Re: [PATCH 2/4] KVM: Add unified KVM_GET/SET_VCPU_STATE IOCTL

[Avi Kivity <avi@redhat.com>]

On 10/14/2009 01:06 AM, Jan Kiszka wrote:
> Add a new IOCTL pair to retrieve or set the VCPU state in one chunk.
> More precisely, the IOCTL is able to process a list of substates to be
> read or written. This list is easily extensible without breaking the
> existing ABI, thus we will no longer have to add new IOCTLs when we
> discover a missing VCPU state field or want to support new hardware
> features.
>
> This patch establishes the generic infrastructure for KVM_GET/
> SET_VCPU_STATE and adds support for the generic substates REGS, SREGS,
> FPU, and MP. To avoid code duplication, the entry point for the
> corresponding original IOCTLs are converted to make use of the new
> infrastructure internally, too.
>
>
>
> +/* for KVM_GET_VCPU_STATE and KVM_SET_VCPU_STATE */
> +#define KVM_VCPU_REGS			0
> +#define KVM_VCPU_SREGS			1
> +#define KVM_VCPU_FPU			2
> +#define KVM_VCPU_MP			3
>    

KVM_VCPU_STATE_*, to avoid collisions.

Better to split sse from fpu since we already know it is about to be 
replaced.

> +
> +struct kvm_vcpu_substate {
> +	__u32 type;
> +	__u32 pad;
> +	__s64 offset;
> +};
> +
> +#define KVM_MAX_VCPU_SUBSTATES		64
> +
> +struct kvm_vcpu_state {
> +	__u32 nsubstates; /* number of elements in substates */
> +	__u32 nprocessed; /* return value: successfully processed substates */
> +	struct kvm_vcpu_substate substates[0];
> +};
> +
>    

Wouldn't having an ordinary struct with lots of reserved space be 
simpler?  If we add a bitmask, we can even selectively get/set the 
fields we want (important if new state extends old state: avx vs sse).


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.