Re: [rfc] epoll interface change and glibc bits ...

From: Mark Mielke (mark@mark.mielke.cc)
Date: Wed Nov 20 2002 - 20:23:34 EST

On Thu, Nov 21, 2002 at 12:28:16AM +0000, Jamie Lokier wrote:
> Davide Libenzi wrote:
> > typedef union epoll_obj {
> > void *ptr;
> > __uint32_t u32[2];
> > __uint64_t u64;
> > } epoll_obj_t;
> > I'm open to suggestions though. The "ptr" enable me to avoid wierd casts
> > to avoid gcc screaming.
> That makes more sense to me, because it will be fine to use `ptr' even
> on 128-bit pointer machines when they arrive, yet preserves the
> property that 64<->32 bit conversion functions don't need to reformat
> the buffer when running 32-bit applications on a 64-bit CPU... even if
> the 32-bit application uses the `ptr' field.
> Did I just write that? :)

The problem with sizeof(void *) being >= sizeof(__uint64_t) is that the
data structure is the wrong length. Binary compatibility would not be
maintained.

Still... I believe that the days of 128-bit pointers are comfortably
far enough away that it does not cause any concerns at all for me. (I
suspect the kernel will need quite a few more changes than just this
to support 128-bit poitners...)

mark 

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