container/storage项目

container/storage是container/image的基础，和containerd snapshotter接口功能类似，但是是两套接口。
storage用于管理layer、image、container。
layer对应的就是overlayfs的一层，image对应的就是一个镜像，container对应的就是基于image+读写layer的容器rootfs。

https://github.com/containers/podman/issues/4739 支持additional layer store（ALS），需要配置addition layer store或者通过以下脚本

假设配置为：
layerstore=:::…:

查找方式：

<ALS root>/base64("key1=value1")/base64("key2=value2")/.../base64("keyX=valueX")/
`-- diff  是个目录，包含这一层的different
`-- info  是文件，包含 "*c/storage.Layer" struct

If the layer content is found in ALS, c/storage.Store creates layer using /…/info as *c/storage.Layer and using /…/diff as its diff directory.

podman --storage-opt "layerstore=/tmp/storage:reference:layerdigest" pull ghcr.io/stargz-containers/rethinkdb:2.3.6-esgz
podman --storage-opt "layerstore=/tmp/storage:reference:layerdigest" run --rm -it ghcr.io/stargz-containers/rethinkdb:2.3.6-esgz /bin/echo 'Hello, World!'

1. stargz-store是mount在“/tmp/storage”
2. storage.store会通过ALS（additional layer store）查找 /tmp/storage/base64(“reference=ghcr.io/stargz-containers/rethinkdb:2.3.6-esgz”)/base64()/{diff, info}
3. 然后 stargz-store会去拉取需要的信息。

stargz-store 作为单独进程启动，在读取文件stargz会通过stargz lazy拉取：
stargz-store

<mountpoint>/base64(imageref)/<layerdigest>/
- diff  : exposes the extracted layer
- info  : contains JSON-formatted "Layer" structure of containers/storage
- use  : files to notify the use of this layer (used for management of reference count)