linux-kernel - Re: [PATCH 2/2] [RFC] packet: experimental support for 64-bit timestamps

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Message-ID: <CAJ+HfNj-2HDuW53sUjgfV4iPnVnMKquV7pgu_zggbRuWf6R3=w@mail.gmail.com>
Date:   Tue, 28 Nov 2017 08:04:41 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Shuah Khan <shuah@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Mike Maloney <maloney@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        "Rosen, Rami" <rami.rosen@...el.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        Sowmini Varadhan <sowmini.varadhan@...cle.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org,
        Björn Töpel <bjorn.topel@...el.com>
Subject: Re: [PATCH 2/2] [RFC] packet: experimental support for 64-bit timestamps

2017-11-27 21:51 GMT+01:00 Arnd Bergmann <arnd@...db.de>:
[...]
>> There already is an effort to come up with a new AF_PACKET V4 [1].
>> We should make sure that any new interface does not have the
>> Y2038/Y2106 issue. But, if a new version is being developed and
>> that subsumes all existing use cases, then there probably is no need
>> for another version that is a very small diff to V3.
>
> Ah, perfect, that's good timing. Adding Björn to Cc here.
>

Unfortunately, for the Y2038/Y2106 cases, we'll be (as a result of
netdevconf discussions) moving the AF_PACKET V4 implementation to a
separate, new, address/packet family.

>> If adding support for existing applications is useful, another approach
>> would be to add a new socket option that changes the semantics for
>> the two u32 fields in each of V1, V2 and V3 to hold nsec. Add a single
>> check after filling in those structs whether the option is set and, if so,
>> overwrite the two fields.
>>
>> [1] https://lwn.net/Articles/737947/
>
> I don't think that's necessary. As long as the V4 capabilities are a
> superset of V1-V3, we should be able to just require all users to
> move to V4 (or later) in the next 89 years, and make sure that they
> use unsigned seconds if they care about 2038.
>

Given that V4 wont be around for AF_PACKET -- at least not in the
shape of our patches -- Willem's suggestion is probably a good way
forward.

>       Arnd