linux-kernel - Re: [PATCH] include/linux/skbuff.h: using '0xffff' instead of '~0U'

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Message-ID: <51AC7546.4010002@asianux.com>
Date:	Mon, 03 Jun 2013 18:51:50 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
CC:	edumazet@...gle.com, Pravin Shelar <pshelar@...ira.com>,
	mgorman@...e.de, David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: [PATCH] include/linux/skbuff.h: using '0xffff' instead of '~0U'

On 06/03/2013 06:14 PM, Andy Shevchenko wrote:
> On Mon, Jun 3, 2013 at 12:23 PM, Chen Gang <gang.chen@...anux.com> wrote:
>> On 06/01/2013 05:05 AM, Andy Shevchenko wrote:
> 
>>> Why not "(u16)~0" ?
>> We'd better to give a meaningful name to it just like Ben said.
> 
> Yeah, you could give a name, though I don't see this needs for
> constants like (u16)~0. It's a usual way to mark some values
> uninitialized.
> Just an example from kernel:
> 
>         /* This is limited by 16 bit "slot" numbers,
>          * and by available on-disk context storage.
>          *
>          * Also (u16)~0 is special (denotes a "free" extent).
> 

After "fgrep -rn 'u16' * | fgrep '~0'", it seems better to define a
meaningful macro for it (e.g. "#define SKB_HEADER_WAS_UNSET    0xffff").


Thanks.
-- 
Chen Gang

Asianux Corporation
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