Add a lockfile function to append to a file

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.

[jc: munged to drop mmap in favor of copy_file.]

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/cache.h b/cache.h
index 5a28dddec931f983a4aeff2ee7129444d07e07aa..396eabf6ed02214f2c9f9e83c06c19aa7b7626e4 100644 (file)
--- 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 663f18f9c40145e5ab772021e0c700e9123a4b01..e9e0095e9f98f9a05d2f88f5e97766930a99d89d 100644 (file)
--- a/lockfile.c
+++ b/lockfile.c
@@ -160,6 +160,34 @@ 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, orig_fd;
+
+       fd = lock_file(lk, path);
+       if (fd < 0) {
+               if (die_on_error)
+                       die("unable to create '%s.lock': %s", path, strerror(errno));
+               return fd;
+       }
+
+       orig_fd = open(path, O_RDONLY);
+       if (orig_fd < 0) {
+               if (errno != ENOENT) {
+                       if (die_on_error)
+                               die("cannot open '%s' for copying", path);
+                       close(fd);
+                       return error("cannot open '%s' for copying", path);
+               }
+       } else if (copy_fd(orig_fd, fd)) {
+               if (die_on_error)
+                       exit(128);
+               close(fd);
+               return -1;
+       }
+       return fd;
+}
+
 int close_lock_file(struct lock_file *lk)
 {
        int fd = lk->fd;