Re: [Qemu-devel] QMP: RFC: I/O error info & query-stop-reason

[Anthony Liguori <anthony@codemonkey.ws>]

On 06/06/2011 10:30 AM, Luiz Capitulino wrote:
> On Mon, 6 Jun 2011 16:27:55 +0100
> "Daniel P. Berrange"<berrange@redhat.com>  wrote:
>
>> On Mon, Jun 06, 2011 at 08:08:51AM -0500, Anthony Liguori wrote:
>>> On 06/06/2011 04:25 AM, Kevin Wolf wrote:
>>>> Am 02.06.2011 20:09, schrieb Luiz Capitulino:
>>>>>>> I'm ok with either way. But in case you meant the second one, I guess
>>>>>>> we should make "reason" a dictionary so that we can group related
>>>>>>> information when we extend the field, for example:
>>>>>>>
>>>>>>>    "reason": { "no space": false, "no permission": true }
>>>>
>>>> Splitting up enums into a number of booleans looks like a bad idea to
>>>> me. It makes things more verbose than they should be, and even worse, it
>>>> implies that more than one field could be true.
>>>
>>> I agree.  What I had suggested was to not have a reason at all.
>>>
>>>>
>>>> If this new schema thing doesn't support proper enums, that's something
>>>> that should be changed.
>>>
>>> It does BTW.
>>>
>>>>>>
>>>>>> Why would we ever have "no permission"?
>>>>>
>>>>> It's an I/O error. I have a report from a developer who was getting
>>>>> the BLOCK_IO_ERROR event and had to debug qemu to know the error cause,
>>>>> it turned out to be no permission.
>>>>
>>>> And I want to add that it's a PITA to handle bug report when the only
>>>> message you get from qemu is "something went wrong". Sorry, that's not
>>>> useful at all. I want to see the real error reason (and at least for
>>>> debugging this means, I want to see the errno value/string).
>>>>
>>>> Finding out that it was -EACCES in fact cost me (and QA who ran into the
>>>> problem) much more time than it should have. It's simply too much that
>>>> you need to attach gdb to find out what really happened.
>>>
>>> You want a log file and you want libvirt to actually let QEMU write
>>> to a log file.
>>
>> Anything QEMU writes to stderr or stdout gets recorded in a
>> per-VM logfile already at /var/log/libvirt/qemu/$GUESTNAME.log
>
> I can submit a patch to write this info to stderr (in case we don't do that
> yet).

That's not terribly friendly to users though.

We need something akin to a -log stderr so that normal users can 
redirect to a file.  I think libvirt would only need to add this to 
their invocation and everything would Just Work.

Regards,

Anthony Liguori

>
>>
>> Regards,
>> Daniel
>
>