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SubjectRe: [PATCH] KVM: Fix the warning by the min()
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On 11/16/21 13:10, zhaoxiao wrote:
> Fix following coccicheck warning:
> virt/kvm/kvm_main.c:4995:10-11: WARNING opportunity for min()
> virt/kvm/kvm_main.c:4924:10-11: WARNING opportunity for min()
>
> Signed-off-by: zhaoxiao <zhaoxiao@uniontech.com>

No, this is unreadable for two reasons:

First, the code in parentheses for min(func(), 0) is very long. Usually
min has very short arguments. By the time you have reached the closing
parentheses, you have completely forgotten that there was a min() at the
beginning. So perhaps one possibility could be

return min(r, 0);

However, the second reason is that "r < 0" is a very common way to
express "if there was an error". In this case that would be

r = __kvm_io_bus_write(vcpu, bus, &range, val);
if (r < 0) // "if __kvm_io_bus_write failed"
return r;

return 0;

That "r < 0" is what will catch the attention of the person that is
reading the code, no matter if it is an "if" or (as in the existing
code), a "return". Using "min" removes the idiom that tells the person
"this is checking for errors".

Thanks,

Paolo

> ---
> virt/kvm/kvm_main.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index d31724500501..bd646c64722d 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4910,7 +4910,6 @@ int kvm_io_bus_write(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
> {
> struct kvm_io_bus *bus;
> struct kvm_io_range range;
> - int r;
>
> range = (struct kvm_io_range) {
> .addr = addr,
> @@ -4920,8 +4919,8 @@ int kvm_io_bus_write(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
> bus = srcu_dereference(vcpu->kvm->buses[bus_idx], &vcpu->kvm->srcu);
> if (!bus)
> return -ENOMEM;
> - r = __kvm_io_bus_write(vcpu, bus, &range, val);
> - return r < 0 ? r : 0;
> +
> + return min(__kvm_io_bus_write(vcpu, bus, &range, val), 0);
> }
> EXPORT_SYMBOL_GPL(kvm_io_bus_write);
>
> @@ -4981,7 +4980,6 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
> {
> struct kvm_io_bus *bus;
> struct kvm_io_range range;
> - int r;
>
> range = (struct kvm_io_range) {
> .addr = addr,
> @@ -4991,8 +4989,8 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
> bus = srcu_dereference(vcpu->kvm->buses[bus_idx], &vcpu->kvm->srcu);
> if (!bus)
> return -ENOMEM;
> - r = __kvm_io_bus_read(vcpu, bus, &range, val);
> - return r < 0 ? r : 0;
> +
> + return min(__kvm_io_bus_read(vcpu, bus, &range, val), 0);
> }
>
> /* Caller must hold slots_lock. */
>

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