netdev - Re: [PATCH 4/11] use ether_addr_equal

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Date:	Tue, 31 Dec 2013 17:40:24 +0100 (CET)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	Ben Greear <greearb@...delatech.com>
cc:	Julia Lawall <julia.lawall@...6.fr>, Joe Perches <joe@...ches.com>,
	Johannes Berg <johannes@...solutions.net>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	kernel-janitors@...r.kernel.org,
	Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
	Intel Linux Wireless <ilw@...ux.intel.com>,
	"John W. Linville" <linville@...driver.com>,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/11]  use ether_addr_equal_64bits



On Tue, 31 Dec 2013, Ben Greear wrote:

> On 12/31/2013 08:09 AM, Julia Lawall wrote:
> >
> >
> > On Tue, 31 Dec 2013, Ben Greear wrote:
> >
> > > On 12/30/2013 10:32 PM, Julia Lawall wrote:
> > > > > > > > I'm just thinking of a programmer, e.g. changing a struct like
> > > > > > > > this:
> > > > > > > >
> > > > > > > >    struct foo {
> > > > > > > >      u8 addr[ETH_ALEN];
> > > > > > > > -  u16 dummy;
> > > > > > > >    };
> > > > >
> > > > > I don't know of a way to catch that.
> > > > > Anyone else?
> > > >
> > > > Well, one could have a semantic patch that checks for that.  But the
> > > > problem is that it is very slow, and it only covers the cases that I can
> > > > transform automatically, which currently means no pointers, only
> > > > explicit
> > > > arrays.
> > > >
> > > > On the other hand, I am finding the structure definition, so I can
> > > > easily
> > > > update the structure definition with an appropriate comment.
> > > >
> > > > struct foo {
> > > >       u8 addr[ETH_ALEN]; /* must be followed by two bytes in the
> > > > structure */
> > > >       u16 dummy;
> > > > };
> > > >
> > > > Unfortunately it is kind of verbose.  Could there be an attribute?  That
> > > > could even easily be checked.
> > >
> > > Can you not just add a build-time macro to check that sizeof(foo) >= 8
> > > for each of these struct foos?  Or, is it required that the dummy field
> > > be there and be not used by anything else?
> >
> > It doesn't matter what the field is used for.  The problem is that is it
> > necessary to ensure a property of the position of addr within the
> > structure.  It has to have at least 16 bytes after it.
>
> You mean 16 bits?

Oops, yes.  16 bits.

> >
> > But maybe something with sizeof(foo) and offset_of would do?
> >
> > Could the macro be put near the declaration of the structure somehow?
>
> I think that would work, but do not know all of the details of such
> macros, so it's possible there is some catch.
>
> If nothing else, then some run-time code that calculates the offset off
> and asserts if it is broken in module initialization or similar might
> be good enough.

Could be OK.  Something right in or after the structure declaration would
be nicest.

julia

>
> Thanks,
> Ben
>
> --
> Ben Greear <greearb@...delatech.com>
> Candela Technologies Inc  http://www.candelatech.com
>
> --
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