Re: [RFC PATCH v3 2/3] virtio/vsock: send credit update during setting SO_RCVLOWAT

[Stefano Garzarella]

On Wed, Nov 22, 2023 at 09:05:09PM +0300, Arseniy Krasnov wrote:
> Send credit update message when SO_RCVLOWAT is updated and it is bigger
> than number of bytes in rx queue. It is needed, because 'poll()' will
> wait until number of bytes in rx queue will be not smaller than
> SO_RCVLOWAT, so kick sender to send more data. Otherwise mutual hungup
> for tx/rx is possible: sender waits for free space and receiver is
> waiting data in 'poll()'.
>
> Signed-off-by: Arseniy Krasnov <avkrasnov@xxxxxxxxxxxxxxxxx>
> ---
> Changelog:
> v1 -> v2:
>  * Update commit message by removing 'This patch adds XXX' manner.
>  * Do not initialize 'send_update' variable - set it directly during
>    first usage.
>
> drivers/vhost/vsock.c                   |  2 ++
> include/linux/virtio_vsock.h            |  1 +
> net/vmw_vsock/virtio_transport.c        |  2 ++
> net/vmw_vsock/virtio_transport_common.c | 28 +++++++++++++++++++++++++
> net/vmw_vsock/vsock_loopback.c          |  2 ++
> 5 files changed, 35 insertions(+)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index f75731396b7e..ecfa5c11f5ee 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -451,6 +451,8 @@ static struct virtio_transport vhost_transport = {
> 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
>
> 		.read_skb = virtio_transport_read_skb,
> +
> +		.set_rcvlowat             = virtio_transport_set_rcvlowat

Since now we don't set it anymore in the callback, what about following
the notify_* callbacks and rename it in `notify_set_rcvlowat`?

Eventually I think we can rename it in the previous patch.

> 	},
>
> 	.send_pkt = vhost_transport_send_pkt,
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index ebb3ce63d64d..97dc1bebc69c 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -256,4 +256,5 @@ void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit);
> void virtio_transport_deliver_tap_pkt(struct sk_buff *skb);
> int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *list);
> int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t read_actor);
> +int virtio_transport_set_rcvlowat(struct vsock_sock *vsk, int val);
> #endif /* _LINUX_VIRTIO_VSOCK_H */
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index af5bab1acee1..cf3431189d0c 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -539,6 +539,8 @@ static struct virtio_transport virtio_transport = {
> 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
>
> 		.read_skb = virtio_transport_read_skb,
> +
> +		.set_rcvlowat             = virtio_transport_set_rcvlowat
> 	},
>
> 	.send_pkt = virtio_transport_send_pkt,
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index f6dc896bf44c..4acee21b4350 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -1684,6 +1684,34 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
> }
> EXPORT_SYMBOL_GPL(virtio_transport_read_skb);
>
> +int virtio_transport_set_rcvlowat(struct vsock_sock *vsk, int val)
> +{
> +	struct virtio_vsock_sock *vvs = vsk->trans;
> +	bool send_update;
> +
> +	spin_lock_bh(&vvs->rx_lock);
> +
> +	/* If number of available bytes is less than new
> +	 * SO_RCVLOWAT value, kick sender to send more
> +	 * data, because sender may sleep in its 'send()'
> +	 * syscall waiting for enough space at our side.
> +	 */

Let's try to use at least the full 80 characters so we can reduce the
lines in this comment block.

> +	send_update = vvs->rx_bytes < val;
> +
> +	spin_unlock_bh(&vvs->rx_lock);
> +
> +	if (send_update) {
> +		int err;
> +
> +		err = virtio_transport_send_credit_update(vsk);
> +		if (err < 0)
> +			return err;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(virtio_transport_set_rcvlowat);
> +
> MODULE_LICENSE("GPL v2");
> MODULE_AUTHOR("Asias He");
> MODULE_DESCRIPTION("common code for virtio vsock");
> diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> index 048640167411..388c157f6633 100644
> --- a/net/vmw_vsock/vsock_loopback.c
> +++ b/net/vmw_vsock/vsock_loopback.c
> @@ -98,6 +98,8 @@ static struct virtio_transport loopback_transport = {
> 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
>
> 		.read_skb = virtio_transport_read_skb,
> +
> +		.set_rcvlowat             = virtio_transport_set_rcvlowat
> 	},
>
> 	.send_pkt = vsock_loopback_send_pkt,
> --
> 2.25.1