Add pause/resume implementation

[estesp]

This adds pause and resume to containerd's execution service and the
same commands to the ctr client.

Fixes: #794
Signed-off-by: Phil Estes estesp@linux.vnet.ibm.com

[estesp]

Open questions:

• Names: I picked pause and unpause; no strong opinion vs. resume (now pause/resume)
• Code does not check for current process state to 'error' if pausing a paused container or unpausing an unpaused container. Is that necessary? Should we let higher level engines choose to add that strict checking?
• Windows does not implement pause/unpause. I personally don't know if it's possible or not so I stubbed it out as I don't see capabilities in the hcs or process implementation in the codebase. @jhowardmsft

[mlaventure]

Actually windows do support pause/resume if the container is running under HyperV. It's a matter of calling Pause()/Resume() on the hcsshim.Container type.

You can check that a container was started using HyperV by checking the UseHyperV flag within the windows runtime container object.

[mlaventure]

Thanks to taking care of this one!

[mlaventure]

Code does not check for current process state to 'error' if pausing a paused container or unpausing an unpaused container. Is that necessary?

We just need consistency across runtime I think. We need to decide to either error or on that case or silently succeed.

[mlaventure]

Names: I picked pause and unpause; no strong opinion vs. resume

Looks like both the Linux and Windows Shim are using Resume maybe do the same for consistency.

[codecov-io]

Codecov Report

Merging #807 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #807   +/-   ##
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  Coverage   59.26%   59.26%           
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  Files           5        5           
  Lines         739      739           
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  Hits          438      438           
  Misses        198      198           
  Partials      103      103

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[estesp]

@mlaventure thanks! Updated with a Windows implementation, but I have no way to test.

As you mentioned, given the runtimes were "resume," they are all aligned to use the same words "pause" and "resume" now.

Only remaining issue is to decide about checking state and having an error for "invalid" state transitions.

[mlaventure]

@estesp I realized that I actually never tested the HyperV version. So I'll do that later, since it may not work at all 😅

[crosbymichael]

Is there a reason why you placed these methods on the Runtime and not on the Container interfaces?

[estesp]

@crosbymichael obviously a newbie error.. just pushed update with Pause/Resume attached to container operations. This forced (maybe incorrectly?) me to add Pause and Resume to base Container type, so LinuxContainer now is possibly an unnecessary type.

This all hinges on someone validating that pause/resume works for the UseHyperV-configured Windows containers, as that check is now in the base Windows container impl. of Pause and Resume

[mlaventure]

@estesp Pause/Resume is implemented and AFAIK working within docker.

I'm fine with this being merged without me having the time to test it on Windows, if it is broken, I'll fix it :)

[crosbymichael]

LGTM

[dqminh]

LGTM