[Users] Capturing the PID of every VE during startup / shutdown.

[Daniel Pittman]

G'day.

We are currently looking into doing more monitoring and management of our VEs
from the hardware node, and as part of that we would like to have access to a
reasonably reliable mapping of VE id to VE init process PID on the host node.

(This would be, basically, the equivalent of /var/run/foo.pid, where foo was
 the VEID, and the PID was the host-node PID of the init process.)

This mapping would make it easier for our tools to first verify that the init
process was correct[1], then to walk the process tree or otherwise inspect the
children running in that container.


Sadly, to my eye it doesn't look possible to capture this without a private
patch to the vzctl tool[2], since none of the current hooks have access to the
information, and the init process forks away to a new PGIG, SID, etc, quite
deliberately (and sensibly.)

So ... is there any sensibly way I could implement this without needing a
private patch, other than to scan the process table after starting the
container and rebuilding that mapping?

        Daniel

Footnotes: 
[1]  Check /proc/$pid/status for matching envID, and VPid of 1, to verify that
     the init process matches our mapping.  If not, raise a warning because
     something unexpected has happened.

[2]  ...and the assumption that only vzctl starts containers, which is an
     assumption I can live with: this all is supposed to improve our
     monitoring capabilities, not prevent a hostile root-capable user on the
     hardware node from doing something dubious.

-- 
✣ Daniel Pittman            ✉ daniel at rimspace.net            ☎ +61 401 155 707
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