Re: [PATCH] kexec: use min_t/max_t to avoid 'if (foo == bar)' thing

From: Zhang Yanfei <zhangyanfei.yes@gmail.com>
To: Simon Horman <horms@verge.net.au>
Cc: "kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Zhang Yanfei <zhangyanfei@cn.fujitsu.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kexec: use min_t/max_t to avoid 'if (foo == bar)' thing
Date: Sun, 24 Feb 2013 20:59:39 +0800	[thread overview]
Message-ID: <512A0EBB.30406@gmail.com> (raw)
In-Reply-To: <20130224105533.GG18639@verge.net.au>

于 2013年02月24日 18:55, Simon Horman 写道:
> On Sun, Feb 24, 2013 at 12:03:00PM +0800, Zhang Yanfei wrote:
>> This is just a tweak: using min_t/max_t to avoid `if (foo = bar)' thing.
> 
> - s/=/==/; s/[/]max_t//
> 
> 
> But in any case the change is more than that.
> I'd be happier with something like:
> 
> 	kexec: Use min_t to simplify logic

Hmm, agreed.

> 
>> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Simon Horman <horms@verge.net.au>
>> Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
>> ---
>>  kernel/kexec.c |   20 +++++---------------
>>  1 files changed, 5 insertions(+), 15 deletions(-)
>>
>> diff --git a/kernel/kexec.c b/kernel/kexec.c
>> index 2436ffc..065db87 100644
>> --- a/kernel/kexec.c
>> +++ b/kernel/kexec.c
>> @@ -822,13 +822,8 @@ static int kimage_load_normal_segment(struct kimage *image,
>>  		/* Start with a clear page */
>>  		clear_page(ptr);
>>  		ptr += maddr & ~PAGE_MASK;
>> -		mchunk = PAGE_SIZE - (maddr & ~PAGE_MASK);
>> -		if (mchunk > mbytes)
>> -			mchunk = mbytes;
>> -
>> -		uchunk = mchunk;
>> -		if (uchunk > ubytes)
>> -			uchunk = ubytes;
>> +		mchunk = min_t(size_t, mbytes, PAGE_SIZE - (maddr & ~PAGE_MASK));
>> +		uchunk = min_t(size_t, ubytes, mchunk);
>>  
>>  		result = copy_from_user(ptr, buf, uchunk);
>>  		kunmap(page);
>> @@ -874,13 +869,9 @@ static int kimage_load_crash_segment(struct kimage *image,
>>  		}
>>  		ptr = kmap(page);
>>  		ptr += maddr & ~PAGE_MASK;
>> -		mchunk = PAGE_SIZE - (maddr & ~PAGE_MASK);
>> -		if (mchunk > mbytes)
>> -			mchunk = mbytes;
>> -
>> -		uchunk = mchunk;
>> +		mchunk = min_t(size_t, mbytes, PAGE_SIZE - (maddr & ~PAGE_MASK));
>> +		uchunk = min_t(size_t, ubytes, mchunk);
> 
> The line above means that uchunk can now never be greater than ubytes.
> 
>>  		if (uchunk > ubytes) {
> 
> So the following seems more appropriate to me:
> 
> 		if (mchunk > uchunk) {

Oops, this is really a mistake. Thanks.

I will send the v2 patch.

> 
> 
>> -			uchunk = ubytes;
>>  			/* Zero the trailing part of the page */
>>  			memset(ptr + uchunk, 0, mchunk - uchunk);
>>  		}
>> @@ -1461,8 +1452,7 @@ void vmcoreinfo_append_str(const char *fmt, ...)
>>  	r = vsnprintf(buf, sizeof(buf), fmt, args);
>>  	va_end(args);
>>  
>> -	if (r + vmcoreinfo_size > vmcoreinfo_max_size)
>> -		r = vmcoreinfo_max_size - vmcoreinfo_size;
>> +	r = min_t(size_t, r, vmcoreinfo_max_size - vmcoreinfo_size);
>>  
>>  	memcpy(&vmcoreinfo_data[vmcoreinfo_size], buf, r);
>>  
>> -- 
>> 1.7.1
>>
> --
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