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From: "Michael Kerrisk (man-pages)" <>
To: Eric Rannaud <>,,
Cc:, Aleksa Sarai <>
Subject: Re: clock_settime(2) error for non-settable clocks
Date: Thu, 26 Mar 2020 09:37:40 +0100
Message-ID: <> (raw)
In-Reply-To: <>


On 3/20/20 7:02 PM, Eric Rannaud wrote:
> If clock_id is a valid clock on the system (i.e. it can be passed to
> clock_gettime(2)), clock_settime(clock_id, &ts) sets errno to, either:
>   - EINVAL if CONFIG_POSIX_TIMERS is not enabled (kernel/posix-stubs.c);
>   - EINVAL if CONFIG_POSIX_TIMERS is enabled (kernel/posix-timers.c)
> and the k_clock has no set function (e.g. CLOCK_BOOTTIME);
>   - EACCES for dynamic posix clock devices that lack F_WRITE
> (kernel/posix-time.c);
>   - EOPNOTSUPP for dynamic posix clock devices that have F_WRITE but
> don't have a clock_settime op.
>   - EOPNOTSUPP for drivers/ptp/ptp_kvm.c (they provide a clock_settime
> op that returns -EOPNOTSUPP directly, rather than opt to leave
> clock_settime NULL which would do the same thing, see previous point).
> The manpage for clock_settime(2) is not very clear:
>        EINVAL The clk_id specified is not supported on this system.
>        EPERM  clock_settime() does not have permission to set the clock  indi‐
>               cated.
> To me, the manpage reads like EPERM should be expected when trying to
> set a clock that is not settable.
> Should we update the manpage to more fully explain the range of
> possible errors or instead try to have more consistent errors? For
> syscalls, what's the backward-compatibility contract for errno values?

A man-pages patch would be most appropriate. Would you be able to put
something together?



Michael Kerrisk
Linux man-pages maintainer;
Linux/UNIX System Programming Training:

  parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-20 18:02 Eric Rannaud
2020-03-21  3:56 ` Aleksa Sarai
2020-03-26  8:37 ` Michael Kerrisk (man-pages) [this message]
2020-03-29 20:49   ` Michael Kerrisk (man-pages)
2020-04-02 11:48     ` Michael Kerrisk (man-pages)
2020-04-02 14:23       ` [PATCH 1/1] clock_getres.2: dynamic POSIX clock devices can return other errors Eric Rannaud
2020-04-02 19:55         ` Michael Kerrisk (man-pages)
2020-04-02 20:06         ` Eric Rannaud
2020-04-02 20:19           ` Michael Kerrisk (man-pages)
2020-04-02 20:49             ` Eric Rannaud
2020-04-02 20:50               ` Eric Rannaud
2020-04-03  7:02               ` Michael Kerrisk (man-pages)
2020-04-03 16:42                 ` Eric Rannaud
2020-04-02 14:29       ` clock_settime(2) error for non-settable clocks Eric Rannaud

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