netdev - Re: [PATCH] [RFC v2] packet: experimental support for 64-bit timestamps

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Date:   Tue, 28 Nov 2017 09:24:33 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Francis Yan <francisyyan@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        "Rosen, Rami" <rami.rosen@...el.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Mike Maloney <maloney@...gle.com>,
        Sowmini Varadhan <sowmini.varadhan@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] [RFC v2] packet: experimental support for 64-bit timestamps

On Tue, Nov 28, 2017 at 8:14 AM, Arnd Bergmann <arnd@...db.de> wrote:
> This is a second attempt to allow 64-bit timestamps in packet sockets,

Thanks for coding up this variant.

> The implementation is fairly straightforward, but I'm less sure about the
> interface. Using SOF_TIMESTAMPING_* flags in PACKET_TIMESTAMP is a bit
> odd already since most of the other flags make no sense here.  Adding two
> more flags that only make sense for packet sockets but not the normal
> SO_TIMESTAMPING option on other sockets makes this even more confusing.

Agreed.

Unfortunately, we're already stuck with SOL_PACKET/PACKET_TIMESTAMP
accepting SOF_TIMESTAMPING_RAW_HARDWARE.

Perhaps we can define a new PF_PACKET specific enum where the
equivalent option has the same value, so is backwards compatible:

enum {
      PACKET_TIMESTAMP_ORIG = 0,
      PACKET_TIMESTAMP_ZERO = 1 << 0,
      PACKET_TIMESTAMP_NS64 = 1 << 1,
      PACKET_TIMESTAMP_HW = 1 << 6
};

and  BUILD_BUG_ON(PACKET_TIMESTAMP_RAW != SOF_TIMESTAMPING_RAW_HARDWARE)
to document the dependency.

At high level, the code looks great to me, itself.