linux-kernel - Re: [PATCH v2] btrfs: LLVMLinux: Remove VLAIS

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Date:	Thu, 11 Sep 2014 16:38:25 -0500
From:	Behan Webster <behanw@...verseincode.com>
To:	Chris Mason <clm@...com>, jbacik@...com
CC:	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	Vinícius Tinti <viniciustinti@...il.com>,
	Jan-Simon Möller <dl9pf@....de>,
	Mark Charlebois <charlebm@...il.com>
Subject: Re: [PATCH v2] btrfs: LLVMLinux: Remove VLAIS

On 09/11/14 09:34, Chris Mason wrote:
>
> On 09/05/2014 06:58 PM, behanw@...verseincode.com wrote:
>> From: Vinícius Tinti <viniciustinti@...il.com>
>>
>> Replaced the use of a Variable Length Array In Struct (VLAIS) with a C99
>> compliant equivalent. This is the original VLAIS struct.
>>
>> struct {
>> 	struct shash_desc shash;
>> 	char ctx[crypto_shash_descsize(tfm)];
>> } desc;
>>
>> This patch instead allocates the appropriate amount of memory using an char
>> array.
>>
>> The new code can be compiled with both gcc and clang.
>>
>> struct shash_desc contains a flexible array member member ctx declared with
>> CRYPTO_MINALIGN_ATTR, so sizeof(struct shash_desc) aligns the beginning
>> of the array declared after struct shash_desc with long long.
>>
>> No trailing padding is required because it is not a struct type that can
>> be used in an array.
>>
>> The CRYPTO_MINALIGN_ATTR is required so that desc is aligned with long long
>> as would be the case for a struct containing a member with
>> CRYPTO_MINALIGN_ATTR.
> We copied this from one of the other crypto api users, and I'm sure
> cooking up all these patches was not a great way to your afternoon.
>
> But, can I talk you into making a helper macro of some kind for this and
> putting it into the crypto api headers?  Honestly this setup seems
> really error prone.
You're not the only person to ask for this. I've got one already coded 
up based on suggestions from tglx.

I've regenerated all the patches. I will resubmit soon.

Will fix.

Behan

-- 
Behan Webster
behanw@...verseincode.com

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