Merge branch 'mh/packed-ref-store' into next
authorJunio C Hamano <gitster@pobox.com>
Mon, 14 Aug 2017 22:22:50 +0000 (15:22 -0700)
committerJunio C Hamano <gitster@pobox.com>
Mon, 14 Aug 2017 22:22:50 +0000 (15:22 -0700)
The "ref-store" code reorganization continues.

* mh/packed-ref-store: (31 commits)
packed_ref_store: handle a packed-refs file that is a symlink
read_packed_refs(): die if `packed-refs` contains bogus data
t3210: add some tests of bogus packed-refs file contents
repack_without_refs(): don't lock or unlock the packed refs
commit_packed_refs(): remove call to `packed_refs_unlock()`
clear_packed_ref_cache(): don't protest if the lock is held
packed_refs_unlock(), packed_refs_is_locked(): new functions
packed_refs_lock(): report errors via a `struct strbuf *err`
packed_refs_lock(): function renamed from lock_packed_refs()
commit_packed_refs(): use a staging file separate from the lockfile
commit_packed_refs(): report errors rather than dying
packed_ref_store: make class into a subclass of `ref_store`
packed-backend: new module for handling packed references
packed_read_raw_ref(): new function, replacing `resolve_packed_ref()`
packed_ref_store: support iteration
packed_peel_ref(): new function, extracted from `files_peel_ref()`
repack_without_refs(): take a `packed_ref_store *` parameter
get_packed_ref(): take a `packed_ref_store *` parameter
rollback_packed_refs(): take a `packed_ref_store *` parameter
commit_packed_refs(): take a `packed_ref_store *` parameter
...

1  2 
Makefile
refs.c
refs/files-backend.c
refs/packed-backend.c
diff --cc Makefile
Simple merge
diff --cc refs.c
Simple merge
Simple merge
index 0000000000000000000000000000000000000000,59e7d1a5097b51f2358e4970a5253c20c02abe82..412c85034fc3b8632f16d13c4d467ad41060ddeb
mode 000000,100644..100644
--- /dev/null
@@@ -1,0 -1,884 +1,885 @@@
+ #include "../cache.h"
++#include "../config.h"
+ #include "../refs.h"
+ #include "refs-internal.h"
+ #include "ref-cache.h"
+ #include "packed-backend.h"
+ #include "../iterator.h"
+ #include "../lockfile.h"
+ struct packed_ref_cache {
+       struct ref_cache *cache;
+       /*
+        * Count of references to the data structure in this instance,
+        * 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;
+       /* The metadata from when this packed-refs cache was read */
+       struct stat_validity validity;
+ };
+ /*
+  * Increment the reference count of *packed_refs.
+  */
+ static void acquire_packed_ref_cache(struct packed_ref_cache *packed_refs)
+ {
+       packed_refs->referrers++;
+ }
+ /*
+  * Decrease the reference count of *packed_refs.  If it goes to zero,
+  * free *packed_refs and return true; otherwise return false.
+  */
+ static int release_packed_ref_cache(struct packed_ref_cache *packed_refs)
+ {
+       if (!--packed_refs->referrers) {
+               free_ref_cache(packed_refs->cache);
+               stat_validity_clear(&packed_refs->validity);
+               free(packed_refs);
+               return 1;
+       } else {
+               return 0;
+       }
+ }
+ /*
+  * A container for `packed-refs`-related data. It is not (yet) a
+  * `ref_store`.
+  */
+ struct packed_ref_store {
+       struct ref_store base;
+       unsigned int store_flags;
+       /* The path of the "packed-refs" file: */
+       char *path;
+       /*
+        * A cache of the values read from the `packed-refs` file, if
+        * it might still be current; otherwise, NULL.
+        */
+       struct packed_ref_cache *cache;
+       /*
+        * Lock used for the "packed-refs" file. Note that this (and
+        * thus the enclosing `packed_ref_store`) must not be freed.
+        */
+       struct lock_file lock;
+       /*
+        * Temporary file used when rewriting new contents to the
+        * "packed-refs" file. Note that this (and thus the enclosing
+        * `packed_ref_store`) must not be freed.
