linux-kernel - Re: [PATCH] staging: greybus: eclose macro in a do

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Date:   Sun, 12 Mar 2023 15:43:49 +0200
From:   Menna Mahmoud <eng.mennamahmoud.mm@...il.com>
To:     Alex Elder <elder@...e.org>, outreachy@...ts.linux.dev
Cc:     pure.logic@...us-software.ie, johan@...nel.org, elder@...nel.org,
        gregkh@...uxfoundation.org, greybus-dev@...ts.linaro.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: greybus: eclose macro in a do - while loop


On ١١‏/٣‏/٢٠٢٣ ٢١:١٠, Alex Elder wrote:
> On 3/11/23 7:59 AM, Menna Mahmoud wrote:
>> " ERROR: Macros with multiple statements should be enclosed in a do -
>> while loop"
>>
>> Reported by checkpath.
>
> This is also not an issue that should be "fixed."
>
> If you look at where that macro is expanded, you see
> that its purpose is simply to reduce the possibility
> of some errors by enclosing some much-duplicated code
> in this macro.  The expansion is at the top level of
> the source file, so a "do...while" loop ends up being
> an error.
>
> When looking at the output of checkpatch, assume it's
> giving you clues about problems that one *might* like to
> fix.  Its suggestions are most often reasonable, but in
> some cases (like this one) it's just not smart enough
> to recognize the problem that comes from following its
> advice.
>
> Make sure you understand exactly what happens when
> you make a change.  That means understanding the
> code, and then it means ensuring that the fix passes
> at least a compile test, and if possible an actual
> execution test.
>
>                     -Alex


I see, Thanks Alex for explaining. I will check the code before making 
any change.

Menna


>
>>
>> do loop with the conditional expression set to a constant
>> value of zero (0).This creates a loop that
>> will execute exactly one time.This is a coding idiom that
>> allows a multi-line macro to be used anywhere
>> that a single statement can be used.
>>
>> So, enclose `gb_loopback_stats_attrs` macro in do - while (0) to
>> fix checkpath error
>>
>> Signed-off-by: Menna Mahmoud <eng.mennamahmoud.mm@...il.com>
>> ---
>>   drivers/staging/greybus/loopback.c | 10 ++++++----
>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/staging/greybus/loopback.c 
>> b/drivers/staging/greybus/loopback.c
>> index 1a61fce98056..e86d50638cb5 100644
>> --- a/drivers/staging/greybus/loopback.c
>> +++ b/drivers/staging/greybus/loopback.c
>> @@ -162,10 +162,12 @@ static ssize_t name##_avg_show(struct device 
>> *dev,        \
>>   }                                    \
>>   static DEVICE_ATTR_RO(name##_avg)
>>   -#define gb_loopback_stats_attrs(field)                \
>> -    gb_loopback_ro_stats_attr(field, min, u);        \
>> -    gb_loopback_ro_stats_attr(field, max, u);        \
>> -    gb_loopback_ro_avg_attr(field)
>> +#define gb_loopback_stats_attrs(field)                    \
>> +    do { \
>> +        gb_loopback_ro_stats_attr(field, min, u);        \
>> +        gb_loopback_ro_stats_attr(field, max, u);        \
>> +        gb_loopback_ro_avg_attr(field);                \
>> +    } while (0)
>>     #define gb_loopback_attr(field, type)                    \
>>   static ssize_t field##_show(struct device *dev, \
>