netdev - [PATCH v3 6/9] virtio-net: transmit the multi-buffer xdp

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Date:   Tue,  3 Jan 2023 14:40:09 +0800
From:   Heng Qi <hengqi@...ux.alibaba.com>
To:     netdev@...r.kernel.org, bpf@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: [PATCH v3 6/9] virtio-net: transmit the multi-buffer xdp

This serves as the basis for XDP_TX and XDP_REDIRECT
to send a multi-buffer xdp_frame.

Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Acked-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/virtio_net.c | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ab01cf3855bc..fee9ce31f6c7 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -563,22 +563,43 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
 				   struct xdp_frame *xdpf)
 {
 	struct virtio_net_hdr_mrg_rxbuf *hdr;
-	int err;
+	struct skb_shared_info *shinfo;
+	u8 nr_frags = 0;
+	int err, i;
 
 	if (unlikely(xdpf->headroom < vi->hdr_len))
 		return -EOVERFLOW;
 
-	/* Make room for virtqueue hdr (also change xdpf->headroom?) */
+	if (unlikely(xdp_frame_has_frags(xdpf))) {
+		shinfo = xdp_get_shared_info_from_frame(xdpf);
+		nr_frags = shinfo->nr_frags;
+	}
+
+	/* In wrapping function virtnet_xdp_xmit(), we need to free
+	 * up the pending old buffers, where we need to calculate the
+	 * position of skb_shared_info in xdp_get_frame_len() and
+	 * xdp_return_frame(), which will involve to xdpf->data and
+	 * xdpf->headroom. Therefore, we need to update the value of
+	 * headroom synchronously here.
+	 */
+	xdpf->headroom -= vi->hdr_len;
 	xdpf->data -= vi->hdr_len;
 	/* Zero header and leave csum up to XDP layers */
 	hdr = xdpf->data;
 	memset(hdr, 0, vi->hdr_len);
 	xdpf->len   += vi->hdr_len;
 
-	sg_init_one(sq->sg, xdpf->data, xdpf->len);
+	sg_init_table(sq->sg, nr_frags + 1);
+	sg_set_buf(sq->sg, xdpf->data, xdpf->len);
+	for (i = 0; i < nr_frags; i++) {
+		skb_frag_t *frag = &shinfo->frags[i];
+
+		sg_set_page(&sq->sg[i + 1], skb_frag_page(frag),
+			    skb_frag_size(frag), skb_frag_off(frag));
+	}
 
-	err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdp_to_ptr(xdpf),
-				   GFP_ATOMIC);
+	err = virtqueue_add_outbuf(sq->vq, sq->sg, nr_frags + 1,
+				   xdp_to_ptr(xdpf), GFP_ATOMIC);
 	if (unlikely(err))
 		return -ENOSPC; /* Caller handle free/refcnt */
 
-- 
2.19.1.6.gb485710b