NFS: Ensure we return zero if applications attempt to write zero bytes

A zero byte count direct write request should be a successful no-op, not an
error.

Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 88d5d1c7f987..4d726e9db295 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -890,6 +890,8 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
         retval = generic_write_checks(file, &pos, &count, 0);
         if (retval)
                 goto out;
+        if (!count)
+                goto out;       /* return 0 */
 
         retval = -EINVAL;
         if ((ssize_t) count < 0)