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

[Anthony Liguori <anthony@codemonkey.ws>]

On 06/03/2011 07:57 AM, Daniel P. Berrange wrote:
> On Fri, Jun 03, 2011 at 07:43:24AM -0500, Anthony Liguori wrote:
>> On 06/03/2011 04:26 AM, Daniel P. Berrange wrote:
>> errors stop a guest) instead of trying to model an internal QEMU
>> concept (vm_stop()).
>>
>> If you have other user visible concepts that you want to know about,
>> please share the use-cases and we can think about how to model it
>> such that it's not exposing internal QEMU details.
>
> None of the requested info is exposing internal QEMU impl details
> with one exception. The reasons are either administrative commands,
> host OS failures, guest OS failures, or the exception, KVM internal
> emulation failure.
>
> The core problem is that an app connects to QEMU, finds it is paused,
> and wants to decide what action to take. If the guest is paused due
> to a previous admin 'stop' command,

Let's be very clear here.  QEMU does not provide a way to figure out 
what the previous QMP user did.  That is not a use case we support today 
and it's not one we can support by just adding a reason to stop.  It's 
far more complicated than just that.

> it will allow resuming. If it is
> paused due to guest OS poweroff,

This is legitimate but only occurs if you use -no-shutdown.  So having a 
query-state have a "powered-off" flag would be a Good Thing.

> it might decide to issue a 'system_reset'
> command and then 'resume'. If it is paused due to watchdog,

I think what we're getting at is the need for an enumeration.  So let's 
introduce one.  Here's what I propose:

SQMP
query-status
------------

Return a json-object with the following information:

- "running": true if the VM is running, or false if it is paused (json-bool)
- "singlestep": true if the VM is in single step mode,
                 false otherwise (json-bool)
- "status": one of the following values (json-string) (optional)
       "prelaunch" - QEMU was started with -S and guest has not started
       "running" - guest is actively running
       "singlestep" - guest is running in single step mode
       "paused" - guest has been paused via the 'stop' command
       "postmigrate" - guest is paused following a successful 'migrate'
       "shutdown" - guest is shut down (and -no-shutdown is in use)
       "io-error" - the last IOP has failed and the device is configured 
to pause on I/O errors
       "watchdog-error" - the watchdog action is configured to pause and 
has been triggered

Example:

-> { "execute": "query-status" }
<- { "return": { "running": true, "singlestep": false, "status": 
"running" } }

EQMP

Regards,

Anthony Liguori

  it might
> decide it wants to pmemsave the guest OS, and then system_reset+resume.
> If it is paused because KVM hit an emulation failure, it may wish to
> attach to the debugger interface and capture VM/QEMU state.
>
> The other problem is that a sysadmin finds a guest unexpectedly paused,
> and the mgmt app can't tell it why and they want to troubleshoot the
> problem. QEMU should be able to tell the sysadmin why it is in this
> state, so they can proceed with trouble shooting in a suitable direction,
> whether the host OS, KVM itself, or the guest OS, or the mgt tool.
>
> Daniel