fuse: honor iocb sync flags on write

If the IOCB_DSYNC flag is set a sync is not being performed by
fuse_file_write_iter.

Honor IOCB_DSYNC/IOCB_SYNC by setting O_DYSNC/O_SYNC respectively in the
flags filed of the write request.

We don't need to sync data or metadata, since fuse_perform_write() does
write-through and the filesystem is responsible for updating file times.

Original patch by Vitaly Zolotusky.

Reported-by: Nate Clark <nate@neworld.us>
Cc: Vitaly Zolotusky <vitaly@unitc.com>.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
index c5b6b71..e9e9780 100644
--- a/fs/fuse/cuse.c
+++ b/fs/fuse/cuse.c
@@ -90,7 +90,7 @@ static struct list_head *cuse_conntbl_head(dev_t devt)
 
 static ssize_t cuse_read_iter(struct kiocb *kiocb, struct iov_iter *to)
 {
-	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb->ki_filp);
+	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
 	loff_t pos = 0;
 
 	return fuse_direct_io(&io, to, &pos, FUSE_DIO_CUSE);
@@ -98,7 +98,7 @@ static ssize_t cuse_read_iter(struct kiocb *kiocb, struct iov_iter *to)
 
 static ssize_t cuse_write_iter(struct kiocb *kiocb, struct iov_iter *from)
 {
-	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb->ki_filp);
+	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
 	loff_t pos = 0;
 	/*
 	 * No locking or generic_write_checks(), the server is