linux-kernel - Re: [PATCH v5] net: ip, diag -- Add diag interface for raw sockets

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Date:   Wed, 28 Sep 2016 07:06:26 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Cyrill Gorcunov <gorcunov@...il.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        David Ahern <dsa@...ulusnetworks.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
        kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
        kaber@...sh.net, avagin@...nvz.org, stephen@...workplumber.org
Subject: Re: [PATCH v5] net: ip, diag -- Add diag interface for raw sockets

On 16-09-28 06:51 AM, Cyrill Gorcunov wrote:
> On Wed, Sep 28, 2016 at 06:43:01AM -0400, Jamal Hadi Salim wrote:

[..]
>> I dont know how compilation will fail but you may be right with note:
>> that is not how pads have been used in the past. They are supposed to
>> cosmetic annotation which indicates "here's a hole; use it in the
>> future if you are looking to add something". And someone in the
>> future can claim them. I am not sure if MBZ philosophy applies.
>
> This structure is uapi, so anyone has complete rights to reference
> @pad in the userspace programs. Sure it would be more clear to remove
> the @pad completely, but if we choose so I think it's better to do
> on top instead and then if someone complain we can easily revert
> the single trivial commit instead of this big patch.

I am conflicted.
A field labelled "pad" does not appear to be valid as "UAPI". It is
a cosmetic indicator. If you did sizeof() with or without it being
present the value doesnt change.
BTW: There is at least one major structure in inet diag has a hole
today and doesnt have a padding indicator.

> If protocol goes over u8 then complete inet_diag_req_v2 structure will
> have to be reworked becaue @sdiag_protocol is u8 as well. IOW, once
> someone liftup IPPROTO_MAX > 255, he will notice the problem immediately
> because diag for such module simply stop working properly.
>

ok.

cheers,
jamal