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SubjectRe: [PATCH 2/4] block: use the same failfast bits for bio and request
Hello, Christoph.

Christoph Hellwig wrote:
> On Thu, Jul 09, 2009 at 09:45:24AM +0900, Tejun Heo wrote:
>> What's more disturbing to me is the different between RQ and BIO
>> flags. __REQ_* are bit positions, REQ_* are masks while BIO_* are bit
>> positions. Sadly it seems it's already too late to change that. I
>> personally an not a big fan of simple accessors or flags defined as
>> bit positions. They seem to obscure things without much benefit.
>
> flags as bit positions generally only make sense if you use
> test/set/clear_bit, otherwise they just confuse things.

Another shortcoming of bit position flags is masking / multi flag
operations. It's just awful. I think it's always better to define
flags as masks even when it's used with test/set/clear_bit(). If such
usages are common enough, we can easily add test/set/clear_bit_mask().
The conversion from mask to bit would be constant most of the time and
it's not like fls/ffs() are expensive.

> And the accessors are pretty annoying, especially in the block
> layer. Trying to find the places where a BIO flag has an actual
> effect is pretty painful due to the mix of the different flags and
> the accessors.

Yeap, fully agreed.

Thanks.

--
tejun


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