Re: [RFC PATCH v5 02/17] vhost/vsock: read data from non-linear skb

[Stefano Garzarella]

On Sat, Jul 01, 2023 at 09:39:32AM +0300, Arseniy Krasnov wrote:
> This adds copying to guest's virtio buffers from non-linear skbs. Such
> skbs are created by protocol layer when MSG_ZEROCOPY flags is used. It
> replaces call of 'copy_to_iter()' to 'skb_copy_datagram_iter()'- second
> function can read data from non-linear skb. Also this patch uses field
> 'frag_off' from skb control block. This field shows current offset to
> read data from skb which could be both linear or not.
>
> Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
> ---
> Changelog:
> v4 -> v5:
>  * Use local variable for 'frag_off'.
>  * Update commit message by adding some details about 'frag_off' field.
>  * R-b from Bobby Eshleman removed due to patch update.

I think we should merge this patch with the previous one, since
vhost-vsock for example uses virtio_transport_stream_do_dequeue()
that we change in the previous commit, so we will break the bisection.

The patch LGTM!

Stefano

> drivers/vhost/vsock.c | 14 +++++++++-----
> 1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 6578db78f0ae..cb00e0e059e4 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -114,6 +114,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 		struct sk_buff *skb;
> 		unsigned out, in;
> 		size_t nbytes;
> +		u32 frag_off;
> 		int head;
>
> 		skb = virtio_vsock_skb_dequeue(&vsock->send_pkt_queue);
> @@ -156,7 +157,8 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 		}
>
> 		iov_iter_init(&iov_iter, ITER_DEST, &vq->iov[out], in, iov_len);
> -		payload_len = skb->len;
> +		frag_off = VIRTIO_VSOCK_SKB_CB(skb)->frag_off;
> +		payload_len = skb->len - frag_off;
> 		hdr = virtio_vsock_hdr(skb);
>
> 		/* If the packet is greater than the space available in the
> @@ -197,8 +199,10 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 			break;
> 		}
>
> -		nbytes = copy_to_iter(skb->data, payload_len, &iov_iter);
> -		if (nbytes != payload_len) {
> +		if (skb_copy_datagram_iter(skb,
> +					   frag_off,
> +					   &iov_iter,
> +					   payload_len)) {
> 			kfree_skb(skb);
> 			vq_err(vq, "Faulted on copying pkt buf\n");
> 			break;
> @@ -212,13 +216,13 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 		vhost_add_used(vq, head, sizeof(*hdr) + payload_len);
> 		added = true;
>
> -		skb_pull(skb, payload_len);
> +		VIRTIO_VSOCK_SKB_CB(skb)->frag_off += payload_len;
> 		total_len += payload_len;
>
> 		/* If we didn't send all the payload we can requeue the packet
> 		 * to send it with the next available buffer.
> 		 */
> -		if (skb->len > 0) {
> +		if (VIRTIO_VSOCK_SKB_CB(skb)->frag_off < skb->len) {
> 			hdr->flags |= cpu_to_le32(flags_to_restore);
>
> 			/* We are queueing the same skb to handle
> --
> 2.25.1