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

[Luiz Capitulino <lcapitulino@redhat.com>]

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

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 }