linux-kernel - Re: [PATCH v4 0/3] time namespace aware system boot time

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Message-ID: <20201022083644.GA344600@gmail.com>
Date:   Thu, 22 Oct 2020 01:36:44 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     Michael Weiß <michael.weiss@...ec.fraunhofer.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        linux-kernel@...r.kernel.org,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Chuck Lever <chuck.lever@...cle.com>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>
Subject: Re: [PATCH v4 0/3] time namespace aware system boot time

On Mon, Oct 19, 2020 at 09:52:54PM +0200, Michael Weiß wrote:
> Time namespaces make it possible to virtualize time inside of
> containers, e.g., it is feasible to reset the uptime of a container
> to zero by setting the time namespace offset for boottime to the
> negated current value of the CLOCK_BOOTTIME.
> 
> However, the boot time stamp provided by getboottime64() does not
> take care of time namespaces. The resulting boot time stamp 'btime'
> provided by /proc/stat does not show a plausible time stamp inside
> the time namespace of a container.
> 
> We address this by shifting the value returned by getboottime64()
> by subtracting the boottime offset of the time namespace.
> (A selftest to check the expected /proc/stat 'btime' inside the
> namespace is provided.)
> 
> Further, to avoid to show processes as time travelers inside of the
> time namespace the boottime offset then needs to be added to the
> start_boottime provided by the task_struct.
> 
> v4 Changes:
> Avoid type conversions back and forth between timespec64 and ktime_t
> in 'proc/stat.c' as suggested by Andrei.
> Introduced timens_sub_boottime() in 'time_namespace.h' to provide
> better coder readability/consistency.
> 

Reviewed-by: Andrei Vagin <avagin@...il.com>

Thanks,
Andrei