[Qemu-devel] Does kvm_fd mean KVM or VCPU fd?

[Qemu-devel] Does kvm_fd mean KVM or VCPU fd?

[陳韋任 (Wei-Ren Chen)]

Hi all,

  While reading KVM releated code in QEMU, I found the name of one
field in CPU_COMMON (cpu-defs.h), i.e. kvm_fd, might be misleading.
See the code below,

---
int kvm_init_vcpu(CPUArchState *env)
{
    ret = kvm_vm_ioctl(s, KVM_CREATE_VCPU, env->cpu_index);
    env->kvm_fd = ret; /* VCPU fd? */
}
---

  I think KVM_CREATE_VCPU should return VCPU fd, right? AFAIK, in KVM
world, kvm_fd usually means the fd we get after opening "/dev/kvm".
Just want to make sure I understand the code correcly. Thanks.

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj

Re: [Qemu-devel] Does kvm_fd mean KVM or VCPU fd?

[Paolo Bonzini]

Il 14/06/2012 10:24, 陳韋任 (Wei-Ren Chen) ha scritto:
> Hi all,
> 
>   While reading KVM releated code in QEMU, I found the name of one
> field in CPU_COMMON (cpu-defs.h), i.e. kvm_fd, might be misleading.
> See the code below,
> 
> ---
> int kvm_init_vcpu(CPUArchState *env)
> {
>     ret = kvm_vm_ioctl(s, KVM_CREATE_VCPU, env->cpu_index);
>     env->kvm_fd = ret; /* VCPU fd? */
> }
> ---
> 
>   I think KVM_CREATE_VCPU should return VCPU fd, right? AFAIK, in KVM
> world, kvm_fd usually means the fd we get after opening "/dev/kvm".
> Just want to make sure I understand the code correcly. Thanks.

This is the kvm_fd inside struct CPUState, so it's per-CPU.

Paolo

Re: [Qemu-devel] Does kvm_fd mean KVM or VCPU fd?

[陳韋任 (Wei-Ren Chen)]

> >   I think KVM_CREATE_VCPU should return VCPU fd, right? AFAIK, in KVM
> > world, kvm_fd usually means the fd we get after opening "/dev/kvm".
> > Just want to make sure I understand the code correcly. Thanks.
> 
> This is the kvm_fd inside struct CPUState, so it's per-CPU.

  Okay, then it's VCPU fd. Don't know rename it or add a comment to indicate
it's a VCPU fd is a good idea. ;)

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj

Re: [Qemu-devel] Does kvm_fd mean KVM or VCPU fd?

[Andreas Färber]

Am 14.06.2012 12:16, schrieb 陳韋任 (Wei-Ren Chen):
>>>   I think KVM_CREATE_VCPU should return VCPU fd, right? AFAIK, in KVM
>>> world, kvm_fd usually means the fd we get after opening "/dev/kvm".
>>> Just want to make sure I understand the code correcly. Thanks.
>>
>> This is the kvm_fd inside struct CPUState, so it's per-CPU.
> 
>   Okay, then it's VCPU fd. Don't know rename it or add a comment to indicate
> it's a VCPU fd is a good idea. ;)

Not a good idea, those fields need to move from CPU*State to CPUState.
We can rename them then if someone has a good suggestion.

Regards,
Andreas

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