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

[Anthony Liguori <anthony@codemonkey.ws>]

On 06/02/2011 12:57 PM, Luiz Capitulino wrote:
> On Wed, 01 Jun 2011 16:35:03 -0500
> Anthony Liguori<anthony@codemonkey.ws>  wrote:
>
>> On 06/01/2011 04:12 PM, Luiz Capitulino wrote:
>>> Hi there,
>>>
>>> There are people who want to use QMP for thin provisioning. That's, the VM is
>>> started with a small storage and when a no space error is triggered, more space
>>> is allocated and the VM is put to run again.
>>>
>>> QMP has two limitations that prevent people from doing this today:
>>>
>>> 1. The BLOCK_IO_ERROR doesn't contain error information
>>>
>>> 2. Considering we solve item 1, we still have to provide a way for clients
>>>      to query why a VM stopped. This is needed because clients may miss the
>>>      BLOCK_IO_ERROR event or may connect to the VM while it's already stopped
>>>
>>> A proposal to solve both problems follow.
>>>
>>> A. BLOCK_IO_ERROR information
>>> -----------------------------
>>>
>>> We already have discussed this a lot, but didn't reach a consensus. My solution
>>> is quite simple: to add a stringfied errno name to the BLOCK_IO_ERROR event,
>>> for example (see the "reason" key):
>>>
>>> { "event": "BLOCK_IO_ERROR",
>>>      "data": { "device": "ide0-hd1",
>>>                "operation": "write",
>>>                "action": "stop",
>>>                "reason": "enospc", }
>>
>> you can call the reason whatever you want, but don't call it stringfied
>> errno name :-)
>>
>> In fact, just make reason "no space".
>
> You mean, we should do:
>
>    "reason": "no space"
>
> Or that we should make it a boolean, like:
>
>   "no space": true


Do we need reason in BLOCK_IO_ERROR if query-block returns this information?

>
> 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 }

Why would we ever have "no permission"?

Part of my argument for not having reason is I don't think we actually 
need to be this generic.  I think we're over abstracting.

Regards,

Anthony Liguori