[PATCH RFC 4/4] nfsd: key NFSv4.1 connections by clientid for fair queueing

An NFSv4.1 client may bind several connections to its session.  Stamp
each such transport's fairness key with a value derived from the clientid
in nfsd4_init_conn(), so that all of a client's connections share one key
and the fair-queue dispatcher schedules them as a single client rather
than per transport.  A multi-connection v4.1 client is thereby held to
the same per-client share as a single-connection client.

Signed-off-by: Benjamin Coddington <bcodding-F/[email protected]>
Co-Authored-By: Claude Opus 4.8 <noreply-IarDGxEC4Up8UrSeD/[email protected]>
---
 fs/nfsd/nfs4state.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 5982fc9eb6b1..52bd9bc5cdbd 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -2351,11 +2351,28 @@ static int nfsd4_register_conn(struct nfsd4_conn *conn)
 	return register_xpt_user(conn->cn_xprt, &conn->cn_xpt_user);
 }
 
+/*
+ * Derive the transport fairness key from the v4.1 clientid, so that all of a
+ * client's connections (bound to its session) share one key and the sunrpc
+ * fair-queue dispatcher schedules them as a single client rather than per
+ * transport.  cl_boot is the server's boot time and is effectively always
+ * nonzero, so this overrides the source-address default that
+ * svc_xprt_fairq_key() would otherwise use.
+ */
+static unsigned long nfsd4_fairq_key(const clientid_t *clid)
+{
+	u64 id = ((u64)clid->cl_boot << 32) | clid->cl_id;
+
+	return (unsigned long)(id ^ (id >> 32));
+}
+
 static void nfsd4_init_conn(struct svc_rqst *rqstp, struct nfsd4_conn *conn, struct nfsd4_session *ses)
 {
 	int ret;
 
 	nfsd4_hash_conn(conn, ses);
+	conn->cn_xprt->xpt_fairq_key =
+		nfsd4_fairq_key(&ses->se_client->cl_clientid);
 	ret = nfsd4_register_conn(conn);
 	if (ret)
 		/* oops; xprt is already down: */
-- 
2.53.0