+        */
+       struct tempfile tempfile;
+ };
+ struct ref_store *packed_ref_store_create(const char *path,
+                                         unsigned int store_flags)
+ {
+       struct packed_ref_store *refs = xcalloc(1, sizeof(*refs));
+       struct ref_store *ref_store = (struct ref_store *)refs;
+       base_ref_store_init(ref_store, &refs_be_packed);
+       refs->store_flags = store_flags;
+       refs->path = xstrdup(path);
+       return ref_store;
+ }
+ /*
+  * Die if refs is not the main ref store. caller is used in any
+  * necessary error messages.
+  */
+ static void packed_assert_main_repository(struct packed_ref_store *refs,
+                                         const char *caller)
+ {
+       if (refs->store_flags & REF_STORE_MAIN)
+               return;
+       die("BUG: operation %s only allowed for main ref store", caller);
+ }
+ /*
+  * Downcast `ref_store` to `packed_ref_store`. Die if `ref_store` is
+  * not a `packed_ref_store`. Also die if `packed_ref_store` doesn't
+  * support at least the flags specified in `required_flags`. `caller`
+  * is used in any necessary error messages.
+  */
+ static struct packed_ref_store *packed_downcast(struct ref_store *ref_store,
+                                               unsigned int required_flags,
+                                               const char *caller)
+ {
+       struct packed_ref_store *refs;
+       if (ref_store->be != &refs_be_packed)
+               die("BUG: ref_store is type \"%s\" not \"packed\" in %s",
+                   ref_store->be->name, caller);
+       refs = (struct packed_ref_store *)ref_store;
+       if ((refs->store_flags & required_flags) != required_flags)
+               die("BUG: unallowed operation (%s), requires %x, has %x\n",
+                   caller, required_flags, refs->store_flags);
+       return refs;
+ }
+ static void clear_packed_ref_cache(struct packed_ref_store *refs)
+ {
+       if (refs->cache) {
+               struct packed_ref_cache *cache = refs->cache;
+               refs->cache = NULL;
+               release_packed_ref_cache(cache);
+       }
+ }
+ /* The length of a peeled reference line in packed-refs, including EOL: */
+ #define PEELED_LINE_LENGTH 42
+ /*
+  * Parse one line from a packed-refs file.  Write the SHA1 to sha1.
+  * Return a pointer to the refname within the line (null-terminated),
+  * or NULL if there was a problem.
+  */
+ static const char *parse_ref_line(struct strbuf *line, struct object_id *oid)
+ {
+       const char *ref;
+       if (parse_oid_hex(line->buf, oid, &ref) < 0)
+               return NULL;
+       if (!isspace(*ref++))
+               return NULL;
+       if (isspace(*ref))
+               return NULL;
+       if (line->buf[line->len - 1] != '\n')
+               return NULL;
+       line->buf[--line->len] = 0;
+       return ref;
+ }
+ /*
+  * Read from `packed_refs_file` into a newly-allocated
+  * `packed_ref_cache` and return it. The return value will already
+  * have its reference count incremented.
+  *
+  * A comment line of the form "# pack-refs with: " may contain zero or
+  * more traits. We interpret the traits as follows:
+  *
+  *   No traits:
+  *
+  *      Probably no references are peeled. But if the file contains a
+  *      peeled value for a reference, we will use it.
+  *
+  *   peeled:
+  *
+  *      References under "refs/tags/", if they *can* be peeled, *are*
+  *      peeled in this file. References outside of "refs/tags/" are
+  *      probably not peeled even if they could have been, but if we find
+  *      a peeled value for such a reference we will use it.
+  *
+  *   fully-peeled:
+  *
+  *      All references in the file that can be peeled are peeled.
+  *      Inversely (and this is more important), any references in the
+  *      file for which no peeled value is recorded is not peelable. This
+  *      trait should typically be written alongside "peeled" for
+  *      compatibility with older clients, but we do not require it
+  *      (i.e., "peeled" is a no-op if "fully-peeled" is set).
+  */
+ static struct packed_ref_cache *read_packed_refs(const char *packed_refs_file)
+ {
+       FILE *f;
+       struct packed_ref_cache *packed_refs = xcalloc(1, sizeof(*packed_refs));
+       struct ref_entry *last = NULL;
+       struct strbuf line = STRBUF_INIT;
+       enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE;
+       struct ref_dir *dir;
+       acquire_packed_ref_cache(packed_refs);
+       packed_refs->cache = create_ref_cache(NULL, NULL);
+       packed_refs->cache->root->flag &= ~REF_INCOMPLETE;
+       f = fopen(packed_refs_file, "r");
+       if (!f) {
+               if (errno == ENOENT) {
+                       /*
+                        * This is OK; it just means that no
+                        * "packed-refs" file has been written yet,
+                        * which is equivalent to it being empty.
