refs: implement simple transactions for the packed-refs file
Handle simple transactions for the packed-refs file at the packed_ref_cache level via new functions lock_packed_refs(), commit_packed_refs(), and rollback_packed_refs(). Only allow the packed ref cache to be modified (via add_packed_ref()) while the packed refs file is locked. Change clone to add the new references within a transaction. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Michael Haggerty committed
Jun 20, 2013 at 10:37 UTC
9f69d297703bff37c5506276c2565c721347e03f
3 files changed
+98
-21
builtin/clone.c
+4
-1
@@ -493,13 +493,16 @@ static void write_remote_refs(const struct ref *local_refs)
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{
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const struct ref *r;
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+ lock_packed_refs(LOCK_DIE_ON_ERROR);
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+
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for (r = local_refs; r; r = r->next) {
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if (!r->peer_ref)
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continue;
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add_packed_ref(r->peer_ref->name, r->old_sha1);
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}
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- pack_refs(PACK_REFS_ALL);
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+ if (commit_packed_refs())
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+ die_errno("unable to overwrite old ref-pack file");
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}
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static void write_followtags(const struct ref *refs, const char *msg)
refs.c
+70
-18
@@ -808,6 +808,13 @@ static int is_refname_available(const char *refname, const char *oldrefname,
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struct packed_ref_cache {
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struct ref_entry *root;
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+
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+ /*
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+ * Iff the packed-refs file associated with this instance is
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+ * currently locked for writing, this points at the associated
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+ * lock (which is owned by somebody else).
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+ */
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+ struct lock_file *lock;
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};
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/*
@@ -826,9 +833,14 @@ static struct ref_cache {
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char name[1];
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} ref_cache, *submodule_ref_caches;
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+/* Lock used for the main packed-refs file: */
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+static struct lock_file packlock;
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+
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static void clear_packed_ref_cache(struct ref_cache *refs)
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{
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if (refs->packed) {
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+ if (refs->packed->lock)
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+ die("internal error: packed-ref cache cleared while locked");
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free_ref_entry(refs->packed->root);
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free(refs->packed);
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refs->packed = NULL;
@@ -1038,7 +1050,12 @@ static struct ref_dir *get_packed_refs(struct ref_cache *refs)
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void add_packed_ref(const char *refname, const unsigned char *sha1)
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{
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- add_ref(get_packed_refs(&ref_cache),
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+ struct packed_ref_cache *packed_ref_cache =
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+ get_packed_ref_cache(&ref_cache);
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+
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+ if (!packed_ref_cache->lock)
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+ die("internal error: packed refs not locked");
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+ add_ref(get_packed_ref_dir(packed_ref_cache),
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create_ref_entry(refname, sha1, REF_ISPACKED, 1));
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}
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@@ -2035,6 +2052,52 @@ static int write_packed_entry_fn(struct ref_entry *entry, void *cb_data)
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return 0;
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}
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+int lock_packed_refs(int flags)
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+{
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+ struct packed_ref_cache *packed_ref_cache;
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+
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+ /* Discard the old cache because it might be invalid: */
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+ clear_packed_ref_cache(&ref_cache);
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+ if (hold_lock_file_for_update(&packlock, git_path("packed-refs"), flags) < 0)
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+ return -1;
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+ /* Read the current packed-refs while holding the lock: */
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+ packed_ref_cache = get_packed_ref_cache(&ref_cache);
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+ packed_ref_cache->lock = &packlock;
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+ return 0;
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+}
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+
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+int commit_packed_refs(void)
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+{
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+ struct packed_ref_cache *packed_ref_cache =
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+ get_packed_ref_cache(&ref_cache);
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+ int error = 0;
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+
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+ if (!packed_ref_cache->lock)
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+ die("internal error: packed-refs not locked");
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+ write_or_die(packed_ref_cache->lock->fd,
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+ PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
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+
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+ do_for_each_entry_in_dir(get_packed_ref_dir(packed_ref_cache),
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+ 0, write_packed_entry_fn,
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+ &packed_ref_cache->lock->fd);
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+ if (commit_lock_file(packed_ref_cache->lock))
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+ error = -1;
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+ packed_ref_cache->lock = NULL;
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+ return error;
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+}
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+
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+void rollback_packed_refs(void)
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+{
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+ struct packed_ref_cache *packed_ref_cache =
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+ get_packed_ref_cache(&ref_cache);
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+
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+ if (!packed_ref_cache->lock)
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+ die("internal error: packed-refs not locked");
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+ rollback_lock_file(packed_ref_cache->lock);
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+ packed_ref_cache->lock = NULL;
