On Thu, Apr 13, 2017 at 10:37:07AM -0400, Willem de Bruijn wrote: > On Wed, Apr 12, 2017 at 10:17 AM, Miroslav Lichvar <mlich...@redhat.com> > wrote: > > Extend the skb_shared_hwtstamps structure with the index of the > > real interface which received or transmitted the packet and the length > > of the packet at layer 2. > > The original packet is received along with the timestamp.
But only outgoing packets, right? > Why is this L2 length needed? It's needed for incoming packets to allow converting of preamble timestamps to trailer timestamps. > > Add a SOF_TIMESTAMPING_OPT_PKTINFO flag to > > the SO_TIMESTAMPING option to allow applications to get this information > > as struct scm_ts_pktinfo in SCM_TIMESTAMPING_PKTINFO control message. > > This patch saves skb->dev->ifindex, which is the same as existing > SOF_TIMESTAMPING_OPT_CMSG. See also the bug fix for that > feature I sent yesterday: http://patchwork.ozlabs.org/patch/750197/ The main point is that it provides the index of the device which received the packet. It does duplicate the functionality of OPT_CMSG + IP_PKTINFO for outgoing packets, but I thought it might be useful with the TSONLY option. BTW, the original ifindex used to be in skb->skb_iif, but that changed in b6858177. > If the intent is to return a different ifindex, I would still suggest using > the existing pktinfo infrastructure, but changing the ifindex that is > recorded. How would the application get the l2 length? If this (l2 length, if_index) tuple is specific to timestamping, I think it would make sense to keep it out of the IP layer. -- Miroslav Lichvar
