Re: [patch 1/5] KVM: add basic paravirt support (v2)

[Marcelo Tosatti <marcelo@kvack.org>]

On Thu, Feb 21, 2008 at 05:38:30PM +0200, Avi Kivity wrote:
> Marcelo Tosatti wrote:
> >Add basic KVM paravirt support. Avoid vm-exits on IO delays.
> >
> >Add KVM_GET_PARA_FEATURES ioctl so paravirt features can be reported in a
> >single bitmask. This allows the host to disable features on runtime if 
> >appropriate, which would require one ioctl per feature otherwise.
> >
> >The limit of 32 features can be extended to 64 if needed, beyond that a 
> >new MSR is required.
> >
> >v1->v2:
> >- replace KVM_CAP_CLOCKSOURCE with KVM_CAP_PARA_FEATURES
> >- cover FEATURE_CLOCKSOURCE
> >
> >
> >  
> 
> I don't understand the motivation for this.  A handful of ioctl()s at 
> init time are hardly time consuming.
> 
> There is the advantage that paravirt kernel advances are reflected 
> automatically without changes in userspace, but sometimes this is a 
> disadvantage (it means there is no way to disable it, for instance).

One ioctl per feature sounded like unnecessary code duplication. I have
no problems with it though. So you prefer that way?

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