[bug report] If container is committed to a image, after the image is removed, the snapshots for the image still exist.

[wangforthinker]

Ⅰ. Issue Description

A image is built by container committed, when we remove the image, the snapshots for the image still exist.

Ⅱ. Describe what happened

As said above.

Ⅲ. Describe what you expected to happen

If a image is removed, the snapshots for the image should be cleaned. (Except the image is parent of committed containers).

Ⅳ. How to reproduce it (as minimally and precisely as possible)

1. Create a container by a image, like registry.hub.docker.com/library/busybox:1.28.

[root@xxxx /home/allen]
#pouch ps -a
Name   ID       Status                Created        Image                                          Runtime
test   f63087   Exited (0) 1 minute   1 minute ago   registry.hub.docker.com/library/busybox:1.28   runc

[root@xxxx /home/allen]
#ls /home/pouch/containerd/root/io.containerd.snapshotter.v1.overlayfs/snapshots/
1  2

We can see snapshots 1 and 2.

2. Commit the container to a new image ( committed_image:test ). We can know a snapshot (such as 4) is for the new image. We could get it from containerd snapshot dir( such as /home/pouch/containerd/root/io.containerd.snapshotter.v1.overlayfs/snapshots/ ).

[root@xxxx /home/allen]
#pouch commit test committed_image:test
a5931cafb3f2

[root@xxxx /home/allen]
#ls /home/pouch/containerd/root/io.containerd.snapshotter.v1.overlayfs/snapshots/
1  2  4

3. Remove the new image committed_image:test. And the snapshot (a dir as /home/pouch/containerd/root/io.containerd.snapshotter.v1.overlayfs/snapshots/4) still exists.

[root@xxxx /home/allen]
#pouch rmi committed_image:test
committed_image:test

[root@xxxx /home/allen]
#ls /home/pouch/containerd/root/io.containerd.snapshotter.v1.overlayfs/snapshots/
1  2  4

Even though I remove all containers and images, the snapshot 4 is still existed.

[root@xxxx /home/allen]
#pouch ps -a
Name   ID   Status   Created   Image   Runtime

[root@xxxx /home/allen]
#pouch images
IMAGE ID   IMAGE NAME   SIZE

[root@xxxx /home/allen]
#ls /home/pouch/containerd/root/io.containerd.snapshotter.v1.overlayfs/snapshots/
1  4

Ⅴ. Anything else we need to know?

when a container is committed to a image, Pouch will new a snapshot for the diff content in container. When a snapshot is created, it sets a label "containerd.io/gc.root". A snapshot with the label will not be removed, Even though the snapshot is not referred. ( Related to https://github.com/alibaba/pouch/blob/master/ctrd/image_commit.go#L266)

Ⅵ. Environment:

#pouch version
GitCommit:       7acb407
GoVersion:       go1.9.1
KernelVersion:   4.9.93-010.ali3000.alios7.x86_64
Os:              linux
Version:         1.0.0
APIVersion:      1.24
Arch:            amd64
BuildTime:       2018-11-19T07:08:36+00:00

• pouch version (use pouch version):
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[Ace-Tang]

I will figure this out, these days are so busy

[fuweid]

I am working on this @Ace-Tang