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SubjectRe: 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


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