Re: [PATCH v9 bpf-next 07/14] net: xdp: add multi-buff support to xdp_build_skb_from_frame
From: Alexander Duyck <hidden>
Date: 2021-06-28 21:05:58
Also in:
netdev
On Mon, Jun 14, 2021 at 5:51 AM Lorenzo Bianconi [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Introduce xdp multi-buff support to __xdp_build_skb_from_frame/xdp_build_skb_from_frame utility routines. Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org> --- net/core/xdp.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)diff --git a/net/core/xdp.c b/net/core/xdp.c index f61c63115c95..71bedf6049a1 100644 --- a/net/core/xdp.c +++ b/net/core/xdp.c@@ -582,9 +582,15 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf, struct sk_buff *skb, struct net_device *dev) { + struct skb_shared_info *sinfo = xdp_get_shared_info_from_frame(xdpf); unsigned int headroom, frame_size; + int i, num_frags = 0; void *hard_start; + /* xdp multi-buff frame */ + if (unlikely(xdp_frame_is_mb(xdpf))) + num_frags = sinfo->nr_frags; + /* Part of headroom was reserved to xdpf */ headroom = sizeof(*xdpf) + xdpf->headroom;@@ -603,6 +609,13 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf, if (xdpf->metasize) skb_metadata_set(skb, xdpf->metasize); + for (i = 0; i < num_frags; i++) + skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, + skb_frag_page(&sinfo->frags[i]), + skb_frag_off(&sinfo->frags[i]), + skb_frag_size(&sinfo->frags[i]), + xdpf->frame_sz); +
So this is assuming the header frame and all of the frags are using the same size. Rather than reading the frags out and then writing them back, why not just directly rewrite the nr_frags, add the total size to skb->len and skb->data_len, and then update the truesize? Actually, I think you might need to store the truesize somewhere in addition to the data_len that you were storing in the shared info.