linux-kernel - Re: [PATCH v2] BLOCK: fix bio.bi

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Date:	Thu, 12 Aug 2010 18:24:39 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Christoph Hellwig <hch@....de>
CC:	Jiri Slaby <jslaby@...e.cz>, akpm@...ux-foundation.org,
	linux-raid@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v2] BLOCK: fix bio.bi_rw handling

On 08/12/2010 06:08 PM, Christoph Hellwig wrote:
> On Thu, Aug 12, 2010 at 02:31:06PM +0200, Jiri Slaby wrote:
>> Return of the bi_rw tests is no longer bool after commit 74450be1. But
>> results of such tests are stored in bools. This doesn't fit in there
>> for some compilers (gcc 4.5 here), so either use !! magic to get real
>> bools or use ulong where the result is assigned somewhere.
> 
> I'd have to look at my copy of the C standard if it's guaranteed,

§6.5.3.3 of ANSI C99, par 5:
The result of the logical negation operator ! is 0 if the value of its
operand compares unequal to 0, 1 if the value of its operand compares
equal to 0. The result has type int. The expression !E is equivalent to
(0==E).

On == (§6.5.9 par 3):
The == (equal to) and != (not equal to) operators are analogous to the
relational operators except for their lower precedence. Each of the
operators yields 1 if the specified relation is true and 0 if it is
false. The result has type int. For any pair of operands, exactly one of
the relations is true.

On bool => _Bool (§6.2.5 par 2)
An object declared as type _Bool is large enough to store the values 0
and 1.

So it should be safe :).

BTW just of curiosity, sizeof(bool) is 1 here (8 bits).

regards,
-- 
js
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