+                        */
+                       return packed_refs;
+               } else {
+                       die_errno("couldn't read %s", packed_refs_file);
+               }
+       }
+       stat_validity_update(&packed_refs->validity, fileno(f));
+       dir = get_ref_dir(packed_refs->cache->root);
+       while (strbuf_getwholeline(&line, f, '\n') != EOF) {
+               struct object_id oid;
+               const char *refname;
+               const char *traits;
+               if (!line.len || line.buf[line.len - 1] != '\n')
+                       die("unterminated line in %s: %s", packed_refs_file, line.buf);
+               if (skip_prefix(line.buf, "# pack-refs with:", &traits)) {
+                       if (strstr(traits, " fully-peeled "))
+                               peeled = PEELED_FULLY;
+                       else if (strstr(traits, " peeled "))
+                               peeled = PEELED_TAGS;
+                       /* perhaps other traits later as well */
+                       continue;
+               }
+               refname = parse_ref_line(&line, &oid);
+               if (refname) {
+                       int flag = REF_ISPACKED;
+                       if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
+                               if (!refname_is_safe(refname))
+                                       die("packed refname is dangerous: %s", refname);
+                               oidclr(&oid);
+                               flag |= REF_BAD_NAME | REF_ISBROKEN;
+                       }
+                       last = create_ref_entry(refname, &oid, flag);
+                       if (peeled == PEELED_FULLY ||
+                           (peeled == PEELED_TAGS && starts_with(refname, "refs/tags/")))
+                               last->flag |= REF_KNOWS_PEELED;
+                       add_ref_entry(dir, last);
+               } else if (last &&
+                   line.buf[0] == '^' &&
+                   line.len == PEELED_LINE_LENGTH &&
+                   line.buf[PEELED_LINE_LENGTH - 1] == '\n' &&
+                   !get_oid_hex(line.buf + 1, &oid)) {
+                       oidcpy(&last->u.value.peeled, &oid);
+                       /*
+                        * Regardless of what the file header said,
+                        * we definitely know the value of *this*
+                        * reference:
+                        */
+                       last->flag |= REF_KNOWS_PEELED;
+               } else {
+                       strbuf_setlen(&line, line.len - 1);
+                       die("unexpected line in %s: %s", packed_refs_file, line.buf);
+               }
+       }
+       fclose(f);
+       strbuf_release(&line);
+       return packed_refs;
+ }
+ /*
+  * Check that the packed refs cache (if any) still reflects the
+  * contents of the file. If not, clear the cache.
+  */
+ static void validate_packed_ref_cache(struct packed_ref_store *refs)
+ {
+       if (refs->cache &&
+           !stat_validity_check(&refs->cache->validity, refs->path))
+               clear_packed_ref_cache(refs);
+ }
+ /*
+  * Get the packed_ref_cache for the specified packed_ref_store,
+  * creating and populating it if it hasn't been read before or if the
+  * file has been changed (according to its `validity` field) since it
+  * was last read. On the other hand, if we hold the lock, then assume
+  * that the file hasn't been changed out from under us, so skip the
+  * extra `stat()` call in `stat_validity_check()`.
+  */
+ static struct packed_ref_cache *get_packed_ref_cache(struct packed_ref_store *refs)
+ {
+       if (!is_lock_file_locked(&refs->lock))
+               validate_packed_ref_cache(refs);
+       if (!refs->cache)
+               refs->cache = read_packed_refs(refs->path);
+       return refs->cache;
+ }
+ static struct ref_dir *get_packed_ref_dir(struct packed_ref_cache *packed_ref_cache)
+ {
+       return get_ref_dir(packed_ref_cache->cache->root);
+ }
+ static struct ref_dir *get_packed_refs(struct packed_ref_store *refs)
+ {
+       return get_packed_ref_dir(get_packed_ref_cache(refs));
+ }
+ /*
+  * Add or overwrite a reference in the in-memory packed reference
+  * cache. This may only be called while the packed-refs file is locked
+  * (see packed_refs_lock()). To actually write the packed-refs file,
+  * call commit_packed_refs().
