Re: PATCH: type safe(r) list_entry repacement: generic_out_cast

[Linus Torvalds]

In article <[e-mail]>,
Mikael Pettersson  <[e-mail]> wrote:
>On Tue, 23 Jul 2002 18:58:52 -0400, Kevin O'Connor wrote:
>>#define BackPtr(ptr, type, member) ({                                         \
>>        typeof( ((type *)0)->member ) *__mptr = (ptr);                        \
>>        ((type *)( (char *)__mptr - (unsigned long)(&((type *)0)->member) ));})
>
>I've seen this sort of code several times now in the Linux kernel,
>and I've never liked it. Is there some reason why you guys avoid
>offsetof() like the plague?

Trivial answer: offsetof() does not exist when you don't have system
header files. 

So it's not that it's getting avoided, it _has_ to be re-implemented
anyway.  And once you do that, you might as well do it right (ie what
the kernel wants is not offsetof, but a new pointer.

		Linus