On 01/30, Marcus Wichelmann wrote:
> Enable the support for bpf_xdp_adjust_meta for XDP buffers initialized
> by the tun driver. This is useful to pass metadata from an XDP program
> that's attached to a tap device to following XDP/TC programs.
>
> When used together with vhost_net, the batched XDP buffers were already
> initialized with metadata support by the vhost_net driver, but the
> metadata was not yet passed to the skb on XDP_PASS. So this also adds
> the required skb_metadata_set calls.
Can you expand more on what kind of metadata is present with vhost_net
and who fills it in? Is it virtio header stuff? I wonder how you
want to consume it..
Can you also add a selftest to use this new functionality?
> Signed-off-by: Marcus Wichelmann <marcus.wichelmann@xxxxxxxxxxxxxxxx>
> ---
> drivers/net/tun.c | 23 ++++++++++++++++++-----
> 1 file changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index e816aaba8..d3cfea40a 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1600,7 +1600,8 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
>
> static struct sk_buff *__tun_build_skb(struct tun_file *tfile,
> struct page_frag *alloc_frag, char *buf,
> - int buflen, int len, int pad)
> + int buflen, int len, int pad,
> + int metasize)
> {
> struct sk_buff *skb = build_skb(buf, buflen);
>
> @@ -1609,6 +1610,8 @@ static struct sk_buff *__tun_build_skb(struct tun_file *tfile,
>
> skb_reserve(skb, pad);
> skb_put(skb, len);
> + if (metasize)
> + skb_metadata_set(skb, metasize);
> skb_set_owner_w(skb, tfile->socket.sk);
>
> get_page(alloc_frag->page);
> @@ -1668,6 +1671,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
> char *buf;
> size_t copied;
> int pad = TUN_RX_PAD;
> + int metasize = 0;
> int err = 0;
>
> rcu_read_lock();
> @@ -1695,7 +1699,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
> if (hdr->gso_type || !xdp_prog) {
> *skb_xdp = 1;
> return __tun_build_skb(tfile, alloc_frag, buf, buflen, len,
> - pad);
> + pad, metasize);
> }
>
> *skb_xdp = 0;
> @@ -1709,7 +1713,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
> u32 act;
>
> xdp_init_buff(&xdp, buflen, &tfile->xdp_rxq);
> - xdp_prepare_buff(&xdp, buf, pad, len, false);
> + xdp_prepare_buff(&xdp, buf, pad, len, true);
>
> act = bpf_prog_run_xdp(xdp_prog, &xdp);
> if (act == XDP_REDIRECT || act == XDP_TX) {
> @@ -1730,12 +1734,16 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
>
> pad = xdp.data - xdp.data_hard_start;
> len = xdp.data_end - xdp.data;
> +
> + metasize = xdp.data - xdp.data_meta;
[..]
> + metasize = metasize > 0 ? metasize : 0;
Why is this part needed?
