* container-of Implementation
@ 2013-01-14 10:46 Schrober
2013-01-14 12:22 ` Mikael Pettersson
2013-01-14 12:23 ` Geert Uytterhoeven
0 siblings, 2 replies; 3+ messages in thread
From: Schrober @ 2013-01-14 10:46 UTC (permalink / raw)
To: linux-kernel
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)))
--
Franz Schrober
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: container-of Implementation
2013-01-14 10:46 container-of Implementation Schrober
@ 2013-01-14 12:22 ` Mikael Pettersson
2013-01-14 12:23 ` Geert Uytterhoeven
1 sibling, 0 replies; 3+ messages in thread
From: Mikael Pettersson @ 2013-01-14 12:22 UTC (permalink / raw)
To: Schrober; +Cc: linux-kernel
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.
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: container-of Implementation
2013-01-14 10:46 container-of Implementation Schrober
2013-01-14 12:22 ` Mikael Pettersson
@ 2013-01-14 12:23 ` Geert Uytterhoeven
1 sibling, 0 replies; 3+ messages in thread
From: Geert Uytterhoeven @ 2013-01-14 12:23 UTC (permalink / raw)
To: Schrober; +Cc: linux-kernel
On Mon, Jan 14, 2013 at 11:46 AM, Schrober <franzschrober@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 -- geert@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
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2013-01-14 12:23 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2013-01-14 10:46 container-of Implementation Schrober
2013-01-14 12:22 ` Mikael Pettersson
2013-01-14 12:23 ` Geert Uytterhoeven
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®