linux-kernel - Re: [PATCH v2 04/16] KVM: MMU: return bool in __rmap_write

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Message-Id: <20120416231455.f978b3ac9fb995cfce2853ae@gmail.com>
Date:	Mon, 16 Apr 2012 23:14:55 +0900
From:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 04/16] KVM: MMU: return bool in __rmap_write_protect

On Sun, 15 Apr 2012 14:25:30 +0300
Avi Kivity <avi@...hat.com> wrote:

> > > @@ -1689,7 +1690,7 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
> > > 
> > >  	kvm_mmu_pages_init(parent, &parents, &pages);
> > >  	while (mmu_unsync_walk(parent, &pages)) {
> > > -		int protected = 0;
> > > +		bool protected = false;
> > > 
> > >  		for_each_sp(pages, sp, parents, i)
> > >  			protected |= rmap_write_protect(vcpu->kvm, sp->gfn);
> >
> > Isn't this the reason we prefer int to bool?
> >
> > Not sure people like to use |= with boolean.
> >
> 
> Why not?
> 

The code "bitwise OR assignment" is assuming the internal representations
of true and false: true=1, false=0.

I might have seen some point if it had been
	protected = protected || rmap_...


But the real question is whether there is any point in re-writing completely
correct C code: there are tons of int like this in the kernel code.

__rmap_write_protect() was introduced recently, so if this conversion is
really worthwhile, I should have been told to use bool at that time, no?


Thanks,
	Takuya
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