Subject: [RFC PATCH v2 15/21] net/tcp: add MSG_NETDMA flag for sendmsg()

From: Jonathan Lemon <[email-masked]>
Date: Mon, 27 Jul 2020 15:44:38 -0700

This flag indicates that the attached data is a zero-copy send,
and the pages should be retrieved from the netgpu module.  The
socket should should already have been attached to a netgpu queue.

Signed-off-by: Jonathan Lemon <[email-masked]>
---
 include/linux/socket.h | 1 +
 net/ipv4/tcp.c         | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 04d2bc97f497..63816cc25dee 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -310,6 +310,7 @@ struct ucred {
 					  */
 
 #define MSG_ZEROCOPY	0x4000000	/* Use user data in kernel path */
+#define MSG_NETDMA  	0x8000000
 #define MSG_FASTOPEN	0x20000000	/* Send data in TCP SYN */
 #define MSG_CMSG_CLOEXEC 0x40000000	/* Set close_on_exec for file
 					   descriptor received through
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 261c28ccc8f6..340ce319edc9 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1214,6 +1214,14 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 			uarg->zerocopy = 0;
 	}
 
+	if (flags & MSG_NETDMA && size && sock_flag(sk, SOCK_ZEROCOPY)) {
+		zc = sk->sk_route_caps & NETIF_F_SG;
+		if (!zc) {
+			err = -EFAULT;
+			goto out_err;
+		}
+	}
+
 	if (unlikely(flags & MSG_FASTOPEN || inet_sk(sk)->defer_connect) &&
 	    !tp->repair) {
 		err = tcp_sendmsg_fastopen(sk, msg, &copied_syn, size, uarg);
-- 
2.24.1