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

[Markus Armbruster]

"address@hidden" <address@hidden> writes:

> 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.

Flags to select a format could perhaps work.

>>>> 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 encouraged you to *break* the existing HMP command instead of
adding a new one.  I'd like to second that.