linux-kernel - Re: [PATCH 3/3] acpi, memory-hotplug: Support getting hotplug info from SRAT.

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Date:	Wed, 6 Feb 2013 13:54:09 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	jiang.liu@...wei.com, wujianguo@...wei.com, hpa@...or.com,
	wency@...fujitsu.com, laijs@...fujitsu.com, linfeng@...fujitsu.com,
	yinghai@...nel.org, isimatu.yasuaki@...fujitsu.com,
	rob@...dley.net, kosaki.motohiro@...fujitsu.com,
	minchan.kim@...il.com, mgorman@...e.de, rientjes@...gle.com,
	guz.fnst@...fujitsu.com, rusty@...tcorp.com.au, lliubbo@...il.com,
	jaegeuk.hanse@...il.com, tony.luck@...el.com,
	glommer@...allels.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 3/3] acpi, memory-hotplug: Support getting hotplug info
 from SRAT.

On Wed, 06 Feb 2013 10:20:57 +0800
Tang Chen <tangchen@...fujitsu.com> wrote:

> >>
> >> +	if (!strncmp(p, "acpi", max(4, strlen(p))))
> >> +		movablemem_map.acpi = true;
> >
> > Generates a warning:
> >
> > mm/page_alloc.c: In function 'cmdline_parse_movablemem_map':
> > mm/page_alloc.c:5312: warning: comparison of distinct pointer types lacks a cast
> >
> > due to max(int, size_t).
> >
> > This is easily fixed, but the code looks rather pointless.  If the
> > incoming string is supposed to be exactly "acpi" then use strcmp().  If
> > the incoming string must start with "acpi" then use strncmp(p, "acpi", 4).
> >
> > IOW, the max is unneeded?
> 
> Hi Andrew,
> 
> I think I made another mistake here. I meant to use min(4, strlen(p)) in 
> case p is
> something like 'aaa' whose length is less then 4. But I mistook it with 
> max().
> 
> But after I dig into strcmp() in the kernel, I think it is OK to use 
> strcmp().
> min() or max() is not needed.

OK, I did that.

But the code still looks a bit more complex than we need.  Could we do

static int __init cmdline_parse_movablemem_map(char *p)
{
	char *oldp;
	u64 start_at, mem_size;

	if (!p)
		goto err;

	/*
	 * If user decide to use info from BIOS, all the other user specified
	 * ranges will be ingored.
	 */
	if (!strcmp(p, "acpi")) {
		movablemem_map.acpi = true;
		if (movablemem_map.nr_map) {
			memset(movablemem_map.map, 0,
				sizeof(struct movablemem_entry)
				* movablemem_map.nr_map);
			movablemem_map.nr_map = 0;
		}
		return 0;
	}

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