NFSv4.1: Don't set up a backchannel if the server didn't agree to do so

If the server doesn't agree to out backchannel setup request, then
don't set one up.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/callback_proc.c

@@ -427,6 +427,8 @@ __be32 nfs4_callback_sequence(struct cb_sequenceargs *args,
 	if (clp == NULL)
 		goto out;
 
+	if (!(clp->cl_session->flags & SESSION4_BACK_CHAN))
+		goto out;
 	tbl = &clp->cl_session->bc_slot_table;
 
 	spin_lock(&tbl->slot_tbl_lock);

fs/nfs/nfs4proc.c

@@ -7195,6 +7195,8 @@ static int nfs4_verify_back_channel_attrs(struct nfs41_create_session_args *args
 	struct nfs4_channel_attrs *sent = &args->bc_attrs;
 	struct nfs4_channel_attrs *rcvd = &res->bc_attrs;
 
+	if (!(res->flags & SESSION4_BACK_CHAN))
+		goto out;
 	if (rcvd->max_rqst_sz > sent->max_rqst_sz)
 		return -EINVAL;
 	if (rcvd->max_resp_sz < sent->max_resp_sz)
@@ -7206,6 +7208,7 @@ static int nfs4_verify_back_channel_attrs(struct nfs41_create_session_args *args
 		return -EINVAL;
 	if (rcvd->max_reqs != sent->max_reqs)
 		return -EINVAL;
+out:
 	return 0;
 }
 
@@ -7226,7 +7229,9 @@ static void nfs4_update_session(struct nfs4_session *session,
 	nfs4_copy_sessionid(&session->sess_id, &res->sessionid);
 	session->flags = res->flags;
 	memcpy(&session->fc_attrs, &res->fc_attrs, sizeof(session->fc_attrs));
-	memcpy(&session->bc_attrs, &res->bc_attrs, sizeof(session->bc_attrs));
+	if (res->flags & SESSION4_BACK_CHAN)
+		memcpy(&session->bc_attrs, &res->bc_attrs,
+				sizeof(session->bc_attrs));
 }
 
 static int _nfs4_proc_create_session(struct nfs_client *clp,

fs/nfs/nfs4session.c

@@ -450,7 +450,7 @@ int nfs4_setup_session_slot_tables(struct nfs4_session *ses)
 	tbl = &ses->fc_slot_table;
 	tbl->session = ses;
 	status = nfs4_realloc_slot_table(tbl, ses->fc_attrs.max_reqs, 1);
-	if (status) /* -ENOMEM */
+	if (status || !(ses->flags & SESSION4_BACK_CHAN)) /* -ENOMEM */
 		return status;
 	/* Back channel */
 	tbl = &ses->bc_slot_table;