[PATCH v3 03/55] net: Declare MSG_SPLICE_PAGES internal sendmsg() flag

David Howells
2023-03-31T16:10:56Z

Declare MSG_SPLICE_PAGES, an internal sendmsg() flag, that hints to a
network protocol that it should splice pages from the source iterator
rather than copying the data if it can. This flag is added to a list that
is cleared by sendmsg and recvmsg syscalls on entry.

This is intended as a replacement for the ->sendpage() op, allowing a way
to splice in several multipage folios in one go.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: netdev@vger.kernel.org
---
include/linux/socket.h | 3 +++
net/socket.c | 2 ++
2 files changed, 5 insertions(+)

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 13c3a237b9c9..bd1cc3238851 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -327,6 +327,7 @@ struct ucred {
*/

#define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */
+#define MSG_SPLICE_PAGES 0x8000000 /* Splice the pages from the iterator in sendmsg() */
#define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
#define MSG_CMSG_CLOEXEC 0x40000000 /* Set close_on_exec for file
descriptor received through
@@ -337,6 +338,8 @@ struct ucred {
#define MSG_CMSG_COMPAT 0 /* We never have 32 bit fixups */
#endif

+/* Flags to be cleared on entry by sendmsg and sendmmsg syscalls */
+#define MSG_INTERNAL_SENDMSG_FLAGS (MSG_SPLICE_PAGES)

/* Setsockoptions(2) level. Thanks to BSD these must match IPPROTO_xxx */
#define SOL_IP 0
diff --git a/net/socket.c b/net/socket.c
index 6bae8ce7059e..0c39ce57d603 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2139,6 +2139,7 @@ int __sys_sendto(int fd, void __user *buff, size_t len, unsigned int flags,
msg.msg_name = (struct sockaddr *)&address;
msg.msg_namelen = addr_len;
}
+ flags &= ~MSG_INTERNAL_SENDMSG_FLAGS;
if (sock->file->f_flags & O_NONBLOCK)
flags |= MSG_DONTWAIT;
msg.msg_flags = flags;
@@ -2486,6 +2487,7 @@ static int ____sys_sendmsg(struct socket *sock, struct msghdr *msg_sys,
}
msg_sys->msg_flags = flags;

+ flags &= ~MSG_INTERNAL_SENDMSG_FLAGS;
if (sock->file->f_flags & O_NONBLOCK)
msg_sys->msg_flags |= MSG_DONTWAIT;
/*