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https://github.com/giuseppe/crfs-plugin


https://github.com/giuseppe/crfs-plugin

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# crfs-plugin



A [fuse-overlayfs](https://github.com/containers/fuse-overlayfs/)

plugin for using [CRFS](https://github.com/google/crfs) for loading

lower layers.



This is still experimental, use at your own risk.



# Build



You need to have both the Go toolchain and the C compiler installed.

Use `make` from the upper directory for building `crfs-plugin`:



```

$ make

```



If everything worked correctly and all the needed dependencies were

present, the build generates a single `crfs-plugin.so` artifact that

can be directly used from fuse-overlayfs.



You need to use fuse-overlayfs with plugins support from:



https://github.com/containers/fuse-overlayfs/pull/119



# Build a CRFS image



Before using `crfs-plugin`, you need to have a CRFS image.



To create one, you can use:



[stargzify](https://github.com/google/crfs/blob/master/stargz/stargzify/stargzify.go).



You can install it with:



```

$ go get -u github.com/google/crfs/stargz/stargzify

```



Once stargzify is installed, you can convert a image to the .stargz

format with:

```

$ stargzify docker.io/fedora localhost:5000/myimages/fedora:stargz

```



# Usage



There are a few new options needed to pass to fuse-overlays to

work with `crfs-plugin`:



- `fast_ino=1`: force fuse-overlayfs to stop looking for an inode

  number after the first one found during the lookup.

- `plugins=/path/a.so:/path2/b.so`: list of plugins that

  fuse-overlayfs loads and can be used to handle lower layers.

- `lowerdir=//$PLUGIN/$CONF/lowerdirpath`: when a lowerdir path starts

  with `//`, fuse-overlay uses the plugin `$PLUGIN` to manage

  `lowerdir` with the specified configuration `$CONF`, that is

  specific to the plugin.

  For `crfs-plugin`, the configuration is the image/layer to use in

  base64 encoding.



Accepted configuration strings are:



- https://www.example.com/layer.stargz: use directly the layer at the URL.

- docker://docker.io/image:stargz: use the image at the specified registry.

- /path/to/the/file.stargz: use the file as a .stargz layer.



The easiest way run fuse-overlayfs is from a user namespace (or if you

like danger, directly as root user).



When an image `docker://` is used, `fuse-overlayfs` will internally

create more lower layers depending on how many there are present in

the image.



`podman unshare` can be helpful to create a user+mount namespace that

can be used by an unprivileged user.



```

$ podman unshare

# mkdir lower upper workdir merged

# fuse-overlayfs -o fast_ino=1,plugins=/path/to/crfs-plugin.so,lowerdir=//crfs/$(echo -n docker://localhost:5000/myimages/fedora:stargz | base64 -w0)/$(pwd)/lower,upperdir=upper,workdir=work merged

# podman run --rm -ti --rootfs $(pwd)/merged echo hello

```



It is possible to use directly a URL for retrieving a `.stargz`

layer.  When the lowerdir location starts with the `https://`

prefix, then the file at that URL will be used directly.



```

# fuse-overlayfs -o fast_ino=1,plugins=/path/to/crfs-plugin.so,lowerdir=//crfs/$(echo -n https://url/to/stargzified-layer.tar.gz | base64 -w0)/$(pwd)/lower,upperdir=upper,workdir=work merged

```



Alternatively, it is possible to use a local file:



```

# fuse-overlayfs -o fast_ino=1,plugins=/path/to/crfs-plugin.so,lowerdir=//crfs/$(echo -n /path/to/stargzified-layer.tar.gz | base64 -w0)/$(pwd)/lower,upperdir=upper,workdir=work merged

```



# Installation



`make install` will install crfs-plugin.so under `$PREFIX/libexec/fuse-overlayfs/`.



fuse-overlayfs will automatically load the plugins from that location,

without requiring the additional `-oplugins=...` configuration at run

time.