[RFC PATCH v1 05/12] vsock/virtio: non-linear skb support

[Arseniy Krasnov <AVKrasnov@sberdevices.ru>]

Use pages of non-linear skb as buffers in virtio tx queue.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
---
 net/vmw_vsock/virtio_transport.c | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 28b5a8e8e094..b8a7d6dc9f46 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -100,7 +100,8 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 	vq = vsock->vqs[VSOCK_VQ_TX];
 
 	for (;;) {
-		struct scatterlist hdr, buf, *sgs[2];
+		struct scatterlist *sgs[MAX_SKB_FRAGS + 1];
+		struct scatterlist bufs[MAX_SKB_FRAGS + 1];
 		int ret, in_sg = 0, out_sg = 0;
 		struct sk_buff *skb;
 		bool reply;
@@ -111,12 +112,30 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 
 		virtio_transport_deliver_tap_pkt(skb);
 		reply = virtio_vsock_skb_reply(skb);
+		sg_init_one(&bufs[0], virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb)));
+		sgs[out_sg++] = &bufs[0];
+
+		if (skb_is_nonlinear(skb)) {
+			int i;
+
+			for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+				struct page *data_page = skb_shinfo(skb)->frags[i].bv_page;
+
+				/* We will use 'page_to_virt()' for userspace page here,
+				 * because virtio layer will call 'virt_to_phys()' later
+				 * to fill buffer descriptor. We don't touch memory at
+				 * "virtual" address of this page.
+				 */
+				sg_init_one(&bufs[i + 1],
+					    page_to_virt(data_page), PAGE_SIZE);
+				sgs[out_sg++] = &bufs[i + 1];
+			}
+		} else {
+			if (skb->len > 0) {
+				sg_init_one(&bufs[1], skb->data, skb->len);
+				sgs[out_sg++] = &bufs[1];
+			}
 
-		sg_init_one(&hdr, virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb)));
-		sgs[out_sg++] = &hdr;
-		if (skb->len > 0) {
-			sg_init_one(&buf, skb->data, skb->len);
-			sgs[out_sg++] = &buf;
 		}
 
 		ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL);
-- 
2.25.1