+  */
+ void add_packed_ref(struct ref_store *ref_store,
+                   const char *refname, const struct object_id *oid)
+ {
+       struct packed_ref_store *refs =
+               packed_downcast(ref_store, REF_STORE_WRITE,
+                               "add_packed_ref");
+       struct ref_dir *packed_refs;
+       struct ref_entry *packed_entry;
+       if (!is_lock_file_locked(&refs->lock))
+               die("BUG: packed refs not locked");
+       if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
+               die("Reference has invalid format: '%s'", refname);
+       packed_refs = get_packed_refs(refs);
+       packed_entry = find_ref_entry(packed_refs, refname);
+       if (packed_entry) {
+               /* Overwrite the existing entry: */
+               oidcpy(&packed_entry->u.value.oid, oid);
+               packed_entry->flag = REF_ISPACKED;
+               oidclr(&packed_entry->u.value.peeled);
+       } else {
+               packed_entry = create_ref_entry(refname, oid, REF_ISPACKED);
+               add_ref_entry(packed_refs, packed_entry);
+       }
+ }
+ /*
+  * 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(struct packed_ref_store *refs,
+                                       const char *refname)
+ {
+       return find_ref_entry(get_packed_refs(refs), refname);
+ }
+ static int packed_read_raw_ref(struct ref_store *ref_store,
+                              const char *refname, unsigned char *sha1,
+                              struct strbuf *referent, unsigned int *type)
+ {
+       struct packed_ref_store *refs =
+               packed_downcast(ref_store, REF_STORE_READ, "read_raw_ref");
+       struct ref_entry *entry;
+       *type = 0;
+       entry = get_packed_ref(refs, refname);
+       if (!entry) {
+               errno = ENOENT;
+               return -1;
+       }
+       hashcpy(sha1, entry->u.value.oid.hash);
+       *type = REF_ISPACKED;
+       return 0;
+ }
+ static int packed_peel_ref(struct ref_store *ref_store,
+                          const char *refname, unsigned char *sha1)
+ {
+       struct packed_ref_store *refs =
+               packed_downcast(ref_store, REF_STORE_READ | REF_STORE_ODB,
+                               "peel_ref");
+       struct ref_entry *r = get_packed_ref(refs, refname);
+       if (!r || peel_entry(r, 0))
+               return -1;
+       hashcpy(sha1, r->u.value.peeled.hash);
+       return 0;
+ }
+ struct packed_ref_iterator {
+       struct ref_iterator base;
+       struct packed_ref_cache *cache;
+       struct ref_iterator *iter0;
+       unsigned int flags;
+ };
+ static int packed_ref_iterator_advance(struct ref_iterator *ref_iterator)
+ {
+       struct packed_ref_iterator *iter =
+               (struct packed_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,
+                                           iter->iter0->flags))
+                       continue;
+               iter->base.refname = iter->iter0->refname;
+               iter->base.oid = iter->iter0->oid;
+               iter->base.flags = iter->iter0->flags;
+               return ITER_OK;
+       }
+       iter->iter0 = NULL;
+       if (ref_iterator_abort(ref_iterator) != ITER_DONE)
+               ok = ITER_ERROR;
+       return ok;
+ }
+ static int packed_ref_iterator_peel(struct ref_iterator *ref_iterator,
+                                  struct object_id *peeled)
+ {
+       struct packed_ref_iterator *iter =
+               (struct packed_ref_iterator *)ref_iterator;
+       return ref_iterator_peel(iter->iter0, peeled);
+ }
+ static int packed_ref_iterator_abort(struct ref_iterator *ref_iterator)
+ {
+       struct packed_ref_iterator *iter =
+               (struct packed_ref_iterator *)ref_iterator;
+       int ok = ITER_DONE;
+       if (iter->iter0)
+               ok = ref_iterator_abort(iter->iter0);
+       release_packed_ref_cache(iter->cache);
+       base_ref_iterator_free(ref_iterator);
+       return ok;
+ }
+ static struct ref_iterator_vtable packed_ref_iterator_vtable = {
+       packed_ref_iterator_advance,
+       packed_ref_iterator_peel,
+       packed_ref_iterator_abort
+ };
+ static struct ref_iterator *packed_ref_iterator_begin(
+               struct ref_store *ref_store,
+               const char *prefix, unsigned int flags)
+ {
+       struct packed_ref_store *refs;
+       struct packed_ref_iterator *iter;
+       struct ref_iterator *ref_iterator;
+       unsigned int required_flags = REF_STORE_READ;
+       if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN))
+               required_flags |= REF_STORE_ODB;
+       refs = packed_downcast(ref_store, required_flags, "ref_iterator_begin");
+       iter = xcalloc(1, sizeof(*iter));
+       ref_iterator = &iter->base;
+       base_ref_iterator_init(ref_iterator, &packed_ref_iterator_vtable);
+       /*
+        * Note that get_packed_ref_cache() internally checks whether
+        * the packed-ref cache is up to date with what is on disk,
+        * and re-reads it if not.
