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

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Date:   Wed, 12 Jul 2023 22:31:34 +0000
From:   Bobby Eshleman <bobbyeshleman@...il.com>
To:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...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()').
> 
>  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)) {
> +			/* 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) {
> +		if (optname == SO_ZEROCOPY) {
> +			int zc_val;
> +
> +			/* 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);
> +			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);
> +

I found that because datagrams have !ops->setsockopt this bit causes
setsockopt() to fail (the related logic can be found in
__sys_setsockopt). Maybe we should only set this for connectibles?

Best,
Bobby

>  	vsock_insert_unbound(vsk);
>  
>  	return 0;
> -- 
> 2.25.1
>