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https://github.com/checkpoint-restore/criu
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0b2c951358
We have a slight mess with how criu restores root task.
Right now we have the following options.
1) CLI
a) Usually
task calling criu
`- criu
`- root restored task
b) when --restore-detached AND root has pdeath_sig
task calling criu
`- criu
`- root restored task
2) Library/SWRK
task using lib/swrk
`- criu
`- root restored task
3) Standalone service
a) Usually
service
`- service sub task
`- root restored task
b) when root has pdeath_sig
criu service
`- criu sub task
`- root restored task
It would be better is CRIU always restored the root task as sibling,
but we have 3 constraints:
First, the case 1.a is kept for zdtm to run tests in pid namespaces
on 3.11, which in turn doesn't allow CLONE_PARENT | CLONE_NEWPID.
Second, CLI w/o --restore-detach waits for the restored task to die and
this behavior can be "expected" already.
Third, in case of standalone service tasks shouldn't become service's
children.
And I have one "plan". The p.haul project while live migrating tasks
on destination node starts a service, which uses library/swrk mode. In
this case the restored processes become p.haul service's kids which is
also not great.
That said, here's the option called --restore-child that pairs the
--restore-detach like this:
* detached AND child:
task
`- criu restore (exits at the end)
`- root task
The root task will become task's child.
This will be default to library/swrk.
This is what LXC needs.
* detach AND !child
task
`- criu restore (exits at the end)
`- root task
The root task will get re-parented to init.
This will be compatible with 1.3.
This will be default to standalone service and
to my wish with the p.haul case.
* !detach AND child
task
`- criu restore (waits for root task to die)
`- root task
This should be deprecated, so that criu restore doesn't mess
with task <-> root task signalling.
* !detach AND !child
task
`- criu restore (waits for root task to die)
`- root task
This is how plain criu restore works now.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Tycho Andersen <tycho.andersen@canonical.com>
Acked-by: Andrew Vagin <avagin@openvz.org>