libcontainerd: change the digest used when restoring

[huang-jl]

• fixes: Docker start from checkpoint fails occasionally as content sha256 already exists #42900

For current implementation of Checkpoint Restore (C/R) in docker, it will write the checkpoint to content store. However, when restoring libcontainerd uses .Digest().Encoded(), which will remove the info of algorithms, leading to a NotFound error.

- What I did

For now when using C/R to start a container like:

docker run  --name=demo -d ubuntu sleep infinity
docker checkpoint create demo ckpt1
docker start --checkpoint ckpt1 demo

It will failed like:

Error response from daemon: failed to create task for container: content digest 4ba0864fec064b253c12a12d4a2369086d6036c3dd1ecda0239f96796181b705: not found: unknown

The reason is that when restoring, it query the content store with .Digest().Encoded().

- How I did it
Change it to use .Diegest().String()

- How to verify it

docker run  --name=demo -d ubuntu sleep infinity
docker checkpoint create demo ckpt1
docker start --checkpoint ckpt1 demo

- Description for the changelog

Fix `docker start` failing when used with `--checkpoint`

[vvoland]

LGTM; thanks!

Looks to be a regression in v25: fd6dd69#diff-c3c703e02023ce6a127448365c946281594c6ee77acf7981fbfba77d3d97a89cR740

So no need for a v24 cherry-pick.

[thaJeztah]

Looks to be a regression in v25

Oh, good catch! I bookmarked this one as I was wondering indeed if this never worked, or if we regressed, so thanks for doing the digging 😄

[thaJeztah]

LGTM

[vvoland]

@huang-jl Are you interested in opening a cherry-pick for v25.0?

[huang-jl]

@vvoland Of course, but I do not understand what means "cherry-pick for v25.0". Do you mean send a pull request to branch "25.0"?

[vvoland]

That's correct! Basically create a new branch based off the 25.0 branch and cherry-pick your commit there, something like:

$ git checkout -b fix_restore_digest_25 upstream/25.0
$ git cherry-pick -x fix_restore_digest

[dannykopping]

I'm still getting the original error, running on v25:

root@siegfried:/home/coder# docker run --name cr1 -d busybox /bin/sh -c 'i=0; while true; do echo $i; i=$(expr $i + 1); sleep 1; done'
245eb5fe28af02b9d9b0ce404d50673db886330be7fb348b9e709f93f1aa52cb
root@siegfried:/home/coder# docker checkpoint create cr1 sleepy1
sleepy1
root@siegfried:/home/coder# docker start --checkpoint sleepy1 cr1
Error response from daemon: failed to upload checkpoint to containerd: commit failed: content sha256:8fae2a5b4ca0ece5c2a72fcf8424e2a8c80b07badfd040892961f6deb1c480ef: already exists

Versions:

# docker version | grep -e Client -e Engine -A1
Client: Docker Engine - Community
 Version:           25.0.3
--
Server: Docker Engine - Community
 Engine:
  Version:          25.0.3

[thaJeztah]

@dannykopping I see the backport linked to this ticket was included in 25.0.4; #47466

[dannykopping]

Ah, missed that; thank you @thaJeztah