[Crash-utility] faulty use of "set" command when running against the xen hypervisor

[Dave Anderson]

Cai Quan bumped into another problem when running against the xen hypervisor,
where entering the "set" command alone with no arguments generates a SIGSEGV.

I also note that "set -c #" and "set -p" options make no sense either:

   # crash --xen_phys_start 3ee00000 xen-syms-2.6.18-92.el5 vmcore

   crash 4.0-7.2
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      KERNEL: xen-syms-2.6.18-92.el5
   DEBUGINFO: ./xen-syms-2.6.18-92.el5.debug
    DUMPFILE: vmcore
        CPUS: 2
     DOMAINS: 4
      UPTIME: 00:34:18
     MACHINE: Intel(R) Pentium(R) 4 CPU 3.40GHz  (3400 Mhz)
      MEMORY: 1 GB
     PCPU-ID: 1
        PCPU: ffff83003f05ff28
     VCPU-ID: 1
        VCPU: ffff83003eef6080  (VCPU_RUNNING)
   DOMAIN-ID: 0
      DOMAIN: ffff83003eef8080  (DOMAIN_RUNNING)
       STATE: CRASH

   crash> set -c 0
   set: invalid cpu number: system has only 0 cpu
   crash> set -p
   set: no panic task found!
   crash> set
   Segmentation fault

   #

Admittedly it's a nonsensical usages of "set", since there's no concept of
a PID "context" in the hypervisor.

The attached patch changes the behavior to:

   crash> set -c 0
   set: -c option not supported on this architecture or kernel
   crash> set -p
   set: -p option not supported on this architecture or kernel
   crash> set
   set: requires an option with the Xen hypervisor
   crash>

Itsura, are you OK with the attached patch?

Thanks,
   Dave


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