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 <mhag...@alum.mit.edu>
---
The API docs are not clear about whether it is kosher to read
lock_file::fd directly. It is only done in one file outside of
lockfile.c. So this patch stores the fd of the lockfile separately in
struct packed_ref_cache, even though the same struct also has a
pointer to the struct lock_file.
So please let me know if it is OK to read lock_file::fd directly. If
so, then I will drop the fd member of struct packed_ref_cache, as well
as the local variable "fd" in lock_packed_refs().
builtin/clone.c | 7 ++++-
refs.c | 91 +++++++++++++++++++++++++++++++++++++++++++++++----------
refs.h | 27 +++++++++++++++--
3 files changed, 106 insertions(+), 19 deletions(-)
diff --git a/builtin/clone.c b/builtin/clone.c
index 66bff57..b0c000a 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -489,17 +489,22 @@ static struct ref *wanted_peer_refs(const struct ref
*refs,
return local_refs;
}
+static struct lock_file packed_refs_lock;
+
static void write_remote_refs(const struct ref *local_refs)
{
const struct ref *r;
+ lock_packed_refs(&packed_refs_lock, LOCK_DIE_ON_ERROR);
+
for (r = local_refs; r; r = r->next) {
if (!r->peer_ref)
continue;
add_packed_ref(r->peer_ref->name, r->old_sha1);
}
- pack_refs(PACK_REFS_ALL);
+ if (commit_packed_refs())
+ die_errno("unable to overwrite old ref-pack file");
}
static void write_followtags(const struct ref *refs, const char *msg)
diff --git a/refs.c b/refs.c
index 4cee36b..114bd5b 100644
--- a/refs.c
+++ b/refs.c
@@ -804,6 +804,16 @@ static int is_refname_available(const char *refname, const
char *oldrefname,
struct packed_ref_cache {
struct ref_entry *root;
+
+ /*
+ * Iff the packed-refs file associated with this instance is
+ * currently locked for writing, this points at the associated
+ * lock (which is owned by somebody else).
+ */
+ struct lock_file *lock;
+
+ /* If locked, the file descriptor of the lock file. */
+ int fd;
};
/*
@@ -825,6 +835,8 @@ static struct ref_cache {
static void clear_packed_ref_cache(struct ref_cache *refs)
{
if (refs->packed) {
+ if (refs->packed->lock)
+ die("internal error: packed-ref cache cleared while
locked");
free_ref_entry(refs->packed->root);
free(refs->packed);
refs->packed = NULL;
@@ -1009,6 +1021,7 @@ static struct packed_ref_cache
*get_packed_ref_cache(struct ref_cache *refs)
refs->packed = xcalloc(1, sizeof(*refs->packed));
refs->packed->root = create_dir_entry(refs, "", 0, 0);
+ refs->packed->fd = -1;
if (*refs->name)
packed_refs_file = git_path_submodule(refs->name,
"packed-refs");
else
@@ -1034,7 +1047,12 @@ static struct ref_dir *get_packed_refs(struct ref_cache
*refs)
void add_packed_ref(const char *refname, const unsigned char *sha1)
{
- add_ref(get_packed_refs(&ref_cache),
+ struct packed_ref_cache *packed_ref_cache =
+ get_packed_ref_cache(&ref_cache);
+
+ if (!packed_ref_cache->lock)
+ die("internal error: packed refs not locked");
+ add_ref(get_packed_ref_dir(packed_ref_cache),
create_ref_entry(refname, sha1, REF_ISPACKED, 1));
}
@@ -2031,6 +2049,56 @@ static int write_packed_entry_fn(struct ref_entry
*entry, void *cb_data)
return 0;
}
+int lock_packed_refs(struct lock_file *lock, int flags)
+{
+ int fd;
+ struct packed_ref_cache *packed_ref_cache;
+
+ /* Discard the old cache because it might be invalid: */
+ clear_packed_ref_cache(&ref_cache);
+ fd = hold_lock_file_for_update(lock, git_path("packed-refs"), flags);
+ if (fd < 0)
+ return -1;
+ /* Read the current packed-refs while holding the lock: */
+ packed_ref_cache = get_packed_ref_cache(&ref_cache);
+ packed_ref_cache->lock = lock;
+ packed_ref_cache->fd = fd;
+ return 0;
+}
+
+int commit_packed_refs(void)
+{
+ struct packed_ref_cache *packed_ref_cache =
+ get_packed_ref_cache(&ref_cache);
+ int fd = packed_ref_cache->fd;
+ int error = 0;
+
+ if (!packed_ref_cache->lock)
+ die("internal error: packed-refs not locked");
+ write_or_die(fd, PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
+
+ do_for_each_entry_in_dir(get_packed_ref_dir(packed_ref_cache),
+ 0, write_packed_entry_fn, &fd);
+ if (commit_lock_file(packed_ref_cache->lock))
+ error = -1;
+ packed_ref_cache->lock = NULL;
+ packed_ref_cache->fd = -1;
+ return error;
+}
+
+void rollback_packed_refs(void)
+{
+ struct packed_ref_cache *packed_ref_cache =
