[Crash-utility] crash cannot work for the newest qemu's core

[HATAYAMA Daisuke]

From: Dave Anderson <anderson at redhat.com>
Subject: Re: [Crash-utility] crash cannot work for the newest qemu's core
Date: Thu, 28 Jun 2012 16:38:56 -0400

> 
> 
> ----- Original Message -----
>> At 06/22/2012 09:06 PM, Dave Anderson Wrote:
>> > 
>> > 
>> > ----- Original Message -----
>> >>
>> >>
>> >> ----- Original Message -----
>> >>> Hi, all
>> >>>
>> >>> When I use crash to deal with the vmcore generated by 'vrish dump',
>> >>> I meet the following error:
>> >>>
>> >>> crash: seek error: kernel virtual address: ffffffff8180f1e0  type: "cpu_possible_mask".
>> >>>
>> >>> When I specify '-d 8' to get more information, I found the following message:
>> >>>
>> >>> NOTE: KVM/QEMU CPU_SAVE_VERSION 12 is greater than supported version 9
>> >>>
>> >>> So I guess crash does not support it now. Does anyone have plan to fix it?
>> >>>
>> >>> Thanks
>> >>> Wen Congyang
>> >>
>> >> Hi Wen,
>> >>
>> >> Also, because of your familiarity with this area, I certainly invite you
>> >> to take a look at this...  ;-)
>> >>
>> >> Thanks,
>> >>   Dave
>> > 
>> > Hi Wen,
>> > 
>> > On a related note, what is the status with your "virsh dump-guest-memory"
>> > replacement of "virsh dump"?  The last I saw, it seemed like the qemu guys
>> > finally seemed willing to accept it?
>> 
>> dump-guest-memory is not a virsh's sub command. It is a qemu monitor command.
>> The patches for qemu and libvirt have been merged into newest qemu/libvirt.
> 
> OK, but now I'm confused...  
> 
> I was presuming that you could run the new "dump-guest-memory" command from
> the KVM host, specifying a particular guest, and it will create an ELF vmcore
> that the crash utility can read.  But I don't know what the term "qemu monitor
> command" means?  Is it a command that can be executed from a shell command line?
> 
> And will "virsh dump" still exist?  And if so, why?
> 
> Dave

This is a patch set in libvirt side:

  https://www.redhat.com/archives/libvir-list/2012-June/msg00404.html

In summary:

  - dump-guest-memory is a qemu monitor command, the protocol of which
    is explained in http://wiki.qemu.org/QMP.

  - To get ELF-formatted vmcore, we specify --memory-only option to
    virsh dump command, then virsh dump uses dump-guest-memory monitor
    command vir QMP protocol, instead of migrate monitor command.

  - Note that the default behaviour remains calling migrate command.


BTW, we can call monitor commands using virsh qemu-monitor-command but
they are restricted, according to this FAQ:

 - http://wiki.libvirt.org/page/FAQ#Can_I_connect_to_the_QEMU_monitor_with_libvirt.3F

Also, this is helpful to know how virsh commands use qemu monitor
commands:

 - http://wiki.libvirt.org/page/QEMUSwitchToLibvirt#Monitor_command_equivalence


Thanks.
HATAYAMA, Daisuke