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Subject[PATCH 6/9] virtio-net: unmark scatterlist ending after virtqueue_add_buf
Date
Prepare for when virtqueue_add_buf will use sg_next instead of
ignoring ending markers.

Note that for_each_sg (and thus virtqueue_add_sg) allows you
to pass a "truncated" scatterlist that does not have a marker
on the last item. We rely on this in add_recvbuf_mergeable.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
drivers/net/virtio_net.c | 19 ++++++++++++++-----
1 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 35c00c5..78b6f51 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -440,13 +440,16 @@ static int add_recvbuf_small(struct receive_queue *rq, gfp_t gfp)

hdr = skb_vnet_hdr(skb);
sg_set_buf(rq->sg, &hdr->hdr, sizeof hdr->hdr);
-
skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);

err = virtqueue_add_buf(rq->vq, rq->sg, 0, 2, skb, gfp);
if (err < 0)
dev_kfree_skb(skb);

+ /* An optimization: clear the end bit set by skb_to_sgvec, so
+ * we can simply re-use rq->sg[] next time.
+ */
+ sg_unmark_end(rq->sg + 1);
return err;
}

@@ -505,8 +508,7 @@ static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
if (!page)
return -ENOMEM;

- sg_init_one(rq->sg, page_address(page), PAGE_SIZE);
-
+ sg_set_page(rq->sg, page, PAGE_SIZE, 0);
err = virtqueue_add_buf(rq->vq, rq->sg, 0, 1, page, gfp);
if (err < 0)
give_pages(rq, page);
@@ -671,6 +673,7 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
struct virtnet_info *vi = sq->vq->vdev->priv;
unsigned num_sg;
+ int ret;

pr_debug("%s: xmit %p %pM\n", vi->dev->name, skb, dest);

@@ -710,8 +713,14 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
sg_set_buf(sq->sg, &hdr->hdr, sizeof hdr->hdr);

num_sg = skb_to_sgvec(skb, sq->sg + 1, 0, skb->len) + 1;
- return virtqueue_add_buf(sq->vq, sq->sg, num_sg,
- 0, skb, GFP_ATOMIC);
+ ret = virtqueue_add_buf(sq->vq, sq->sg, num_sg,
+ 0, skb, GFP_ATOMIC);
+
+ /* An optimization: clear the end bit set by skb_to_sgvec, so
+ * we can simply re-use sq->sg[] next time.
+ */
+ sg_unmark_end(&sq->sg[num_sg-1]);
+ return ret;
}

static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
--
1.7.1



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