linux-kernel - Re: [PATCH v2] uapi, posix-timers: provide clockid-related macros and functions to UAPI

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Message-ID: <CALAqxLWkQmiFOCY=YhQLCJHwGHCO9kfZzysCEDLzJFTvgapUwA@mail.gmail.com>
Date:   Wed, 13 May 2020 10:11:32 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Sergey Organov <sorganov@...il.com>
Cc:     Eugene Syromiatnikov <esyr@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] uapi, posix-timers: provide clockid-related macros and
 functions to UAPI

On Wed, May 13, 2020 at 2:13 AM Sergey Organov <sorganov@...il.com> wrote:
>
> John Stultz <john.stultz@...aro.org> writes:
>
> > On Tue, May 12, 2020 at 3:31 PM Eugene Syromiatnikov <esyr@...hat.com> wrote:
> >> On Tue, May 12, 2020 at 10:58:16PM +0300, Sergey Organov wrote:
> >> > Eugene Syromiatnikov <esyr@...hat.com> writes:
> >> >
> >> > > As of now, there is no interface exposed for converting pid/fd into
> >> > > clockid and vice versa; linuxptp, for example, has been carrying these
> >> > > definitions in missing.h header for quite some time[1].
> >> > >
> >> > > [1] https://sourceforge.net/p/linuxptp/code/ci/af380e86/tree/missing.h
> >> > >
> >> > > Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> >> > > ---
> >> > > Changes since v1[1]:
> >> > >  * Actually tried to build with the patch and fixed the build error
> >> > >    reported by kbuild test robot[2].
> >> > >
> >> > > [1] https://lkml.org/lkml/2019/9/20/698
> >> > > [2] https://lkml.org/lkml/2019/9/22/13
> >> > > ---
> >> > >  include/linux/posix-timers.h | 47 +------------------------------------------
> >> > >  include/uapi/linux/time.h    | 48 ++++++++++++++++++++++++++++++++++++++++++++
> >> > >  2 files changed, 49 insertions(+), 46 deletions(-)
> >> >
> >> > Was this patch applied, rejected, lost?
> >> >
> >> > I can't find it in the current master.
> >>
> >> IIRC, it was ignored.
> >
> > Overlooked. :)  Not intentionally ignored.
> >
> > I don't have any major objection with adding helpers, though I feel
> > like you're exporting a lot more to the uapi then applications likely
> > need.
> >
> > Would it be better to add just the bits from the missing.h header you
> > pointed to:
> > #define CLOCKFD 3
> > #define FD_TO_CLOCKID(fd) ((~(clockid_t) (fd) << 3) | CLOCKFD)
> > #define CLOCKID_TO_FD(clk) ((unsigned int) ~((clk) >> 3))
> >
> >  to the uapi header?
>
> Please, no:
>
> 1. These macros were copied almost verbatim from the kernel code long
> ago, and since then kernel has changed them to inline functions, so
> getting back to these obsolete macros is pointless.
>
> 2. If we do need to export macroses, then kernel inline functions are
> better to be re-implemented in terms of these macros, not to have 2
> different points of implementation.
>
> Overall, I'd vote for the current approach of the patch, provided
> exporting inline functions to user-space is allowed.

Sure, I just want to make sure we're only exporting the minimal
necessary amount of details to userland. The current patch is
exporting a bit more than that.

thanks
-john