Re: [Qemu-block] Enable debugging in a running vServer

[Peter Lieven]

Am 26.03.2015 um 16:02 schrieb Kevin Wolf:
> Am 26.03.2015 um 15:54 hat Peter Lieven geschrieben:
>> Hi Block people,
>>
>> we recently observed some strange I/O stalls on some vServers. I suspect a 
>> bug in the target and
>> already added some debugging output to libiscsi that could have helped to 
>> track the issue.
>>
>> However, to enable this debugging I would need to call
>>
>> iscsi_set_log_level
>>
>> during runtime from the hmp or qmp.
>>
>> I wonder what would be the best way to do this and/or if it would be 
>> interesting to have a generic
>> way to tell a block backend to enter debugging whereas I would leave it up 
>> to the backend driver
>> what exactly that means?
>>
>> Other option would be to set an enviroment variable during runtime. But as 
>> far as I know thats
>> not possible.
> I think debugging should be controlled with driver-specific options to
> bdrv_open(). For changing the debugging options at runtime, we'd need to
> provide a way to directly call bdrv_reopen() from the monitor.
>
> Before this can work, we need some more infrastructure work that even
> introduces the concept of QDict *options to bdrv_reopen(). I have
> patches to do this, but even though that branch mostly works, it is
> still rather messy and not in a mergable state. If you're interested
> anyway, it's the blockdev branch in my tree.
>
> For your immediate case, you'll probably want a downstream ad-hoc hack
> rather than waiting for the real thing.

That sounds like the best approach. Would it make sense to already
introduce a debug option in the options and honour it at least in bdrv_open?

Thank you,
Peter