netdev - Re: [RFC PATCH 3/7] net: add option to get information about timestamped packets

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Date:   Thu, 13 Apr 2017 10:37:07 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Miroslav Lichvar <mlichvar@...hat.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Richard Cochran <richardcochran@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        "Keller, Jacob E" <jacob.e.keller@...el.com>,
        Denny Page <dennypage@...com>, Jiri Benc <jbenc@...hat.com>
Subject: Re: [RFC PATCH 3/7] net: add option to get information about
 timestamped packets

On Wed, Apr 12, 2017 at 10:17 AM, Miroslav Lichvar <mlichvar@...hat.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. Why is this L2
length needed?

> 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/

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.