add a vfs_fsync helper

Fsync currently has a fdatawrite/fdatawait pair around the method call,
and a mutex_lock/unlock of the inode mutex.  All callers of fsync have
to duplicate this, but we have a few and most of them don't quite get
it right.  This patch adds a new vfs_fsync that takes care of this.
It's a little more complicated as usual as ->fsync might get a NULL file
pointer and just a dentry from nfsd, but otherwise gets afile and we
want to take the mapping and file operations from it when it is there.

Notes on the fsync callers:

 - ecryptfs wasn't calling filemap_fdatawrite / filemap_fdatawait on the
   	lower file
 - coda wasn't calling filemap_fdatawrite / filemap_fdatawait on the host
	file, and returning 0 when ->fsync was missing
 - shm wasn't calling either filemap_fdatawrite / filemap_fdatawait nor
   taking i_mutex.  Now given that shared memory doesn't have disk
   backing not doing anything in fsync seems fine and I left it out of
   the vfs_fsync conversion for now, but in that case we might just
   not pass it through to the lower file at all but just call the no-op
   simple_sync_file directly.

[and now actually export vfs_fsync]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 1 insertions, 17 deletions

diff --git a/drivers/usb/gadget/file_storage.c b/drivers/usb/gadget/file_storage.c
index c4e62a6297d7..2e71368f45b4 100644
--- a/drivers/usb/gadget/file_storage.c
+++ b/drivers/usb/gadget/file_storage.c
@@ -1863,26 +1863,10 @@ static int do_write(struct fsg_dev *fsg)
 static int fsync_sub(struct lun *curlun)
 {
 	struct file	*filp = curlun->filp;
-	struct inode	*inode;
-	int		rc, err;
 
 	if (curlun->ro || !filp)
 		return 0;
-	if (!filp->f_op->fsync)
-		return -EINVAL;
-
-	inode = filp->f_path.dentry->d_inode;
-	mutex_lock(&inode->i_mutex);
-	rc = filemap_fdatawrite(inode->i_mapping);
-	err = filp->f_op->fsync(filp, filp->f_path.dentry, 1);
-	if (!rc)
-		rc = err;
-	err = filemap_fdatawait(inode->i_mapping);
-	if (!rc)
-		rc = err;
-	mutex_unlock(&inode->i_mutex);
-	VLDBG(curlun, "fdatasync -> %d\n", rc);
-	return rc;
+	return vfs_fsync(filp, filp->f_path.dentry, 1);
 }
 
 static void fsync_all(struct fsg_dev *fsg)