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

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Date:   Wed, 28 Sep 2016 13:51:47 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.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 Wed, Sep 28, 2016 at 06:43:01AM -0400, Jamal Hadi Salim wrote:
...
> > 
> > Someone may have set it to zero explicitly on source level, and the
> > compilation will fail on new kernel then. So no, keeping the name
> > is reasonable.
> > 
> 
> 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.

> 
> > > Should you not just rename it?
> > > Also I notice when things like __raw_v4_lookup() are claiming it is unsigned
> > > short instead of a u8?
> > 
> > The protocol is still up to 255 for a while, is it expected that IPPROTO_MAX
> > will be increased in more-less near future? Of course I can drop the idea
> > of using @pad here and switch to some extended reauest but prefer to stick
> > with simplier solution. Hm?
> > 
> 
> Ok. If i understood correctly it was already unsigned short before your
> patch -so i agree it doesnt matter. Maybe just put a comment to express
> that if ever protocol goes above 255 it wont be sufficient.

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.