linux-kernel - Re: [KVM timekeeping 30/35] IOCTL for setting TSC rate

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Message-Id: <201008211811.50962.arnd@arndb.de>
Date:	Sat, 21 Aug 2010 18:11:50 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Glauber Costa <glommer@...hat.com>
Cc:	Zachary Amsden <zamsden@...hat.com>, kvm@...r.kernel.org,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [KVM timekeeping 30/35] IOCTL for setting TSC rate

On Friday 20 August 2010 19:56:20 Glauber Costa wrote:
> > @@ -675,6 +676,9 @@ struct kvm_clock_data {
> >  #define KVM_SET_PIT2              _IOW(KVMIO,  0xa0, struct kvm_pit_state2)
> >  /* Available with KVM_CAP_PPC_GET_PVINFO */
> >  #define KVM_PPC_GET_PVINFO     _IOW(KVMIO,  0xa1, struct kvm_ppc_pvinfo)
> > +/* Available with KVM_CAP_SET_TSC_RATE */
> > +#define KVM_X86_GET_TSC_RATE      _IOR(KVMIO,  0xa2, __u32)
> > +#define KVM_X86_SET_TSC_RATE      _IOW(KVMIO,  0xa3, __u32)
> 
> wrap this into a struct?

I don't think that would improve the code. Generally, we try to *avoid* using
structs in ioctl arguments, although KVM does have a precedent of using structs
there.

In fact, the code here could be simplified by using get_user/put_user on the
simple argument, which would not be possibly with a struct.

	Arnd
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