linux-kernel - Re: [PATCH 4/11] use ether_addr_equal

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Message-ID: <1388445188.18164.0.camel@jlt4.sipsolutions.net>
Date:	Tue, 31 Dec 2013 00:13:08 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Julia Lawall <julia.lawall@...6.fr>,
	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 Mon, 2013-12-30 at 19:57 -0200, Henrique de Moraes Holschuh wrote:
> On Mon, 30 Dec 2013, Johannes Berg wrote:
> > On Mon, 2013-12-30 at 20:58 +0100, Julia Lawall wrote:
> > > > Is there any way we could catch (sparse, or some other script?) that
> > > > struct reorganising won't break the condition needed ("within a
> > > > structure that contains at least two more bytes")?
> > > 
> > > What kind of reorganizing could happen?  Do you mean that the programmer 
> > > might do at some time in the future, or something the compiler might do?
> > 
> > I'm just thinking of a programmer, e.g. changing a struct like this:
> > 
> >  struct foo {
> >    u8 addr[ETH_ALEN];
> > -  u16 dummy;
> >  };
> > 
> > for example.
> 
> That is easily resolved by:
> 
> struct foo {
> 	u8 addr[ETH_ALEN];
> 	u16 required_padding;	/* do not remove upon pain of death */
> };

That'd be a stupid waste of struct space. If anything, there should be
*only* a comment saying that at least two bytes are needed - I'd still
prefer an automated check.

johannes

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