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

[Anthony Liguori <anthony@codemonkey.ws>]

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".

>     "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
>
> Valid error reasons could be: "enospc", "eio", etc.

No etc :-)  Error reasons should we be well known and well documented.

> B. query-stop-reason
> --------------------
>
> I also have a simple solution for item 2. The vm_stop() accepts a reason
> argument, so we could store it somewhere and return it as a string, like:
>
> ->  { "execute": "query-stop-reason" }
> <- { "return": { "reason": "user" } }
>
> Valid reasons could be: "user", "debug", "shutdown", "diskfull" (hey,
> this should be "ioerror", no?), "watchdog", "panic", "savevm", "loadvm",
> "migrate".
>
> Also note that we have a STOP event. It should be extended with the
> stop reason too, for completeness.


Can we just extend query-block?

Regards,

Anthony Liguori