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

[Jan Kiszka]

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.

Jan

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