Re: [PATCH 5/5] HPET interaction with in-kernel PIT (v6)

[Avi Kivity <avi@redhat.com>]

Jan Kiszka wrote:
>>>  
>>>  struct kvm_pit_state {
>>>      struct kvm_pit_channel_state channels[3];
>>> +    u8 hpet_legacy_mode;
>>>  };
>>>   
>>>       
>> This changes the ABI, breaking older binaries running on newer kernels,
>> or newer binaries running on older kernels.
>>     
>
> As we have KVM_CREATE_PIT2 now, which includes struct kvm_pit_config
> with a lot of unused flags, it should be straightforward to negotiate
> the kvm_pit_state format between kernel and user space: kernel
> advertises support for the new one via capability, user space requests
> it via a bit in kvm_pit_state.flags.
>   

We still need a new ioctl.  The structure size is embedded in the ioctl 
number, so any additions automatically cause version mismatches.

I sent patches some time ago to have the kernel automatically adjust for 
this, but they weren't well received.

-- 
error compiling committee.c: too many arguments to function