Re: [PATCH/RFC] KVM: s390: Add S390 configuration and control kvm device

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 01/04/14 16:58, Alexander Graf wrote:
> On 04/01/2014 04:47 PM, Christian Borntraeger wrote:
>> From: Ekaterina Tumanova <tumanova@linux.vnet.ibm.com>
>>
>> Add KVM_DEV_TYPE_S390_CONFIG kvm device that contains
>> configuration and control attributes of particular vm.
>> The device is created by KVM_CREATE_DEVICE ioctl.
>> The attributes may be retrieved and stored by calling
>> KVM_GET_DEVICE_ATTR and KVM_SET_DEVICE_ATTR ioctls.
>>
>> Signed-off-by: Ekaterina Tumanova <tumanova@linux.vnet.ibm.com>
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> 
> I don't think a device is particularly the best fit. A device can usually be instantiated multiple times. The configuration device can only be created once. A device also gets created by user space which enables it to receive the fd to drive it. Your device has to be created during VM creation.

I remember some discussion a year or 2 ago, and IIRC a config device
was actually your idea ;-) (The other idea that we had, was ONE_REG for the VM)

> 
> I think VM configuration is common enough to just make this a separate interface.

So you propose to define a new base ioctl (e.g. VM_REG) on the vm fd, instead?
Seems like an easy enough change. Would you reuse the kvm_attr structure for that?

> 
> 
> Alex
>