nfsd: add callback encoding and decoding linkages for CB_NOTIFY

Add routines for encoding and decoding CB_NOTIFY messages. These call
into the code generated by xdrgen to do the actual encoding and
decoding.

For now, the encoder is a stub. Later patches will flesh out the payload
encoding.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260616-dir-deleg-v7-7-6cbc7eac0ade@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>

Documentation/sunrpc/xdr/nfs4_1.x

@@ -490,6 +490,7 @@ struct CB_NOTIFY4args {
         nfs_fh4     cna_fh;
         notify4     cna_changes<>;
 };
+pragma public CB_NOTIFY4args;
 
 struct CB_NOTIFY4res {
         nfsstat4    cnr_status;

fs/nfsd/nfs4callback.c

@@ -891,6 +891,51 @@ static void encode_stateowner(struct xdr_stream *xdr, struct nfs4_stateowner *so
 	xdr_encode_opaque(p, so->so_owner.data, so->so_owner.len);
 }
 
+static void nfs4_xdr_enc_cb_notify(struct rpc_rqst *req,
+				   struct xdr_stream *xdr,
+				   const void *data)
+{
+	const struct nfsd4_callback *cb = data;
+	struct nfs4_cb_compound_hdr hdr = {
+		.ident = 0,
+		.minorversion = cb->cb_clp->cl_minorversion,
+	};
+	struct CB_NOTIFY4args args = { };
+
+	WARN_ON_ONCE(hdr.minorversion == 0);
+
+	encode_cb_compound4args(xdr, &hdr);
+	encode_cb_sequence4args(xdr, cb, &hdr);
+
+	/*
+	 * FIXME: get stateid and fh from delegation. Inline the cna_changes
+	 * buffer, and zero it.
+	 */
+	xdrgen_encode_CB_NOTIFY4args(xdr, &args);
+
+	hdr.nops++;
+	encode_cb_nops(&hdr);
+}
+
+static int nfs4_xdr_dec_cb_notify(struct rpc_rqst *rqstp,
+				  struct xdr_stream *xdr,
+				  void *data)
+{
+	struct nfsd4_callback *cb = data;
+	struct nfs4_cb_compound_hdr hdr;
+	int status;
+
+	status = decode_cb_compound4res(xdr, &hdr);
+	if (unlikely(status))
+		return status;
+
+	status = decode_cb_sequence4res(xdr, cb);
+	if (unlikely(status || cb->cb_seq_status))
+		return status;
+
+	return decode_cb_op_status(xdr, OP_CB_NOTIFY, &cb->cb_status);
+}
+
 static void nfs4_xdr_enc_cb_notify_lock(struct rpc_rqst *req,
 					struct xdr_stream *xdr,
 					const void *data)
@@ -1052,6 +1097,7 @@ static const struct rpc_procinfo nfs4_cb_procedures[] = {
 #ifdef CONFIG_NFSD_PNFS
 	PROC(CB_LAYOUT,	COMPOUND,	cb_layout,	cb_layout),
 #endif
+	PROC(CB_NOTIFY,		COMPOUND,	cb_notify,	cb_notify),
 	PROC(CB_NOTIFY_LOCK,	COMPOUND,	cb_notify_lock,	cb_notify_lock),
 	PROC(CB_OFFLOAD,	COMPOUND,	cb_offload,	cb_offload),
 	PROC(CB_RECALL_ANY,	COMPOUND,	cb_recall_any,	cb_recall_any),

fs/nfsd/nfs4xdr_gen.c

@@ -713,7 +713,7 @@ xdrgen_decode_notify4(struct xdr_stream *xdr, struct notify4 *ptr)
 	return true;
 }
 
-static bool __maybe_unused
+bool
 xdrgen_decode_CB_NOTIFY4args(struct xdr_stream *xdr, struct CB_NOTIFY4args *ptr)
 {
 	if (!xdrgen_decode_stateid4(xdr, &ptr->cna_stateid))
@@ -1135,7 +1135,7 @@ xdrgen_encode_notify4(struct xdr_stream *xdr, const struct notify4 *value)
 	return true;
 }
 
-static bool __maybe_unused
+bool
 xdrgen_encode_CB_NOTIFY4args(struct xdr_stream *xdr, const struct CB_NOTIFY4args *value)
 {
 	if (!xdrgen_encode_stateid4(xdr, &value->cna_stateid))

fs/nfsd/nfs4xdr_gen.h

@@ -32,4 +32,7 @@ bool xdrgen_decode_posixaceperm4(struct xdr_stream *xdr, posixaceperm4 *ptr);
 bool xdrgen_encode_posixaceperm4(struct xdr_stream *xdr, const posixaceperm4 value);
 
 
+bool xdrgen_decode_CB_NOTIFY4args(struct xdr_stream *xdr, struct CB_NOTIFY4args *ptr);
+bool xdrgen_encode_CB_NOTIFY4args(struct xdr_stream *xdr, const struct CB_NOTIFY4args *value);
+
 #endif /* _LINUX_XDRGEN_NFS4_1_DECL_H */

fs/nfsd/state.h

@@ -190,6 +190,13 @@ struct nfs4_cb_fattr {
 	u64 ncf_cur_fsize;
 };
 
+/*
+ * FIXME: the current backchannel encoder can't handle a send buffer longer
+ *        than a single page (see bc_malloc/bc_free).
+ */
+#define NOTIFY4_EVENT_QUEUE_SIZE	3
+#define NOTIFY4_PAGE_ARRAY_SIZE		1
+
 /*
  * Represents a delegation stateid. The nfs4_client holds references to these
  * and they are put when it is being destroyed or when the delegation is
@@ -776,6 +783,7 @@ enum nfsd4_cb_op {
 	NFSPROC4_CLNT_CB_NOTIFY_LOCK,
 	NFSPROC4_CLNT_CB_RECALL_ANY,
 	NFSPROC4_CLNT_CB_GETATTR,
+	NFSPROC4_CLNT_CB_NOTIFY,
 };
 
 /* Returns true iff a is later than b: */

fs/nfsd/xdr4cb.h

@@ -33,6 +33,18 @@
 					cb_sequence_dec_sz +            \
 					op_dec_sz)
 
+#define NFS4_enc_cb_notify_sz		(cb_compound_enc_hdr_sz +       \
+					cb_sequence_enc_sz +            \
+					1 + enc_stateid_sz +            \
+					enc_nfs4_fh_sz +		\
+					1 +				\
+					NOTIFY4_EVENT_QUEUE_SIZE *	\
+					(2 + (NFS4_OPAQUE_LIMIT >> 2)))
+
+#define NFS4_dec_cb_notify_sz		(cb_compound_dec_hdr_sz  +      \
+					cb_sequence_dec_sz +            \
+					op_dec_sz)
+
 #define NFS4_enc_cb_notify_lock_sz	(cb_compound_enc_hdr_sz +        \
 					cb_sequence_enc_sz +             \
 					2 + 1 +				 \