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Date:   Thu, 6 Jul 2023 18:49:06 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Bobby Eshleman <bobby.eshleman@bytedance.com>,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@sberdevices.ru, oxffffaa@gmail.com
Subject: Re: [RFC PATCH v5 02/17] vhost/vsock: read data from non-linear skb
Message-ID: <cgq3d3j25doy7qar6xsepsrly5ypyjwahf2gybfi3fnozp3kjx@hh5q5bps37ws>
References: <20230701063947.3422088-1-AVKrasnov@sberdevices.ru>
 <20230701063947.3422088-3-AVKrasnov@sberdevices.ru>
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In-Reply-To: <20230701063947.3422088-3-AVKrasnov@sberdevices.ru>
Precedence: bulk

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@sberdevices.ru>
>---
> 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
>