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Re: [PATCH 02/10] KVM: x86: MMU: Add helper function to clear a bit in unsync child bitmap

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  Re: [PATCH 02/10] KVM: x86: MMU: Add helper function to clear a bit  in unsync child bitmap Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-11-18 04:00 +0100
    Re: [PATCH 02/10] KVM: x86: MMU: Add helper function to clear a bit  in unsync child bitmap Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-19 02:00 +0100
      Re: [PATCH 02/10] KVM: x86: MMU: Add helper function to clear a bit  in unsync child bitmap Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-11-19 04:00 +0100
        Re: [PATCH 02/10] KVM: x86: MMU: Add helper function to clear a bit  in unsync child bitmap Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> - 2015-11-19 05:10 +0100

#1271822 — Re: [PATCH 02/10] KVM: x86: MMU: Add helper function to clear a bit in unsync child bitmap

On 11/12/2015 07:50 PM, Takuya Yoshikawa wrote:
> +			if (!ret) {
> +				clear_unsync_child_bit(sp, i);
> +				continue;
> +			} else if (ret > 0) {
>   				nr_unsync_leaf += ret;

Just a single line here, braces are unnecessary.

> -			else
> +			} else
>   				return ret;
>   		} else if (child->unsync) {
>   			nr_unsync_leaf++;
>   			if (mmu_pages_add(pvec, child, i))
>   				return -ENOSPC;
>   		} else
> -			 goto clear_child_bitmap;
> -
> -		continue;
> -
> -clear_child_bitmap:
> -		__clear_bit(i, sp->unsync_child_bitmap);
> -		sp->unsync_children--;
> -		WARN_ON((int)sp->unsync_children < 0);
> +			clear_unsync_child_bit(sp, i);
>   	}
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#1272722

On 2015/11/18 11:44, Xiao Guangrong wrote:

> On 11/12/2015 07:50 PM, Takuya Yoshikawa wrote:
>> +            if (!ret) {
>> +                clear_unsync_child_bit(sp, i);
>> +                continue;
>> +            } else if (ret > 0) {
>>                   nr_unsync_leaf += ret;
>
> Just a single line here, braces are unnecessary.
>
>> -            else
>> +            } else
>>                   return ret;

I know we can eliminate the braces, but that does not mean
we should do so: there seems to be no consensus about this
style issue and checkpatch accepts both ways.

Actually, some people prefer to put braces when one of the
if/else-if/else cases has multiple lines.  You can see
some examples in kernel/sched/core.c: see hrtick_start(),
sched_fork(), free_sched_domain().

In our case, I thought putting braces would align the else-if
and else and make the code look a bit nicer, but I know this
may be just a matter of personal feeling.

In short, unless the maintainer, Paolo for this file, has any
preference, both ways will be accepted.

   Takuya

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#1272767

On 11/19/2015 08:59 AM, Takuya Yoshikawa wrote:
> On 2015/11/18 11:44, Xiao Guangrong wrote:
>
>> On 11/12/2015 07:50 PM, Takuya Yoshikawa wrote:
>>> +            if (!ret) {
>>> +                clear_unsync_child_bit(sp, i);
>>> +                continue;
>>> +            } else if (ret > 0) {
>>>                   nr_unsync_leaf += ret;
>>
>> Just a single line here, braces are unnecessary.
>>
>>> -            else
>>> +            } else
>>>                   return ret;
>
> I know we can eliminate the braces, but that does not mean
> we should do so: there seems to be no consensus about this
> style issue and checkpatch accepts both ways.
>
> Actually, some people prefer to put braces when one of the
> if/else-if/else cases has multiple lines.  You can see
> some examples in kernel/sched/core.c: see hrtick_start(),
> sched_fork(), free_sched_domain().
>
> In our case, I thought putting braces would align the else-if
> and else and make the code look a bit nicer, but I know this
> may be just a matter of personal feeling.
>
> In short, unless the maintainer, Paolo for this file, has any
> preference, both ways will be accepted.

The reason why i pointed this out is that it is the style documented
in Documentation/CodingStyle:
| Do not unnecessarily use braces where a single statement will do.
|
|        if (condition)
|                action();
|

Actually, Ingo Molnar hated this braces-style too much and blamed
many developers who used this style (include me, that why i was
nervous to see this style :( ).

If this style is commonly accepted now, it is worth making a patch
to update Documentation/CodingStyle.

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#1272830

On 2015/11/19 11:46, Xiao Guangrong wrote:

>> Actually, some people prefer to put braces when one of the
>> if/else-if/else cases has multiple lines.  You can see
>> some examples in kernel/sched/core.c: see hrtick_start(),
>> sched_fork(), free_sched_domain().
>>
>> In our case, I thought putting braces would align the else-if
>> and else and make the code look a bit nicer, but I know this
>> may be just a matter of personal feeling.
>>
>> In short, unless the maintainer, Paolo for this file, has any
>> preference, both ways will be accepted.
>
> The reason why i pointed this out is that it is the style documented
> in Documentation/CodingStyle:
> | Do not unnecessarily use braces where a single statement will do.
> |
> |        if (condition)
> |                action();
> |

Ah, this is a different thing.  For this case, there is a consensus
and checkpatch will complain if we don't obey the rule.

What I explained was:

   if (condition) {
      line1;
      line2;  // multiple lines
   } else if {
      single-line-statement;  -- (*1)
   } else
      single-line-statement;  -- (*2)

For (*1) and (*2), especially for (*1), some people put braces.

> Actually, Ingo Molnar hated this braces-style too much and blamed
> many developers who used this style (include me, that why i was
> nervous to see this style :( ).

I think he likes the coding style of kernel/sched/core.c very much,
as you know.  Actually that is one reason why I took it as an example.

Let's just choose the way which Paolo prefers for this time, I don't
know which is better.

Thank you,
   Takuya


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