Re: [PATCH net-next v2 1/2] vsock: support SO_INQ on stream sockets

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Thu, Oct 15, 2026 at 04:43:33PM +0100, David Carlier wrote:
> SO_INQ makes recvmsg() return the bytes left in the receive queue in an
> SCM_INQ cmsg, saving a SIOCINQ call per receive. AF_UNIX stream sockets
> support it, AF_VSOCK fails with ENOPROTOOPT.
> 
> Add it for SOCK_STREAM, reusing the hint already computed for io_uring.
> As with TCP_INQ, 1 is reported once the stream is finished so the caller
> reads again and sees EOF, and accepted sockets inherit the setting from
> the listener. No cmsg is sent when the transport cannot report the queue
> length.
> 
> SOCK_SEQPACKET is refused, as on AF_UNIX: its transport callback counts
> messages, not bytes.
> 
> Signed-off-by: David Carlier <devnexen@gmail.com>
> ---
>  include/net/af_vsock.h   |   1 +
>  net/vmw_vsock/af_vsock.c | 111 +++++++++++++++++++++++++++++----------
>  2 files changed, 84 insertions(+), 28 deletions(-)
> 
> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> index 5549298c1ec6..e8481f12312e 100644
> --- a/include/net/af_vsock.h
> +++ b/include/net/af_vsock.h
> @@ -68,6 +68,7 @@ struct vsock_sock {
>  	u64 buffer_size;
>  	u64 buffer_min_size;
>  	u64 buffer_max_size;
> +	bool recvmsg_inq;
>  
>  	/* Private to transport. */
>  	void *trans;
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 1c2d1cea67f4..186ed57fd797 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -984,6 +984,7 @@ static struct sock *__vsock_create(struct net *net,
>  		vsk->buffer_size = psk->buffer_size;
>  		vsk->buffer_min_size = psk->buffer_min_size;
>  		vsk->buffer_max_size = psk->buffer_max_size;
> +		vsk->recvmsg_inq = psk->recvmsg_inq;
>  		security_sk_clone(parent, sk);
>  	} else {
>  		vsk->trusted = ns_capable_noaudit(&init_user_ns, CAP_NET_ADMIN);
> @@ -2014,6 +2015,66 @@ static void vsock_update_buffer_size(struct vsock_sock *vsk,
>  	vsk->buffer_size = val;
>  }
>  
> +static bool vsock_custom_sockopt(int optname)
> +{
> +	switch (optname) {
> +	case SO_ZEROCOPY:
> +	case SO_INQ:
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
> +static int vsock_sol_socket_setsockopt(struct sock *sk, int optname,
> +				       sockptr_t optval, unsigned int optlen)
> +{
> +	struct vsock_sock *vsk = vsock_sk(sk);
> +	int err = 0;
> +	int val;
> +
> +	/* Use 'int' type here, because variable to
> +	 * set these options usually has this type.
> +	 */
> +	if (optlen < sizeof(val))
> +		return -EINVAL;
> +
> +	if (copy_from_sockptr(&val, optval, sizeof(val)))
> +		return -EFAULT;
> +
> +	if (val < 0 || val > 1)
> +		return -EINVAL;
> +
> +	lock_sock(sk);
> +
> +	switch (optname) {
> +	case SO_ZEROCOPY:
> +		if (vsk->transport && !vsock_msgzerocopy_allow(vsk->transport)) {
> +			err = -EOPNOTSUPP;
> +			break;
> +		}
> +
> +		sock_valbool_flag(sk, SOCK_ZEROCOPY, val);
> +		break;
> +
> +	case SO_INQ:
> +		if (sk->sk_type != SOCK_STREAM) {
> +			err = -ENOPROTOOPT;
> +			break;
> +		}
> +
> +		vsk->recvmsg_inq = val;
> +		break;
> +
> +	default:
> +		err = -ENOPROTOOPT;
> +		break;
> +	}
> +
> +	release_sock(sk);
> +	return err;
> +}
> +
>  static int vsock_connectible_setsockopt(struct socket *sock,
>  					int level,
>  					int optname,
> @@ -2045,36 +2106,16 @@ static int vsock_connectible_setsockopt(struct socket *sock,
>  	sk = sock->sk;
>  	vsk = vsock_sk(sk);
>  
> -	lock_sock(sk);
> -
> -	transport = vsk->transport;
> -
>  	if (level == SOL_SOCKET) {
> -		int zerocopy;
> -
> -		if (optname != SO_ZEROCOPY) {
> -			release_sock(sk);
> +		if (!vsock_custom_sockopt(optname))
>  			return sock_setsockopt(sock, level, optname, optval, optlen);
> -		}
> -
> -		/* Use 'int' type here, because variable to
> -		 * set this option usually has this type.
> -		 */
> -		COPY_IN(zerocopy);
>  
> -		if (zerocopy < 0 || zerocopy > 1) {
> -			err = -EINVAL;
> -			goto exit;
> -		}
> +		return vsock_sol_socket_setsockopt(sk, optname, optval, optlen);
> +	}
>  
> -		if (transport && !vsock_msgzerocopy_allow(transport)) {
> -			err = -EOPNOTSUPP;
> -			goto exit;
> -		}
> +	lock_sock(sk);
>  
> -		sock_valbool_flag(sk, SOCK_ZEROCOPY, zerocopy);
> -		goto exit;
> -	}
> +	transport = vsk->transport;
>  
>  	switch (optname) {
>  	case SO_VM_SOCKETS_BUFFER_SIZE:
> @@ -2581,6 +2622,7 @@ __vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>  	struct sock *sk;
>  	struct vsock_sock *vsk;
>  	const struct vsock_transport *transport;
> +	bool do_cmsg = false;
>  	int err;
>  
>  	sk = sock->sk;
> @@ -2637,13 +2679,26 @@ __vsock_connectible_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>  		err = __vsock_seqpacket_recvmsg(sk, msg, len, flags);
>  
>  out:
> -	/* Seqpacket has_data counts messages, while io_uring treats msg_inq as
> -	 * a byte length when sizing retries, so only streams report a hint.
> +	/* Seqpacket has_data counts messages, while SCM_INQ reports bytes and
> +	 * io_uring treats msg_inq as a byte length when sizing retries, so
> +	 * only streams report it.
>  	 */
> -	if (msg->msg_get_inq && err >= 0 && sk->sk_type == SOCK_STREAM)
> +	if ((vsk->recvmsg_inq || msg->msg_get_inq) && err >= 0 &&
> +	    sk->sk_type == SOCK_STREAM) {
>  		msg->msg_inq = vsock_stream_inq_hint(sk);
>  
> +		/* A negative hint means the transport could not tell. SCM_INQ
> +		 * has no encoding for that, so report nothing.
> +		 */
> +		do_cmsg = vsk->recvmsg_inq && msg->msg_inq >= 0;
> +	}
> +
>  	release_sock(sk);
> +
> +	if (do_cmsg)
> +		put_cmsg(msg, SOL_SOCKET, SCM_INQ, sizeof(msg->msg_inq),
> +			 &msg->msg_inq);
> +
>  	return err;
>  }
>  
> -- 
> 2.55.0
> 

All LGTM.

Acked-by: Bobby Eshleman <bobbyeshleman@meta.com>