[RFC PATCH 1/4] net: Introduce read_sock_cmsg proto_ops for control message delivery

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

Kernel TCP consumers that use the read_sock interface
(proto_ops.read_sock) cannot receive TLS control messages (Alerts,
Handshake records) when kTLS is active. The current
tls_sw_read_sock() method rejects non-data records with -EINVAL, and
the sk_read_actor_t callback has no channel for delivering record-
type metadata.

Four kernel subsystems are affected: NFSD (sunrpc svcsock), NFS
client (sunrpc xprtsock), NVMe target (nvmet-tcp), and NVMe host
(nvme-tcp). Each of these either falls back to the slower
sock_recvmsg() API or lacks TLS alert handling entirely.

A new read_sock_cmsg method in struct proto_ops provides a separate
code path that delivers non-data TLS records to a callback, without
changing the existing read_sock behavior used by consumers of the
existing read_sock method.

The new sk_read_cmsg_actor_t callback type extends the
sk_read_actor_t signature with a content_type parameter carrying the
protocol-layer record type (for example, TLS_RECORD_TYPE_ALERT).

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 include/linux/net.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/net.h b/include/linux/net.h
index f58b38ab37f8..94eb1c3c1cb6 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -154,6 +154,10 @@ struct sk_buff;
 struct proto_accept_arg;
 typedef int (*sk_read_actor_t)(read_descriptor_t *, struct sk_buff *,
 			       unsigned int, size_t);
+typedef int (*sk_read_cmsg_actor_t)(read_descriptor_t *,
+				    struct sk_buff *,
+				    unsigned int, size_t,
+				    u8 content_type);
 typedef int (*skb_read_actor_t)(struct sock *, struct sk_buff *);
 
 
@@ -218,6 +222,10 @@ struct proto_ops {
 	 */
 	int		(*read_sock)(struct sock *sk, read_descriptor_t *desc,
 				     sk_read_actor_t recv_actor);
+	int		(*read_sock_cmsg)(struct sock *sk,
+					  read_descriptor_t *desc,
+					  sk_read_actor_t recv_actor,
+					  sk_read_cmsg_actor_t cmsg_actor);
 	/* This is different from read_sock(), it reads an entire skb at a time. */
 	int		(*read_skb)(struct sock *sk, skb_read_actor_t recv_actor);
 	int		(*sendmsg_locked)(struct sock *sk, struct msghdr *msg,
-- 
2.53.0