[Crash-utility] [PATCH] Support cpu_map/cpu_mask changes in 2.6.29

[Dave Anderson]

----- "Robin Holt" <holt at sgi.com> wrote:

> On Mon, Apr 27, 2009 at 10:27:22AM -0400, Dave Anderson wrote:
> > 
> > ----- "Michael Holzheu" <holzheu at linux.vnet.ibm.com> wrote:
> > 
> > > > So yes, while STRUCT_SIZE("cpumask_t") would always be appropriate for that
> > > > data type, it would fail for the older kernel types which don't use it.
> > > 
> > > So if for older kernels it was an unsigned long, the function should
> > > work:
> > > 
> > > +static int
> > > +cpu_map_size(void)
> > > +{
> > > +	int len;
> > > +
> > > +	len = STRUCT_SIZE("cpumask_t");
> > > +	if (len < 0)
> > > +		return sizeof(ulong);
> > > +	else
> > > +		return len;
> > > +}
> > 
> > Yeah, you're right, that will probably work.  There were definitions for
> > "cpumask_t" that existed prior to the transition of cpu_online_map symbol
> > from being an unsigned long to a cpumask_t.  But except for mips64 (unsupported)
> > they all appear to have been unsigned longs anyway.
> 
> IIRC, cpumask_t on ia64 hasn't been an unsigned long for a very long time.
> The generic_defconfig was at 512 until it recently jumped to 2048.
> Only some configs limited it down to an unsigned long.  Unfortunately,
> I don't have much time to test this week.  Maybe next, but a quick code
> inspection should raise flags if I am remembering correctly.
> 
> Thanks,
> Robin

OK, so then there are two functions in Michael's patch that are
primarily relevant to maintaining backwards compatibility, cpu_map_addr()
and cpu_map_size().

cpu_map_addr() basically replaces the hardwired usage of the relevant
symbol address as an argument to kernel_symbol_exists("cpu_xxxx_map").
But when the pre-2.6.29 "cpu_xxxx_map" symbols exist, the code still
does the right thing:

+ulong
+cpu_map_addr(const char *type)
+{
+       char cpu_map_symbol[32];
+
+       sprintf(cpu_map_symbol, "cpu_%s_map", type);
+       if (symbol_exists(cpu_map_symbol))
+               return symbol_value(cpu_map_symbol);
+       else
+               return get_cpu_map_addr_from_mask(type);
+}

Although, for safety's sake above, the symbol_value() call should
be replaced with kernel_symbol_value() in order to rule out the
invalid usage of stray module symbols of the same name.

The cpu_map_size() function is the real bone of contention:

+static int
+cpu_map_size(void)
+{
+       int len;
+
+       len = STRUCT_SIZE("cpumask_t");
+       if (len < 0)
+               return sizeof(ulong);
+       else
+               return len;
+}

because it is used like so:

-       if (LKCD_KERNTYPES()) {
-               if ((len = STRUCT_SIZE("cpumask_t")) < 0)
-                       error(FATAL, "cannot determine type cpumask_t\n");
-       } else
-               len = get_symbol_type("cpu_online_map", NULL, &req) ==
-                       TYPE_CODE_UNDEF ?  sizeof(ulong) : req.length;
+       len = cpu_map_size();

So to cover all bases, perhaps cpu_map_size() should still incorporate
the get_symbol_type() mechanism *if* the "cpu_xxxx_map" symbol still
exists?

Michael, does that make sense?

Dave