linux-kernel - Re: [PATCH] arch: x86: kvm: mmu.c: use true/false for bool type

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Message-ID: <4af9e3b9-36f4-217f-c25c-3f4d64c0dde7@redhat.com>
Date:   Thu, 31 Oct 2019 11:13:04 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     SAURAV GIREPUNJE <saurav.girepunje@...il.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     rkrcmar@...hat.com, sean.j.christopherson@...el.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, saurav.girepunje@...mail.com
Subject: Re: [PATCH] arch: x86: kvm: mmu.c: use true/false for bool type

On 31/10/19 07:57, SAURAV GIREPUNJE wrote:
> On Tue, Oct 29, 2019 at 04:44:23PM +0100, Peter Zijlstra wrote:
>> On Tue, Oct 29, 2019 at 07:12:46PM +0530, SAURAV GIREPUNJE wrote:
>>> On Tue, Oct 29, 2019 at 11:13:00AM +0100, Peter Zijlstra wrote:
>>>> On Tue, Oct 29, 2019 at 03:11:04PM +0530, Saurav Girepunje wrote:
>>>>> Use true/false for bool type "dbg" in mmu.c
>>>>>
>>>>> Signed-off-by: Saurav Girepunje <saurav.girepunje@...il.com>
>>>>> ---
>>>>>  arch/x86/kvm/mmu.c | 2 +-
>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>>>>> index 24c23c66b226..c0b1df69ce0f 100644
>>>>> --- a/arch/x86/kvm/mmu.c
>>>>> +++ b/arch/x86/kvm/mmu.c
>>>>> @@ -68,7 +68,7 @@ enum {
>>>>>  #undef MMU_DEBUG
>>>>>  
>>>>>  #ifdef MMU_DEBUG
>>>>> -static bool dbg = 0;
>>>>> +static bool dbg = true;
>>>>
>>>> You're actually changing the value from false to true. Please, if you
>>>> don't know C, don't touch things.
>>> Hi,
>>>
>>> Thanks for your review.
>>> I accept that I have given wrong value "true" to debug variable. It's my bad my typo mistake.  
>>> I will make sure that I will not touch your exclusive C code where we can assign 0/1 to a bool variable,
>>> As you have given me a free advice, I also request you to please don't review such small patches from newbie to discourage them.
>>
>> I will most certainly review whatever I want, and clearly it is needed.
> Do you want me to discard this patch or resend ?
> 

Hi Saurav,

In general I would be happy with replacing 0/1 with false/true, but not
in this particular case.  Despite working on KVM for quite some time I
have never found MMU_DEBUG particularly useful, therefore it is going to
go away soon and will be replaced with kernel tracepoints; see for
example commit 335e192a3fa4 ("KVM: x86: add tracepoints around
__direct_map and FNAME(fetch)", 2019-07-05).  Therefore, even such a
simple change would be very short lived.

Regarding this patch, I for one am happy that Peter caught the problem
in your patch.  His message was perhaps blunt but also honest;
contributing to the kernel requires a very good discipline.  I don't
want to discourage you from contributing, but I suggest that you look
into how you developed the patch (from the idea down to sending it) and
figure out how your mistake managed to slip.

Thanks,

Paolo