Sync with 2.12.5
[gitweb.git] / refs / files-backend.c
index 2455564352e1dafd5a95cd25b7279ead69b24660..83ea080e013f90e95d1897258dd80b44ac9b5db6 100644 (file)
@@ -1,6 +1,7 @@
 #include "../cache.h"
 #include "../refs.h"
 #include "refs-internal.h"
+#include "ref-cache.h"
 #include "../iterator.h"
 #include "../dir-iterator.h"
 #include "../lockfile.h"
@@ -13,507 +14,6 @@ struct ref_lock {
        struct object_id old_oid;
 };
 
-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.
-        */
-       struct object_id oid;
-
-       /*
-        * 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".
-        */
-       struct object_id peeled;
-};
-
-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, REF_ISBROKEN=0x04 and REF_BAD_NAME=0x08 are
- * public values; see refs.h.
- */
-
-/*
- * The field ref_entry->u.value.peeled of this value entry contains
- * the correct peeled value for the reference, which might be
- * null_sha1 if the reference is not a tag or if it is broken.
- */
-#define REF_KNOWS_PEELED 0x10
-
-/* ref_entry represents a directory of references */
-#define REF_DIR 0x20
-
-/*
- * Entry has not yet been read from disk (used only for REF_DIR
- * entries representing loose references)
- */
-#define REF_INCOMPLETE 0x40
-
-/*
- * 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 verify_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 int search_ref_dir(struct ref_dir *dir, const char *refname, size_t len);
-static struct ref_entry *create_dir_entry(struct ref_cache *ref_cache,
-                                         const char *dirname, size_t len,
-                                         int incomplete);
-static void add_entry_to_dir(struct ref_dir *dir, struct ref_entry *entry);
-
-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);
-
-               /*
-                * Manually add refs/bisect, which, being
-                * per-worktree, might not appear in the directory
-                * listing for refs/ in the main repo.
-                */
-               if (!strcmp(entry->name, "refs/")) {
-                       int pos = search_ref_dir(dir, "refs/bisect/", 12);
-                       if (pos < 0) {
-                               struct ref_entry *child_entry;
-                               child_entry = create_dir_entry(dir->ref_cache,
-                                                              "refs/bisect/",
-                                                              12, 1);
-                               add_entry_to_dir(dir, child_entry);
-                               read_loose_refs("refs/bisect",
-                                               &child_entry->u.subdir);
-                       }
-               }
-               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)
-{
-       struct ref_entry *ref;
-
-       if (check_name &&
-           check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
-               die("Reference has invalid format: '%s'", refname);
-       FLEX_ALLOC_STR(ref, name, refname);
-       hashcpy(ref->u.value.oid.hash, sha1);
-       oidclr(&ref->u.value.peeled);
-       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;
-       FLEX_ALLOC_MEM(direntry, name, dirname, len);
-       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 (oidcmp(&ref1->u.value.oid, &ref2->u.value.oid))
-               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;
-}
-
 /*
  * Return true if refname, which has the specified oid and flags, can
  * be resolved to an object in the database. If the referred-to object
@@ -532,364 +32,14 @@ static int ref_resolves_to_object(const char *refname,
        return 1;
 }
 
-/*
- * Return true if the reference described by entry can be resolved to
- * an object in the database; otherwise, emit a warning and return
- * false.
- */
-static int entry_resolves_to_object(struct ref_entry *entry)
-{
-       return ref_resolves_to_object(entry->name,
-                                     &entry->u.value.oid, entry->flag);
-}
-
-typedef int each_ref_entry_fn(struct ref_entry *entry, void *cb_data);
-
-/*
- * 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;
-}
-
-/*
- * 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));
-       }
-}
-
-/*
- * A level in the reference hierarchy that is currently being iterated
- * through.
- */
-struct cache_ref_iterator_level {
-       /*
-        * The ref_dir being iterated over at this level. The ref_dir
-        * is sorted before being stored here.
-        */
-       struct ref_dir *dir;
-
-       /*
-        * The index of the current entry within dir (which might
-        * itself be a directory). If index == -1, then the iteration
-        * hasn't yet begun. If index == dir->nr, then the iteration
-        * through this level is over.
-        */
-       int index;
-};
-
-/*
- * Represent an iteration through a ref_dir in the memory cache. The
- * iteration recurses through subdirectories.
- */
-struct cache_ref_iterator {
-       struct ref_iterator base;
-
-       /*
-        * The number of levels currently on the stack. This is always
-        * at least 1, because when it becomes zero the iteration is
-        * ended and this struct is freed.
-        */
-       size_t levels_nr;
-
-       /* The number of levels that have been allocated on the stack */
-       size_t levels_alloc;
-
-       /*
-        * A stack of levels. levels[0] is the uppermost level that is
-        * being iterated over in this iteration. (This is not
-        * necessary the top level in the references hierarchy. If we
-        * are iterating through a subtree, then levels[0] will hold
-        * the ref_dir for that subtree, and subsequent levels will go
-        * on from there.)
-        */
-       struct cache_ref_iterator_level *levels;
-};
-
-static int cache_ref_iterator_advance(struct ref_iterator *ref_iterator)
-{
-       struct cache_ref_iterator *iter =
-               (struct cache_ref_iterator *)ref_iterator;
-
-       while (1) {
-               struct cache_ref_iterator_level *level =
-                       &iter->levels[iter->levels_nr - 1];
-               struct ref_dir *dir = level->dir;
-               struct ref_entry *entry;
-
-               if (level->index == -1)
-                       sort_ref_dir(dir);
-
-               if (++level->index == level->dir->nr) {
-                       /* This level is exhausted; pop up a level */
-                       if (--iter->levels_nr == 0)
-                               return ref_iterator_abort(ref_iterator);
-
-                       continue;
-               }
-
-               entry = dir->entries[level->index];
-
-               if (entry->flag & REF_DIR) {
-                       /* push down a level */
-                       ALLOC_GROW(iter->levels, iter->levels_nr + 1,
-                                  iter->levels_alloc);
-
-                       level = &iter->levels[iter->levels_nr++];
-                       level->dir = get_ref_dir(entry);
-                       level->index = -1;
-               } else {
-                       iter->base.refname = entry->name;
-                       iter->base.oid = &entry->u.value.oid;
-                       iter->base.flags = entry->flag;
-                       return ITER_OK;
-               }
-       }
-}
-
-static enum peel_status peel_entry(struct ref_entry *entry, int repeel);
-
-static int cache_ref_iterator_peel(struct ref_iterator *ref_iterator,
-                                  struct object_id *peeled)
-{
-       struct cache_ref_iterator *iter =
-               (struct cache_ref_iterator *)ref_iterator;
-       struct cache_ref_iterator_level *level;
-       struct ref_entry *entry;
-
-       level = &iter->levels[iter->levels_nr - 1];
-
-       if (level->index == -1)
-               die("BUG: peel called before advance for cache iterator");
-
-       entry = level->dir->entries[level->index];
-
-       if (peel_entry(entry, 0))
-               return -1;
-       hashcpy(peeled->hash, entry->u.value.peeled.hash);
-       return 0;
-}
-
-static int cache_ref_iterator_abort(struct ref_iterator *ref_iterator)
-{
-       struct cache_ref_iterator *iter =
-               (struct cache_ref_iterator *)ref_iterator;
-
-       free(iter->levels);
-       base_ref_iterator_free(ref_iterator);
-       return ITER_DONE;
-}
-
-static struct ref_iterator_vtable cache_ref_iterator_vtable = {
-       cache_ref_iterator_advance,
-       cache_ref_iterator_peel,
-       cache_ref_iterator_abort
-};
-
-static struct ref_iterator *cache_ref_iterator_begin(struct ref_dir *dir)
-{
-       struct cache_ref_iterator *iter;
-       struct ref_iterator *ref_iterator;
-       struct cache_ref_iterator_level *level;
-
-       iter = xcalloc(1, sizeof(*iter));
-       ref_iterator = &iter->base;
-       base_ref_iterator_init(ref_iterator, &cache_ref_iterator_vtable);
-       ALLOC_GROW(iter->levels, 10, iter->levels_alloc);
-
-       iter->levels_nr = 1;
-       level = &iter->levels[0];
-       level->index = -1;
-       level->dir = dir;
-
-       return ref_iterator;
-}
-
-struct nonmatching_ref_data {
-       const struct string_list *skip;
-       const char *conflicting_refname;
-};
-
-static int nonmatching_ref_fn(struct ref_entry *entry, void *vdata)
-{
-       struct nonmatching_ref_data *data = vdata;
-
-       if (data->skip && string_list_has_string(data->skip, entry->name))
-               return 0;
-
-       data->conflicting_refname = entry->name;
-       return 1;
-}
-
-/*
- * Return 0 if a reference named refname could be created without
- * conflicting with the name of an existing reference in dir.
- * See verify_refname_available for more information.
- */
-static int verify_refname_available_dir(const char *refname,
-                                       const struct string_list *extras,
-                                       const struct string_list *skip,
-                                       struct ref_dir *dir,
-                                       struct strbuf *err)
-{
-       const char *slash;
-       const char *extra_refname;
-       int pos;
-       struct strbuf dirname = STRBUF_INIT;
-       int ret = -1;
-
-       /*
-        * For the sake of comments in this function, suppose that
-        * refname is "refs/foo/bar".
-        */
-
-       assert(err);
-
-       strbuf_grow(&dirname, strlen(refname) + 1);
-       for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
-               /* Expand dirname to the new prefix, not including the trailing slash: */
-               strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);
-
-               /*
-                * We are still at a leading dir of the refname (e.g.,
-                * "refs/foo"; if there is a reference with that name,
-                * it is a conflict, *unless* it is in skip.
-                */
-               if (dir) {
-                       pos = search_ref_dir(dir, dirname.buf, dirname.len);
-                       if (pos >= 0 &&
-                           (!skip || !string_list_has_string(skip, dirname.buf))) {
-                               /*
-                                * We found a reference whose name is
-                                * a proper prefix of refname; e.g.,
-                                * "refs/foo", and is not in skip.
-                                */
-                               strbuf_addf(err, "'%s' exists; cannot create '%s'",
-                                           dirname.buf, refname);
-                               goto cleanup;
-                       }
-               }
-
-               if (extras && string_list_has_string(extras, dirname.buf) &&
-                   (!skip || !string_list_has_string(skip, dirname.buf))) {
-                       strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
-                                   refname, dirname.buf);
-                       goto cleanup;
-               }
-
-               /*
-                * Otherwise, we can try to continue our search with
-                * the next component. So try to look up the
-                * directory, e.g., "refs/foo/". If we come up empty,
-                * we know there is nothing under this whole prefix,
-                * but even in that case we still have to continue the
-                * search for conflicts with extras.
-                */
-               strbuf_addch(&dirname, '/');
-               if (dir) {
-                       pos = search_ref_dir(dir, dirname.buf, dirname.len);
-                       if (pos < 0) {
-                               /*
-                                * There was no directory "refs/foo/",
-                                * so there is nothing under this
-                                * whole prefix. So there is no need
-                                * to continue looking for conflicting
-                                * references. But we need to continue
-                                * looking for conflicting extras.
-                                */
-                               dir = NULL;
-                       } else {
-                               dir = get_ref_dir(dir->entries[pos]);
-                       }
-               }
-       }
-
-       /*
-        * We are at the leaf of our refname (e.g., "refs/foo/bar").
-        * There is no point in searching for a reference with that
-        * name, because a refname isn't considered to conflict with
-        * itself. But we still need to check for references whose
-        * names are in the "refs/foo/bar/" namespace, because they
-        * *do* conflict.
-        */
-       strbuf_addstr(&dirname, refname + dirname.len);
-       strbuf_addch(&dirname, '/');
-
-       if (dir) {
-               pos = search_ref_dir(dir, dirname.buf, dirname.len);
-
-               if (pos >= 0) {
-                       /*
-                        * We found a directory named "$refname/"
-                        * (e.g., "refs/foo/bar/"). It is a problem
-                        * iff it contains any ref that is not in
-                        * "skip".
-                        */
-                       struct nonmatching_ref_data data;
-
-                       data.skip = skip;
-                       data.conflicting_refname = NULL;
-                       dir = get_ref_dir(dir->entries[pos]);
-                       sort_ref_dir(dir);
-                       if (do_for_each_entry_in_dir(dir, 0, nonmatching_ref_fn, &data)) {
-                               strbuf_addf(err, "'%s' exists; cannot create '%s'",
-                                           data.conflicting_refname, refname);
-                               goto cleanup;
-                       }
-               }
-       }
-
-       extra_refname = find_descendant_ref(dirname.buf, extras, skip);
-       if (extra_refname)
-               strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
-                           refname, extra_refname);
-       else
-               ret = 0;
-
-cleanup:
-       strbuf_release(&dirname);
-       return ret;
-}
-
 struct packed_ref_cache {
-       struct ref_entry *root;
+       struct ref_cache *cache;
 
        /*
         * 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.
+        * including the pointer from files_ref_store::packed if any.
+        * The data will not be freed as long as the reference count
+        * is nonzero.
         */
        unsigned int referrers;
 
@@ -910,17 +60,17 @@ struct packed_ref_cache {
  * 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 files_ref_store {
+       struct ref_store base;
+       unsigned int store_flags;
+
+       char *gitdir;
+       char *gitcommondir;
+       char *packed_refs_path;
+
+       struct ref_cache *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;
@@ -940,7 +90,7 @@ static void acquire_packed_ref_cache(struct packed_ref_cache *packed_refs)
 static int release_packed_ref_cache(struct packed_ref_cache *packed_refs)
 {
        if (!--packed_refs->referrers) {
-               free_ref_entry(packed_refs->root);
+               free_ref_cache(packed_refs->cache);
                stat_validity_clear(&packed_refs->validity);
                free(packed_refs);
                return 1;
@@ -949,7 +99,7 @@ static int release_packed_ref_cache(struct packed_ref_cache *packed_refs)
        }
 }
 
-static void clear_packed_ref_cache(struct ref_cache *refs)
+static void clear_packed_ref_cache(struct files_ref_store *refs)
 {
        if (refs->packed) {
                struct packed_ref_cache *packed_refs = refs->packed;
@@ -961,10 +111,10 @@ static void clear_packed_ref_cache(struct ref_cache *refs)
        }
 }
 
