20-24 September 2021
US/Pacific timezone

Mount-v2 CRIU migration engine: status update

20 Sep 2021, 08:10
25m
Microconference2/Virtual-Room (LPC Virtual)

Microconference2/Virtual-Room

LPC Virtual

150
Containers and Checkpoint/Restore MC Containers and Checkpoint/Restore MC

Speaker

Pavel Tikhomirov (Virtuozzo)

Description

Mount checkpoint/restore is an important part of CRIU, it is responsible for
consistency of the file system view of dumped processes. In current state we
can only restore simple mount configurations, something more complex would
either make us fail or, which is even worse, make us creating wrong file
system view for restored processes.

In CRIU we only see the final state, the result of probably multiple kernel API
calls inside a container, and on restore we need to recreate the sequence of
calls which would lead to the exact same state, in general this task can be
very complex. So sometimes the only way is to simplify the API so that it
become easier to restore all possible configurations.

Last year [1] we discussed a variety of problems CRIU faces with mounts, most
important ones related to mount propagation and how to simplify mount
propagation configuration so that even complex setups can be re-created simply
and correctly.

This talk will start with showing more complex mount configurations to
demonstrate that that we still need an API change. Then there will be a status
update on kernel patch progress and changes that were done during the last year
followed by the discussion on how to make the patch [2] mergeable to the
upstream kernel.

Here are links:

  • [1] https://www.linuxplumbersconf.org/event/7/contributions/640/
  • [2] https://lore.kernel.org/linux-api/20210715100714.120228-1-ptikhomirov@virtuozzo.com/
  • mount-v2 draft for criu - https://github.com/Snorch/criu/commits/mount-v2-poc
  • mount-v2 for VZ criu - https://src.openvz.org/projects/OVZ/repos/criu/browse/criu/mount-v2.c

Thanks to Andrei Vagin and Christian Brauner for a great help with it!

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Primary author

Pavel Tikhomirov (Virtuozzo)

Presentation Materials

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