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

[Michael Holzheu]

Am Montag, den 27.04.2009, 09:27 -0400 schrieb Dave Anderson:
> ----- "Michael Holzheu" <holzheu at linux.vnet.ibm.com> wrote:
> 
> > Hi Dave,
> > 
> > I found some time to fix the cpu_map issue in 2.6.29.
> > Here my proposal:
> 
> Thanks, man -- much appreciated... 
> 
> > From: Michael Holzheu <holzheu at linux.vnet.ibm.com>
> > 
> > In Linux 2.6.29 the cpu_(online, possible, present, active)_map global variables
> > have been moved to cpu_(...)_mask variables that are pointers to structures
> > with bitmaps now. This patch allows crash to work with the new variables.
> > 
> > Note: The cpu_map_size() function now only uses STRUCT_SIZE("cpumask_t")
> > to get the size of the cpu map. I removed the get_symbol_type() call
> > since STRUCT_SIZE("cpumask_t") should always work.
> > 
> > Correct me if I am wrong here!
> 
> Actually, this would break backwards compatibility.  The "cpu_online_map"
> used to be an "unsigned long", back when NR_CPUS was hardwired to 32.
> So the get_symbol_type() is used to differentiate between that type and
> its current invocation as a variably-sized cpumask_t struct based upon
> NR_CPUS.
> 
> 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;
+}

Michael