Re: [PATCH 31/31] aio: implement io_pgetevents

On Wed, Jan 10, 2018 at 3:59 PM, Christoph Hellwig [off-list ref] wrote:

On Wed, Jan 10, 2018 at 12:03:24PM +0100, Arnd Bergmann wrote:

quoted

I'd suggest passing a variant of timespec with two 64-bit members.
Deepa has posted patches for this structure in the past and was planning
to do a new version (with minor changes from review) soon, but we
can just well use it in your patch if that gets merged first.

If we merge io_pgetevents quickly (before the bulk of the y2038 syscall
conversion), I'd say we should use

struct __kernel_timespec64 {
         __s64 tv_sec;
         __s64 tv_nsec;
};

The tv_nsec type is unfortunately much trickier than it should be:
C99 requires it to be 'long', so user space needs to define the 64-bit
'struct timespec' with internal padding in the right places depending
on endianess, and the kernel has to be careful about either zeroing
the upper half or checking it for being zeroed by user space depending
on whether we come from a 32-bit or 64-bit task, but I'm fairly sure
we have that part worked out by now.

Eww.  Being the ginea pig is never good, and in this the fact that
the aio syscalls aren't in glibc is just going to make things worse
in chances of diverging from the future 'standard'.

I'm tempted to say I'd rather deal with the new 64-bit time_t version
later, especially as that should only affect 32-bit ports.

Ok, fair enough. Given that the old version gets obsoleted by this
one, it shouldn't get much uglier than it already is here when you
start out with a regular timespec. We just need to be aware of possible
clashes when we get the patches merged at the same time.

      Arnd
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