+        */
+       iter->cache = get_packed_ref_cache(refs);
+       acquire_packed_ref_cache(iter->cache);
+       iter->iter0 = cache_ref_iterator_begin(iter->cache->cache, prefix, 0);
+       iter->flags = flags;
+       return ref_iterator;
+ }
+ /*
+  * 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. On
+  * error, return a nonzero value and leave errno set at the value left
+  * by the failing call to `fprintf()`.
+  */
+ static int write_packed_entry(FILE *fh, const char *refname,
+                             const unsigned char *sha1,
+                             const unsigned char *peeled)
+ {
+       if (fprintf(fh, "%s %s\n", sha1_to_hex(sha1), refname) < 0 ||
+           (peeled && fprintf(fh, "^%s\n", sha1_to_hex(peeled)) < 0))
+               return -1;
+       return 0;
+ }
+ int packed_refs_lock(struct ref_store *ref_store, int flags, struct strbuf *err)
+ {
+       struct packed_ref_store *refs =
+               packed_downcast(ref_store, REF_STORE_WRITE | REF_STORE_MAIN,
+                               "packed_refs_lock");
+       static int timeout_configured = 0;
+       static int timeout_value = 1000;
+       struct packed_ref_cache *packed_ref_cache;
+       if (!timeout_configured) {
+               git_config_get_int("core.packedrefstimeout", &timeout_value);
+               timeout_configured = 1;
+       }
+       /*
+        * Note that we close the lockfile immediately because we
+        * don't write new content to it, but rather to a separate
+        * tempfile.
+        */
+       if (hold_lock_file_for_update_timeout(
+                           &refs->lock,
+                           refs->path,
+                           flags, timeout_value) < 0) {
+               unable_to_lock_message(refs->path, errno, err);
+               return -1;
+       }
+       if (close_lock_file(&refs->lock)) {
+               strbuf_addf(err, "unable to close %s: %s", refs->path, strerror(errno));
+               return -1;
+       }
+       /*
+        * Now that we hold the `packed-refs` lock, make sure that our
+        * cache matches the current version of the file. Normally
+        * `get_packed_ref_cache()` does that for us, but that
+        * function assumes that when the file is locked, any existing
+        * cache is still valid. We've just locked the file, but it
+        * might have changed the moment *before* we locked it.
+        */
+       validate_packed_ref_cache(refs);
+       packed_ref_cache = get_packed_ref_cache(refs);
+       /* Increment the reference count to prevent it from being freed: */
+       acquire_packed_ref_cache(packed_ref_cache);
+       return 0;
+ }
+ void packed_refs_unlock(struct ref_store *ref_store)
+ {
+       struct packed_ref_store *refs = packed_downcast(
+                       ref_store,
+                       REF_STORE_READ | REF_STORE_WRITE,
+                       "packed_refs_unlock");
+       if (!is_lock_file_locked(&refs->lock))
+               die("BUG: packed_refs_unlock() called when not locked");
+       rollback_lock_file(&refs->lock);
+       release_packed_ref_cache(refs->cache);
+ }
+ int packed_refs_is_locked(struct ref_store *ref_store)
+ {
+       struct packed_ref_store *refs = packed_downcast(
+                       ref_store,
+                       REF_STORE_READ | REF_STORE_WRITE,
+                       "packed_refs_is_locked");
+       return is_lock_file_locked(&refs->lock);
+ }
+ /*
+  * The packed-refs header line that we write out.  Perhaps other
+  * traits will be added later.  The trailing space is required.
