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

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Message-Id: <20130226005328.e2d31a97.akpm@linux-foundation.org>
Date:	Tue, 26 Feb 2013 00:53:28 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
Cc:	Joe Perches <joe@...ches.com>,
	"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

On Tue, 26 Feb 2013 16:49:02 +0800 Zhang Yanfei <zhangyanfei@...fujitsu.com> wrote:

> >> 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?

I mean that a cast (or min_t, which is a cast) will be needed. 
The code you have here casts the same thing two times, which isn't
necessary.

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