Re: [kvm-devel] [PATCH 0/15] KVM userspace interface updates

[Avi Kivity <avi@argo.co.il>]

Heiko Carstens wrote:
>>>  
>>>       
>> What benefit would a syscall interface have?
>>     
>
> Another thing is that this patch set already introduces a way to pass a
> sigset. Passing a sigset to a device node is sort of strange.
>   

The sigset is passed to the device node just for safekeeping, as it 
doesn't normally change.  It's only used when switching to guest mode.

> In addition, if we would port kvm to s390, then we would need to
> make sure that each virtual cpu only gets executed from the thread
> that created it. That is simply because the upper half of our page
> tables contain information about the guest page states. This is yet
> another thing that would be strange to do via an ioctl based interface.
>   

Right.  I agree it's more natural to associate a vcpu with a task 
instead of a vcpu being an independent entry.  We'd still need a handle 
for it, and in Linux that's an fd (pid doesn't cut it as it's racy, and 
probably slower too as it has to go through a global structure).

> Of course everthing can be done via an iotcl interface too, but IMHO
> that's just the wrong interface.
>   

I guess once we have smp, and preferably an additional arch port, we can 
do another round of API consolidation around a syscall based API.  We'll 
need to support the ioctl based API in parallel until the distros flush 
out older userspace.

-- 
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