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Re: [libvirt] [PATCH RFC 3/4] Create new virDrvDomainSuspendFlags API



On 01/26/2012 07:31 AM, Michal Privoznik wrote:
> On 26.01.2012 15:17, Eric Blake wrote:
>> On 01/26/2012 07:06 AM, Michal Privoznik wrote:
>>> define these flags:
>>>
>>>    VIR_DOMAIN_SUSPEND_SLEEP     = 0,        /* Suspend to RAM */
>>>    VIR_DOMAIN_SUSPEND_HIBERNATE = (1 << 0), /* Suspend to disk */
>>
>> Not quite right.  Our policy when fixing old APIs that forgot a flags
>> argument is that the new API with flags 0 must be identical to the old
>> API.  Which means you need:
>>
>> VIR_DOMAIN_SUSPEND_PAUSE = 0, /* pause CPUs */
>> VIR_DOMAIN_SUSPEND_SLEEP = 1<<0, /* Suspend to RAM, power stays on */
> 
> Honestly, in case of virtual machines I can't see the difference between
> these two. But okay, I'll rewrite it.

VIR_DOMAIN_SUSPEND_PAUSE is what we have now, when you click the pause
button in virt-manager - it means that qemu stops all guest CPUs, with
no input from the guest.  Resuming from this state requires
virDomainResume to issue a monitor command.

VIR_DOMAIN_SUSPEND_SLEEP involves the guest.  S3 might be a very fast op
with qemu, but it is not an instant op - the guest CPU continues to run,
and the guest really does flush state to RAM.  Furthermore, qemu is
implementing S3 so that you can re-wake the guest via input (such as a
keypress into a serial device, or a mouse click), with no intervening
monitor command.

That said, qemu is also implementing a new monitor command to wake up a
guest that is in S3 state; so we _also_ need to add a new API
virDomainResumeFlags, to give use the flexibility to expose that new
monitor command.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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