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

[Wen Congyang]

At 10/10/2011 03:22 PM, Jan Kiszka Write:
> 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.

Is the following is right?

1. execute the monitor command 'gdbserver'
2. run gdb and then 'target remote :1234'

But, unfortunately, the monitor command gdbserver does not exit when we use 
json to connect to monitor.

Thanks
Wen Congyang

> 
> Jan
>