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

[Jan Kiszka]

On 2011-10-10 09:17, Wen Congyang wrote:
> At 10/10/2011 03:01 PM, Jan Kiszka Write:
>> On 2011-10-10 08:59, Wen Congyang wrote:
>>> At 10/10/2011 02:52 PM, Jan Kiszka Write:
>>>> On 2011-10-10 04:21, 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 do not want to reject this proposal categorically, but I would like to
>>>> see the gdb path fail /wrt essential requirements first. So far I don't
>>>> see it would.
>>>
>>> ‘gdb path fail /wrt essential requirements’
>>>
>>> what does it mean?
>>
>> That you explain why reading reading memory and processor states via the
>> remote gdb interface and dumping it into a proper core file cannot be
>> made working for you.
> 
> First, I think crash can not analyze such core file. But it is not very 
> important.
> 
> What is remote gdb interface?

man qemu -> gdb.

> Do you mean that: the supporter uses gdb from another machine

Or locally. There are various transports possible.

> to connect to customer's machine and get the data? If so, this way can not be
> used when the customer needs to dump the guest's memory automatically when 
> watchdog timeouts.

It is just another channel that can conceptually be used like the
monitor, by a management app like libvirt, directly or indirectly via a
scripted gdb frontend, or also by a human who wants to save some ongoing
gdb session for later analysis. This dual use make such an approach the
preferred one.

Jan

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