+  */
+ static const char PACKED_REFS_HEADER[] =
+       "# pack-refs with: peeled fully-peeled \n";
+ /*
+  * Write the current version of the packed refs cache from memory to
+  * disk. The packed-refs file must already be locked for writing (see
+  * packed_refs_lock()). Return zero on success. On errors, rollback
+  * the lockfile, write an error message to `err`, and return a nonzero
+  * value.
+  */
+ int commit_packed_refs(struct ref_store *ref_store, struct strbuf *err)
+ {
+       struct packed_ref_store *refs =
+               packed_downcast(ref_store, REF_STORE_WRITE | REF_STORE_MAIN,
+                               "commit_packed_refs");
+       struct packed_ref_cache *packed_ref_cache =
+               get_packed_ref_cache(refs);
+       int ok;
+       int ret = -1;
+       struct strbuf sb = STRBUF_INIT;
+       FILE *out;
+       struct ref_iterator *iter;
+       char *packed_refs_path;
+       if (!is_lock_file_locked(&refs->lock))
+               die("BUG: commit_packed_refs() called when unlocked");
+       /*
+        * If packed-refs is a symlink, we want to overwrite the
+        * symlinked-to file, not the symlink itself. Also, put the
+        * staging file next to it:
+        */
+       packed_refs_path = get_locked_file_path(&refs->lock);
+       strbuf_addf(&sb, "%s.new", packed_refs_path);
+       if (create_tempfile(&refs->tempfile, sb.buf) < 0) {
+               strbuf_addf(err, "unable to create file %s: %s",
+                           sb.buf, strerror(errno));
+               strbuf_release(&sb);
+               goto out;
+       }
+       strbuf_release(&sb);
+       out = fdopen_tempfile(&refs->tempfile, "w");
+       if (!out) {
+               strbuf_addf(err, "unable to fdopen packed-refs tempfile: %s",
+                           strerror(errno));
+               goto error;
+       }
+       if (fprintf(out, "%s", PACKED_REFS_HEADER) < 0) {
+               strbuf_addf(err, "error writing to %s: %s",
+                           get_tempfile_path(&refs->tempfile), strerror(errno));
+               goto error;
+       }
+       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);
+               if (write_packed_entry(out, iter->refname, iter->oid->hash,
+                                      peel_error ? NULL : peeled.hash)) {
+                       strbuf_addf(err, "error writing to %s: %s",
+                                   get_tempfile_path(&refs->tempfile),
+                                   strerror(errno));
+                       ref_iterator_abort(iter);
+                       goto error;
+               }
+       }
+       if (ok != ITER_DONE) {
+               strbuf_addf(err, "unable to rewrite packed-refs file: "
+                           "error iterating over old contents");
+               goto error;
+       }
+       if (rename_tempfile(&refs->tempfile, packed_refs_path)) {
+               strbuf_addf(err, "error replacing %s: %s",
+                           refs->path, strerror(errno));
+               goto out;
+       }
+       ret = 0;
+       goto out;
+ error:
+       delete_tempfile(&refs->tempfile);
+ out:
+       free(packed_refs_path);
+       return ret;
+ }
+ /*
+  * Rewrite the packed-refs file, omitting any refs listed in
+  * 'refnames'. On error, leave packed-refs unchanged, write an error
+  * message to 'err', and return a nonzero value. The packed refs lock
+  * must be held when calling this function; it will still be held when
+  * the function returns.
+  *
+  * The refs in 'refnames' needn't be sorted. `err` must not be NULL.
+  */
+ int repack_without_refs(struct ref_store *ref_store,
+                       struct string_list *refnames, struct strbuf *err)
+ {
+       struct packed_ref_store *refs =
+               packed_downcast(ref_store, REF_STORE_WRITE | REF_STORE_MAIN,
+                               "repack_without_refs");
+       struct ref_dir *packed;
+       struct string_list_item *refname;
+       int needs_repacking = 0, removed = 0;
+       packed_assert_main_repository(refs, "repack_without_refs");
+       assert(err);
+       if (!is_lock_file_locked(&refs->lock))
+               die("BUG: repack_without_refs called without holding lock");
+       /* Look for a packed ref */
+       for_each_string_list_item(refname, refnames) {
+               if (get_packed_ref(refs, refname->string)) {
+                       needs_repacking = 1;
+                       break;
+               }
+       }
+       /* Avoid locking if we have nothing to do */
+       if (!needs_repacking)
+               return 0; /* no refname exists in packed refs */
+       packed = get_packed_refs(refs);
+       /* Remove refnames from the cache */
+       for_each_string_list_item(refname, refnames)
+               if (remove_entry_from_dir(packed, refname->string) != -1)
+                       removed = 1;
+       if (!removed) {
+               /*
+                * All packed entries disappeared while we were
+                * acquiring the lock.