-static void clear_loose_ref_cache(struct ref_cache *refs)
+static void clear_loose_ref_cache(struct files_ref_store *refs)
 {
        if (refs->loose) {
-               free_ref_entry(refs->loose);
+               free_ref_cache(refs->loose);
                refs->loose = NULL;
        }
 }
@@ -973,51 +123,59 @@ static void clear_loose_ref_cache(struct ref_cache *refs)
  * Create a new submodule ref cache and add it to the internal
  * set of caches.
  */
-static struct ref_cache *create_ref_cache(const char *submodule)
-{
-       struct ref_cache *refs;
-       if (!submodule)
-               submodule = "";
-       FLEX_ALLOC_STR(refs, name, submodule);
-       refs->next = submodule_ref_caches;
-       submodule_ref_caches = refs;
-       return refs;
+static struct ref_store *files_ref_store_create(const char *gitdir,
+                                               unsigned int flags)
+{
+       struct files_ref_store *refs = xcalloc(1, sizeof(*refs));
+       struct ref_store *ref_store = (struct ref_store *)refs;
+       struct strbuf sb = STRBUF_INIT;
+
+       base_ref_store_init(ref_store, &refs_be_files);
+       refs->store_flags = flags;
+
+       refs->gitdir = xstrdup(gitdir);
+       get_common_dir_noenv(&sb, gitdir);
+       refs->gitcommondir = strbuf_detach(&sb, NULL);
+       strbuf_addf(&sb, "%s/packed-refs", refs->gitcommondir);
+       refs->packed_refs_path = strbuf_detach(&sb, NULL);
+
+       return ref_store;
 }
 
-static struct ref_cache *lookup_ref_cache(const char *submodule)
+/*
+ * Die if refs is not the main ref store. caller is used in any
+ * necessary error messages.
+ */
+static void files_assert_main_repository(struct files_ref_store *refs,
+                                        const char *caller)
 {
-       struct ref_cache *refs;
-
-       if (!submodule || !*submodule)
-               return &ref_cache;
+       if (refs->store_flags & REF_STORE_MAIN)
+               return;
 
-       for (refs = submodule_ref_caches; refs; refs = refs->next)
-               if (!strcmp(submodule, refs->name))
-                       return refs;
-       return NULL;
+       die("BUG: operation %s only allowed for main ref store", caller);
 }
 
 /*
- * Return a pointer to a ref_cache for the specified submodule. For
- * the main repository, use submodule==NULL; such a call cannot fail.
- * For a submodule, the submodule must exist and be a nonbare
- * repository, otherwise return NULL.
- *
- * The returned structure will be allocated and initialized but not
- * necessarily populated; it should not be freed.
+ * Downcast ref_store to files_ref_store. Die if ref_store is not a
+ * files_ref_store. required_flags is compared with ref_store's
+ * store_flags to ensure the ref_store has all required capabilities.
+ * "caller" is used in any necessary error messages.
  */
-static struct ref_cache *get_ref_cache(const char *submodule)
+static struct files_ref_store *files_downcast(struct ref_store *ref_store,
+                                             unsigned int required_flags,
+                                             const char *caller)
 {
-       struct ref_cache *refs = lookup_ref_cache(submodule);
+       struct files_ref_store *refs;
 
-       if (!refs) {
-               struct strbuf submodule_sb = STRBUF_INIT;
+       if (ref_store->be != &refs_be_files)
+               die("BUG: ref_store is type \"%s\" not \"files\" in %s",
+                   ref_store->be->name, caller);
 
-               strbuf_addstr(&submodule_sb, submodule);
-               if (is_nonbare_repository_dir(&submodule_sb))
-                       refs = create_ref_cache(submodule);
-               strbuf_release(&submodule_sb);
-       }
+       refs = (struct files_ref_store *)ref_store;
+
+       if ((refs->store_flags & required_flags) != required_flags)
+               die("BUG: operation %s requires abilities 0x%x, but only have 0x%x",
+                   caller, required_flags, refs->store_flags);
 
        return refs;
 }
@@ -1129,7 +287,7 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
                        if (peeled == PEELED_FULLY ||
                            (peeled == PEELED_TAGS && starts_with(refname, "refs/tags/")))
                                last->flag |= REF_KNOWS_PEELED;
-                       add_ref(dir, last);
+                       add_ref_entry(dir, last);
                        continue;
                }
                if (last &&
@@ -1150,18 +308,63 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
        strbuf_release(&line);
 }
 
+static const char *files_packed_refs_path(struct files_ref_store *refs)
+{
+       return refs->packed_refs_path;
+}
+
+static void files_reflog_path(struct files_ref_store *refs,
+                             struct strbuf *sb,
+                             const char *refname)
+{
+       if (!refname) {
+               /*
+                * FIXME: of course this is wrong in multi worktree
+                * setting. To be fixed real soon.
+                */
+               strbuf_addf(sb, "%s/logs", refs->gitcommondir);
+               return;
+       }
+
+       switch (ref_type(refname)) {
+       case REF_TYPE_PER_WORKTREE:
+       case REF_TYPE_PSEUDOREF:
+               strbuf_addf(sb, "%s/logs/%s", refs->gitdir, refname);
+               break;
+       case REF_TYPE_NORMAL:
+               strbuf_addf(sb, "%s/logs/%s", refs->gitcommondir, refname);
+               break;
+       default:
+               die("BUG: unknown ref type %d of ref %s",
+                   ref_type(refname), refname);
+       }
+}
+
+static void files_ref_path(struct files_ref_store *refs,
+                          struct strbuf *sb,
+                          const char *refname)
+{
+       switch (ref_type(refname)) {
+       case REF_TYPE_PER_WORKTREE:
+       case REF_TYPE_PSEUDOREF:
+               strbuf_addf(sb, "%s/%s", refs->gitdir, refname);
+               break;
+       case REF_TYPE_NORMAL:
+               strbuf_addf(sb, "%s/%s", refs->gitcommondir, refname);
+               break;
+       default:
+               die("BUG: unknown ref type %d of ref %s",
+                   ref_type(refname), refname);
+       }
+}
+
 /*
- * Get the packed_ref_cache for the specified ref_cache, creating it
- * if necessary.
+ * Get the packed_ref_cache for the specified files_ref_store,
+ * creating it if necessary.
  */
-static struct packed_ref_cache *get_packed_ref_cache(struct ref_cache *refs)
+static struct packed_ref_cache *get_packed_ref_cache(struct files_ref_store *refs)
 {
-       char *packed_refs_file;
-
-       if (*refs->name)
-               packed_refs_file = git_pathdup_submodule(refs->name, "packed-refs");
-       else
-               packed_refs_file = git_pathdup("packed-refs");
+       const char *packed_refs_file = files_packed_refs_path(refs);
 
        if (refs->packed &&
            !stat_validity_check(&refs->packed->validity, packed_refs_file))
@@ -1172,24 +375,24 @@ static struct packed_ref_cache *get_packed_ref_cache(struct ref_cache *refs)
 
                refs->packed = xcalloc(1, sizeof(*refs->packed));
                acquire_packed_ref_cache(refs->packed);
-               refs->packed->root = create_dir_entry(refs, "", 0, 0);
+               refs->packed->cache = create_ref_cache(&refs->base, NULL);
+               refs->packed->cache->root->flag &= ~REF_INCOMPLETE;
                f = fopen(packed_refs_file, "r");
                if (f) {
                        stat_validity_update(&refs->packed->validity, fileno(f));
-                       read_packed_refs(f, get_ref_dir(refs->packed->root));
+                       read_packed_refs(f, get_ref_dir(refs->packed->cache->root));
                        fclose(f);
                }
        }
-       free(packed_refs_file);
        return refs->packed;
 }
 
 static struct ref_dir *get_packed_ref_dir(struct packed_ref_cache *packed_ref_cache)
 {
-       return get_ref_dir(packed_ref_cache->root);
+       return get_ref_dir(packed_ref_cache->cache->root);
 }
 
-static struct ref_dir *get_packed_refs(struct ref_cache *refs)
+static struct ref_dir *get_packed_refs(struct files_ref_store *refs)
 {
        return get_packed_ref_dir(get_packed_ref_cache(refs));
 }
@@ -1200,15 +403,15 @@ static struct ref_dir *get_packed_refs(struct ref_cache *refs)
  * lock_packed_refs()).  To actually write the packed-refs file, call
  * commit_packed_refs().
  */
-static void add_packed_ref(const char *refname, const unsigned char *sha1)
+static void add_packed_ref(struct files_ref_store *refs,
+                          const char *refname, const unsigned char *sha1)
 {
-       struct packed_ref_cache *packed_ref_cache =
-               get_packed_ref_cache(&ref_cache);
+       struct packed_ref_cache *packed_ref_cache = get_packed_ref_cache(refs);
 
        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));
+       add_ref_entry(get_packed_ref_dir(packed_ref_cache),
+                     create_ref_entry(refname, sha1, REF_ISPACKED, 1));
 }
 
 /*
@@ -1216,9 +419,11 @@ static void add_packed_ref(const char *refname, const unsigned char *sha1)
  * (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)
+static void loose_fill_ref_dir(struct ref_store *ref_store,
+                              struct ref_dir *dir, const char *dirname)
 {
-       struct ref_cache *refs = dir->ref_cache;
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ, "fill_ref_dir");
        DIR *d;
        struct dirent *de;
        int dirnamelen = strlen(dirname);
@@ -1226,10 +431,7 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
        struct strbuf path = STRBUF_INIT;
        size_t path_baselen;
 
-       if (*refs->name)
-               strbuf_git_path_submodule(&path, refs->name, "%s", dirname);
-       else
-               strbuf_git_path(&path, "%s", dirname);
+       files_ref_path(refs, &path, dirname);
        path_baselen = path.len;
 
        d = opendir(path.buf);
@@ -1257,23 +459,13 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
                } else if (S_ISDIR(st.st_mode)) {
                        strbuf_addch(&refname, '/');
                        add_entry_to_dir(dir,
-                                        create_dir_entry(refs, refname.buf,
+                                        create_dir_entry(dir->cache, refname.buf,
                                                          refname.len, 1));
                } else {
-                       int read_ok;
-
-                       if (*refs->name) {
-                               hashclr(sha1);
-                               flag = 0;
-                               read_ok = !resolve_gitlink_ref(refs->name,
-                                                              refname.buf, sha1);
-                       } else {
-                               read_ok = !read_ref_full(refname.buf,
-                                                        RESOLVE_REF_READING,
-                                                        sha1, &flag);
-                       }
-
-                       if (!read_ok) {
+                       if (!refs_resolve_ref_unsafe(&refs->base,
+                                                    refname.buf,
+                                                    RESOLVE_REF_READING,
+                                                    sha1, &flag)) {
                                hashclr(sha1);
                                flag |= REF_ISBROKEN;
                        } else if (is_null_sha1(sha1)) {
@@ -1304,9 +496,24 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
        strbuf_release(&refname);
        strbuf_release(&path);
        closedir(d);
+
+       /*
+        * Manually add refs/bisect, which, being per-worktree, might
+        * not appear in the directory listing for refs/ in the main
+        * repo.
+        */
+       if (!strcmp(dirname, "refs/")) {
+               int pos = search_ref_dir(dir, "refs/bisect/", 12);
+
+               if (pos < 0) {
+                       struct ref_entry *child_entry = create_dir_entry(
+                                       dir->cache, "refs/bisect/", 12, 1);
+                       add_entry_to_dir(dir, child_entry);
+               }
+       }
 }
 
-static struct ref_dir *get_loose_refs(struct ref_cache *refs)
+static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs)
 {
        if (!refs->loose) {
                /*
@@ -1314,115 +521,37 @@ static struct ref_dir *get_loose_refs(struct ref_cache *refs)
                 * 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 get_ref_dir(refs->loose);
-}
-
-#define MAXREFLEN (1024)
+               refs->loose = create_ref_cache(&refs->base, loose_fill_ref_dir);
 
-/*
- * 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)
-{
-       struct ref_entry *ref;
-       struct ref_dir *dir = get_packed_refs(refs);
-
-       ref = find_ref(dir, refname);
-       if (ref == NULL)
-               return -1;
+               /* We're going to fill the top level ourselves: */
+               refs->loose->root->flag &= ~REF_INCOMPLETE;
 
-       hashcpy(sha1, ref->u.value.oid.hash);
-       return 0;
-}
-
-static int resolve_gitlink_ref_recursive(struct ref_cache *refs,
-                                        const char *refname, unsigned char *sha1,
-                                        int recursion)
-{
-       int fd, len;
-       char buffer[128], *p;
-       char *path;
-
-       if (recursion > SYMREF_MAXDEPTH || strlen(refname) > MAXREFLEN)
-               return -1;
-       path = *refs->name
-               ? git_pathdup_submodule(refs->name, "%s", refname)
-               : git_pathdup("%s", refname);
-       fd = open(path, O_RDONLY);
-       free(path);
-       if (fd < 0)
-               return resolve_gitlink_packed_ref(refs, refname, sha1);
-
-       len = read(fd, buffer, sizeof(buffer)-1);
-       close(fd);
-       if (len < 0)
-               return -1;
-       while (len && isspace(buffer[len-1]))
-               len--;
-       buffer[len] = 0;
-
-       /* Was it a detached head or an old-fashioned symlink? */
-       if (!get_sha1_hex(buffer, sha1))
-               return 0;
-
-       /* Symref? */
-       if (strncmp(buffer, "ref:", 4))
-               return -1;
-       p = buffer + 4;
-       while (isspace(*p))
-               p++;
-
-       return resolve_gitlink_ref_recursive(refs, p, sha1, recursion+1);
-}
-
-int resolve_gitlink_ref(const char *path, const char *refname, unsigned char *sha1)
-{
-       int len = strlen(path), retval;
-       struct strbuf submodule = STRBUF_INIT;
-       struct ref_cache *refs;
-
-       while (len && path[len-1] == '/')
-               len--;
-       if (!len)
-               return -1;
-
-       strbuf_add(&submodule, path, len);
-       refs = get_ref_cache(submodule.buf);
-       if (!refs) {
-               strbuf_release(&submodule);
-               return -1;
+               /*
+                * Add an incomplete entry for "refs/" (to be filled
+                * lazily):
+                */
+               add_entry_to_dir(get_ref_dir(refs->loose->root),
+                                create_dir_entry(refs->loose, "refs/", 5, 1));
        }
-       strbuf_release(&submodule);
-
-       retval = resolve_gitlink_ref_recursive(refs, refname, sha1, 0);
-       return retval;
+       return refs->loose;
 }
 
