Re: container-of Implementation
On Mon, Jan 14, 2013 at 11:46 AM, Schrober wrote:
> I wondered why the container_of implementation is so complicated.
>
> #define container_of(ptr, type, member) ({ \
> const typeof( ((type *)0)->member ) *__mptr = (ptr);\
> (type *)( (char *)__mptr - offsetof(type,member) );})
>
> isn't the __mptr not unnecessary? Why not following version?
>
> #define container_of(ptr, type, member) \
> ((type *)((char *)(ptr) - offsetof(type, member)))
The __mptr construct will cause a compiler warning if ptr is of the
wrong type.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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Re: container-of Implementation
Schrober writes:
> Hi,
>
> I wondered why the container_of implementation is so complicated.
>
> #define container_of(ptr, type, member) ({ \
> const typeof( ((type *)0)->member ) *__mptr = (ptr);\
> (type *)( (char *)__mptr - offsetof(type,member) );})
>
> isn't the __mptr not unnecessary? Why not following version?
>
> #define container_of(ptr, type, member) \
> ((type *)((char *)(ptr) - offsetof(type, member)))
Compile-time type checking. The first version requires ptr to be
assignment-compatible with the type of the struct member, the second
version accepts random junk for ptr.
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Please read the FAQ at http://www.tux.org/lkml/
Re: container-of Implementation
Schrober writes:
Hi,
I wondered why the container_of implementation is so complicated.
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)-member ) *__mptr = (ptr);\
(type *)( (char *)__mptr - offsetof(type,member) );})
isn't the __mptr not unnecessary? Why not following version?
#define container_of(ptr, type, member) \
((type *)((char *)(ptr) - offsetof(type, member)))
Compile-time type checking. The first version requires ptr to be
assignment-compatible with the type of the struct member, the second
version accepts random junk for ptr.
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: container-of Implementation
On Mon, Jan 14, 2013 at 11:46 AM, Schrober franzschro...@yahoo.de wrote:
I wondered why the container_of implementation is so complicated.
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)-member ) *__mptr = (ptr);\
(type *)( (char *)__mptr - offsetof(type,member) );})
isn't the __mptr not unnecessary? Why not following version?
#define container_of(ptr, type, member) \
((type *)((char *)(ptr) - offsetof(type, member)))
The __mptr construct will cause a compiler warning if ptr is of the
wrong type.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say programmer or something like that.
-- Linus Torvalds
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
