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

[Jamal Hadi Salim]

On 16-09-28 06:17 AM, Cyrill Gorcunov wrote:
> On Wed, Sep 28, 2016 at 06:08:00AM -0400, Jamal Hadi Salim wrote:
> ...
> > > @@ -38,7 +38,10 @@ struct inet_diag_req_v2 {
> > >  	__u8	sdiag_family;
> > >  	__u8	sdiag_protocol;
> > >  	__u8	idiag_ext;
> > > -	__u8	pad;
> > > +	union {
> > > +		__u8	pad;
> > > +		__u8	sdiag_raw_protocol;	/* SOCK_RAW only, @pad for others */
> > > +	};
> >
> >
> > Above looks funny. Why is it a union? pad is for exposing a byte-hole
> > for padding/alignment reasons and i doubt anybody is using it.
>
> 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.

> > 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.



cheers,
jamal

PS:- sorry for butting in the discussion - i blame it on coffee.