 /*
  * 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)
+static struct ref_entry *get_packed_ref(struct files_ref_store *refs,
+                                       const char *refname)
 {
-       return find_ref(get_packed_refs(&ref_cache), refname);
+       return find_ref_entry(get_packed_refs(refs), refname);
 }
 
 /*
  * A loose ref file doesn't exist; check for a packed ref.
  */
-static int resolve_missing_loose_ref(const char *refname,
-                                    unsigned char *sha1,
-                                    unsigned int *flags)
+static int resolve_packed_ref(struct files_ref_store *refs,
+                             const char *refname,
+                             unsigned char *sha1, unsigned int *flags)
 {
        struct ref_entry *entry;
 
@@ -1430,7 +559,7 @@ static int resolve_missing_loose_ref(const char *refname,
         * The loose reference file does not exist; check for a packed
         * reference.
         */
-       entry = get_packed_ref(refname);
+       entry = get_packed_ref(refs, refname);
        if (entry) {
                hashcpy(sha1, entry->u.value.oid.hash);
                *flags |= REF_ISPACKED;
@@ -1440,9 +569,12 @@ static int resolve_missing_loose_ref(const char *refname,
        return -1;
 }
 
-int read_raw_ref(const char *refname, unsigned char *sha1,
-                struct strbuf *referent, unsigned int *type)
+static int files_read_raw_ref(struct ref_store *ref_store,
+                             const char *refname, unsigned char *sha1,
+                             struct strbuf *referent, unsigned int *type)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ, "read_raw_ref");
        struct strbuf sb_contents = STRBUF_INIT;
        struct strbuf sb_path = STRBUF_INIT;
        const char *path;
@@ -1455,7 +587,9 @@ int read_raw_ref(const char *refname, unsigned char *sha1,
 
        *type = 0;
        strbuf_reset(&sb_path);
-       strbuf_git_path(&sb_path, "%s", refname);
+
+       files_ref_path(refs, &sb_path, refname);
+
        path = sb_path.buf;
 
 stat_ref:
@@ -1478,7 +612,7 @@ int read_raw_ref(const char *refname, unsigned char *sha1,
        if (lstat(path, &st) < 0) {
                if (errno != ENOENT)
                        goto out;
-               if (resolve_missing_loose_ref(refname, sha1, type)) {
+               if (resolve_packed_ref(refs, refname, sha1, type)) {
                        errno = ENOENT;
                        goto out;
                }
@@ -1517,7 +651,7 @@ int read_raw_ref(const char *refname, unsigned char *sha1,
                 * ref is supposed to be, there could still be a
                 * packed ref:
                 */
-               if (resolve_missing_loose_ref(refname, sha1, type)) {
+               if (resolve_packed_ref(refs, refname, sha1, type)) {
                        errno = EISDIR;
                        goto out;
                }
@@ -1599,7 +733,7 @@ static void unlock_ref(struct ref_lock *lock)
  *
  * If the reference doesn't already exist, verify that refname doesn't
  * have a D/F conflict with any existing references. extras and skip
- * are passed to verify_refname_available_dir() for this check.
+ * are passed to refs_verify_refname_available() for this check.
  *
  * If mustexist is not set and the reference is not found or is
  * broken, lock the reference anyway but clear sha1.
@@ -1614,11 +748,12 @@ static void unlock_ref(struct ref_lock *lock)
  *
  * but it includes a lot more code to
  * - Deal with possible races with other processes
- * - Avoid calling verify_refname_available_dir() when it can be
+ * - Avoid calling refs_verify_refname_available() when it can be
  *   avoided, namely if we were successfully able to read the ref
  * - Generate informative error messages in the case of failure
  */
-static int lock_raw_ref(const char *refname, int mustexist,
+static int lock_raw_ref(struct files_ref_store *refs,
+                       const char *refname, int mustexist,
                        const struct string_list *extras,
                        const struct string_list *skip,
                        struct ref_lock **lock_p,
@@ -1632,6 +767,8 @@ static int lock_raw_ref(const char *refname, int mustexist,
        int ret = TRANSACTION_GENERIC_ERROR;
 
        assert(err);
+       files_assert_main_repository(refs, "lock_raw_ref");
+
        *type = 0;
 
        /* First lock the file so it can't change out from under us. */
@@ -1639,7 +776,7 @@ static int lock_raw_ref(const char *refname, int mustexist,
        *lock_p = lock = xcalloc(1, sizeof(*lock));
 
        lock->ref_name = xstrdup(refname);
-       strbuf_git_path(&ref_file, "%s", refname);
+       files_ref_path(refs, &ref_file, refname);
 
 retry:
        switch (safe_create_leading_directories(ref_file.buf)) {
@@ -1654,7 +791,8 @@ static int lock_raw_ref(const char *refname, int mustexist,
                 * another reference such as "refs/foo". There is no
                 * reason to expect this error to be transitory.
                 */
-               if (verify_refname_available(refname, extras, skip, err)) {
+               if (refs_verify_refname_available(&refs->base, refname,
+                                                 extras, skip, err)) {
                        if (mustexist) {
                                /*
                                 * To the user the relevant error is
@@ -1667,7 +805,8 @@ static int lock_raw_ref(const char *refname, int mustexist,
                        } else {
                                /*
                                 * The error message set by
-                                * verify_refname_available_dir() is OK.
+                                * refs_verify_refname_available() is
+                                * OK.
                                 */
                                ret = TRANSACTION_NAME_CONFLICT;
                        }
@@ -1715,7 +854,8 @@ static int lock_raw_ref(const char *refname, int mustexist,
         * fear that its value will change.
         */
 
-       if (read_raw_ref(refname, lock->old_oid.hash, referent, type)) {
+       if (files_read_raw_ref(&refs->base, refname,
+                              lock->old_oid.hash, referent, type)) {
                if (errno == ENOENT) {
                        if (mustexist) {
                                /* Garden variety missing reference. */
@@ -1756,10 +896,9 @@ static int lock_raw_ref(const char *refname, int mustexist,
                                goto error_return;
                        } else if (remove_dir_recursively(&ref_file,
                                                          REMOVE_DIR_EMPTY_ONLY)) {
-                               if (verify_refname_available_dir(
-                                                   refname, extras, skip,
-                                                   get_loose_refs(&ref_cache),
-                                                   err)) {
+                               if (refs_verify_refname_available(
+                                                   &refs->base, refname,
+                                                   extras, skip, err)) {
                                        /*
                                         * The error message set by
                                         * verify_refname_available() is OK.
@@ -1791,16 +930,13 @@ static int lock_raw_ref(const char *refname, int mustexist,
 
                /*
                 * If the ref did not exist and we are creating it,
-                * make sure there is no existing packed ref whose
-                * name begins with our refname, nor a packed ref
-                * whose name is a proper prefix of our refname.
+                * make sure there is no existing ref that conflicts
+                * with refname:
                 */
-               if (verify_refname_available_dir(
-                                   refname, extras, skip,
-                                   get_packed_refs(&ref_cache),
-                                   err)) {
+               if (refs_verify_refname_available(
+                                   &refs->base, refname,
+                                   extras, skip, err))
                        goto error_return;
-               }
        }
 
        ret = 0;
@@ -1815,43 +951,12 @@ static int lock_raw_ref(const char *refname, int mustexist,
        return ret;
 }
 
-/*
- * 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;
-                       oidclr(&entry->u.value.peeled);
-               } else {
-                       return is_null_oid(&entry->u.value.peeled) ?
-                               PEEL_NON_TAG : PEEL_PEELED;
-               }
-       }
-       if (entry->flag & REF_ISBROKEN)
-               return PEEL_BROKEN;
-       if (entry->flag & REF_ISSYMREF)
-               return PEEL_IS_SYMREF;
-
-       status = peel_object(entry->u.value.oid.hash, entry->u.value.peeled.hash);
-       if (status == PEEL_PEELED || status == PEEL_NON_TAG)
-               entry->flag |= REF_KNOWS_PEELED;
-       return status;
-}
-
-int peel_ref(const char *refname, unsigned char *sha1)
+static int files_peel_ref(struct ref_store *ref_store,
+                         const char *refname, unsigned char *sha1)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ | REF_STORE_ODB,
+                              "peel_ref");
        int flag;
        unsigned char base[20];
 
@@ -1864,7 +969,8 @@ int peel_ref(const char *refname, unsigned char *sha1)
                return 0;
        }
 
-       if (read_ref_full(refname, RESOLVE_REF_READING, base, &flag))
+       if (refs_read_ref_full(ref_store, refname,
+                              RESOLVE_REF_READING, base, &flag))
                return -1;
 
        /*
@@ -1876,7 +982,7 @@ int peel_ref(const char *refname, unsigned char *sha1)
         * have REF_KNOWS_PEELED.
         */
        if (flag & REF_ISPACKED) {
-               struct ref_entry *r = get_packed_ref(refname);
+               struct ref_entry *r = get_packed_ref(refs, refname);
                if (r) {
                        if (peel_entry(r, 0))
                                return -1;
@@ -1903,6 +1009,10 @@ static int files_ref_iterator_advance(struct ref_iterator *ref_iterator)
        int ok;
 
        while ((ok = ref_iterator_advance(iter->iter0)) == ITER_OK) {
+               if (iter->flags & DO_FOR_EACH_PER_WORKTREE_ONLY &&
+                   ref_type(iter->iter0->refname) != REF_TYPE_PER_WORKTREE)
+                       continue;
+
                if (!(iter->flags & DO_FOR_EACH_INCLUDE_BROKEN) &&
                    !ref_resolves_to_object(iter->iter0->refname,
                                            iter->iter0->oid,
@@ -1951,24 +1061,24 @@ static struct ref_iterator_vtable files_ref_iterator_vtable = {
        files_ref_iterator_abort
 };
 
-struct ref_iterator *files_ref_iterator_begin(
-               const char *submodule,
+static struct ref_iterator *files_ref_iterator_begin(
+               struct ref_store *ref_store,
                const char *prefix, unsigned int flags)
 {
-       struct ref_cache *refs = get_ref_cache(submodule);
-       struct ref_dir *loose_dir, *packed_dir;
+       struct files_ref_store *refs;
        struct ref_iterator *loose_iter, *packed_iter;
        struct files_ref_iterator *iter;
        struct ref_iterator *ref_iterator;
 
-       if (!refs)
-               return empty_ref_iterator_begin();
-
        if (ref_paranoia < 0)
                ref_paranoia = git_env_bool("GIT_REF_PARANOIA", 0);
        if (ref_paranoia)
                flags |= DO_FOR_EACH_INCLUDE_BROKEN;
 
+       refs = files_downcast(ref_store,
+                             REF_STORE_READ | (ref_paranoia ? 0 : REF_STORE_ODB),
+                             "ref_iterator_begin");
+
        iter = xcalloc(1, sizeof(*iter));
        ref_iterator = &iter->base;
        base_ref_iterator_init(ref_iterator, &files_ref_iterator_vtable);
@@ -1979,41 +1089,24 @@ struct ref_iterator *files_ref_iterator_begin(
         * condition if loose refs are migrated to the packed-refs
         * file by a simultaneous process, but our in-memory view is
         * from before the migration. We ensure this as follows:
-        * First, we call prime_ref_dir(), which pre-reads the loose
-        * references for the subtree into the cache. (If they've
-        * already been read, that's OK; we only need to guarantee
-        * that they're read before the packed refs, not *how much*
-        * before.) After that, we call get_packed_ref_cache(), which
-        * internally checks whether the packed-ref cache is up to
-        * date with what is on disk, and re-reads it if not.
+        * First, we call start the loose refs iteration with its
+        * `prime_ref` argument set to true. This causes the loose
+        * references in the subtree to be pre-read into the cache.
+        * (If they've already been read, that's OK; we only need to
+        * guarantee that they're read before the packed refs, not
+        * *how much* before.) After that, we call
+        * get_packed_ref_cache(), which internally checks whether the
+        * packed-ref cache is up to date with what is on disk, and
+        * re-reads it if not.
         */
 
-       loose_dir = get_loose_refs(refs);
-
-       if (prefix && *prefix)
-               loose_dir = find_containing_dir(loose_dir, prefix, 0);
-
-       if (loose_dir) {
-               prime_ref_dir(loose_dir);
-               loose_iter = cache_ref_iterator_begin(loose_dir);
-       } else {
-               /* There's nothing to iterate over. */
-               loose_iter = empty_ref_iterator_begin();
-       }
+       loose_iter = cache_ref_iterator_begin(get_loose_ref_cache(refs),
+                                             prefix, 1);
 
        iter->packed_ref_cache = get_packed_ref_cache(refs);
        acquire_packed_ref_cache(iter->packed_ref_cache);
-       packed_dir = get_packed_ref_dir(iter->packed_ref_cache);
-
-       if (prefix && *prefix)
-               packed_dir = find_containing_dir(packed_dir, prefix, 0);
-
-       if (packed_dir) {
-               packed_iter = cache_ref_iterator_begin(packed_dir);
-       } else {
-               /* There's nothing to iterate over. */
-               packed_iter = empty_ref_iterator_begin();
-       }
+       packed_iter = cache_ref_iterator_begin(iter->packed_ref_cache->cache,
+                                              prefix, 0);
 
        iter->iter0 = overlay_ref_iterator_begin(loose_iter, packed_iter);
        iter->flags = flags;
@@ -2027,15 +1120,15 @@ struct ref_iterator *files_ref_iterator_begin(
  * on success. On error, write an error message to err, set errno, and
  * return a negative value.
  */
-static int verify_lock(struct ref_lock *lock,
+static int verify_lock(struct ref_store *ref_store, struct ref_lock *lock,
                       const unsigned char *old_sha1, int mustexist,
                       struct strbuf *err)
 {
        assert(err);
 
-       if (read_ref_full(lock->ref_name,
-                         mustexist ? RESOLVE_REF_READING : 0,
-                         lock->old_oid.hash, NULL)) {
+       if (refs_read_ref_full(ref_store, lock->ref_name,
+                              mustexist ? RESOLVE_REF_READING : 0,
+                              lock->old_oid.hash, NULL)) {
                if (old_sha1) {
                        int save_errno = errno;
                        strbuf_addf(err, "can't verify ref '%s'", lock->ref_name);
@@ -2067,11 +1160,19 @@ static int remove_empty_directories(struct strbuf *path)
        return remove_dir_recursively(path, REMOVE_DIR_EMPTY_ONLY);
 }
 
