nfsd: Return the correct number of bytes written to the file

We must allow for the fact that iov_iter_write() could have returned
a short write (e.g. if there was an ENOSPC issue).

Fixes: d890be159a "nfsd: Add I/O trace points in the NFSv4 write path"
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/vfs.c

@@ -975,6 +975,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 	host_err = vfs_iter_write(file, &iter, &pos, flags);
 	if (host_err < 0)
 		goto out_nfserr;
+	*cnt = host_err;
 	nfsdstats.io_write += *cnt;
 	fsnotify_modify(file);