fuse: fix flock

Commit a9ff4f87 "fuse: support BSD locking semantics" overlooked a
number of issues with supporing flock locks over existing POSIX
locking infrastructure:

  - it's not backward compatible, passing flock(2) calls to userspace
    unconditionally (if userspace sets FUSE_POSIX_LOCKS)

  - it doesn't cater for the fact that flock locks are automatically
    unlocked on file release

  - it doesn't take into account the fact that flock exclusive locks
    (write locks) don't need an fd opened for write.

The last one invalidates the original premise of the patch that flock
locks can be emulated with POSIX locks.

This patch fixes the first two issues.  The last one needs to be fixed
in userspace if the filesystem assumed that a write lock will happen
only on a file operned for write (as in the case of the current fuse
library).

Reported-by: Sebastian Pipping <webmaster@hartwork.org>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 10 insertions, 1 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 82a66466a24..e3278492435 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -245,6 +245,12 @@ void fuse_release_common(struct file *file, int opcode)
 	req = ff->reserved_req;
 	fuse_prepare_release(ff, file->f_flags, opcode);
 
+	if (ff->flock) {
+		struct fuse_release_in *inarg = &req->misc.release.in;
+		inarg->release_flags |= FUSE_RELEASE_FLOCK_UNLOCK;
+		inarg->lock_owner = fuse_lock_owner_id(ff->fc,
+						       (fl_owner_t) file);
+	}
 	/* Hold vfsmount and dentry until release is finished */
 	path_get(&file->f_path);
 	req->misc.release.path = file->f_path;
@@ -1547,11 +1553,14 @@ static int fuse_file_flock(struct file *file, int cmd, struct file_lock *fl)
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	int err;
 
-	if (fc->no_lock) {
+	if (fc->no_flock) {
 		err = flock_lock_file_wait(file, fl);
 	} else {
+		struct fuse_file *ff = file->private_data;
+
 		/* emulate flock with POSIX locks */
 		fl->fl_owner = (fl_owner_t) file;
+		ff->flock = true;
 		err = fuse_setlk(file, fl, 1);
 	}