+static int create_reflock(const char *path, void *cb)
+{
+       struct lock_file *lk = cb;
+
+       return hold_lock_file_for_update(lk, path, LOCK_NO_DEREF) < 0 ? -1 : 0;
+}
+
 /*
  * Locks a ref returning the lock on success and NULL on failure.
  * On failure errno is set to something meaningful.
  */
-static struct ref_lock *lock_ref_sha1_basic(const char *refname,
+static struct ref_lock *lock_ref_sha1_basic(struct files_ref_store *refs,
+                                           const char *refname,
                                            const unsigned char *old_sha1,
                                            const struct string_list *extras,
                                            const struct string_list *skip,
@@ -2081,12 +1182,11 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
        struct strbuf ref_file = STRBUF_INIT;
        struct ref_lock *lock;
        int last_errno = 0;
-       int lflags = LOCK_NO_DEREF;
        int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
        int resolve_flags = RESOLVE_REF_NO_RECURSE;
-       int attempts_remaining = 3;
        int resolved;
 
+       files_assert_main_repository(refs, "lock_ref_sha1_basic");
        assert(err);
 
        lock = xcalloc(1, sizeof(struct ref_lock));
@@ -2096,9 +1196,10 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
        if (flags & REF_DELETING)
                resolve_flags |= RESOLVE_REF_ALLOW_BAD_NAME;
 
-       strbuf_git_path(&ref_file, "%s", refname);
-       resolved = !!resolve_ref_unsafe(refname, resolve_flags,
-                                       lock->old_oid.hash, type);
+       files_ref_path(refs, &ref_file, refname);
+       resolved = !!refs_resolve_ref_unsafe(&refs->base,
+                                            refname, resolve_flags,
+                                            lock->old_oid.hash, type);
        if (!resolved && errno == EISDIR) {
                /*
                 * we are trying to lock foo but we used to
@@ -2108,20 +1209,22 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
                 */
                if (remove_empty_directories(&ref_file)) {
                        last_errno = errno;
-                       if (!verify_refname_available_dir(refname, extras, skip,
-                                                         get_loose_refs(&ref_cache), err))
+                       if (!refs_verify_refname_available(
+                                           &refs->base,
+                                           refname, extras, skip, err))
                                strbuf_addf(err, "there are still refs under '%s'",
                                            refname);
                        goto error_return;
                }
-               resolved = !!resolve_ref_unsafe(refname, resolve_flags,
-                                               lock->old_oid.hash, type);
+               resolved = !!refs_resolve_ref_unsafe(&refs->base,
+                                                    refname, resolve_flags,
+                                                    lock->old_oid.hash, type);
        }
        if (!resolved) {
                last_errno = errno;
                if (last_errno != ENOTDIR ||
-                   !verify_refname_available_dir(refname, extras, skip,
-                                                 get_loose_refs(&ref_cache), err))
+                   !refs_verify_refname_available(&refs->base, refname,
+                                                  extras, skip, err))
                        strbuf_addf(err, "unable to resolve reference '%s': %s",
                                    refname, strerror(last_errno));
 
@@ -2135,46 +1238,23 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
         * our refname.
         */
        if (is_null_oid(&lock->old_oid) &&
-           verify_refname_available_dir(refname, extras, skip,
-                                        get_packed_refs(&ref_cache), err)) {
+           refs_verify_refname_available(&refs->base, refname,
+                                         extras, skip, err)) {
                last_errno = ENOTDIR;
-               goto error_return;
-       }
-
-       lock->lk = xcalloc(1, sizeof(struct lock_file));
-
-       lock->ref_name = xstrdup(refname);
-
- retry:
-       switch (safe_create_leading_directories_const(ref_file.buf)) {
-       case SCLD_OK:
-               break; /* success */
-       case SCLD_VANISHED:
-               if (--attempts_remaining > 0)
-                       goto retry;
-               /* fall through */
-       default:
-               last_errno = errno;
-               strbuf_addf(err, "unable to create directory for '%s'",
-                           ref_file.buf);
-               goto error_return;
-       }
-
-       if (hold_lock_file_for_update(lock->lk, ref_file.buf, lflags) < 0) {
-               last_errno = errno;
-               if (errno == ENOENT && --attempts_remaining > 0)
-                       /*
-                        * Maybe somebody just deleted one of the
-                        * directories leading to ref_file.  Try
-                        * again:
-                        */
-                       goto retry;
-               else {
-                       unable_to_lock_message(ref_file.buf, errno, err);
-                       goto error_return;
-               }
+               goto error_return;
+       }
+
+       lock->lk = xcalloc(1, sizeof(struct lock_file));
+
+       lock->ref_name = xstrdup(refname);
+
+       if (raceproof_create_file(ref_file.buf, create_reflock, lock->lk)) {
+               last_errno = errno;
+               unable_to_lock_message(ref_file.buf, errno, err);
+               goto error_return;
        }
-       if (verify_lock(lock, old_sha1, mustexist, err)) {
+
+       if (verify_lock(&refs->base, lock, old_sha1, mustexist, err)) {
                last_errno = errno;
                goto error_return;
        }
@@ -2194,49 +1274,35 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
  * Write an entry to the packed-refs file for the specified refname.
  * If peeled is non-NULL, write it as the entry's peeled value.
  */
-static void write_packed_entry(FILE *fh, char *refname, unsigned char *sha1,
-                              unsigned char *peeled)
+static void write_packed_entry(FILE *fh, const char *refname,
+                              const unsigned char *sha1,
+                              const unsigned char *peeled)
 {
        fprintf_or_die(fh, "%s %s\n", sha1_to_hex(sha1), refname);
        if (peeled)
                fprintf_or_die(fh, "^%s\n", sha1_to_hex(peeled));
 }
 
-/*
- * An each_ref_entry_fn that writes the entry to a packed-refs file.
- */
-static int write_packed_entry_fn(struct ref_entry *entry, void *cb_data)
-{
-       enum peel_status peel_status = peel_entry(entry, 0);
-
-       if (peel_status != PEEL_PEELED && peel_status != PEEL_NON_TAG)
-               error("internal error: %s is not a valid packed reference!",
-                     entry->name);
-       write_packed_entry(cb_data, entry->name, entry->u.value.oid.hash,
-                          peel_status == PEEL_PEELED ?
-                          entry->u.value.peeled.hash : NULL);
-       return 0;
-}
-
 /*
  * Lock the packed-refs file for writing. Flags is passed to
  * hold_lock_file_for_update(). Return 0 on success. On errors, set
  * errno appropriately and return a nonzero value.
  */
-static int lock_packed_refs(int flags)
+static int lock_packed_refs(struct files_ref_store *refs, int flags)
 {
        static int timeout_configured = 0;
        static int timeout_value = 1000;
-
        struct packed_ref_cache *packed_ref_cache;
 
+       files_assert_main_repository(refs, "lock_packed_refs");
+
        if (!timeout_configured) {
                git_config_get_int("core.packedrefstimeout", &timeout_value);
                timeout_configured = 1;
        }
 
        if (hold_lock_file_for_update_timeout(
-                           &packlock, git_path("packed-refs"),
+                           &packlock, files_packed_refs_path(refs),
                            flags, timeout_value) < 0)
                return -1;
        /*
@@ -2245,7 +1311,7 @@ static int lock_packed_refs(int flags)
         * 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 = get_packed_ref_cache(refs);
        packed_ref_cache->lock = &packlock;
        /* Increment the reference count to prevent it from being freed: */
        acquire_packed_ref_cache(packed_ref_cache);
@@ -2258,13 +1324,16 @@ static int lock_packed_refs(int flags)
  * lock_packed_refs()). Return zero on success. On errors, set errno
  * and return a nonzero value
  */
-static int commit_packed_refs(void)
+static int commit_packed_refs(struct files_ref_store *refs)
 {
        struct packed_ref_cache *packed_ref_cache =
-               get_packed_ref_cache(&ref_cache);
-       int error = 0;
+               get_packed_ref_cache(refs);
+       int ok, error = 0;
        int save_errno = 0;
        FILE *out;
+       struct ref_iterator *iter;
+
+       files_assert_main_repository(refs, "commit_packed_refs");
 
        if (!packed_ref_cache->lock)
                die("internal error: packed-refs not locked");
@@ -2274,8 +1343,18 @@ static int commit_packed_refs(void)
                die_errno("unable to fdopen packed-refs descriptor");
 
        fprintf_or_die(out, "%s", PACKED_REFS_HEADER);
-       do_for_each_entry_in_dir(get_packed_ref_dir(packed_ref_cache),
-                                0, write_packed_entry_fn, out);
+
+       iter = cache_ref_iterator_begin(packed_ref_cache->cache, NULL, 0);
+       while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
+               struct object_id peeled;
+               int peel_error = ref_iterator_peel(iter, &peeled);
+
+               write_packed_entry(out, iter->refname, iter->oid->hash,
+                                  peel_error ? NULL : peeled.hash);
+       }
+
+       if (ok != ITER_DONE)
+               die("error while iterating over references");
 
        if (commit_lock_file(packed_ref_cache->lock)) {
                save_errno = errno;
@@ -2292,17 +1371,19 @@ static int commit_packed_refs(void)
  * in-memory packed reference cache.  (The packed-refs file will be
  * read anew if it is needed again after this function is called.)
  */
-static void rollback_packed_refs(void)
+static void rollback_packed_refs(struct files_ref_store *refs)
 {
        struct packed_ref_cache *packed_ref_cache =
-               get_packed_ref_cache(&ref_cache);
+               get_packed_ref_cache(refs);
+
+       files_assert_main_repository(refs, "rollback_packed_refs");
 
        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);
+       clear_packed_ref_cache(refs);
 }
 
 struct ref_to_prune {
@@ -2311,74 +1392,28 @@ struct ref_to_prune {
        char name[FLEX_ARRAY];
 };
 
-struct pack_refs_cb_data {
-       unsigned int flags;
-       struct ref_dir *packed_refs;
-       struct ref_to_prune *ref_to_prune;
+enum {
+       REMOVE_EMPTY_PARENTS_REF = 0x01,
+       REMOVE_EMPTY_PARENTS_REFLOG = 0x02
 };
 
 /*
- * 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 = starts_with(entry->name, "refs/tags/");
-
-       /* Do not pack per-worktree refs: */
-       if (ref_type(entry->name) != REF_TYPE_NORMAL)
-               return 0;
-
-       /* 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) || !entry_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, oid_to_hex(&entry->u.value.oid));
-       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;
-               oidcpy(&packed_entry->u.value.oid, &entry->u.value.oid);
-       } else {
-               packed_entry = create_ref_entry(entry->name, entry->u.value.oid.hash,
-                                               REF_ISPACKED | REF_KNOWS_PEELED, 0);
-               add_ref(cb->packed_refs, packed_entry);
-       }
-       oidcpy(&packed_entry->u.value.peeled, &entry->u.value.peeled);
-
-       /* Schedule the loose reference for pruning if requested. */
-       if ((cb->flags & PACK_REFS_PRUNE)) {
-               struct ref_to_prune *n;
-               FLEX_ALLOC_STR(n, name, entry->name);
-               hashcpy(n->sha1, entry->u.value.oid.hash);
-               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.
+ * Remove empty parent directories associated with the specified
+ * reference and/or its reflog, but spare [logs/]refs/ and immediate
+ * subdirs. flags is a combination of REMOVE_EMPTY_PARENTS_REF and/or
+ * REMOVE_EMPTY_PARENTS_REFLOG.
  */
-static void try_remove_empty_parents(char *name)
+static void try_remove_empty_parents(struct files_ref_store *refs,
+                                    const char *refname,
+                                    unsigned int flags)
 {
+       struct strbuf buf = STRBUF_INIT;
+       struct strbuf sb = STRBUF_INIT;
        char *p, *q;
        int i;
-       p = name;
+
+       strbuf_addstr(&buf, refname);
+       p = buf.buf;
        for (i = 0; i < 2; i++) { /* refs/{heads,tags,...}/ */
                while (*p && *p != '/')
                        p++;
@@ -2386,23 +1421,32 @@ static void try_remove_empty_parents(char *name)
                while (*p == '/')
                        p++;
        }
-       for (q = p; *q; q++)
-               ;
-       while (1) {
+       q = buf.buf + buf.len;
+       while (flags & (REMOVE_EMPTY_PARENTS_REF | REMOVE_EMPTY_PARENTS_REFLOG)) {
                while (q > p && *q != '/')
                        q--;
                while (q > p && *(q-1) == '/')
                        q--;
                if (q == p)
                        break;
-               *q = '\0';
-               if (rmdir(git_path("%s", name)))
-                       break;
+               strbuf_setlen(&buf, q - buf.buf);
+
+               strbuf_reset(&sb);
+               files_ref_path(refs, &sb, buf.buf);
+               if ((flags & REMOVE_EMPTY_PARENTS_REF) && rmdir(sb.buf))
+                       flags &= ~REMOVE_EMPTY_PARENTS_REF;
+
+               strbuf_reset(&sb);
+               files_reflog_path(refs, &sb, buf.buf);
+               if ((flags & REMOVE_EMPTY_PARENTS_REFLOG) && rmdir(sb.buf))
+                       flags &= ~REMOVE_EMPTY_PARENTS_REFLOG;
        }
+       strbuf_release(&buf);
+       strbuf_release(&sb);
 }
 
 /* make sure nobody touched the ref, and unlink */
-static void prune_ref(struct ref_to_prune *r)
+static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
 {
        struct ref_transaction *transaction;
        struct strbuf err = STRBUF_INIT;
@@ -2410,7 +1454,7 @@ static void prune_ref(struct ref_to_prune *r)
        if (check_refname_format(r->name, 0))
                return;
 
-       transaction = ref_transaction_begin(&err);
+       transaction = ref_store_transaction_begin(&refs->base, &err);
        if (!transaction ||
            ref_transaction_delete(transaction, r->name, r->sha1,
                                   REF_ISPRUNING | REF_NODEREF, NULL, &err) ||
@@ -2422,34 +1466,88 @@ static void prune_ref(struct ref_to_prune *r)
        }
        ref_transaction_free(transaction);
        strbuf_release(&err);
-       try_remove_empty_parents(r->name);
 }
 
