On 2020/4/30 下午5:54, Jesper Dangaard Brouer wrote:
On Mon, 27 Apr 2020 13:50:15 +0800
Jason Wang <jasowang@xxxxxxxxxx> wrote:
On 2020/4/23 上午12:09, Jesper Dangaard Brouer wrote:
In vhost_net_build_xdp() the 'buf' that gets queued via an xdp_buff
have embedded a struct tun_xdp_hdr (located at xdp->data_hard_start)
which contains the buffer length 'buflen' (with tailroom for
skb_shared_info). Also storing this buflen in xdp->frame_sz, does not
obsolete struct tun_xdp_hdr, as it also contains a struct
virtio_net_hdr with other information.
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
---
drivers/vhost/net.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 87469d67ede8..69af007e22f4 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -745,6 +745,7 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
xdp->data = buf + pad;
xdp->data_end = xdp->data + len;
hdr->buflen = buflen;
+ xdp->frame_sz = buflen;
--net->refcnt_bias;
alloc_frag->offset += buflen;
Tun_xdp_one() will use hdr->buflen as the frame_sz (patch 19), so it
looks to me there's no need to do this?
I was thinking to go the "other way", meaning let tun_xdp_one() use
xdp->frame_sz, which gets set here. This would allow us to refactor
the code, and drop struct tun_xdp_hdr, as (see pahole below) it only
carries 'buflen' and the remaining part comes from struct
virtio_net_hdr, which could be used directly instead.
As this will be a code refactor, I would prefer we do it after this
patchseries is agreed upon.
$ pahole -C tun_xdp_hdr drivers/net/tap.o
struct tun_xdp_hdr {
int buflen; /* 0 4 */
struct virtio_net_hdr gso; /* 4 10 */
/* size: 16, cachelines: 1, members: 2 */
/* padding: 2 */
/* last cacheline: 16 bytes */
};
Ok I get this.
Thanks
