
 
-                       if (de->d_name[0] == '.')
-                               continue;
-                       namelen = strlen(de->d_name);
-                       if (namelen > 255)
-                               continue;
-                       if (has_extension(de->d_name, ".lock"))
-                               continue;
-                       memcpy(log + baselen, de->d_name, namelen+1);
-                       if (stat(git_path("logs/%s", log), &st) < 0)
-                               continue;
+               if (de->d_name[0] == '.')
+                       continue;
+               if (has_extension(de->d_name, ".lock"))
+                       continue;
+               strbuf_addstr(name, de->d_name);
+               if (stat(git_path("logs/%s", name->buf), &st) < 0) {
+                       ; /* silently ignore */
+               } else {
                        if (S_ISDIR(st.st_mode)) {
-                               retval = do_for_each_reflog(log, fn, cb_data);
+                               strbuf_addch(name, '/');
+                               retval = do_for_each_reflog(name, fn, cb_data);
                        } else {
                                unsigned char sha1[20];
-                               if (!resolve_ref(log, sha1, 0, NULL))
-                                       retval = error("bad ref for %s", log);
+                               if (read_ref_full(name->buf, sha1, 0, NULL))
+                                       retval = error("bad ref for %s", name->buf);
                                else
-                                       retval = fn(log, sha1, 0, cb_data);
+                                       retval = fn(name->buf, sha1, 0, cb_data);
                        }
                        if (retval)
                                break;
                }
-               free(log);
-               closedir(dir);
+               strbuf_setlen(name, oldlen);
        }
-       else if (*base)
-               return errno;
+       closedir(d);
        return retval;
 }
 
 int for_each_reflog(each_ref_fn fn, void *cb_data)
 {
-       return do_for_each_reflog("", fn, cb_data);
+       int retval;
+       struct strbuf name;
+       strbuf_init(&name, PATH_MAX);
+       retval = do_for_each_reflog(&name, fn, cb_data);
+       strbuf_release(&name);
+       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)
+static struct ref_lock *update_ref_lock(const char *refname,
+                                       const unsigned char *oldval,
+                                       int flags, int *type_p,
+                                       enum action_on_err onerr)
 {
-       static struct ref_lock *lock;
-       lock = lock_any_ref_for_update(refname, oldval, flags);
+       struct ref_lock *lock;
+       lock = lock_any_ref_for_update(refname, oldval, flags, type_p);
        if (!lock) {
                const char *str = "Cannot lock the ref '%s'.";
                switch (onerr) {
@@ -1631,8 +3203,14 @@ int update_ref(const char *action, const char *refname,
                case DIE_ON_ERR: die(str, refname); break;
                case QUIET_ON_ERR: break;
                }
-               return 1;
        }
+       return lock;
+}
+
+static int update_ref_write(const char *action, const char *refname,
+                           const unsigned char *sha1, struct ref_lock *lock,
+                           enum action_on_err onerr)
+{
        if (write_ref_sha1(lock, sha1, action) < 0) {
                const char *str = "Cannot update the ref '%s'.";
                switch (onerr) {
@@ -1645,12 +3223,115 @@ int update_ref(const char *action, const char *refname,
        return 0;
 }
 
-struct ref *find_ref_by_name(const struct ref *list, const char *name)
+int update_ref(const char *action, const char *refname,
+              const unsigned char *sha1, const unsigned char *oldval,
+              int flags, enum action_on_err onerr)
 {
-       for ( ; list; list = list->next)
-               if (!strcmp(list->name, name))
-                       return (struct ref *)list;
-       return NULL;
+       struct ref_lock *lock;
+       lock = update_ref_lock(refname, oldval, flags, NULL, onerr);
+       if (!lock)
+               return 1;
+       return update_ref_write(action, refname, sha1, lock, onerr);
+}
+
+static int ref_update_compare(const void *r1, const void *r2)
+{
+       const struct ref_update * const *u1 = r1;
+       const struct ref_update * const *u2 = r2;
+       return strcmp((*u1)->ref_name, (*u2)->ref_name);
+}
+
+static int ref_update_reject_duplicates(struct ref_update **updates, int n,
+                                       enum action_on_err onerr)
+{
+       int i;
+       for (i = 1; i < n; i++)
+               if (!strcmp(updates[i - 1]->ref_name, updates[i]->ref_name)) {
+                       const char *str =
+                               "Multiple updates for ref '%s' not allowed.";
+                       switch (onerr) {
+                       case MSG_ON_ERR:
+                               error(str, updates[i]->ref_name); break;
+                       case DIE_ON_ERR:
+                               die(str, updates[i]->ref_name); break;
+                       case QUIET_ON_ERR:
+                               break;
+                       }
+                       return 1;
+               }
+       return 0;
+}
+
+int update_refs(const char *action, const struct ref_update **updates_orig,
+               int n, enum action_on_err onerr)
+{
+       int ret = 0, delnum = 0, i;
+       struct ref_update **updates;
+       int *types;
+       struct ref_lock **locks;
+       const char **delnames;
+
+       if (!updates_orig || !n)
+               return 0;
+
+       /* Allocate work space */
+       updates = xmalloc(sizeof(*updates) * n);
+       types = xmalloc(sizeof(*types) * n);
+       locks = xcalloc(n, sizeof(*locks));
+       delnames = xmalloc(sizeof(*delnames) * n);
+
+       /* Copy, sort, and reject duplicate refs */
+       memcpy(updates, updates_orig, sizeof(*updates) * n);
+       qsort(updates, n, sizeof(*updates), ref_update_compare);
+       ret = ref_update_reject_duplicates(updates, n, onerr);
+       if (ret)
+               goto cleanup;
+
+       /* Acquire all locks while verifying old values */
+       for (i = 0; i < n; i++) {
+               locks[i] = update_ref_lock(updates[i]->ref_name,
+                                          (updates[i]->have_old ?
+                                           updates[i]->old_sha1 : NULL),
+                                          updates[i]->flags,
+                                          &types[i], onerr);
+               if (!locks[i]) {
+                       ret = 1;
+                       goto cleanup;
+               }
+       }
+
+       /* Perform updates first so live commits remain referenced */
+       for (i = 0; i < n; i++)
+               if (!is_null_sha1(updates[i]->new_sha1)) {
+                       ret = update_ref_write(action,
+                                              updates[i]->ref_name,
+                                              updates[i]->new_sha1,
+                                              locks[i], onerr);
+                       locks[i] = NULL; /* freed by update_ref_write */
+                       if (ret)
+                               goto cleanup;
+               }
+
+       /* Perform deletes now that updates are safely completed */
+       for (i = 0; i < n; i++)
+               if (locks[i]) {
+                       delnames[delnum++] = locks[i]->ref_name;
+                       ret |= delete_ref_loose(locks[i], types[i]);
+               }
+       ret |= repack_without_refs(delnames, delnum);
+       for (i = 0; i < delnum; i++)
+               unlink_or_warn(git_path("logs/%s", delnames[i]));
+       clear_loose_ref_cache(&ref_cache);
+
+cleanup:
+       for (i = 0; i < n; i++)
+               if (locks[i])
+                       unlock_ref(locks[i]);
+       free(updates);
+       free(types);
+       free(locks);
+       free(delnames);
+       return ret;
 }
 
