Daniel Barkalow <barkalow@xxxxxxxxxxxx> writes:
> 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>
> ---
> 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));
Copying and checking are the other way around, aren't they? Grab the
lock, error out if you cannot, then read and copy.
> + return fd;
> +}
> +
> int close_lock_file(struct lock_file *lk)
> {
> int fd = lk->fd;
> --
> 1.5.4.3.610.gea6cd
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