fs: nfs: Error if a port is unregistered

If a server doesn't provide a service the port lookup will return 0.

Check for this, return an appropriate error code and give a hint as to
why this might be happening.

This was tested by running NFS with UDP disabled, which seems to be
the default in Arch at least.

Signed-off-by: John Watts <contact@jookia.org>
Link: https://lore.barebox.org/20230202112024.2458085-1-contact@jookia.org
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/nfs.c b/fs/nfs.c
index 446d0f7946..1a0b28442d 100644
--- a/fs/nfs.c
+++ b/fs/nfs.c
@@ -571,6 +571,12 @@ static int rpc_lookup_req(struct nfs_priv *npriv, uint32_t prog, uint32_t ver)
 
 	nfs_free_packet(nfs_packet);
 
+	if (port == 0) {
+		pr_warn("No UDP port for RPC program %i! "
+		        "Is your NFS server TCP only?\n", prog);
+		return -ENOENT;
+	}
+
 	return port;
 }