Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Cc:     mtk.manpages@gmail.com, linux-man <linux-man@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>, arul.jeniston@gmail.com,
        "devi R.K" <devi.feb27@gmail.com>,
        Marc Lehmann <debian-reportbug@plan9.de>,
        John Stultz <john.stultz@linaro.org>,
        Andrei Vagin <avagin@gmail.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>
Subject: Re: timer_settime() and ECANCELED
To:     Thomas Gleixner <tglx@linutronix.de>
References: <87pncrf6gd.fsf@nanos.tec.linutronix.de>
 <4c557b44-4e4e-a689-a17b-f95e6c5ee4b0@gmail.com>
 <87mu7unugh.fsf@nanos.tec.linutronix.de>
 <8ae32d2f-e4a8-240f-c7bd-580c26bba2d0@gmail.com>
 <87bloanh89.fsf@nanos.tec.linutronix.de>
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Message-ID: <5052f8a7-c6b9-be30-878e-053a3d035f7a@gmail.com>
Date:   Thu, 2 Apr 2020 21:48:04 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.6.0
MIME-Version: 1.0
In-Reply-To: <87bloanh89.fsf@nanos.tec.linutronix.de>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 4/2/20 3:35 PM, Thomas Gleixner wrote:
> "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> writes:
>> NOTES
>>        Suppose  the  following scenario for CLOCK_REALTIME or CLOCK_REAL‐
>>        TIME_ALARM timer that was created with timerfd_create():
>>
>>        (a) The  timer  has  been  started  (timerfd_settime())  with  the
>>            TFD_TIMER_ABSTIME and TFD_TIMER_CANCEL_ON_SET flags;
>>
>>        (b) A discontinuous change (e.g.  settimeofday(2)) is subsequently
>>            made to the CLOCK_REALTIME clock; and
>>
>>        (c) the caller once more  calls  timerfd_settime()  to  rearm  the
>>            timer (without first doing a read(2) on the file descriptor).
>>
>>        In this case the following occurs:
>>
>>        · The  timerfd_settime()  returns  -1 with errno set to ECANCELED.
>>          (This enables the caller to know that  the  previous  timer  was
>>          affected by a discontinuous change to the clock.)
>>
>>        · The  timer is successfully rearmed with the settings provided in
>>          the second timerfd_settime() call.  (This was probably an imple‐
>>          mentation  accident,  but  won't be fixed now, in case there are
>>          applications that depend on this behaviour.)
> 
> Clear enough.
> 
> Thanks Michael!

Thanks. Committed. (But, next time you change the API. maybe a 
man-pages patch to go with that? :-).)

Cheers,

Michael

 
-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/