linux-kernel - Re: [PATCH] CodingStyle: delete "kmalloc(sizeof(*var))" as preferred allocation form

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Date:   Mon, 22 May 2017 14:43:18 -0700
From:   Joe Perches <joe@...ches.com>
To:     Alexey Dobriyan <adobriyan@...il.com>, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] CodingStyle: delete "kmalloc(sizeof(*var))" as
 preferred allocation form

On Tue, 2017-05-23 at 00:38 +0300, Alexey Dobriyan wrote:
> There are valid reasons for
> 
> 	malloc(sizeof(struct S))
> 
> form:
> 
> * struct S acts as an anchor for ctags quickly reminding which type is
>   in focus
> 
> * argument re changing name prevents bugs is semi bogus:
>   such changes are rare,
>   "void *" cast gives both forms equal opportunity to be screwed up
> 
> * proper way to fix those rare misallocation bugs (which indeed happened)
>   is type safe allocation macros (see tmalloc from Samba).
> 
>   However amount of disruption will be so high so it may never be done.
> 
> * ratio of allocation styles is ~6400:12000 which is about 1:2
>   so the amount of churn to maintain this rule is pretty high in theory.
> 
> The winning move is to not play and not encourage people send trivial stuff.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
> 
>  Documentation/process/coding-style.rst |   10 ----------
>  1 file changed, 10 deletions(-)
> 
> --- a/Documentation/process/coding-style.rst
> +++ b/Documentation/process/coding-style.rst
> @@ -808,16 +808,6 @@ kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc(), and
>  vzalloc().  Please refer to the API documentation for further information
>  about them.
>  
> -The preferred form for passing a size of a struct is the following:
> -
> -.. code-block:: c
> -
> -	p = kmalloc(sizeof(*p), ...);
> -
> -The alternative form where struct name is spelled out hurts readability and
> -introduces an opportunity for a bug when the pointer variable type is changed
> -but the corresponding sizeof that is passed to a memory allocator is not.
> -
>  Casting the return value which is a void pointer is redundant. The conversion
>  from void pointer to any other pointer type is guaranteed by the C programming
>  language.

Thanks.  I agree with this deletion.