-static void prune_refs(struct ref_to_prune *r)
+static void prune_refs(struct files_ref_store *refs, struct ref_to_prune *r)
 {
        while (r) {
-               prune_ref(r);
+               prune_ref(refs, r);
                r = r->next;
        }
 }
 
-int pack_refs(unsigned int flags)
+static int files_pack_refs(struct ref_store *ref_store, unsigned int flags)
 {
-       struct pack_refs_cb_data cbdata;
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE | REF_STORE_ODB,
+                              "pack_refs");
+       struct ref_iterator *iter;
+       struct ref_dir *packed_refs;
+       int ok;
+       struct ref_to_prune *refs_to_prune = NULL;
+
+       lock_packed_refs(refs, LOCK_DIE_ON_ERROR);
+       packed_refs = get_packed_refs(refs);
+
+       iter = cache_ref_iterator_begin(get_loose_ref_cache(refs), NULL, 0);
+       while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
+               /*
+                * 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 refs_to_prune.
+                */
+               struct ref_entry *packed_entry;
+               int is_tag_ref = starts_with(iter->refname, "refs/tags/");
+
+               /* Do not pack per-worktree refs: */
+               if (ref_type(iter->refname) != REF_TYPE_NORMAL)
+                       continue;
+
+               /* ALWAYS pack tags */
+               if (!(flags & PACK_REFS_ALL) && !is_tag_ref)
+                       continue;
 
-       memset(&cbdata, 0, sizeof(cbdata));
-       cbdata.flags = flags;
+               /* Do not pack symbolic or broken refs: */
+               if (iter->flags & REF_ISSYMREF)
+                       continue;
 
-       lock_packed_refs(LOCK_DIE_ON_ERROR);
-       cbdata.packed_refs = get_packed_refs(&ref_cache);
+               if (!ref_resolves_to_object(iter->refname, iter->oid, iter->flags))
+                       continue;
 
-       do_for_each_entry_in_dir(get_loose_refs(&ref_cache), 0,
-                                pack_if_possible_fn, &cbdata);
+               /*
+                * Create an entry in the packed-refs cache equivalent
+                * to the one from the loose ref cache, except that
+                * we don't copy the peeled status, because we want it
+                * to be re-peeled.
+                */
+               packed_entry = find_ref_entry(packed_refs, iter->refname);
+               if (packed_entry) {
+                       /* Overwrite existing packed entry with info from loose entry */
+                       packed_entry->flag = REF_ISPACKED;
+                       oidcpy(&packed_entry->u.value.oid, iter->oid);
+               } else {
+                       packed_entry = create_ref_entry(iter->refname, iter->oid->hash,
+                                                       REF_ISPACKED, 0);
+                       add_ref_entry(packed_refs, packed_entry);
+               }
+               oidclr(&packed_entry->u.value.peeled);
+
+               /* Schedule the loose reference for pruning if requested. */
+               if ((flags & PACK_REFS_PRUNE)) {
+                       struct ref_to_prune *n;
+                       FLEX_ALLOC_STR(n, name, iter->refname);
+                       hashcpy(n->sha1, iter->oid->hash);
+                       n->next = refs_to_prune;
+                       refs_to_prune = n;
+               }
+       }
+       if (ok != ITER_DONE)
+               die("error while iterating over references");
 
-       if (commit_packed_refs())
+       if (commit_packed_refs(refs))
                die_errno("unable to overwrite old ref-pack file");
 
-       prune_refs(cbdata.ref_to_prune);
+       prune_refs(refs, refs_to_prune);
        return 0;
 }
 
@@ -2460,17 +1558,19 @@ int pack_refs(unsigned int flags)
  *
  * The refs in 'refnames' needn't be sorted. `err` must not be NULL.
  */
-static int repack_without_refs(struct string_list *refnames, struct strbuf *err)
+static int repack_without_refs(struct files_ref_store *refs,
+                              struct string_list *refnames, struct strbuf *err)
 {
        struct ref_dir *packed;
        struct string_list_item *refname;
        int ret, needs_repacking = 0, removed = 0;
 
+       files_assert_main_repository(refs, "repack_without_refs");
        assert(err);
 
        /* Look for a packed ref */
        for_each_string_list_item(refname, refnames) {
-               if (get_packed_ref(refname->string)) {
+               if (get_packed_ref(refs, refname->string)) {
                        needs_repacking = 1;
                        break;
                }
@@ -2480,60 +1580,45 @@ static int repack_without_refs(struct string_list *refnames, struct strbuf *err)
        if (!needs_repacking)
                return 0; /* no refname exists in packed refs */
 
-       if (lock_packed_refs(0)) {
-               unable_to_lock_message(git_path("packed-refs"), errno, err);
+       if (lock_packed_refs(refs, 0)) {
+               unable_to_lock_message(files_packed_refs_path(refs), errno, err);
                return -1;
        }
-       packed = get_packed_refs(&ref_cache);
+       packed = get_packed_refs(refs);
 
        /* Remove refnames from the cache */
        for_each_string_list_item(refname, refnames)
-               if (remove_entry(packed, refname->string) != -1)
+               if (remove_entry_from_dir(packed, refname->string) != -1)
                        removed = 1;
        if (!removed) {
                /*
                 * All packed entries disappeared while we were
                 * acquiring the lock.
                 */
-               rollback_packed_refs();
+               rollback_packed_refs(refs);
                return 0;
        }
 
        /* Write what remains */
-       ret = commit_packed_refs();
+       ret = commit_packed_refs(refs);
        if (ret)
                strbuf_addf(err, "unable to overwrite old ref-pack file: %s",
                            strerror(errno));
        return ret;
 }
 
-static int delete_ref_loose(struct ref_lock *lock, int flag, struct strbuf *err)
-{
-       assert(err);
-
-       if (!(flag & REF_ISPACKED) || flag & REF_ISSYMREF) {
-               /*
-                * loose.  The loose file name is the same as the
-                * lockfile name, minus ".lock":
-                */
-               char *loose_filename = get_locked_file_path(lock->lk);
-               int res = unlink_or_msg(loose_filename, err);
-               free(loose_filename);
-               if (res)
-                       return 1;
-       }
-       return 0;
-}
-
-int delete_refs(struct string_list *refnames, unsigned int flags)
+static int files_delete_refs(struct ref_store *ref_store,
+                            struct string_list *refnames, unsigned int flags)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "delete_refs");
        struct strbuf err = STRBUF_INIT;
        int i, result = 0;
 
        if (!refnames->nr)
                return 0;
 
-       result = repack_without_refs(refnames, &err);
+       result = repack_without_refs(refs, refnames, &err);
        if (result) {
                /*
                 * If we failed to rewrite the packed-refs file, then
@@ -2554,7 +1639,7 @@ int delete_refs(struct string_list *refnames, unsigned int flags)
        for (i = 0; i < refnames->nr; i++) {
                const char *refname = refnames->items[i].string;
 
-               if (delete_ref(refname, NULL, flags))
+               if (refs_delete_ref(&refs->base, NULL, refname, NULL, flags))
                        result |= error(_("could not remove reference %s"), refname);
        }
 
@@ -2570,110 +1655,117 @@ int delete_refs(struct string_list *refnames, unsigned int flags)
  * 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"
+#define TMP_RENAMED_LOG  "refs/.tmp-renamed-log"
 
-static int rename_tmp_log(const char *newrefname)
-{
-       int attempts_remaining = 4;
-       struct strbuf path = STRBUF_INIT;
-       int ret = -1;
+struct rename_cb {
+       const char *tmp_renamed_log;
+       int true_errno;
+};
 
- retry:
-       strbuf_reset(&path);
-       strbuf_git_path(&path, "logs/%s", newrefname);
-       switch (safe_create_leading_directories_const(path.buf)) {
-       case SCLD_OK:
-               break; /* success */
-       case SCLD_VANISHED:
-               if (--attempts_remaining > 0)
-                       goto retry;
-               /* fall through */
-       default:
-               error("unable to create directory for %s", newrefname);
-               goto out;
-       }
+static int rename_tmp_log_callback(const char *path, void *cb_data)
+{
+       struct rename_cb *cb = cb_data;
 
-       if (rename(git_path(TMP_RENAMED_LOG), path.buf)) {
-               if ((errno==EISDIR || errno==ENOTDIR) && --attempts_remaining > 0) {
-                       /*
-                        * rename(a, b) when b is an existing
-                        * directory ought to result in ISDIR, but
-                        * Solaris 5.8 gives ENOTDIR.  Sheesh.
-                        */
-                       if (remove_empty_directories(&path)) {
-                               error("Directory not empty: logs/%s", newrefname);
-                               goto out;
-                       }
-                       goto retry;
-               } else if (errno == ENOENT && --attempts_remaining > 0) {
-                       /*
-                        * Maybe another process just deleted one of
-                        * the directories in the path to newrefname.
-                        * Try again from the beginning.
-                        */
-                       goto retry;
-               } else {
-                       error("unable to move logfile "TMP_RENAMED_LOG" to logs/%s: %s",
-                               newrefname, strerror(errno));
-                       goto out;
-               }
+       if (rename(cb->tmp_renamed_log, path)) {
+               /*
+                * rename(a, b) when b is an existing directory ought
+                * to result in ISDIR, but Solaris 5.8 gives ENOTDIR.
+                * Sheesh. Record the true errno for error reporting,
+                * but report EISDIR to raceproof_create_file() so
+                * that it knows to retry.
+                */
+               cb->true_errno = errno;
+               if (errno == ENOTDIR)
+                       errno = EISDIR;
+               return -1;
+       } else {
+               return 0;
        }
-       ret = 0;
-out:
-       strbuf_release(&path);
-       return ret;
 }
 
-int verify_refname_available(const char *newname,
-                            const struct string_list *extras,
-                            const struct string_list *skip,
-                            struct strbuf *err)
+static int rename_tmp_log(struct files_ref_store *refs, const char *newrefname)
 {
-       struct ref_dir *packed_refs = get_packed_refs(&ref_cache);
-       struct ref_dir *loose_refs = get_loose_refs(&ref_cache);
+       struct strbuf path = STRBUF_INIT;
+       struct strbuf tmp = STRBUF_INIT;
+       struct rename_cb cb;
+       int ret;
 
-       if (verify_refname_available_dir(newname, extras, skip,
-                                        packed_refs, err) ||
-           verify_refname_available_dir(newname, extras, skip,
-                                        loose_refs, err))
-               return -1;
+       files_reflog_path(refs, &path, newrefname);
+       files_reflog_path(refs, &tmp, TMP_RENAMED_LOG);
+       cb.tmp_renamed_log = tmp.buf;
+       ret = raceproof_create_file(path.buf, rename_tmp_log_callback, &cb);
+       if (ret) {
+               if (errno == EISDIR)
+                       error("directory not empty: %s", path.buf);
+               else
+                       error("unable to move logfile %s to %s: %s",
+                             tmp.buf, path.buf,
+                             strerror(cb.true_errno));
+       }
 
-       return 0;
+       strbuf_release(&path);
+       strbuf_release(&tmp);
+       return ret;
 }
 
 static int write_ref_to_lockfile(struct ref_lock *lock,
                                 const unsigned char *sha1, struct strbuf *err);
-static int commit_ref_update(struct ref_lock *lock,
+static int commit_ref_update(struct files_ref_store *refs,
+                            struct ref_lock *lock,
                             const unsigned char *sha1, const char *logmsg,
                             struct strbuf *err);
 
-int rename_ref(const char *oldrefname, const char *newrefname, const char *logmsg)
+static int files_rename_ref(struct ref_store *ref_store,
+                           const char *oldrefname, const char *newrefname,
+                           const char *logmsg)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "rename_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", oldrefname), &loginfo);
+       struct strbuf sb_oldref = STRBUF_INIT;
+       struct strbuf sb_newref = STRBUF_INIT;
+       struct strbuf tmp_renamed_log = STRBUF_INIT;
+       int log, ret;
        struct strbuf err = STRBUF_INIT;
 
-       if (log && S_ISLNK(loginfo.st_mode))
-               return error("reflog for %s is a symlink", oldrefname);
+       files_reflog_path(refs, &sb_oldref, oldrefname);
+       files_reflog_path(refs, &sb_newref, newrefname);
+       files_reflog_path(refs, &tmp_renamed_log, TMP_RENAMED_LOG);
 
-       if (!resolve_ref_unsafe(oldrefname, RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
-                               orig_sha1, &flag))
-               return error("refname %s not found", oldrefname);
+       log = !lstat(sb_oldref.buf, &loginfo);
+       if (log && S_ISLNK(loginfo.st_mode)) {
+               ret = error("reflog for %s is a symlink", oldrefname);
+               goto out;
+       }
 
-       if (flag & REF_ISSYMREF)
-               return error("refname %s is a symbolic ref, renaming it is not supported",
-                       oldrefname);
-       if (!rename_ref_available(oldrefname, newrefname))
-               return 1;
+       if (!refs_resolve_ref_unsafe(&refs->base, oldrefname,
+                                    RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
+                               orig_sha1, &flag)) {
+               ret = error("refname %s not found", oldrefname);
+               goto out;
+       }
 
-       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 (flag & REF_ISSYMREF) {
+               ret = error("refname %s is a symbolic ref, renaming it is not supported",
+                           oldrefname);
+               goto out;
+       }
+       if (!refs_rename_ref_available(&refs->base, oldrefname, newrefname)) {
+               ret = 1;
+               goto out;
+       }
+
+       if (log && rename(sb_oldref.buf, tmp_renamed_log.buf)) {
+               ret = error("unable to move logfile logs/%s to logs/"TMP_RENAMED_LOG": %s",
+                           oldrefname, strerror(errno));
+               goto out;
+       }
 
-       if (delete_ref(oldrefname, orig_sha1, REF_NODEREF)) {
+       if (refs_delete_ref(&refs->base, logmsg, oldrefname,
+                           orig_sha1, REF_NODEREF)) {
                error("unable to delete old %s", oldrefname);
                goto rollback;
        }
@@ -2685,14 +1777,16 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
         * the safety anyway; we want to delete the reference whatever
         * its current value.
         */
-       if (!read_ref_full(newrefname, RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
-                          sha1, NULL) &&
-           delete_ref(newrefname, NULL, REF_NODEREF)) {
-               if (errno==EISDIR) {
+       if (!refs_read_ref_full(&refs->base, newrefname,
+                               RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
+                               sha1, NULL) &&
+           refs_delete_ref(&refs->base, NULL, newrefname,
+                           NULL, REF_NODEREF)) {
+               if (errno == EISDIR) {
                        struct strbuf path = STRBUF_INIT;
                        int result;
 
