Re: [PATCH net v2 2/2] virtio-net: xsk: rx: move the xdp->data adjustment to buf_to_xdp()

[Bui Quang Minh]

On 6/24/25 17:17, Paolo Abeni wrote:
On 6/21/25 4:49 PM, Bui Quang Minh wrote:
This commit does not do any functional changes. It moves xdp->data
adjustment for buffer other than first buffer to buf_to_xdp() helper so
that the xdp_buff adjustment does not scatter over different functions.
Signed-off-by: Bui Quang Minh <minhquangbu...@gmail.com>
---
  drivers/net/virtio_net.c | 16 ++++++++++++++--
  1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 1eb237cd5d0b..4e942ea1bfa3 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1159,7 +1159,19 @@ static struct xdp_buff *buf_to_xdp(struct virtnet_info 
*vi,
                return NULL;
        }
  
-	xsk_buff_set_size(xdp, len);
+       if (first_buf) {
+               xsk_buff_set_size(xdp, len);
+       } else {
+               /* This is the same as xsk_buff_set_size but with the adjusted
+                * xdp->data.
+                */
+               xdp->data = xdp->data_hard_start + XDP_PACKET_HEADROOM;
+               xdp->data -= vi->hdr_len;
+               xdp->data_meta = xdp->data;
+               xdp->data_end = xdp->data + len;
+               xdp->flags = 0;
+       }
+
        xsk_buff_dma_sync_for_cpu(xdp);
  
  	return xdp;
@@ -1284,7 +1296,7 @@ static int xsk_append_merge_buffer(struct virtnet_info 
*vi,
                        goto err;
                }
  
-		memcpy(buf, xdp->data - vi->hdr_len, len);
+               memcpy(buf, xdp->data, len);
  
  		xsk_buff_free(xdp);
  
I'm unsure if this change is in the right direction because it almost
open-code the existing xsk_buff_set_size() helper - any changes there
should be reflected here, too.

I've found out that there is xdp_prepare_buff helper which gives more 
control over the headroom so it can be used here. I'll update in the 
next version.

Thanks,
Quang Minh.