Michael Haggerty <mhagger@xxxxxxxxxxxx> writes:
> 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@xxxxxxxxxxxx>
> ---
> builtin/clone.c | 7 ++++-
> refs.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++-----------
> refs.h | 27 +++++++++++++++++--
> 3 files changed, 98 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");
> }
The calling convention used here looks somewhat strange. You allow
callers to specify which lock-file structure is used when locking,
but when you are done, commit_packed_refs() does not take any
parameter.
lock_packed_refs() make the singleton in-core packed-ref-cache be
aware of which lock it is under, so commit_packed_refs() does not
need to be told (the singleton already knows what lockfile is in
effect), so I am not saying the code is broken, though.
Does the caller need to even have an access to this lock_file
instance?
> static void write_followtags(const struct ref *refs, const char *msg)
> diff --git a/refs.c b/refs.c
> index 373d95b..ad73251 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -808,6 +808,13 @@ 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;
> };
>
> /*
> @@ -829,6 +836,8 @@ 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;
> @@ -1038,7 +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));
> }
>
> @@ -2035,6 +2049,52 @@ 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)
> +{
> + struct packed_ref_cache *packed_ref_cache;
> +
> + /* Discard the old cache because it might be invalid: */
> + clear_packed_ref_cache(&ref_cache);
> + if (hold_lock_file_for_update(lock, git_path("packed-refs"), flags) < 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;
> + return 0;
> +}
> +
> +int commit_packed_refs(void)
> +{
> + struct packed_ref_cache *packed_ref_cache =
> + get_packed_ref_cache(&ref_cache);
> + int error = 0;
> +
> + if (!packed_ref_cache->lock)
> + die("internal error: packed-refs not locked");
> + write_or_die(packed_ref_cache->lock->fd,
> + PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
> +
> + do_for_each_entry_in_dir(get_packed_ref_dir(packed_ref_cache),
> + 0, write_packed_entry_fn,
> + &packed_ref_cache->lock->fd);
> + if (commit_lock_file(packed_ref_cache->lock))
> + error = -1;
> + packed_ref_cache->lock = NULL;
> + 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;
> + clear_packed_ref_cache(&ref_cache);
> +}
> +
> struct ref_to_prune {
> struct ref_to_prune *next;
> unsigned char sha1[20];
> @@ -2153,23 +2213,19 @@ 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;
> }
> @@ -2233,7 +2289,6 @@ 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;
> @@ -2241,12 +2296,10 @@ 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: */
> @@ -2255,7 +2308,7 @@ 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;
> }
>
> @@ -2267,9 +2320,7 @@ static int repack_without_ref(const char *refname)
> }
>
> /* Write what remains: */
> - 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
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