netdev - Re: [PATCH v3] net: ip, diag -- Add diag interface for raw sockets

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Date:   Tue, 27 Sep 2016 10:48:12 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     Eric Dumazet <eric.dumazet@...il.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 v3] net: ip, diag -- Add diag interface for raw sockets

On Mon, Sep 26, 2016 at 07:54:37PM -0600, David Ahern wrote:
> On 9/26/16 4:38 PM, Cyrill Gorcunov wrote:
> > Something like
> > 
> > Index: linux-ml.git/include/uapi/linux/inet_diag.h
> > ===================================================================
> > --- linux-ml.git.orig/include/uapi/linux/inet_diag.h    2016-09-11 20:56:18.191584145 +0300
> > +++ linux-ml.git/include/uapi/linux/inet_diag.h 2016-09-27 01:34:08.413172394 +0300
> > @@ -38,7 +38,7 @@ struct inet_diag_req_v2 {
> >         __u8    sdiag_family;
> >         __u8    sdiag_protocol;
> >         __u8    idiag_ext;
> > -       __u8    pad;
> > +       __u8    sdiag_raw_protocol;     /* SOCK_RAW only, @pad for others */
> 
> Seems like that should be a union to keep the API.

Is anonymous union (which is not part of c99) are acceptable in uapi?
Initially I declared it as union but then scratched my head if this
would be acceptable.

> 
> 
> >         __u32   idiag_states;
> >         struct inet_diag_sockid id;
> >  };
> > 
> > and in raw-diag module we will use @sdiag_raw_protocol instead of
> > @sdiag_protocol field. Didn't cover ss tool source code yet but
> > I think the idea is seen. Still not sure if start using @pad here
> > is a good idea (it's uapi), maybe beter to ask nla attribute which would
> > come right afterh the inet_diag_req_v2 message?
> > 
> 
> seems reasonable to me since 2 protocols need to be sent to the kernel.
> 
> Alternatively, sdiag_protocol could be the actual protocol and the pad union be a flag field
> with say bit 0 = INET_DIAG_FLAG_SOCK_RAW. Allows other overrides in the future if needed.

The @sdiag_protocol used for matching in diag module handler, so no, I think
we should not change this semantics. I would stick with @pad usage and if
anonymous unions are acceptable this would be just great.

	Cyrill