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

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