linux-kernel - Re: Style Question

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Date:	Sun, 11 Mar 2007 23:18:55 -0700 (PDT)
From:	"Randy.Dunlap" <rdunlap@...otime.net>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
cc:	Cong WANG <xiyou.wangcong@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: Style Question

On Mon, 12 Mar 2007, Jan Engelhardt wrote:

>
> On Mar 12 2007 13:37, Cong WANG wrote:
> >
> > The following code is picked from drivers/kvm/kvm_main.c:
> >
> > static struct kvm_vcpu *vcpu_load(struct kvm *kvm, int vcpu_slot)
> > {
> > struct kvm_vcpu *vcpu = &kvm->vcpus[vcpu_slot];
> >
> > mutex_lock(&vcpu->mutex);
> > if (unlikely(!vcpu->vmcs)) {
> > mutex_unlock(&vcpu->mutex);
> > return 0;
> > }
> > return kvm_arch_ops->vcpu_load(vcpu);
> > }
> >
> > Obviously, it used 0 rather than NULL when returning a pointer to
> > indicate an error. Should we fix such issue?
>
> Indeed. If it was for me, something like that should throw a compile error.

At least it does throw a sparse warning, and yes, it should
be fixed.

> >>[...]
> > I think it's more clear to indicate we are using a pointer rather than
> > an integer when we use NULL in kernel. But in userspace, using NULL is
> > for portbility of the program, although most (*just* most, NOT all) of
> > NULL's defination is ((void*)0). ;-)
>
> NULL has the same bit pattern as the number zero. (I'm not saying the bit
> pattern is all zeroes. And I am not even sure if NULL ought to have the same
> pattern as zero.) So C++ could use (void *)0, if it would let itself :p
>
>
> >
> >
>
> Jan
>

-- 
~Randy
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