Re: [Qemu-devel] [Question] dump memory when host pci device is used by guest

[Wen Congyang]

At 10/10/2011 06:19 PM, Daniel P. Berrange Write:
> On Mon, Oct 10, 2011 at 11:34:44AM +0200, Jan Kiszka wrote:
>> On 2011-10-10 11:10, Daniel P. Berrange wrote:
>>> On Mon, Oct 10, 2011 at 10:08:26AM +0100, Daniel P. Berrange wrote:
>>>> On Mon, Oct 10, 2011 at 10:21:02AM +0800, Wen Congyang wrote:
>>>>> At 10/09/2011 06:23 PM, Richard W.M. Jones Write:
>>>>>> On Sun, Oct 09, 2011 at 10:49:57AM +0200, Jan Kiszka wrote:
>>>>>>> As explained in the other replies: It is way more future-proof to use an
>>>>>>> interface for this which was designed for it (remote gdb) instead of
>>>>>>> artificially relaxing reasonable constraints of the migration mechanism
>>>>>>> plus having to follow that format with the post-processing tool.
>>>>>>
>>>>>> Any interface that isn't "get this information off my production
>>>>>> server *now*" so that I can get the server restarted, and send it to
>>>>>> an expert to analyse -- is a poor interface, whether it was designed
>>>>>> like that or not.  Perhaps we don't have the right interface at all,
>>>>>> but remote gdb is not it.
>>>>>
>>>>> What about the following idea?
>>>>>
>>>>> Introduce a new monitor command named dump, and this command accepts a 
>>>>> filename.
>>>>> We can use almost all migration's code. We use this command to dump 
>>>>> guest's
>>>>> memory, so there is no need to check whether the guest has a unmigratable 
>>>>> device.
>>>>
>>>> I think it would be a good idea of QEMU had a dedicated 'dump' command
>>>> for this purpose, even if it was just an alias for 'migrate' initially.
>>>> I have never really liked the fact that we abuse the 'migrate' command
>>>> to generate a core dump. The resulting data file from this is more
>>>> complex than it really needs to be, causing complexity for post-processing
>>>> it. The needs of migration, are not entirely aligned with the needs of
>>>> core dumping in the long term, so we should allow the possibility of
>>>> their impls diverging without impacting apps using them.
>>>>
>>>> So adding a 'dump' command which wrote out data in a format that was
>>>> optimized for offline processing by tools like 'crash' (or the windows
>>>> equivalent) would be a good improvement, even if it just reuses the
>>>> migrate code for now.
>>>
>>> The other reason why it would be good, is that we would then have a clearly
>>> defined standard "QEMU dump format", instead of "libvirt dump format for 
>>> QEMU"
>>
>> A core file would be that format - for direct gdb processing. No
>> proprietary re-inventions please.
> 
> I have no personal attachment to any particular format, so if the standard
> core file format is possible, then we should definitely try to use it in
> QEMU.

I do not know whether there is such standard format. But IIRC, the format of 
kdump,
netdump, and diskdump is very similar.

If we want to use such format in qemu, I think we can not do live dump in 
libvirt.

Thanks
Wen Congyang

> 
> 
> Daniel