-                       strbuf_git_path(&path, "%s", newrefname);
+                       files_ref_path(refs, &path, newrefname);
                        result = remove_empty_directories(&path);
                        strbuf_release(&path);
 
@@ -2706,13 +1800,13 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
                }
        }
 
-       if (log && rename_tmp_log(newrefname))
+       if (log && rename_tmp_log(refs, newrefname))
                goto rollback;
 
        logmoved = log;
 
-       lock = lock_ref_sha1_basic(newrefname, NULL, NULL, NULL, REF_NODEREF,
-                                  NULL, &err);
+       lock = lock_ref_sha1_basic(refs, newrefname, NULL, NULL, NULL,
+                                  REF_NODEREF, NULL, &err);
        if (!lock) {
                error("unable to rename '%s' to '%s': %s", oldrefname, newrefname, err.buf);
                strbuf_release(&err);
@@ -2721,17 +1815,18 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
        hashcpy(lock->old_oid.hash, orig_sha1);
 
        if (write_ref_to_lockfile(lock, orig_sha1, &err) ||
-           commit_ref_update(lock, orig_sha1, logmsg, &err)) {
+           commit_ref_update(refs, lock, orig_sha1, logmsg, &err)) {
                error("unable to write current sha1 into %s: %s", newrefname, err.buf);
                strbuf_release(&err);
                goto rollback;
        }
 
-       return 0;
+       ret = 0;
+       goto out;
 
  rollback:
-       lock = lock_ref_sha1_basic(oldrefname, NULL, NULL, NULL, REF_NODEREF,
-                                  NULL, &err);
+       lock = lock_ref_sha1_basic(refs, oldrefname, NULL, NULL, NULL,
+                                  REF_NODEREF, NULL, &err);
        if (!lock) {
                error("unable to lock %s for rollback: %s", oldrefname, err.buf);
                strbuf_release(&err);
@@ -2739,24 +1834,29 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
        }
 
        flag = log_all_ref_updates;
-       log_all_ref_updates = 0;
+       log_all_ref_updates = LOG_REFS_NONE;
        if (write_ref_to_lockfile(lock, orig_sha1, &err) ||
-           commit_ref_update(lock, orig_sha1, NULL, &err)) {
+           commit_ref_update(refs, lock, orig_sha1, NULL, &err)) {
                error("unable to write current sha1 into %s: %s", oldrefname, err.buf);
                strbuf_release(&err);
        }
        log_all_ref_updates = flag;
 
  rollbacklog:
-       if (logmoved && rename(git_path("logs/%s", newrefname), git_path("logs/%s", oldrefname)))
+       if (logmoved && rename(sb_newref.buf, sb_oldref.buf))
                error("unable to restore logfile %s from %s: %s",
                        oldrefname, newrefname, strerror(errno));
        if (!logmoved && log &&
-           rename(git_path(TMP_RENAMED_LOG), git_path("logs/%s", oldrefname)))
-               error("unable to restore logfile %s from "TMP_RENAMED_LOG": %s",
+           rename(tmp_renamed_log.buf, sb_oldref.buf))
+               error("unable to restore logfile %s from logs/"TMP_RENAMED_LOG": %s",
                        oldrefname, strerror(errno));
+       ret = 1;
+ out:
+       strbuf_release(&sb_newref);
+       strbuf_release(&sb_oldref);
+       strbuf_release(&tmp_renamed_log);
 
-       return 1;
+       return ret;
 }
 
 static int close_ref(struct ref_lock *lock)
@@ -2797,61 +1897,93 @@ static int commit_ref(struct ref_lock *lock)
        return 0;
 }
 
+static int open_or_create_logfile(const char *path, void *cb)
+{
+       int *fd = cb;
+
+       *fd = open(path, O_APPEND | O_WRONLY | O_CREAT, 0666);
+       return (*fd < 0) ? -1 : 0;
+}
+
 /*
- * Create a reflog for a ref.  If force_create = 0, the reflog will
- * only be created for certain refs (those for which
- * should_autocreate_reflog returns non-zero.  Otherwise, create it
- * regardless of the ref name.  Fill in *err and return -1 on failure.
+ * Create a reflog for a ref. If force_create = 0, only create the
+ * reflog for certain refs (those for which should_autocreate_reflog
+ * returns non-zero). Otherwise, create it regardless of the reference
+ * name. If the logfile already existed or was created, return 0 and
+ * set *logfd to the file descriptor opened for appending to the file.
+ * If no logfile exists and we decided not to create one, return 0 and
+ * set *logfd to -1. On failure, fill in *err, set *logfd to -1, and
+ * return -1.
  */
-static int log_ref_setup(const char *refname, struct strbuf *logfile, struct strbuf *err, int force_create)
+static int log_ref_setup(struct files_ref_store *refs,
+                        const char *refname, int force_create,
+                        int *logfd, struct strbuf *err)
 {
-       int logfd, oflags = O_APPEND | O_WRONLY;
+       struct strbuf logfile_sb = STRBUF_INIT;
+       char *logfile;
 
-       strbuf_git_path(logfile, "logs/%s", refname);
-       if (force_create || should_autocreate_reflog(refname)) {
-               if (safe_create_leading_directories(logfile->buf) < 0) {
-                       strbuf_addf(err, "unable to create directory for '%s': "
-                                   "%s", logfile->buf, strerror(errno));
-                       return -1;
-               }
-               oflags |= O_CREAT;
-       }
+       files_reflog_path(refs, &logfile_sb, refname);
+       logfile = strbuf_detach(&logfile_sb, NULL);
 
-       logfd = open(logfile->buf, oflags, 0666);
-       if (logfd < 0) {
-               if (!(oflags & O_CREAT) && (errno == ENOENT || errno == EISDIR))
-                       return 0;
+       if (force_create || should_autocreate_reflog(refname)) {
+               if (raceproof_create_file(logfile, open_or_create_logfile, logfd)) {
+                       if (errno == ENOENT)
+                               strbuf_addf(err, "unable to create directory for '%s': "
+                                           "%s", logfile, strerror(errno));
+                       else if (errno == EISDIR)
+                               strbuf_addf(err, "there are still logs under '%s'",
+                                           logfile);
+                       else
+                               strbuf_addf(err, "unable to append to '%s': %s",
+                                           logfile, strerror(errno));
 
-               if (errno == EISDIR) {
-                       if (remove_empty_directories(logfile)) {
-                               strbuf_addf(err, "there are still logs under "
-                                           "'%s'", logfile->buf);
-                               return -1;
-                       }
-                       logfd = open(logfile->buf, oflags, 0666);
+                       goto error;
                }
-
-               if (logfd < 0) {
-                       strbuf_addf(err, "unable to append to '%s': %s",
-                                   logfile->buf, strerror(errno));
-                       return -1;
+       } else {
+               *logfd = open(logfile, O_APPEND | O_WRONLY, 0666);
+               if (*logfd < 0) {
+                       if (errno == ENOENT || errno == EISDIR) {
+                               /*
+                                * The logfile doesn't already exist,
+                                * but that is not an error; it only
+                                * means that we won't write log
+                                * entries to it.
+                                */
+                               ;
+                       } else {
+                               strbuf_addf(err, "unable to append to '%s': %s",
+                                           logfile, strerror(errno));
+                               goto error;
+                       }
                }
        }
 
-       adjust_shared_perm(logfile->buf);
-       close(logfd);
+       if (*logfd >= 0)
+               adjust_shared_perm(logfile);
+
+       free(logfile);
        return 0;
-}
 
+error:
+       free(logfile);
+       return -1;
+}
 
-int safe_create_reflog(const char *refname, int force_create, struct strbuf *err)
+static int files_create_reflog(struct ref_store *ref_store,
+                              const char *refname, int force_create,
+                              struct strbuf *err)
 {
-       int ret;
-       struct strbuf sb = STRBUF_INIT;
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "create_reflog");
+       int fd;
 
-       ret = log_ref_setup(refname, &sb, err, force_create);
-       strbuf_release(&sb);
-       return ret;
+       if (log_ref_setup(refs, refname, force_create, &fd, err))
+               return -1;
+
+       if (fd >= 0)
+               close(fd);
+
+       return 0;
 }
 
 static int log_ref_write_fd(int fd, const unsigned char *old_sha1,
@@ -2880,59 +2012,51 @@ static int log_ref_write_fd(int fd, const unsigned char *old_sha1,
        return 0;
 }
 
-static int log_ref_write_1(const char *refname, const unsigned char *old_sha1,
-                          const unsigned char *new_sha1, const char *msg,
-                          struct strbuf *logfile, int flags,
-                          struct strbuf *err)
+static int files_log_ref_write(struct files_ref_store *refs,
+                              const char *refname, const unsigned char *old_sha1,
+                              const unsigned char *new_sha1, const char *msg,
+                              int flags, struct strbuf *err)
 {
-       int logfd, result, oflags = O_APPEND | O_WRONLY;
+       int logfd, result;
 
-       if (log_all_ref_updates < 0)
-               log_all_ref_updates = !is_bare_repository();
+       if (log_all_ref_updates == LOG_REFS_UNSET)
+               log_all_ref_updates = is_bare_repository() ? LOG_REFS_NONE : LOG_REFS_NORMAL;
 
-       result = log_ref_setup(refname, logfile, err, flags & REF_FORCE_CREATE_REFLOG);
+       result = log_ref_setup(refs, refname,
+                              flags & REF_FORCE_CREATE_REFLOG,
+                              &logfd, err);
 
        if (result)
                return result;
 
-       logfd = open(logfile->buf, oflags);
        if (logfd < 0)
                return 0;
        result = log_ref_write_fd(logfd, old_sha1, new_sha1,
                                  git_committer_info(0), msg);
        if (result) {
-               strbuf_addf(err, "unable to append to '%s': %s", logfile->buf,
-                           strerror(errno));
+               struct strbuf sb = STRBUF_INIT;
+               int save_errno = errno;
+
+               files_reflog_path(refs, &sb, refname);
+               strbuf_addf(err, "unable to append to '%s': %s",
+                           sb.buf, strerror(save_errno));
+               strbuf_release(&sb);
                close(logfd);
                return -1;
        }
        if (close(logfd)) {
-               strbuf_addf(err, "unable to append to '%s': %s", logfile->buf,
-                           strerror(errno));
+               struct strbuf sb = STRBUF_INIT;
+               int save_errno = errno;
+
+               files_reflog_path(refs, &sb, refname);
+               strbuf_addf(err, "unable to append to '%s': %s",
+                           sb.buf, strerror(save_errno));
+               strbuf_release(&sb);
                return -1;
        }
        return 0;
 }
 
-static int log_ref_write(const char *refname, const unsigned char *old_sha1,
-                        const unsigned char *new_sha1, const char *msg,
-                        int flags, struct strbuf *err)
-{
-       return files_log_ref_write(refname, old_sha1, new_sha1, msg, flags,
-                                  err);
-}
-
-int files_log_ref_write(const char *refname, const unsigned char *old_sha1,
-                       const unsigned char *new_sha1, const char *msg,
-                       int flags, struct strbuf *err)
-{
-       struct strbuf sb = STRBUF_INIT;
-       int ret = log_ref_write_1(refname, old_sha1, new_sha1, msg, &sb, flags,
-                                 err);
-       strbuf_release(&sb);
-       return ret;
-}
-
 /*
  * Write sha1 into the open lockfile, then close the lockfile. On
  * errors, rollback the lockfile, fill in *err and
@@ -2977,12 +2101,17 @@ static int write_ref_to_lockfile(struct ref_lock *lock,
  * to the loose reference lockfile. Also update the reflogs if
  * necessary, using the specified lockmsg (which can be NULL).
  */
-static int commit_ref_update(struct ref_lock *lock,
+static int commit_ref_update(struct files_ref_store *refs,
+                            struct ref_lock *lock,
                             const unsigned char *sha1, const char *logmsg,
                             struct strbuf *err)
 {
-       clear_loose_ref_cache(&ref_cache);
-       if (log_ref_write(lock->ref_name, lock->old_oid.hash, sha1, logmsg, 0, err)) {
+       files_assert_main_repository(refs, "commit_ref_update");
+
+       clear_loose_ref_cache(refs);
+       if (files_log_ref_write(refs, lock->ref_name,
+                               lock->old_oid.hash, sha1,
+                               logmsg, 0, err)) {
                char *old_msg = strbuf_detach(err, NULL);
                strbuf_addf(err, "cannot update the ref '%s': %s",
                            lock->ref_name, old_msg);
@@ -3008,13 +2137,15 @@ static int commit_ref_update(struct ref_lock *lock,
                int head_flag;
                const char *head_ref;
 
-               head_ref = resolve_ref_unsafe("HEAD", RESOLVE_REF_READING,
-                                             head_sha1, &head_flag);
+               head_ref = refs_resolve_ref_unsafe(&refs->base, "HEAD",
+                                                  RESOLVE_REF_READING,
+                                                  head_sha1, &head_flag);
                if (head_ref && (head_flag & REF_ISSYMREF) &&
                    !strcmp(head_ref, lock->ref_name)) {
                        struct strbuf log_err = STRBUF_INIT;
-                       if (log_ref_write("HEAD", lock->old_oid.hash, sha1,
-                                         logmsg, 0, &log_err)) {
+                       if (files_log_ref_write(refs, "HEAD",
+                                               lock->old_oid.hash, sha1,
+                                               logmsg, 0, &log_err)) {
                                error("%s", log_err.buf);
                                strbuf_release(&log_err);
                        }
@@ -3046,23 +2177,28 @@ static int create_ref_symlink(struct ref_lock *lock, const char *target)
        return ret;
 }
 
-static void update_symref_reflog(struct ref_lock *lock, const char *refname,
+static void update_symref_reflog(struct files_ref_store *refs,
+                                struct ref_lock *lock, const char *refname,
                                 const char *target, const char *logmsg)
 {
        struct strbuf err = STRBUF_INIT;
        unsigned char new_sha1[20];
-       if (logmsg && !read_ref(target, new_sha1) &&
-           log_ref_write(refname, lock->old_oid.hash, new_sha1, logmsg, 0, &err)) {
+       if (logmsg &&
+           !refs_read_ref_full(&refs->base, target,
+                               RESOLVE_REF_READING, new_sha1, NULL) &&
+           files_log_ref_write(refs, refname, lock->old_oid.hash,
+                               new_sha1, logmsg, 0, &err)) {
                error("%s", err.buf);
                strbuf_release(&err);
        }
 }
 
