btime is not virtualized in /proc/stat

[hallyn]

See https://bugs.launchpad.net/ubuntu/+source/lxcfs/+bug/1654310

This should be a trivial fix.

[gozdal]

This introduces a different problem: process creation time is counted as offset from btime:

(22) starttime  %llu
          The time the process started after system boot.  In
          kernels before Linux 2.6, this value was expressed
          in jiffies.  Since Linux 2.6, the value is expressed
          in clock ticks (divide by sysconf(_SC_CLK_TCK)).

(http://man7.org/linux/man-pages/man5/proc.5.html)

This means that because starttime is not virtualized, all the processes within the LXC container appear as time travellers from the future.

[brauner]

We've reverted the commit just yesterday for exactly this reason. :)

[zerkms]

If it was reverted, shouldn't this be re-opened as well?

Also, is it relevant that the sysinfo's uptime field is also not virtualised?

#include <stdio.h>
#include <sys/sysinfo.h>

int main ()
{
 struct sysinfo si;
 sysinfo (&si);
 printf ("uptime %lu\n", si.uptime);
 return 0;
}

This would show the uptime of the host, not of the container.

[hallyn]

So just to be clear, is re-applying this patch plus virtualizing /proc/stat's starttime all that is needed?

I had thought there was a more complicated design issue blocking us...

[brauner]

Not sure if btime is safe now. If it is, someone please send a patch!