On Mon, Apr 24, 2017 at 11:18:13AM -0400, Willem de Bruijn wrote: > On Mon, Apr 24, 2017 at 5:00 AM, Miroslav Lichvar <mlich...@redhat.com> wrote: > > Would "skb->data - skb->head - > > skb->mac_header + skb->len" always work as the L2 length for received > > packets at the time when the cmsg is prepared? > > (skb->data - skb->head) - skb->mac_header computes the length > of data before the mac, such as reserve?
data - head includes the reserve, but mac_header does too, so I think it should be just the length of MAC header and everything up to the data. > Do you mean skb->data - > skb->mac_header (or - skb_mac_offset(skb))? That would give me a pointer? If I used skb_mac_offset(), the total length would be just skb->len - skb_mac_offset()? > > As for the original ifindex, it seems to me it does need to be saved > > to a new field since __netif_receive_skb_core() intentionally > > overwrites skb->skb_iif. What would be the best place for it, sk_buff > > or skb_shared_info? > > Finding storage space on the receive path will not be easy. > > One shortcut to avoid storing this information explicitly is to look up > the device from skb->napi_id. Thanks. This looks promising. It will depend on CONFIG_NET_RX_BUSY_POLL, but I guess that's ok. It nicely isolates all costs to the timestamping option. -- Miroslav Lichvar
