Re: [PATCH 3/3] acpi, memory-hotplug: Support getting hotplug infofrom SRAT.

[Tang Chen]

On 02/07/2013 05:54 AM, Andrew Morton wrote:
> On Wed, 06 Feb 2013 10:20:57 +0800
> Tang Chen<tangchen@xxxxxxxxxxxxxx>  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;
> 	}
No, I don't think so.

If user specified like this:

1) movablemem_map=aaa@bbb ---------- will be added into array
2) movablemem_map=acpi    ---------- will empty the array
3) movablemem_map=ccc@ddd ---------- will be added into array again (wrong!)

So, we need to code like this:

+	if (!strncmp(p, "acpi", max(4, strlen(p))))
+		movablemem_map.acpi = true;

In this way, 3) movablemem_map=ccc@ddd will not go into this if segment.

+
+	/*
+	 * If user decide to use info from BIOS, all the other user specified
+	 * ranges will be ingored.
+	 */
+	if (movablemem_map.acpi) {
+		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;
+	}

But it will go into this if segment, and will not add the range into array.

Thanks. :)




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