netdev - Re: [RFC PATCH v5 13/17] vsock: enable setting SO

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Date: Thu, 6 Jul 2023 18:56:23 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Cc: Stefan Hajnoczi <stefanha@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
	Bobby Eshleman <bobby.eshleman@...edance.com>, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, kernel@...rdevices.ru, 
	oxffffaa@...il.com
Subject: Re: [RFC PATCH v5 13/17] vsock: enable setting SO_ZEROCOPY

On Sat, Jul 01, 2023 at 09:39:43AM +0300, Arseniy Krasnov wrote:
>For AF_VSOCK, zerocopy tx mode depends on transport, so this option must
>be set in AF_VSOCK implementation where transport is accessible (if
>transport is not set during setting SO_ZEROCOPY: for example socket is
>not connected, then SO_ZEROCOPY will be enabled, but once transport will
>be assigned, support of this type of transmission will be checked).
>
>To handle SO_ZEROCOPY, AF_VSOCK implementation uses SOCK_CUSTOM_SOCKOPT
>bit, thus handling SOL_SOCKET option operations, but all of them except
>SO_ZEROCOPY will be forwarded to the generic handler by calling
>'sock_setsockopt()'.
>
>Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
>---
> Changelog:
> v4 -> v5:
>  * This patch is totally reworked. Previous version added check for
>    PF_VSOCK directly to 'net/core/sock.c', thus allowing to set
>    SO_ZEROCOPY for AF_VSOCK type of socket. This new version catches
>    attempt to set SO_ZEROCOPY in 'af_vsock.c'. All other options
>    except SO_ZEROCOPY are forwarded to generic handler. Only this
>    option is processed in 'af_vsock.c'. Handling this option includes
>    access to transport to check that MSG_ZEROCOPY transmission is
>    supported by the current transport (if it is set, if not - transport
>    will be checked during 'connect()').

Yeah, great, this is much better!

>
> net/vmw_vsock/af_vsock.c | 44 ++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 42 insertions(+), 2 deletions(-)
>
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index da22ae0ef477..8acc77981d01 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -1406,8 +1406,18 @@ static int vsock_connect(struct socket *sock, struct sockaddr *addr,
> 			goto out;
> 		}
>
>-		if (vsock_msgzerocopy_allow(transport))
>+		if (!vsock_msgzerocopy_allow(transport)) {

Can you leave `if (vsock_msgzerocopy_allow(transport))` and just add
the else branch with this new check?

		if (vsock_msgzerocopy_allow(transport)) {
			...
		} else if (sock_flag(sk, SOCK_ZEROCOPY)) {
			...
		}

>+			/* If this option was set before 'connect()',
>+			 * when transport was unknown, check that this
>+			 * feature is supported here.
>+			 */
>+			if (sock_flag(sk, SOCK_ZEROCOPY)) {
>+				err = -EOPNOTSUPP;
>+				goto out;
>+			}
>+		} else {
> 			set_bit(SOCK_SUPPORT_ZC, &sk->sk_socket->flags);
>+		}
>
> 		err = vsock_auto_bind(vsk);
> 		if (err)
>@@ -1643,7 +1653,7 @@ static int vsock_connectible_setsockopt(struct socket *sock,
> 	const struct vsock_transport *transport;
> 	u64 val;
>
>-	if (level != AF_VSOCK)
>+	if (level != AF_VSOCK && level != SOL_SOCKET)
> 		return -ENOPROTOOPT;
>
> #define COPY_IN(_v)                                       \
>@@ -1666,6 +1676,34 @@ static int vsock_connectible_setsockopt(struct socket *sock,
>
> 	transport = vsk->transport;
>
>+	if (level == SOL_SOCKET) {

We could reduce the indentation here:
		if (optname != SO_ZEROCOPY) {
			release_sock(sk);
			return sock_setsockopt(sock, level, optname, optval, optlen);
		}

Then remove the next indentation.

>+		if (optname == SO_ZEROCOPY) {
>+			int zc_val;

`zerocopy` is more readable.
>+
>+			/* Use 'int' type here, because variable to
>+			 * set this option usually has this type.
>+			 */
>+			COPY_IN(zc_val);
>+
>+			if (zc_val < 0 || zc_val > 1) {
>+				err = -EINVAL;
>+				goto exit;
>+			}
>+
>+			if (transport && !vsock_msgzerocopy_allow(transport)) {
>+				err = -EOPNOTSUPP;
>+				goto exit;
>+			}
>+
>+			sock_valbool_flag(sk, SOCK_ZEROCOPY,
>+					  zc_val ? true : false);

Why not using directly `zc_val`?
The 3rd param of sock_valbool_flag() is an int.

>+			goto exit;
>+		}
>+
>+		release_sock(sk);
>+		return sock_setsockopt(sock, level, optname, optval, optlen);
>+	}
>+
> 	switch (optname) {
> 	case SO_VM_SOCKETS_BUFFER_SIZE:
> 		COPY_IN(val);
>@@ -2321,6 +2359,8 @@ static int vsock_create(struct net *net, struct socket *sock,
> 		}
> 	}
>
>+	set_bit(SOCK_CUSTOM_SOCKOPT, &sk->sk_socket->flags);
>+
> 	vsock_insert_unbound(vsk);
>
> 	return 0;
>-- 
>2.25.1
>