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

[Anthony Liguori]

On 06/02/2011 12:57 PM, Luiz Capitulino wrote:
> On Wed, 01 Jun 2011 16:35:03 -0500
> Anthony Liguori<address@hidden>  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