linux-kernel - Re: [PATCH] Fix setting bio flags in drivers (sd

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Date:	Thu, 01 Mar 2012 21:25:34 +0100
From:	Jens Axboe <axboe@...nel.dk>
To:	Muthu Kumar <muthu.lkml@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	martin.petersen@...cle.com
Subject: Re: [PATCH] Fix setting bio flags in drivers (sd_dif/floppy).

On 2012-03-01 21:23, Muthu Kumar wrote:
>>>                       kunmap_atomic(sdt, KM_USER0);
>>>               }
>>>
>>> -             bio->bi_flags |= BIO_MAPPED_INTEGRITY;
>>> +             bio->bi_flags |= (1 << BIO_MAPPED_INTEGRITY);
>>>       }
>>>
>>>       return 0;
>>
>> urgh.  This isn't the first time.
>>
>> It's too easy for people to make this mistake.  I'm not sure what a
>> good fix would be - I don't think sparse can save us with __bitwise or
>> similar.
>>
>> The approach we took in buffer_head.h with BH_Foo and BUFFER_FNS
>> accessors worked pretty well.
>>
> 
> Does this look good? BTW, I used the non-atomic variants __set/__clear
> to match the behavior of current usage.
> If this looks good, I can send the proper patch as attachment (so no
> line wraps :)

Lets not wrap this in macros, it just makes the code harder to read.
Making the BIO_ flags a bit shift value was a mistake in hindsight, too
easy to get wrong.

If we're going to be changing everything anyway, it'd be better to have
__ variants if we really need the bit shifts, and the non __ variants be
the value. Similar to what is done for request flags.

-- 
Jens Axboe

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