Re: [PATCH v3 1/2] epoll: add nsec timeout support with epoll_pwait2

[Arnd Bergmann]

On Fri, Nov 20, 2020 at 11:28 PM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
> On Fri, Nov 20, 2020 at 2:23 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> > On Fri, Nov 20, 2020 at 5:01 PM Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx> wrote:
>
> I think it'll be better to split the patchsets:
>
> epoll: convert internal api to timespec64
> epoll: add syscall epoll_pwait2
> epoll: wire up syscall epoll_pwait2
> selftests/filesystems: expand epoll with epoll_pwait2
>
> and
>
> select: compute slack based on relative time
> epoll: compute slack based on relative time
>
> and judge the slack conversion on its own merit.

Yes, makes sense.

> I also would rather not tie this up with the compat deduplication.
> Happy to take a stab at that though. On that note, when combining
> functions like
>
>   int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
>                            fd_set __user *exp, struct timespec64 *end_time,
>                            u64 slack)
>
> and
>
>   static int compat_core_sys_select(int n, compat_ulong_t __user *inp,
>         compat_ulong_t __user *outp, compat_ulong_t __user *exp,
>         struct timespec64 *end_time, u64 slack)
>
> by branching on in_compat_syscall() inside get_fd_set/set_fd_set and
> deprecating their compat_.. counterparts, what would the argument
> pointers look like? Or is that not the approach you have in mind?

In this case, the top-level entry points becomes unified, and you get
the prototype from core_sys_select() with the native arguments.

I would imagine this can be done like the way I proposed
for get_bitmap() in sys_migrate_pages:

https://lore.kernel.org/lkml/20201102123151.2860165-4-arnd@xxxxxxxxxx/

        Arnd