nfsd: print status when nfsd4_open fails to open file it just created

It's possible for nfsd to fail opening a file that it has just created.
When that happens, we throw a WARN but it doesn't include any info about
the error code. Print the status code to give us a bit more info.

Our QA group hit some of these warnings under some very heavy stress
testing. My suspicion is that they hit the file-max limit, but it's hard
to know for sure. Go ahead and add a -ENFILE mapping to
nfserr_serverfault to make the error more distinct (and correct).
Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4proc.c

@@ -460,7 +460,9 @@ nfsd4_open(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	 * set, (2) sets open->op_stateid, (3) sets open->op_delegation.
 	 */
 	status = nfsd4_process_open2(rqstp, resfh, open);
-	WARN_ON(status && open->op_created);
+	WARN(status && open->op_created,
+	     "nfsd4_process_open2 failed to open newly-created file! status=%u\n",
+	     be32_to_cpu(status));
 out:
 	if (resfh && resfh != &cstate->current_fh) {
 		fh_dup2(&cstate->current_fh, resfh);

fs/nfsd/nfsproc.c

@@ -745,6 +745,7 @@ nfserrno (int errno)
 		{ nfserr_notsupp, -EOPNOTSUPP },
 		{ nfserr_toosmall, -ETOOSMALL },
 		{ nfserr_serverfault, -ESERVERFAULT },
+		{ nfserr_serverfault, -ENFILE },
 	};
 	int	i;