[PATCH 2/8] Add a lockfile function to append to a file
From: Daniel Barkalow <hidden>
Date: 2016-06-15 22:44:29
Subsystem:
the rest · Maintainer:
Linus Torvalds
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 <redacted> --- How about this? Also doesn't leak a fd and catches trying to append to a file you can't read. Should I worry about mmap failing after the open? cache.h | 1 + lockfile.c | 23 +++++++++++++++++++++++ 2 files changed, 24 insertions(+), 0 deletions(-)
diff --git a/cache.h b/cache.h
index 50b28fa..8d066bf 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..f1b5416 100644
--- a/lockfile.c
+++ b/lockfile.c@@ -160,6 +160,29 @@ 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 (fd < 0) { + if (die_on_error) + die("unable to create '%s.lock': %s", + path, strerror(errno)); + } else if (!stat(path, &st)) { + int orig_fd = open(path, O_RDONLY); + size_t mmap_size = xsize_t(st.st_size); + void *mmap; + if (orig_fd < 0) + die("unable to read %s to append to it", path); + mmap = xmmap(NULL, mmap_size, PROT_READ, MAP_PRIVATE, + orig_fd, 0); + write_or_die(fd, mmap, mmap_size); + munmap(mmap, mmap_size); + close(orig_fd); + } + return fd; +} + int close_lock_file(struct lock_file *lk) { int fd = lk->fd;
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1.5.4.3.610.gea6cd