linux-kernel - Re: [PATCH v3 2/2] kexec: Use min

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Message-ID: <512C76FE.4070109@cn.fujitsu.com>
Date:	Tue, 26 Feb 2013 16:49:02 +0800
From:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
To:	Joe Perches <joe@...ches.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Simon Horman <horms@...ge.net.au>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] kexec: Use min_t to simplify logic

于 2013年02月26日 16:38, Joe Perches 写道:
> On Tue, 2013-02-26 at 13:30 +0800, Zhang Yanfei wrote:
>> This is just a tweak: using min_t to simplify logic of variable
>> assignments.
>>
>> v3:
>> - cast type of (PAGE_SIZE - (maddr & ~PAGE_MASK)) into size_t.
> 
> Why?  Isn't this just a redundant cast?
> 
>> diff --git a/kernel/kexec.c b/kernel/kexec.c
> []
>> @@ -822,13 +822,9 @@ static int kimage_load_normal_segment(struct kimage *image,
> []
>> +		mchunk = min_t(size_t, mbytes,
>> +			       (size_t)(PAGE_SIZE - (maddr & ~PAGE_MASK)));
> 
> #define min_t(type, x, y) ({			\
> 	type __min1 = (x);			\
> 	type __min2 = (y);			\
> 	__min1 < __min2 ? __min1: __min2; })
> 
> 
> 

Hmm, from the definition, the cast is redundant.

Maybe I misunderstood what Andrew meant in the mail related to v2:

"The types of PAGE_SIZE and PAGE_MASK are vague - iirc they once had
different types on different architectures, so some form of casting is
unavoidable here."

Andrew, could you please explain the casting you meant above?

Thanks
Zhang
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