netdev - Re: [PATCH v3 net-next 4/7] net: add new control message for incoming HW-timestamped packets

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Date:   Tue, 16 May 2017 18:29:47 -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>
Subject: Re: [PATCH v3 net-next 4/7] net: add new control message for incoming
 HW-timestamped packets

On Tue, May 16, 2017 at 8:44 AM, Miroslav Lichvar <mlichvar@...hat.com> wrote:
> Add SOF_TIMESTAMPING_OPT_PKTINFO option to request a new control message
> for incoming packets with hardware timestamps. It contains the index of
> the real interface which received the packet and the length of the
> packet at layer 2.
>
> The index is useful with bonding, bridges and other interfaces, where
> IP_PKTINFO doesn't allow applications to determine which PHC made the
> timestamp. With the L2 length (and link speed) it is possible to
> transpose preamble timestamps to trailer timestamps, which are used in
> the NTP protocol.
>
> While this information could be provided by two new socket options
> independently from timestamping, it doesn't look like they would be very
> useful. With this option any performance impact is limited to hardware
> timestamping.
>
> Use dev_get_by_napi_id() to get the device and its index. On kernels
> with disabled CONFIG_NET_RX_BUSY_POLL or drivers not using NAPI, a zero
> index will be returned in the control message.
>
> CC: Richard Cochran <richardcochran@...il.com>
> CC: Willem de Bruijn <willemb@...gle.com>
> Signed-off-by: Miroslav Lichvar <mlichvar@...hat.com>

Acked-by: Willem de Bruijn <willemb@...gle.com>