-static int create_symref_locked(struct ref_lock *lock, const char *refname,
+static int create_symref_locked(struct files_ref_store *refs,
+                               struct ref_lock *lock, const char *refname,
                                const char *target, const char *logmsg)
 {
        if (prefer_symlink_refs && !create_ref_symlink(lock, target)) {
-               update_symref_reflog(lock, refname, target, logmsg);
+               update_symref_reflog(refs, lock, refname, target, logmsg);
                return 0;
        }
 
@@ -3070,7 +2206,7 @@ static int create_symref_locked(struct ref_lock *lock, const char *refname,
                return error("unable to fdopen %s: %s",
                             lock->lk->tempfile.filename.buf, strerror(errno));
 
-       update_symref_reflog(lock, refname, target, logmsg);
+       update_symref_reflog(refs, lock, refname, target, logmsg);
 
        /* no error check; commit_ref will check ferror */
        fprintf(lock->lk->tempfile.fp, "ref: %s\n", target);
@@ -3080,13 +2216,18 @@ static int create_symref_locked(struct ref_lock *lock, const char *refname,
        return 0;
 }
 
-int create_symref(const char *refname, const char *target, const char *logmsg)
+static int files_create_symref(struct ref_store *ref_store,
+                              const char *refname, const char *target,
+                              const char *logmsg)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "create_symref");
        struct strbuf err = STRBUF_INIT;
        struct ref_lock *lock;
        int ret;
 
-       lock = lock_ref_sha1_basic(refname, NULL, NULL, NULL, REF_NODEREF, NULL,
+       lock = lock_ref_sha1_basic(refs, refname, NULL,
+                                  NULL, NULL, REF_NODEREF, NULL,
                                   &err);
        if (!lock) {
                error("%s", err.buf);
@@ -3094,13 +2235,22 @@ int create_symref(const char *refname, const char *target, const char *logmsg)
                return -1;
        }
 
-       ret = create_symref_locked(lock, refname, target, logmsg);
+       ret = create_symref_locked(refs, lock, refname, target, logmsg);
        unlock_ref(lock);
        return ret;
 }
 
-int set_worktree_head_symref(const char *gitdir, const char *target)
+int set_worktree_head_symref(const char *gitdir, const char *target, const char *logmsg)
 {
+       /*
+        * FIXME: this obviously will not work well for future refs
+        * backends. This function needs to die.
+        */
+       struct files_ref_store *refs =
+               files_downcast(get_main_ref_store(),
+                              REF_STORE_WRITE,
+                              "set_head_symref");
+
        static struct lock_file head_lock;
        struct ref_lock *lock;
        struct strbuf head_path = STRBUF_INIT;
@@ -3127,38 +2277,55 @@ int set_worktree_head_symref(const char *gitdir, const char *target)
        lock->lk = &head_lock;
        lock->ref_name = xstrdup(head_rel);
 
-       ret = create_symref_locked(lock, head_rel, target, NULL);
+       ret = create_symref_locked(refs, lock, head_rel, target, logmsg);
 
        unlock_ref(lock); /* will free lock */
        strbuf_release(&head_path);
        return ret;
 }
 
-int reflog_exists(const char *refname)
+static int files_reflog_exists(struct ref_store *ref_store,
+                              const char *refname)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ, "reflog_exists");
+       struct strbuf sb = STRBUF_INIT;
        struct stat st;
+       int ret;
 
-       return !lstat(git_path("logs/%s", refname), &st) &&
-               S_ISREG(st.st_mode);
+       files_reflog_path(refs, &sb, refname);
+       ret = !lstat(sb.buf, &st) && S_ISREG(st.st_mode);
+       strbuf_release(&sb);
+       return ret;
 }
 
-int delete_reflog(const char *refname)
+static int files_delete_reflog(struct ref_store *ref_store,
+                              const char *refname)
 {
-       return remove_path(git_path("logs/%s", refname));
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "delete_reflog");
+       struct strbuf sb = STRBUF_INIT;
+       int ret;
+
+       files_reflog_path(refs, &sb, refname);
+       ret = remove_path(sb.buf);
+       strbuf_release(&sb);
+       return ret;
 }
 
 static int show_one_reflog_ent(struct strbuf *sb, each_reflog_ent_fn fn, void *cb_data)
 {
-       unsigned char osha1[20], nsha1[20];
+       struct object_id ooid, noid;
        char *email_end, *message;
        unsigned long timestamp;
        int tz;
+       const char *p = sb->buf;
 
        /* 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, '>')) ||
+       if (!sb->len || sb->buf[sb->len - 1] != '\n' ||
+           parse_oid_hex(p, &ooid, &p) || *p++ != ' ' ||
+           parse_oid_hex(p, &noid, &p) || *p++ != ' ' ||
+           !(email_end = strchr(p, '>')) ||
            email_end[1] != ' ' ||
            !(timestamp = strtoul(email_end + 2, &message, 10)) ||
            !message || message[0] != ' ' ||
@@ -3172,7 +2339,7 @@ static int show_one_reflog_ent(struct strbuf *sb, each_reflog_ent_fn fn, void *c
                message += 6;
        else
                message += 7;
-       return fn(osha1, nsha1, sb->buf + 82, timestamp, tz, message, cb_data);
+       return fn(&ooid, &noid, p, timestamp, tz, message, cb_data);
 }
 
 static char *find_beginning_of_line(char *bob, char *scan)
@@ -3186,21 +2353,29 @@ static char *find_beginning_of_line(char *bob, char *scan)
        return scan;
 }
 
-int for_each_reflog_ent_reverse(const char *refname, each_reflog_ent_fn fn, void *cb_data)
+static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
+                                            const char *refname,
+                                            each_reflog_ent_fn fn,
+                                            void *cb_data)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ,
+                              "for_each_reflog_ent_reverse");
        struct strbuf sb = STRBUF_INIT;
        FILE *logfp;
        long pos;
        int ret = 0, at_tail = 1;
 
-       logfp = fopen(git_path("logs/%s", refname), "r");
+       files_reflog_path(refs, &sb, refname);
+       logfp = fopen(sb.buf, "r");
+       strbuf_release(&sb);
        if (!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));
+               ret = error("cannot seek back reflog for %s: %s",
+                           refname, strerror(errno));
        pos = ftell(logfp);
        while (!ret && 0 < pos) {
                int cnt;
@@ -3210,13 +2385,17 @@ int for_each_reflog_ent_reverse(const char *refname, each_reflog_ent_fn fn, void
 
                /* 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));
+               if (fseek(logfp, pos - cnt, SEEK_SET)) {
+                       ret = error("cannot seek back reflog for %s: %s",
+                                   refname, strerror(errno));
+                       break;
+               }
                nread = fread(buf, cnt, 1, logfp);
-               if (nread != 1)
-                       return error("cannot read %d bytes from reflog for %s: %s",
-                                    cnt, refname, strerror(errno));
+               if (nread != 1) {
+                       ret = error("cannot read %d bytes from reflog for %s: %s",
+                                   cnt, refname, strerror(errno));
+                       break;
+               }
                pos -= cnt;
 
                scanp = endp = buf + cnt;
@@ -3288,13 +2467,20 @@ int for_each_reflog_ent_reverse(const char *refname, each_reflog_ent_fn fn, void
        return ret;
 }
 
-int for_each_reflog_ent(const char *refname, each_reflog_ent_fn fn, void *cb_data)
+static int files_for_each_reflog_ent(struct ref_store *ref_store,
+                                    const char *refname,
+                                    each_reflog_ent_fn fn, void *cb_data)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ,
+                              "for_each_reflog_ent");
        FILE *logfp;
        struct strbuf sb = STRBUF_INIT;
        int ret = 0;
 
-       logfp = fopen(git_path("logs/%s", refname), "r");
+       files_reflog_path(refs, &sb, refname);
+       logfp = fopen(sb.buf, "r");
+       strbuf_release(&sb);
        if (!logfp)
                return -1;
 
@@ -3308,6 +2494,7 @@ int for_each_reflog_ent(const char *refname, each_reflog_ent_fn fn, void *cb_dat
 struct files_reflog_iterator {
        struct ref_iterator base;
 
+       struct ref_store *ref_store;
        struct dir_iterator *dir_iterator;
        struct object_id oid;
 };
@@ -3329,8 +2516,9 @@ static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
                if (ends_with(diter->basename, ".lock"))
                        continue;
 
-               if (read_ref_full(diter->relative_path, 0,
-                                 iter->oid.hash, &flags)) {
+               if (refs_read_ref_full(iter->ref_store,
+                                      diter->relative_path, 0,
+                                      iter->oid.hash, &flags)) {
                        error("bad ref for %s", diter->path.buf);
                        continue;
                }
@@ -3372,22 +2560,23 @@ static struct ref_iterator_vtable files_reflog_iterator_vtable = {
        files_reflog_iterator_abort
 };
 
-struct ref_iterator *files_reflog_iterator_begin(void)
+static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_store)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ,
+                              "reflog_iterator_begin");
        struct files_reflog_iterator *iter = xcalloc(1, sizeof(*iter));
        struct ref_iterator *ref_iterator = &iter->base;
+       struct strbuf sb = STRBUF_INIT;
 
        base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable);
-       iter->dir_iterator = dir_iterator_begin(git_path("logs"));
+       files_reflog_path(refs, &sb, NULL);
+       iter->dir_iterator = dir_iterator_begin(sb.buf);
+       iter->ref_store = ref_store;
+       strbuf_release(&sb);
        return ref_iterator;
 }
 
-int for_each_reflog(each_ref_fn fn, void *cb_data)
-{
-       return do_for_each_ref_iterator(files_reflog_iterator_begin(),
-                                       fn, cb_data);
-}
-
 static int ref_update_reject_duplicates(struct string_list *refnames,
                                        struct strbuf *err)
 {
@@ -3460,7 +2649,8 @@ static int split_head_update(struct ref_update *update,
  * Note that the new update will itself be subject to splitting when
  * the iteration gets to it.
  */
-static int split_symref_update(struct ref_update *update,
+static int split_symref_update(struct files_ref_store *refs,
+                              struct ref_update *update,
                               const char *referent,
                               struct ref_transaction *transaction,
                               struct string_list *affected_refnames,
@@ -3574,7 +2764,8 @@ static int check_old_oid(struct ref_update *update, struct object_id *oid,
  * - If it is an update of head_ref, add a corresponding REF_LOG_ONLY
  *   update of HEAD.
  */
-static int lock_ref_for_update(struct ref_update *update,
+static int lock_ref_for_update(struct files_ref_store *refs,
+                              struct ref_update *update,
                               struct ref_transaction *transaction,
                               const char *head_ref,
                               struct string_list *affected_refnames,
@@ -3586,6 +2777,8 @@ static int lock_ref_for_update(struct ref_update *update,
        int ret;
        struct ref_lock *lock;
 
+       files_assert_main_repository(refs, "lock_ref_for_update");
+
        if ((update->flags & REF_HAVE_NEW) && is_null_sha1(update->new_sha1))
                update->flags |= REF_DELETING;
 
@@ -3596,11 +2789,10 @@ static int lock_ref_for_update(struct ref_update *update,
                        return ret;
        }
 
-       ret = lock_raw_ref(update->refname, mustexist,
+       ret = lock_raw_ref(refs, update->refname, mustexist,
                           affected_refnames, NULL,
-                          &update->lock, &referent,
+                          &lock, &referent,
                           &update->type, err);
-
        if (ret) {
                char *reason;
 
@@ -3611,7 +2803,7 @@ static int lock_ref_for_update(struct ref_update *update,
                return ret;
        }
 
-       lock = update->lock;
+       update->backend_data = lock;
 
        if (update->type & REF_ISSYMREF) {
                if (update->flags & REF_NODEREF) {
@@ -3620,8 +2812,9 @@ static int lock_ref_for_update(struct ref_update *update,
                         * the transaction, so we have to read it here
                         * to record and possibly check old_sha1:
                         */
-                       if (read_ref_full(referent.buf, 0,
-                                         lock->old_oid.hash, NULL)) {
+                       if (refs_read_ref_full(&refs->base,
+                                              referent.buf, 0,
+                                              lock->old_oid.hash, NULL)) {
                                if (update->flags & REF_HAVE_OLD) {
                                        strbuf_addf(err, "cannot lock ref '%s': "
                                                    "error reading reference",
@@ -3639,7 +2832,8 @@ static int lock_ref_for_update(struct ref_update *update,
                         * of processing the split-off update, so we
                         * don't have to do it here.
                         */
-                       ret = split_symref_update(update, referent.buf, transaction,
+                       ret = split_symref_update(refs, update,
+                                                 referent.buf, transaction,
                                                  affected_refnames, err);
                        if (ret)
                                return ret;
@@ -3658,7 +2852,8 @@ static int lock_ref_for_update(struct ref_update *update,
                for (parent_update = update->parent_update;
                     parent_update;
                     parent_update = parent_update->parent_update) {
-                       oidcpy(&parent_update->lock->old_oid, &lock->old_oid);
+                       struct ref_lock *parent_lock = parent_update->backend_data;
+                       oidcpy(&parent_lock->old_oid, &lock->old_oid);
                }
        }
 
@@ -3679,7 +2874,7 @@ static int lock_ref_for_update(struct ref_update *update,
                         * The lock was freed upon failure of
                         * write_ref_to_lockfile():
                         */
-                       update->lock = NULL;
+                       update->backend_data = NULL;
                        strbuf_addf(err,
                                    "cannot update ref '%s': %s",
                                    update->refname, write_err);
@@ -3704,9 +2899,13 @@ static int lock_ref_for_update(struct ref_update *update,
        return 0;
 }
 
-int ref_transaction_commit(struct ref_transaction *transaction,
-                          struct strbuf *err)
+static int files_transaction_commit(struct ref_store *ref_store,
+                                   struct ref_transaction *transaction,
+                                   struct strbuf *err)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE,
+                              "ref_transaction_commit");
        int ret = 0, i;
        struct string_list refs_to_delete = STRING_LIST_INIT_NODUP;
        struct string_list_item *ref_to_delete;
@@ -3714,6 +2913,7 @@ int ref_transaction_commit(struct ref_transaction *transaction,
        char *head_ref = NULL;
        int head_type;
        struct object_id head_oid;
+       struct strbuf sb = STRBUF_INIT;
 
        assert(err);
 
