linux-kernel - A further though on /proc/PID/timens

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Date:   Tue, 7 Apr 2020 15:24:13 +0200
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Andrey Vagin <avagin@...nvz.org>, Dmitry Safonov <dima@...sta.com>
Cc:     mtk.manpages@...il.com, Linux API <linux-api@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Containers <containers@...ts.linux-foundation.org>,
        Christian Brauner <christian@...uner.io>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrey Vagin <avagin@...nvz.org>,
        Adrian Reber <adrian@...as.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>
Subject: A further though on /proc/PID/timens_offsets

Hello Dmitry, Andrei,

Quoting the draft time_namespaces manual page:

       Associated with each time namespace are  offsets,  expressed  with
       respect  to  the initial time namespace, that define the values of
       the monotonic and boot-time clocks in that namespace.  These  off‐
       sets  are  exposed  via the file /proc/PID/timens_offsets.  Within
       this file, the offsets are expressed as lines consisting of  three
       space-delimited fields:

           <clock-id> <offset-secs> <offset-nanosecs>

       The  clock-id  identifies the clock whose offsets are being shown.
       This field is either 1, for CLOCK_MONOTONIC, or 7, for CLOCK_BOOT‐
       TIME.

What was the reason for exposing numeric clock IDs in the
timens_offsets file? In API terms, that seems a little ugly.

I think it would have been much nicer if the clocks were defined
symbolically in this file. I.e., that reading the file would have
shown something like

monotonic    x    y
boottime     x    y

And that records similarly with symbolic clock names could have
been written to the file. Was there a reason not to do this?

Thanks,

Michael

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