This takes care of copying the original contents into the replacement
file after the lock is held, so that concurrent additions can't miss
each other's changes.
Signed-off-by: Daniel Barkalow <barkalow@xxxxxxxxxxxx>
---
These two together replace [PATCH 5/11] from my earlier series; the
lockfile API turned out not to have anything for O_APPEND (for the simple
reason that it always creates a new replacement file). But appending is an
obvious logical operation to support internally, especially since it
actually has a clear semantics by itself for avoiding races.
cache.h | 1 +
lockfile.c | 17 +++++++++++++++++
2 files changed, 18 insertions(+), 0 deletions(-)
diff --git a/cache.h b/cache.h
index 2a1e7ec..4a113b0 100644
--- a/cache.h
+++ b/cache.h
@@ -391,6 +391,7 @@ struct lock_file {
char filename[PATH_MAX];
};
extern int hold_lock_file_for_update(struct lock_file *, const char *path, int);
+extern int hold_lock_file_for_append(struct lock_file *, const char *path, int);
extern int commit_lock_file(struct lock_file *);
extern int hold_locked_index(struct lock_file *, int);
diff --git a/lockfile.c b/lockfile.c
index 663f18f..95fd3d1 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -160,6 +160,23 @@ int hold_lock_file_for_update(struct lock_file *lk, const char *path, int die_on
return fd;
}
+int hold_lock_file_for_append(struct lock_file *lk, const char *path, int die_on_error)
+{
+ int fd = lock_file(lk, path);
+ struct stat st;
+ if (!stat(path, &st)) {
+ int orig_fd = open(path, O_RDONLY);
+ size_t mmap_size = xsize_t(st.st_size);
+ void *mmap = xmmap(NULL, mmap_size, PROT_READ, MAP_PRIVATE,
+ orig_fd, 0);
+ write_or_die(fd, mmap, mmap_size);
+ munmap(mmap, mmap_size);
+ }
+ if (fd < 0 && die_on_error)
+ die("unable to create '%s.lock': %s", path, strerror(errno));
+ return fd;
+}
+
int close_lock_file(struct lock_file *lk)
{
int fd = lk->fd;
--
1.5.4.3.610.gea6cd
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
