# [PATCH 2/8] Add a lockfile function to append to a file 3 messages from 2008-04-17 to 2008-04-17. Participants: Daniel Barkalow, Junio C Hamano. Thread: https://gitlist.dev/t/13167 ## Daniel Barkalow, 2008-04-17 23:32 Subject: [PATCH 2/8] Add a lockfile function to append to a file Message-ID: URL: https://gitlist.dev/e/alpine.LNX.1.00.0804171931480.19665%40iabervon.org ``` 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 --- 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 ``` ## Junio C Hamano, 2008-04-17 23:41 Subject: Re: [PATCH 2/8] Add a lockfile function to append to a file Message-ID: <7v3apkm4lz.fsf@gitster.siamese.dyndns.org> URL: https://gitlist.dev/e/7v3apkm4lz.fsf%40gitster.siamese.dyndns.org In-Reply-To: ``` Daniel Barkalow 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 > --- > 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 ``` ## Junio C Hamano, 2008-04-17 23:51 Subject: Re: [PATCH 2/8] Add a lockfile function to append to a file Message-ID: <7vy77ckpkk.fsf@gitster.siamese.dyndns.org> URL: https://gitlist.dev/e/7vy77ckpkk.fsf%40gitster.siamese.dyndns.org In-Reply-To: ``` Daniel Barkalow writes: > +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; > +} Another glitch. What should we do when stat(path) fails but the file cannot be read? I think the sequence actually should be: fd = lock_file(); if (fd < 0) error out; orig_fd = open(path, O_RDONLY); if (orig_fd < 0) { if (errno != ENOENT) die("unable to open %s", path); copy; } return fd; ```