Re: [Qemu-devel] hmp interface for kdump compressed format

["qiaonuohan@cn.fujitsu.com" <qiaonuohan@cn.fujitsu.com>]

On 03/21/2014 05:12 AM, Laszlo Ersek wrote:
 > Two additional points:
 >
 > On 03/20/14 21:56, Laszlo Ersek wrote:
 >> On 03/20/14 21:38, Christian Borntraeger wrote:
 >>> Qiao Nuohan,
 >>>
 >>> is there a reason why you did not implemented the HMP part for that format
 >>> of kdump compressed format? After all this is a patch mostly for developers,
 >>> so a HMP interface might come handy. Do you already have some patch in
 >>> preparation or know somebody doing it?
 >>
 >> http://thread.gmane.org/gmane.comp.emulators.qemu/249283/focus=250059
 >
 > - HMP interface could be implemented as a fully new command of course,
 >
 > - the feature being targeted at developers strikes me as a completely
 > unexpected idea. The main goal in my understanding is to allow the
 > management layer (libvirt) to save a compressed vmcore when the guest
 > panicks, crashes, or the admin feels like it. For communication with
 > another program, QMP is actually preferable.
 >
 > So I'm certainly not against anyone adding a HMP interface too, but it
 > cannot be an extension to the current HMP command (because it would
 > break existing HMP command lines unless the HMP parser were reworked
 > too), plus during review I saw no reason to stall the series even
 > longer, for a side feature that I perceived to be of low importance (and
 > I actually thought that Qiao Nuohan shared that notion).

Yes, my main purpose is let "virsh dump --memory-only" can dump a small
core that can be used to analyze kernel. So HMP is not that important to me.


On 03/21/2014 05:51 AM, Paolo Bonzini wrote:
> Il 20/03/2014 22:28, Laszlo Ersek ha scritto:
>> On 03/20/14 22:18, Christian Borntraeger wrote:
>>> On 20/03/14 21:56, Laszlo Ersek wrote:
>>>> On 03/20/14 21:38, Christian Borntraeger wrote:
>>>>> Qiao Nuohan,
>>>>>
>>>>> is there a reason why you did not implemented the HMP part for that format
>>>>> of kdump compressed format? After all this is a patch mostly for developers,
>>>>> so a HMP interface might come handy. Do you already have some patch in
>>>>> preparation or know somebody doing it?
>>>>
>>>> http://thread.gmane.org/gmane.comp.emulators.qemu/249283/focus=250059
>>>>
>>>> Laszlo
>>>>
>>> So in essence: Due to the limitations of the command line parser we cannot
>>> add the format to the hmp command line.
>>> So something like adding
>>>
>>> dump_guest_memory_set_format <format>
>>>
>>> would be the only possible solution with the hmp code as is. Correct?
>>
>> Yes, one possibility would be to make the dump command stateful (=
>> compression format), and to add a new command setting/getting that state.
>>
>> Another option would be to leave the current command intact, and add an
>> independent command that wouldn't take "begin", "end", nor "paging", but
>> would take compression format.
>
> Another possibility is to kill begin/length from the dump-guest-memory command.
> HMP is not stable, so if that's useful we can do it.

AFAIK, kdump-compressed format can only be analyzed by crash-utility right
now. ELF is big but we still need it, then begin/length will help us save
time and space when only part of the memory is need.

IMHO, a new HMP command will be a good choice and it is more simple than
making dump format 'stateful'. I am not so clear about HMP, but I think
the new HMP command can be 'dump-guest-memory-with-format', and still
base on qmp_dump_guest_memory. If you guys like it, I will send a patch
that add this command.

>
> Paolo
>
>
>


-- 
Regards
Qiao Nuohan