[PATCH 4/6] NFSv4.1/pnfs: treat an oversized LAYOUTGET reply as -EMSGSIZE

decode_layoutget() already detects a server that sends a layout body
larger than the reply buffer we provided ("server cheating in
layoutget reply") but maps it to -EINVAL, which pnfs_update_layout()
treats as a transient error: the client falls back to the MDS for
this I/O only and re-sends a doomed LAYOUTGET on every subsequent
pageio attempt.

A server that overruns the reply buffer has ignored loga_maxcount, but
the client can recover the same way it recovers from a conformant
server's NFS4ERR_TOOSMALL: return -EMSGSIZE from exactly this check so
that the layoutget path retries once with a session-sized reply buffer
and otherwise marks the layout mode failed and falls back to the MDS.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Benjamin Coddington <bcodding-F/[email protected]>
---
 fs/nfs/nfs4xdr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index c23c2eee1b5c..6b46ed346a77 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -6154,7 +6154,7 @@ static int decode_layoutget(struct xdr_stream *xdr, struct rpc_rqst *req,
 		dprintk("NFS: server cheating in layoutget reply: "
 				"layout len %u > recvd %u\n",
 				res->layoutp->len, recvd);
-		status = -EINVAL;
+		status = -EMSGSIZE;
 		goto out;
 	}
 
-- 
2.53.0