netdev - Re: [Patch net-next] net: clean up skb headers code

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Message-ID: <20130529194438.GY3333@ritirata.org>
Date:	Wed, 29 May 2013 21:44:38 +0200
From:	Antonio Quartulli <ordex@...istici.org>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>, amwang@...hat.com,
	netdev@...r.kernel.org, horms@...ge.net.au
Subject: Re: [Patch net-next] net: clean up skb headers code

On Wed, May 29, 2013 at 08:34:33PM +0100, Ben Hutchings wrote:
> On Tue, 2013-05-28 at 23:36 -0700, David Miller wrote:
> > From: Cong Wang <amwang@...hat.com>
> > Date: Wed, 29 May 2013 14:09:00 +0800
> > 
> > > commit 1a37e412a0225fcba5587 (net: Use 16bits for *_headers
> > > fields of struct skbuff) converts skb->*_header to u16,
> > > therefore 1) we could just use 0xFFFFF instead of (__u16) ~0U
> > > 2) some #if NET_SKBUFF_DATA_USES_OFFSET is useless now.
> > > 
> > > 
> > > Cc: David S. Miller <davem@...emloft.net>
> > > Cc: Simon Horman <horms@...ge.net.au>
> > > Signed-off-by: Cong Wang <amwang@...hat.com>
> > 
> > I want to use something that will either break the build or
> > automatically work if the type changes again.
> > 
> > So something like "X = (typeof(X)) ~0U;".
> 
> I think you mean ~(typeof(X))0.

Am I wrong or you should cast the value once again, like this:

((typeof(X))~(typeof(X))0)

because the ~ operator will implicitly cast the argument to int (if I remember
correctly).


Cheers,

-- 
Antonio Quartulli

..each of us alone is worth nothing..
Ernesto "Che" Guevara

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