linux-kernel - Re: [PATCH v3 1/2] epoll: add nsec timeout support with epoll

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Date:   Thu, 10 Dec 2020 12:33:51 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Laight <David.Laight@...lab.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Soheil Hassas Yeganeh <soheil.kdev@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Shuo Chen <shuochen@...gle.com>,
        linux-man <linux-man@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] epoll: add nsec timeout support with epoll_pwait2

On Sat, Nov 21, 2020 at 4:27 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> On Fri, Nov 20, 2020 at 11:28 PM Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
> > On Fri, Nov 20, 2020 at 2:23 PM Arnd Bergmann <arnd@...nel.org> wrote:
> > > On Fri, Nov 20, 2020 at 5:01 PM Willem de Bruijn <willemdebruijn.kernel@...il.com> 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@kernel.org/

Coming back to this. Current patchset includes new select and poll
selftests to verify the changes. I need to send a small kselftest
patch for that first.

Assuming there's no time pressure, I will finish up and send the main
changes after the merge window, for the next release then.

Current state against linux-next at
https://github.com/wdebruij/linux-next-mirror/tree/select-compat-1