kata-containers/docs/how-to/how-to-use-erofs-build-rootfs.md

Configure Kata Containers to use EROFS build rootfs

Introduction

For kata containers, rootfs is used in the read-only way. EROFS can noticeably decrease metadata overhead.

mkfs.erofs can generate compressed and uncompressed EROFS images.

For uncompressed images, no files are compressed. However, it is optional to inline the data blocks at the end of the file with the metadata.

For compressed images, each file will be compressed using the lz4 or lz4hc algorithm, and it will be confirmed whether it can save space. Use No compression of the file if compression does not save space.

Performance comparison

	EROFS	EXT4	XFS
Image Size [MB]	106(uncompressed)	256	126

Guidance

Install the erofs-utils

apt/dnf install

On newer Ubuntu/Debian systems, it can be installed directly using the apt command, and on Fedora it can be installed directly using the dnf command.

# Debian/Ubuntu
$ apt install erofs-utils
# Fedora
$ dnf install erofs-utils

Source install

https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git

Compile dependencies

If you need to enable the Lz4 compression feature, Lz4 1.8.0+ is required, and Lz4 1.9.3+ is strongly recommended.

Compilation process

For some old lz4 versions (lz4-1.8.0~1.8.3), if lz4-static is not installed, the lz4hc algorithm will not be supported. lz4-static can be installed with apt install lz4-static.x86_64. However, these versions have some bugs in compression, and it is not recommended to use these versions directly. If you use lz4 1.9.0+, you can directly use the following command to compile.

$ ./autogen.sh
$ ./configure
$ make

The compiled mkfs.erofs program will be saved in the mkfs directory. Afterwards, the generated tools can be installed to a system directory using make install (requires root privileges).

Create a local rootfs

$ export distro="ubuntu"
$ export FS_TYPE="erofs"
$ export ROOTFS_DIR="realpath kata-containers/tools/osbuilder/rootfs-builder/rootfs"
$ sudo rm -rf "${ROOTFS_DIR}"
$ pushd kata-containers/tools/osbuilder/rootfs-builder
$ script -fec 'sudo -E SECCOMP=no ./rootfs.sh "${distro}"'
$ popd

Add a custom agent to the image - OPTIONAL

Note:

• You should only do this step if you are testing with the latest version of the agent.

$ sudo install -o root -g root -m 0550 -t "${ROOTFS_DIR}/usr/bin" "${ROOTFS_DIR}/../../../../src/agent/target/x86_64-unknown-linux-musl/release/kata-agent"
$ sudo install -o root -g root -m 0440 "${ROOTFS_DIR}/../../../../src/agent/kata-agent.service" "${ROOTFS_DIR}/usr/lib/systemd/system/"
$ sudo install -o root -g root -m 0440 "${ROOTFS_DIR}/../../../../src/agent/kata-containers.target" "${ROOTFS_DIR}/usr/lib/systemd/system/"

Build a root image

$ pushd  kata-containers/tools/osbuilder/image-builder
$ script -fec 'sudo -E ./image_builder.sh "${ROOTFS_DIR}"'
$ popd

Install the rootfs image

$ pushd kata-containers/tools/osbuilder/image-builder
$ commit="$(git log --format=%h -1 HEAD)"
$ date="$(date +%Y-%m-%d-%T.%N%z)"
$ rootfs="erofs"
$ image="kata-containers-${rootfs}-${date}-${commit}"
$ sudo install -o root -g root -m 0640 -D kata-containers.img "/usr/share/kata-containers/${image}"
$ (cd /usr/share/kata-containers && sudo ln -sf "$image" kata-containers.img)
$ popd

Use EROFS in the runtime

$ sudo sed -i -e 's/^# *\(rootfs_type\).*=.*$/\1 = erofs/g' /etc/kata-containers/configuration.toml