@@ -3768,8 +2968,9 @@ int ref_transaction_commit(struct ref_transaction *transaction,
         * head_ref within the transaction, then split_head_update()
         * arranges for the reflog of HEAD to be updated, too.
         */
-       head_ref = resolve_refdup("HEAD", RESOLVE_REF_NO_RECURSE,
-                                 head_oid.hash, &head_type);
+       head_ref = refs_resolve_refdup(ref_store, "HEAD",
+                                      RESOLVE_REF_NO_RECURSE,
+                                      head_oid.hash, &head_type);
 
        if (head_ref && !(head_type & REF_ISSYMREF)) {
                free(head_ref);
@@ -3785,8 +2986,8 @@ int ref_transaction_commit(struct ref_transaction *transaction,
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
 
-               ret = lock_ref_for_update(update, transaction, head_ref,
-                                         &affected_refnames, err);
+               ret = lock_ref_for_update(refs, update, transaction,
+                                         head_ref, &affected_refnames, err);
                if (ret)
                        goto cleanup;
        }
@@ -3794,30 +2995,33 @@ int ref_transaction_commit(struct ref_transaction *transaction,
        /* Perform updates first so live commits remain referenced */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
-               struct ref_lock *lock = update->lock;
+               struct ref_lock *lock = update->backend_data;
 
                if (update->flags & REF_NEEDS_COMMIT ||
                    update->flags & REF_LOG_ONLY) {
-                       if (log_ref_write(lock->ref_name, lock->old_oid.hash,
-                                         update->new_sha1,
-                                         update->msg, update->flags, err)) {
+                       if (files_log_ref_write(refs,
+                                               lock->ref_name,
+                                               lock->old_oid.hash,
+                                               update->new_sha1,
+                                               update->msg, update->flags,
+                                               err)) {
                                char *old_msg = strbuf_detach(err, NULL);
 
                                strbuf_addf(err, "cannot update the ref '%s': %s",
                                            lock->ref_name, old_msg);
                                free(old_msg);
                                unlock_ref(lock);
-                               update->lock = NULL;
+                               update->backend_data = NULL;
                                ret = TRANSACTION_GENERIC_ERROR;
                                goto cleanup;
                        }
                }
                if (update->flags & REF_NEEDS_COMMIT) {
-                       clear_loose_ref_cache(&ref_cache);
+                       clear_loose_ref_cache(refs);
                        if (commit_ref(lock)) {
                                strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
                                unlock_ref(lock);
-                               update->lock = NULL;
+                               update->backend_data = NULL;
                                ret = TRANSACTION_GENERIC_ERROR;
                                goto cleanup;
                        }
@@ -3826,34 +3030,67 @@ int ref_transaction_commit(struct ref_transaction *transaction,
        /* Perform deletes now that updates are safely completed */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
+               struct ref_lock *lock = update->backend_data;
 
                if (update->flags & REF_DELETING &&
                    !(update->flags & REF_LOG_ONLY)) {
-                       if (delete_ref_loose(update->lock, update->type, err)) {
-                               ret = TRANSACTION_GENERIC_ERROR;
-                               goto cleanup;
+                       if (!(update->type & REF_ISPACKED) ||
+                           update->type & REF_ISSYMREF) {
+                               /* It is a loose reference. */
+                               strbuf_reset(&sb);
+                               files_ref_path(refs, &sb, lock->ref_name);
+                               if (unlink_or_msg(sb.buf, err)) {
+                                       ret = TRANSACTION_GENERIC_ERROR;
+                                       goto cleanup;
+                               }
+                               update->flags |= REF_DELETED_LOOSE;
                        }
 
                        if (!(update->flags & REF_ISPRUNING))
                                string_list_append(&refs_to_delete,
-                                                  update->lock->ref_name);
+                                                  lock->ref_name);
                }
        }
 
-       if (repack_without_refs(&refs_to_delete, err)) {
+       if (repack_without_refs(refs, &refs_to_delete, err)) {
                ret = TRANSACTION_GENERIC_ERROR;
                goto cleanup;
        }
-       for_each_string_list_item(ref_to_delete, &refs_to_delete)
-               unlink_or_warn(git_path("logs/%s", ref_to_delete->string));
-       clear_loose_ref_cache(&ref_cache);
+
+       /* Delete the reflogs of any references that were deleted: */
+       for_each_string_list_item(ref_to_delete, &refs_to_delete) {
+               strbuf_reset(&sb);
+               files_reflog_path(refs, &sb, ref_to_delete->string);
+               if (!unlink_or_warn(sb.buf))
+                       try_remove_empty_parents(refs, ref_to_delete->string,
+                                                REMOVE_EMPTY_PARENTS_REFLOG);
+       }
+
+       clear_loose_ref_cache(refs);
 
 cleanup:
+       strbuf_release(&sb);
        transaction->state = REF_TRANSACTION_CLOSED;
 
-       for (i = 0; i < transaction->nr; i++)
-               if (transaction->updates[i]->lock)
-                       unlock_ref(transaction->updates[i]->lock);
+       for (i = 0; i < transaction->nr; i++) {
+               struct ref_update *update = transaction->updates[i];
+               struct ref_lock *lock = update->backend_data;
+
+               if (lock)
+                       unlock_ref(lock);
+
+               if (update->flags & REF_DELETED_LOOSE) {
+                       /*
+                        * The loose reference was deleted. Delete any
+                        * empty parent directories. (Note that this
+                        * can only work because we have already
+                        * removed the lockfile.)
+                        */
+                       try_remove_empty_parents(refs, update->refname,
+                                                REMOVE_EMPTY_PARENTS_REF);
+               }
+       }
+
        string_list_clear(&refs_to_delete, 0);
        free(head_ref);
        string_list_clear(&affected_refnames, 0);
@@ -3869,9 +3106,13 @@ static int ref_present(const char *refname,
        return string_list_has_string(affected_refnames, refname);
 }
 
-int initial_ref_transaction_commit(struct ref_transaction *transaction,
-                                  struct strbuf *err)
+static int files_initial_transaction_commit(struct ref_store *ref_store,
+                                           struct ref_transaction *transaction,
+                                           struct strbuf *err)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE,
+                              "initial_ref_transaction_commit");
        int ret = 0, i;
        struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
 
@@ -3902,7 +3143,8 @@ int initial_ref_transaction_commit(struct ref_transaction *transaction,
         * so here we really only check that none of the references
         * that we are creating already exists.
         */
-       if (for_each_rawref(ref_present, &affected_refnames))
+       if (refs_for_each_rawref(&refs->base, ref_present,
+                                &affected_refnames))
                die("BUG: initial ref transaction called with existing refs");
 
        for (i = 0; i < transaction->nr; i++) {
@@ -3911,15 +3153,15 @@ int initial_ref_transaction_commit(struct ref_transaction *transaction,
                if ((update->flags & REF_HAVE_OLD) &&
                    !is_null_sha1(update->old_sha1))
                        die("BUG: initial ref transaction with old_sha1 set");
-               if (verify_refname_available(update->refname,
-                                            &affected_refnames, NULL,
-                                            err)) {
+               if (refs_verify_refname_available(&refs->base, update->refname,
+                                                 &affected_refnames, NULL,
+                                                 err)) {
                        ret = TRANSACTION_NAME_CONFLICT;
                        goto cleanup;
                }
        }
 
-       if (lock_packed_refs(0)) {
+       if (lock_packed_refs(refs, 0)) {
                strbuf_addf(err, "unable to lock packed-refs file: %s",
                            strerror(errno));
                ret = TRANSACTION_GENERIC_ERROR;
@@ -3931,10 +3173,10 @@ int initial_ref_transaction_commit(struct ref_transaction *transaction,
 
                if ((update->flags & REF_HAVE_NEW) &&
                    !is_null_sha1(update->new_sha1))
-                       add_packed_ref(update->refname, update->new_sha1);
+                       add_packed_ref(refs, update->refname, update->new_sha1);
        }
 
-       if (commit_packed_refs()) {
+       if (commit_packed_refs(refs)) {
                strbuf_addf(err, "unable to commit packed-refs file: %s",
                            strerror(errno));
                ret = TRANSACTION_GENERIC_ERROR;
@@ -3952,10 +3194,10 @@ struct expire_reflog_cb {
        reflog_expiry_should_prune_fn *should_prune_fn;
        void *policy_cb;
        FILE *newlog;
-       unsigned char last_kept_sha1[20];
+       struct object_id last_kept_oid;
 };
 
-static int expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
+static int expire_reflog_ent(struct object_id *ooid, struct object_id *noid,
                             const char *email, unsigned long timestamp, int tz,
                             const char *message, void *cb_data)
 {
@@ -3963,9 +3205,9 @@ static int expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
        struct expire_reflog_policy_cb *policy_cb = cb->policy_cb;
 
        if (cb->flags & EXPIRE_REFLOGS_REWRITE)
-               osha1 = cb->last_kept_sha1;
+               ooid = &cb->last_kept_oid;
 
-       if ((*cb->should_prune_fn)(osha1, nsha1, email, timestamp, tz,
+       if ((*cb->should_prune_fn)(ooid->hash, noid->hash, email, timestamp, tz,
                                   message, policy_cb)) {
                if (!cb->newlog)
                        printf("would prune %s", message);
@@ -3974,9 +3216,9 @@ static int expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
        } else {
                if (cb->newlog) {
                        fprintf(cb->newlog, "%s %s %s %lu %+05d\t%s",
-                               sha1_to_hex(osha1), sha1_to_hex(nsha1),
+                               oid_to_hex(ooid), oid_to_hex(noid),
                                email, timestamp, tz, message);
-                       hashcpy(cb->last_kept_sha1, nsha1);
+                       oidcpy(&cb->last_kept_oid, noid);
                }
                if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
                        printf("keep %s", message);
@@ -3984,16 +3226,20 @@ static int expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
        return 0;
 }
 
-int reflog_expire(const char *refname, const unsigned char *sha1,
-                unsigned int flags,
-                reflog_expiry_prepare_fn prepare_fn,
-                reflog_expiry_should_prune_fn should_prune_fn,
-                reflog_expiry_cleanup_fn cleanup_fn,
-                void *policy_cb_data)
+static int files_reflog_expire(struct ref_store *ref_store,
+                              const char *refname, const unsigned char *sha1,
+                              unsigned int flags,
+                              reflog_expiry_prepare_fn prepare_fn,
+                              reflog_expiry_should_prune_fn should_prune_fn,
+                              reflog_expiry_cleanup_fn cleanup_fn,
+                              void *policy_cb_data)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "reflog_expire");
        static struct lock_file reflog_lock;
        struct expire_reflog_cb cb;
        struct ref_lock *lock;
+       struct strbuf log_file_sb = STRBUF_INIT;
        char *log_file;
        int status = 0;
        int type;
@@ -4009,19 +3255,21 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
         * reference itself, plus we might need to update the
         * reference if --updateref was specified:
         */
-       lock = lock_ref_sha1_basic(refname, sha1, NULL, NULL, REF_NODEREF,
+       lock = lock_ref_sha1_basic(refs, refname, sha1,
+                                  NULL, NULL, REF_NODEREF,
                                   &type, &err);
        if (!lock) {
                error("cannot lock ref '%s': %s", refname, err.buf);
                strbuf_release(&err);
                return -1;
        }
-       if (!reflog_exists(refname)) {
+       if (!refs_reflog_exists(ref_store, refname)) {
                unlock_ref(lock);
                return 0;
        }
 
-       log_file = git_pathdup("logs/%s", refname);
+       files_reflog_path(refs, &log_file_sb, refname);
+       log_file = strbuf_detach(&log_file_sb, NULL);
        if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
                /*
                 * Even though holding $GIT_DIR/logs/$reflog.lock has
@@ -4046,7 +3294,7 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
        }
 
        (*prepare_fn)(refname, sha1, cb.policy_cb);
-       for_each_reflog_ent(refname, expire_reflog_ent, &cb);
+       refs_for_each_reflog_ent(ref_store, refname, expire_reflog_ent, &cb);
        (*cleanup_fn)(cb.policy_cb);
 
        if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
@@ -4059,14 +3307,14 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
                 */
                int update = (flags & EXPIRE_REFLOGS_UPDATE_REF) &&
                        !(type & REF_ISSYMREF) &&
-                       !is_null_sha1(cb.last_kept_sha1);
+                       !is_null_oid(&cb.last_kept_oid);
 
                if (close_lock_file(&reflog_lock)) {
                        status |= error("couldn't write %s: %s", log_file,
                                        strerror(errno));
                } else if (update &&
                           (write_in_full(get_lock_file_fd(lock->lk),
-                               sha1_to_hex(cb.last_kept_sha1), 40) != 40 ||
+                               oid_to_hex(&cb.last_kept_oid), GIT_SHA1_HEXSZ) != GIT_SHA1_HEXSZ ||
                            write_str_in_full(get_lock_file_fd(lock->lk), "\n") != 1 ||
                            close_ref(lock) < 0)) {
                        status |= error("couldn't write %s",
@@ -4089,3 +3337,49 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
        unlock_ref(lock);
        return -1;
 }
+
+static int files_init_db(struct ref_store *ref_store, struct strbuf *err)
+{
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "init_db");
+       struct strbuf sb = STRBUF_INIT;
+
+       /*
+        * Create .git/refs/{heads,tags}
+        */
+       files_ref_path(refs, &sb, "refs/heads");
+       safe_create_dir(sb.buf, 1);
+
+       strbuf_reset(&sb);
+       files_ref_path(refs, &sb, "refs/tags");
+       safe_create_dir(sb.buf, 1);
+
+       strbuf_release(&sb);
+       return 0;
+}
+
+struct ref_storage_be refs_be_files = {
+       NULL,
+       "files",
+       files_ref_store_create,
+       files_init_db,
+       files_transaction_commit,
+       files_initial_transaction_commit,
+
+       files_pack_refs,
+       files_peel_ref,
+       files_create_symref,
+       files_delete_refs,
+       files_rename_ref,
+
+       files_ref_iterator_begin,
+       files_read_raw_ref,
+
+       files_reflog_iterator_begin,
+       files_for_each_reflog_ent,
+       files_for_each_reflog_ent_reverse,
+       files_reflog_exists,
+       files_create_reflog,
+       files_delete_reflog,
+       files_reflog_expire
+};