linux-kernel - Re: Style Question

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Message-ID: <Pine.LNX.4.61.0703120638030.4339@yvahk01.tjqt.qr>
Date:	Mon, 12 Mar 2007 06:40:18 +0100 (MET)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Cong WANG <xiyou.wangcong@...il.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: Style Question


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.

>>[...]
> 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
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