* container_of() doubt
@ 2013-02-27 19:13 Felipe Balbi
2013-02-27 19:14 ` Felipe Balbi
0 siblings, 1 reply; 2+ messages in thread
From: Felipe Balbi @ 2013-02-27 19:13 UTC (permalink / raw)
To: Greg KH; +Cc: Luciano Coelho, Linux Kernel Mailing List
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Hi Greg,
hehe, you must've answered this over and over again, but I don't see the
need for __mptr in the container_of() macro. I tried googling it but
couldn't find much.
I get the macro, but not the need __mptr. Wouldn't this work the same
way ?
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 80d3687..bbce857 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -717,8 +717,7 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
*
*/
#define container_of(ptr, type, member) ({ \
- const typeof( ((type *)0)->member ) *__mptr = (ptr); \
- (type *)( (char *)__mptr - offsetof(type,member) );})
+ (type *)( (char *)(ptr) - offsetof(type,member) );})
/* Trap pasters of __FUNCTION__ at compile-time */
#define __FUNCTION__ (__func__)
why do we need this type * NULL ?
thanks
--
balbi
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^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: container_of() doubt
2013-02-27 19:13 container_of() doubt Felipe Balbi
@ 2013-02-27 19:14 ` Felipe Balbi
0 siblings, 0 replies; 2+ messages in thread
From: Felipe Balbi @ 2013-02-27 19:14 UTC (permalink / raw)
To: Felipe Balbi; +Cc: Greg KH, Luciano Coelho, Linux Kernel Mailing List
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Hi again,
On Wed, Feb 27, 2013 at 09:13:22PM +0200, Felipe Balbi wrote:
> Hi Greg,
>
> hehe, you must've answered this over and over again, but I don't see the
> need for __mptr in the container_of() macro. I tried googling it but
> couldn't find much.
>
> I get the macro, but not the need __mptr. Wouldn't this work the same
> way ?
>
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 80d3687..bbce857 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -717,8 +717,7 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
> *
> */
> #define container_of(ptr, type, member) ({ \
> - const typeof( ((type *)0)->member ) *__mptr = (ptr); \
> - (type *)( (char *)__mptr - offsetof(type,member) );})
> + (type *)( (char *)(ptr) - offsetof(type,member) );})
>
> /* Trap pasters of __FUNCTION__ at compile-time */
> #define __FUNCTION__ (__func__)
>
> why do we need this type * NULL ?
nevermind, type safety ;-)
--
balbi
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