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

[Jonathan Lemon]

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 <jonathan.le...@gmail.com>
---
 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