+ get_packed_ref_cache(&ref_cache);
+
+ if (!packed_ref_cache->lock)
+ die("internal error: packed-refs not locked");
+ rollback_lock_file(packed_ref_cache->lock);
+ packed_ref_cache->lock = NULL;
+ packed_ref_cache->fd = -1;
+ clear_packed_ref_cache(&ref_cache);
+}
+
struct ref_to_prune {
struct ref_to_prune *next;
unsigned char sha1[20];
@@ -2149,23 +2217,19 @@ static struct lock_file packlock;
int pack_refs(unsigned int flags)
{
struct pack_refs_cb_data cbdata;
- int fd;
memset(&cbdata, 0, sizeof(cbdata));
cbdata.flags = flags;
- fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"),
- LOCK_DIE_ON_ERROR);
+ lock_packed_refs(&packlock, LOCK_DIE_ON_ERROR);
cbdata.packed_refs = get_packed_refs(&ref_cache);
do_for_each_entry_in_dir(get_loose_refs(&ref_cache), 0,
pack_if_possible_fn, &cbdata);
- write_or_die(fd, PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
- do_for_each_entry_in_dir(cbdata.packed_refs, 0, write_packed_entry_fn,
&fd);
-
- if (commit_lock_file(&packlock) < 0)
+ if (commit_packed_refs())
die_errno("unable to overwrite old ref-pack file");
+
prune_refs(cbdata.ref_to_prune);
return 0;
}
@@ -2222,7 +2286,6 @@ static int curate_packed_ref_fn(struct ref_entry *entry,
void *cb_data)
static int repack_without_ref(const char *refname)
{
- int fd;
struct ref_dir *packed;
struct string_list refs_to_delete = STRING_LIST_INIT_DUP;
struct string_list_item *ref_to_delete;
@@ -2230,12 +2293,10 @@ static int repack_without_ref(const char *refname)
if (!get_packed_ref(refname))
return 0; /* refname does not exist in packed refs */
- fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
- if (fd < 0) {
+ if (lock_packed_refs(&packlock, 0)) {
unable_to_lock_error(git_path("packed-refs"), errno);
return error("cannot delete '%s' from packed refs", refname);
}
- clear_packed_ref_cache(&ref_cache);
packed = get_packed_refs(&ref_cache);
/* Remove refname from the cache. */
if (remove_entry(packed, refname) == -1) {
@@ -2243,7 +2304,7 @@ static int repack_without_ref(const char *refname)
* The packed entry disappeared while we were
* acquiring the lock.
*/
- rollback_lock_file(&packlock);
+ rollback_packed_refs();
return 0;
}
do_for_each_entry_in_dir(packed, 0, curate_packed_ref_fn,
&refs_to_delete);
@@ -2251,9 +2312,7 @@ static int repack_without_ref(const char *refname)
if (remove_entry(packed, ref_to_delete->string) == -1)
die("internal error");
}
- write_or_die(fd, PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
- do_for_each_entry_in_dir(packed, 0, write_packed_entry_fn, &fd);
- return commit_lock_file(&packlock);
+ return commit_packed_refs();
}
int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
diff --git a/refs.h b/refs.h
index 246bf60..b275124 100644
--- a/refs.h
+++ b/refs.h
@@ -77,12 +77,35 @@ extern int for_each_rawref(each_ref_fn, void *);
extern void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char
*refname);
/*
- * Add a reference to the in-memory packed reference cache. To actually
- * write the reference to the packed-refs file, call pack_refs().
+ * Lock the packed-refs file for writing using the specified lock_file
+ * instance. Flags is passed to hold_lock_file_for_update(). Return
+ * 0 on success.
+ */
+extern int lock_packed_refs(struct lock_file *lock, int flags);
+
+/*
+ * Add a reference to the in-memory packed reference cache. This may
+ * only be called while the packed-refs file is locked (see
+ * lock_packed_refs()). To actually write the packed-refs file, call
+ * commit_packed_refs().
*/
extern void add_packed_ref(const char *refname, const unsigned char *sha1);
/*
+ * Write the current version of the packed refs cache from memory to
+ * disk. The packed-refs file must already be locked for writing (see
+ * lock_packed_refs()). Return zero on success.
+ */
+extern int commit_packed_refs(void);
+
+/*
+ * Rollback the lockfile for the packed-refs file, and discard the
+ * in-memory packed reference cache. (The packed-refs file will be
+ * read anew if it is needed again after this function is called.)
+ */
+extern void rollback_packed_refs(void);
+
+/*
* Flags for controlling behaviour of pack_refs()
* PACK_REFS_PRUNE: Prune loose refs after packing
* PACK_REFS_ALL: Pack _all_ refs, not just tags and already packed refs
--
1.8.3
--
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