NFSD: add a userspace-rpcbind flag to listener_set

Describe the interface that lets a caller take over rpcbind registration.

The request gains a userspace-rpcbind flag. The reply echoes the flag,
lists the programs and versions that the caller should register, and
names the listeners that came up.

NLM is absent. lockd owns its own svc_serv and still registers itself.

Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260915-nfsd-norpcb-v3-2-3c60d49ade02@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>

Documentation/netlink/specs/nfsd.yaml

@@ -42,6 +42,15 @@ definitions:
       - none
       - tls
       - mtls
+  -
+    type: flags
+    name: rpcbind-flags
+    doc: >-
+      Constraints that apply to an rpcbind registration. no-udp means the
+      kernel would not have registered this program and version over UDP,
+      so the caller must skip the udp and udp6 netids for it.
+    entries:
+      - no-udp
 
 attribute-sets:
   -
@@ -159,6 +168,23 @@ attribute-sets:
       -
         name: transport-name
         type: string
+  -
+    name: rpcbind
+    attributes:
+      -
+        name: program
+        type: u32
+        doc: RPC program number to register.
+      -
+        name: version
+        type: u32
+        doc: RPC version number to register.
+      -
+        name: flags
+        type: u32
+        enum: rpcbind-flags
+        enum-as-flags: true
+        doc: Constraints on the listeners this entry applies to.
   -
     name: server-sock
     attributes:
@@ -167,6 +193,24 @@ attribute-sets:
         type: nest
         nested-attributes: sock
         multi-attr: true
+      -
+        name: userspace-rpcbind
+        type: flag
+        doc: >-
+          The caller registers the listeners with rpcbind itself, so the
+          kernel must not do it. The kernel echoes this attribute in the
+          reply when it accepts the request. Ownership cannot change while
+          a server exists.
+      -
+        name: rpcbind
+        type: nest
+        nested-attributes: rpcbind
+        multi-attr: true
+        doc: >-
+          A program and version that the caller should register for every
+          listener reported in the same reply, except the netids that flags
+          rules out. Reply only. NLM is absent because lockd still
+          registers itself.
   -
     name: pool-mode
     attributes:
@@ -483,13 +527,22 @@ operations:
             - version
     -
       name: listener-set
-      doc: set nfs running sockets
+      doc: >-
+        set nfs running sockets. A request that carries userspace-rpcbind
+        is answered with a reply rather than a bare ack, and the addr list
+        in that reply names only the listeners that have an rpcbind netid.
       attribute-set: server-sock
       flags: [admin-perm]
       do:
         request:
           attributes:
             - addr
+            - userspace-rpcbind
+        reply:
+          attributes:
+            - addr
+            - userspace-rpcbind
+            - rpcbind
     -
       name: listener-get
       doc: get nfs running listeners

fs/nfsd/netlink.c

@@ -79,8 +79,9 @@ static const struct nla_policy nfsd_version_set_nl_policy[NFSD_A_SERVER_PROTO_VE
 };
 
 /* NFSD_CMD_LISTENER_SET - do */
-static const struct nla_policy nfsd_listener_set_nl_policy[NFSD_A_SERVER_SOCK_ADDR + 1] = {
+static const struct nla_policy nfsd_listener_set_nl_policy[NFSD_A_SERVER_SOCK_USERSPACE_RPCBIND + 1] = {
 	[NFSD_A_SERVER_SOCK_ADDR] = NLA_POLICY_NESTED(nfsd_sock_nl_policy),
+	[NFSD_A_SERVER_SOCK_USERSPACE_RPCBIND] = { .type = NLA_FLAG, },
 };
 
 /* NFSD_CMD_POOL_MODE_SET - do */
@@ -153,7 +154,7 @@ static const struct genl_split_ops nfsd_nl_ops[] = {
 		.cmd		= NFSD_CMD_LISTENER_SET,
 		.doit		= nfsd_nl_listener_set_doit,
 		.policy		= nfsd_listener_set_nl_policy,
-		.maxattr	= NFSD_A_SERVER_SOCK_ADDR,
+		.maxattr	= NFSD_A_SERVER_SOCK_USERSPACE_RPCBIND,
 		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
 	},
 	{

include/uapi/linux/nfsd_netlink.h

@@ -50,6 +50,15 @@ enum nfsd_xprtsec_mode {
 	NFSD_XPRTSEC_MODE_MTLS = 4,
 };
 
+/*
+ * Constraints that apply to an rpcbind registration. no-udp means the kernel
+ * would not have registered this program and version over UDP, so the caller
+ * must skip the udp and udp6 netids for it.
+ */
+enum nfsd_rpcbind_flags {
+	NFSD_RPCBIND_FLAGS_NO_UDP = 1,
+};
+
 enum {
 	NFSD_A_CACHE_NOTIFY_CACHE_TYPE = 1,
 
@@ -113,8 +122,19 @@ enum {
 	NFSD_A_SOCK_MAX = (__NFSD_A_SOCK_MAX - 1)
 };
 
+enum {
+	NFSD_A_RPCBIND_PROGRAM = 1,
+	NFSD_A_RPCBIND_VERSION,
+	NFSD_A_RPCBIND_FLAGS,
+
+	__NFSD_A_RPCBIND_MAX,
+	NFSD_A_RPCBIND_MAX = (__NFSD_A_RPCBIND_MAX - 1)
+};
+
 enum {
 	NFSD_A_SERVER_SOCK_ADDR = 1,
+	NFSD_A_SERVER_SOCK_USERSPACE_RPCBIND,
+	NFSD_A_SERVER_SOCK_RPCBIND,
 
 	__NFSD_A_SERVER_SOCK_MAX,
 	NFSD_A_SERVER_SOCK_MAX = (__NFSD_A_SERVER_SOCK_MAX - 1)