在 2022/12/27 下午3:12, Jason Wang 写道:

在 2022/12/20 22:14, Heng Qi 写道:

quoted

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

Signed-off-by: Heng Qi <redacted>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
  drivers/net/virtio_net.c | 27 ++++++++++++++++++++++-----
  1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 40bc58fa57f5..9f31bfa7f9a6 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -563,22 +563,39 @@ 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;
+    }
+
+    /* Need to adjust this to calculate the correct postion
+     * for shinfo of the xdpf.
+     */
+    xdpf->headroom -= vi->hdr_len;

Any reason we need to do this here? (Or if it is, is it only needed 
for multibuffer XDP?)

Going back to its wrapping function virtnet_xdp_xmit(), we need to free 
up the pending old buffers.
If the "is_xdp_frame(ptr)" condition is met, then 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.

Also, it's not necessary for single-buffer xdp, but we need to keep it 
because it's harmless and as it should be.

Thanks.

Other looks good.

Thanks

quoted

      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 */