+                */
+               clear_packed_ref_cache(refs);
+               return 0;
+       }
+       /* Write what remains */
+       return commit_packed_refs(&refs->base, err);
+ }
+ static int packed_init_db(struct ref_store *ref_store, struct strbuf *err)
+ {
+       /* Nothing to do. */
+       return 0;
+ }
+ static int packed_transaction_prepare(struct ref_store *ref_store,
+                                     struct ref_transaction *transaction,
+                                     struct strbuf *err)
+ {
+       die("BUG: not implemented yet");
+ }
+ static int packed_transaction_abort(struct ref_store *ref_store,
+                                   struct ref_transaction *transaction,
+                                   struct strbuf *err)
+ {
+       die("BUG: not implemented yet");
+ }
+ static int packed_transaction_finish(struct ref_store *ref_store,
+                                    struct ref_transaction *transaction,
+                                    struct strbuf *err)
+ {
+       die("BUG: not implemented yet");
+ }
+ static int packed_initial_transaction_commit(struct ref_store *ref_store,
+                                           struct ref_transaction *transaction,
+                                           struct strbuf *err)
+ {
+       return ref_transaction_commit(transaction, err);
+ }
+ static int packed_delete_refs(struct ref_store *ref_store, const char *msg,
+                            struct string_list *refnames, unsigned int flags)
+ {
+       die("BUG: not implemented yet");
+ }
+ static int packed_pack_refs(struct ref_store *ref_store, unsigned int flags)
+ {
+       /*
+        * Packed refs are already packed. It might be that loose refs
+        * are packed *into* a packed refs store, but that is done by
+        * updating the packed references via a transaction.
+        */
+       return 0;
+ }
+ static int packed_create_symref(struct ref_store *ref_store,
+                              const char *refname, const char *target,
+                              const char *logmsg)
+ {
+       die("BUG: packed reference store does not support symrefs");
+ }
+ static int packed_rename_ref(struct ref_store *ref_store,
+                           const char *oldrefname, const char *newrefname,
+                           const char *logmsg)
+ {
+       die("BUG: packed reference store does not support renaming references");
+ }
+ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_store)
+ {
+       return empty_ref_iterator_begin();
+ }
+ static int packed_for_each_reflog_ent(struct ref_store *ref_store,
+                                     const char *refname,
+                                     each_reflog_ent_fn fn, void *cb_data)
+ {
+       return 0;
+ }
+ static int packed_for_each_reflog_ent_reverse(struct ref_store *ref_store,
+                                             const char *refname,
+                                             each_reflog_ent_fn fn,
+                                             void *cb_data)
+ {
+       return 0;
+ }
+ static int packed_reflog_exists(struct ref_store *ref_store,
+                              const char *refname)
+ {
+       return 0;
+ }
+ static int packed_create_reflog(struct ref_store *ref_store,
+                              const char *refname, int force_create,
+                              struct strbuf *err)
+ {
+       die("BUG: packed reference store does not support reflogs");
+ }
+ static int packed_delete_reflog(struct ref_store *ref_store,
+                              const char *refname)
+ {
+       return 0;
+ }
+ static int packed_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)
+ {
+       return 0;
+ }
+ struct ref_storage_be refs_be_packed = {
+       NULL,
+       "packed",
+       packed_ref_store_create,
+       packed_init_db,
+       packed_transaction_prepare,
+       packed_transaction_finish,
+       packed_transaction_abort,
+       packed_initial_transaction_commit,
+       packed_pack_refs,
+       packed_peel_ref,
+       packed_create_symref,
+       packed_delete_refs,
+       packed_rename_ref,
+       packed_ref_iterator_begin,
+       packed_read_raw_ref,
+       packed_reflog_iterator_begin,
+       packed_for_each_reflog_ent,
+       packed_for_each_reflog_ent_reverse,
+       packed_reflog_exists,
+       packed_create_reflog,
+       packed_delete_reflog,
+       packed_reflog_expire
+ };