 /*
@@ -1676,7 +3357,7 @@ static void gen_scanf_fmt(char *scanf_fmt, const char *rule)
        return;
 }
 
-char *shorten_unambiguous_ref(const char *ref)
+char *shorten_unambiguous_ref(const char *refname, int strict)
 {
        int i;
        static char **scanf_fmts;
@@ -1705,30 +3386,41 @@ char *shorten_unambiguous_ref(const char *ref)
 
        /* bail out if there are no rules */
        if (!nr_rules)
-               return xstrdup(ref);
+               return xstrdup(refname);
 
-       /* buffer for scanf result, at most ref must fit */
-       short_name = xstrdup(ref);
+       /* buffer for scanf result, at most refname must fit */
+       short_name = xstrdup(refname);
 
        /* skip first rule, it will always match */
        for (i = nr_rules - 1; i > 0 ; --i) {
                int j;
+               int rules_to_fail = i;
                int short_name_len;
 
-               if (1 != sscanf(ref, scanf_fmts[i], short_name))
+               if (1 != sscanf(refname, scanf_fmts[i], short_name))
                        continue;
 
                short_name_len = strlen(short_name);
 
+               /*
+                * in strict mode, all (except the matched one) rules
+                * must fail to resolve to a valid non-ambiguous ref
+                */
+               if (strict)
+                       rules_to_fail = nr_rules;
+
                /*
                 * check if the short name resolves to a valid ref,
                 * but use only rules prior to the matched one
                 */
-               for (j = 0; j < i; j++) {
+               for (j = 0; j < rules_to_fail; j++) {
                        const char *rule = ref_rev_parse_rules[j];
-                       unsigned char short_objectname[20];
                        char refname[PATH_MAX];
 
+                       /* skip matched rule */
+                       if (i == j)
+                               continue;
+
                        /*
                         * the short name is ambiguous, if it resolves
                         * (with this previous rule) to a valid ref
@@ -1736,7 +3428,7 @@ char *shorten_unambiguous_ref(const char *ref)
                         */
                        mksnpath(refname, sizeof(refname),
                                 rule, short_name_len, short_name);
-                       if (!read_ref(refname, short_objectname))
+                       if (ref_exists(refname))
                                break;
                }
 
@@ -1744,10 +3436,53 @@ char *shorten_unambiguous_ref(const char *ref)
                 * short name is non-ambiguous if all previous rules
                 * haven't resolved to a valid ref
                 */
-               if (j == i)
+               if (j == rules_to_fail)
                        return short_name;
        }
 
        free(short_name);
-       return xstrdup(ref);
+       return xstrdup(refname);
+}
+
+static struct string_list *hide_refs;
+
+int parse_hide_refs_config(const char *var, const char *value, const char *section)
+{
+       if (!strcmp("transfer.hiderefs", var) ||
+           /* NEEDSWORK: use parse_config_key() once both are merged */
+           (!prefixcmp(var, section) && var[strlen(section)] == '.' &&
+            !strcmp(var + strlen(section), ".hiderefs"))) {
+               char *ref;
+               int len;
+
+               if (!value)
+                       return config_error_nonbool(var);
+               ref = xstrdup(value);
+               len = strlen(ref);
+               while (len && ref[len - 1] == '/')
+                       ref[--len] = '\0';
+               if (!hide_refs) {
+                       hide_refs = xcalloc(1, sizeof(*hide_refs));
+                       hide_refs->strdup_strings = 1;
+               }
+               string_list_append(hide_refs, ref);
+       }
+       return 0;
+}
+
+int ref_is_hidden(const char *refname)
+{
+       struct string_list_item *item;
+
+       if (!hide_refs)
+               return 0;
+       for_each_string_list_item(item, hide_refs) {
+               int len;
+               if (prefixcmp(refname, item->string))
+                       continue;
+               len = strlen(item->string);
+               if (!refname[len] || refname[len] == '/')
+                       return 1;
+       }
+       return 0;
 }