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+ clear_packed_ref_cache(&ref_cache);
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+}
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+
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struct ref_to_prune {
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struct ref_to_prune *next;
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unsigned char sha1[20];
@@ -2148,28 +2211,22 @@ static void prune_refs(struct ref_to_prune *r)
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}
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}
2213
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-static struct lock_file packlock;
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-
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int pack_refs(unsigned int flags)
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{
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struct pack_refs_cb_data cbdata;
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- int fd;
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memset(&cbdata, 0, sizeof(cbdata));
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cbdata.flags = flags;
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- fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"),
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- LOCK_DIE_ON_ERROR);
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+ lock_packed_refs(LOCK_DIE_ON_ERROR);
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cbdata.packed_refs = get_packed_refs(&ref_cache);
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do_for_each_entry_in_dir(get_loose_refs(&ref_cache), 0,
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pack_if_possible_fn, &cbdata);
2226
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- write_or_die(fd, PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
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- do_for_each_entry_in_dir(cbdata.packed_refs, 0, write_packed_entry_fn, &fd);
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-
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- if (commit_lock_file(&packlock) < 0)
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+ if (commit_packed_refs())
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die_errno("unable to overwrite old ref-pack file");
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+
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prune_refs(cbdata.ref_to_prune);
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return 0;
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}
@@ -2233,7 +2290,6 @@ static int curate_packed_ref_fn(struct ref_entry *entry, void *cb_data)
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static int repack_without_ref(const char *refname)
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{
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- int fd;
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struct ref_dir *packed;
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struct string_list refs_to_delete = STRING_LIST_INIT_DUP;
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struct string_list_item *ref_to_delete;
@@ -2241,12 +2297,10 @@ static int repack_without_ref(const char *refname)
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if (!get_packed_ref(refname))
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return 0; /* refname does not exist in packed refs */
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- fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
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- if (fd < 0) {
2300
+ if (lock_packed_refs(0)) {
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unable_to_lock_error(git_path("packed-refs"), errno);
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return error("cannot delete '%s' from packed refs", refname);
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}
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- clear_packed_ref_cache(&ref_cache);
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packed = get_packed_refs(&ref_cache);
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/* Remove refname from the cache: */
@@ -2255,7 +2309,7 @@ static int repack_without_ref(const char *refname)
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* The packed entry disappeared while we were
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* acquiring the lock.
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*/
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- rollback_lock_file(&packlock);
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+ rollback_packed_refs();
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return 0;
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}
2315
@@ -2267,9 +2321,7 @@ static int repack_without_ref(const char *refname)
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}
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/* Write what remains: */
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- write_or_die(fd, PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
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- do_for_each_entry_in_dir(packed, 0, write_packed_entry_fn, &fd);
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- return commit_lock_file(&packlock);
2324
+ return commit_packed_refs();
2325
}
2326
2327
int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
refs.h
+24
-2
@@ -77,11 +77,33 @@ extern int for_each_rawref(each_ref_fn, void *);
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extern void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char *refname);
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/*
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- * Add a reference to the in-memory packed reference cache. To actually
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- * write the reference to the packed-refs file, call pack_refs().
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+ * Lock the packed-refs file for writing. Flags is passed to
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+ * hold_lock_file_for_update(). Return 0 on success.
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+ */
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+extern int lock_packed_refs(int flags);
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+
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+/*
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+ * Add a reference to the in-memory packed reference cache. This may
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+ * only be called while the packed-refs file is locked (see
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+ * lock_packed_refs()). To actually write the packed-refs file, call
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+ * commit_packed_refs().
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*/
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extern void add_packed_ref(const char *refname, const unsigned char *sha1);
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+/*
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+ * Write the current version of the packed refs cache from memory to
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+ * disk. The packed-refs file must already be locked for writing (see
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+ * lock_packed_refs()). Return zero on success.
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+ */
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+extern int commit_packed_refs(void);
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+
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+/*
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+ * Rollback the lockfile for the packed-refs file, and discard the
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+ * in-memory packed reference cache. (The packed-refs file will be
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+ * read anew if it is needed again after this function is called.)
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+ */
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+extern void rollback_packed_refs(void);
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+
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/*
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* Flags for controlling behaviour of pack_refs()
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* PACK_REFS_PRUNE: Prune loose refs after packing