[PATCH] linux/container_of.h: Remove redundant type cast in container_of_const()

[PATCH] linux/container_of.h: Remove redundant type cast in container_of_const()

[Zijun Hu]

From: Zijun Hu <quic_zijuhu@quicinc.com>

Remove redundant (type *) cast for default branch in container_of_const()
since the cast has been done by container_of().

Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
---
 include/linux/container_of.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/container_of.h b/include/linux/container_of.h
index 713890c867be..c36435e7c7f2 100644
--- a/include/linux/container_of.h
+++ b/include/linux/container_of.h
@@ -32,7 +32,7 @@
 #define container_of_const(ptr, type, member)				\
 	_Generic(ptr,							\
 		const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
-		default: ((type *)container_of(ptr, type, member))	\
+		default: container_of(ptr, type, member)	\
 	)
 
 #endif	/* _LINUX_CONTAINER_OF_H */

---
base-commit: 8400291e289ee6b2bf9779ff1c83a291501f017b
change-id: 20240802-container_of_const_fix-87ecdb71ba90

Best regards,
-- 
Zijun Hu <quic_zijuhu@quicinc.com>

Re: [PATCH] linux/container_of.h: Remove redundant type cast in container_of_const()

[Andy Shevchenko]

On Fri, Aug 02, 2024 at 11:15:15PM +0800, Zijun Hu wrote:
> From: Zijun Hu <quic_zijuhu@quicinc.com>
> 
> Remove redundant (type *) cast for default branch in container_of_const()
> since the cast has been done by container_of().

While it might have same effect, the below is explicitly clear about both
cases. With your patch it will become inconsistent.

...

>  #define container_of_const(ptr, type, member)				\
>  	_Generic(ptr,							\
>  		const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\

(see, in the above line the cast is still present / required)

> -		default: ((type *)container_of(ptr, type, member))	\
> +		default: container_of(ptr, type, member)	\
>  	)

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] linux/container_of.h: Remove redundant type cast in container_of_const()

[Zijun Hu]

On 2024/8/9 19:27, Andy Shevchenko wrote:
> On Fri, Aug 02, 2024 at 11:15:15PM +0800, Zijun Hu wrote:
>> From: Zijun Hu <quic_zijuhu@quicinc.com>
>>
>> Remove redundant (type *) cast for default branch in container_of_const()
>> since the cast has been done by container_of().
> 
> While it might have same effect, the below is explicitly clear about both
> cases. With your patch it will become inconsistent.
> 

my change is more obvious to say that container_of_const() is same as
container_of() for none const pointer parameter @ptr. it is simpler and
easier to understand.

> ...
> 
>>  #define container_of_const(ptr, type, member)				\
>>  	_Generic(ptr,							\
>>  		const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
> 
> (see, in the above line the cast is still present / required)
> 

yes, for above case, (const type *) is suitable and required.

>> -		default: ((type *)container_of(ptr, type, member))	\
>> +		default: container_of(ptr, type, member)	\
>>  	)
> 

Re: [PATCH] linux/container_of.h: Remove redundant type cast in container_of_const()

[Sakari Ailus]

Hi Andy, Zijun,

On Fri, Aug 09, 2024 at 02:27:23PM +0300, Andy Shevchenko wrote:
> On Fri, Aug 02, 2024 at 11:15:15PM +0800, Zijun Hu wrote:
> > From: Zijun Hu <quic_zijuhu@quicinc.com>
> > 
> > Remove redundant (type *) cast for default branch in container_of_const()
> > since the cast has been done by container_of().
> 
> While it might have same effect, the below is explicitly clear about both
> cases. With your patch it will become inconsistent.

In the const case it's actually required whereas container_of() already
does exactly the same cast, rendering the cast done below redundant.
There's nothing inconsistent in removing a needless cast.

Removing it is my preference as well.

> 
> ...
> 
> >  #define container_of_const(ptr, type, member)				\
> >  	_Generic(ptr,							\
> >  		const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
> 
> (see, in the above line the cast is still present / required)
> 
> > -		default: ((type *)container_of(ptr, type, member))	\
> > +		default: container_of(ptr, type, member)	\
> >  	)
> 

-- 
Kind regards,

Sakari Ailus

Re: [PATCH] linux/container_of.h: Remove redundant type cast in container_of_const()

[Greg Kroah-Hartman]

On Fri, Aug 09, 2024 at 02:27:23PM +0300, Andy Shevchenko wrote:
> On Fri, Aug 02, 2024 at 11:15:15PM +0800, Zijun Hu wrote:
> > From: Zijun Hu <quic_zijuhu@quicinc.com>
> > 
> > Remove redundant (type *) cast for default branch in container_of_const()
> > since the cast has been done by container_of().
> 
> While it might have same effect, the below is explicitly clear about both
> cases. With your patch it will become inconsistent.

Which is why I did it this way.  It's safe to keep as-is, so let's do so
please.

Remember, we write code for people first, compilers second.  There's
nothing wrong with the code as-is and it makes it more obvious what is
happening when someone reads it.

thanks,

greg k-h