Sysbox-fs

The Sysbox file-system (Sysbox-fs) is one of the three active components of the Sysbox runtime, along Sysbox-mgr and Sysbox-runc.

Sysbox-fs provides file-system emulation capabilities to offer a more complete and secure "virtual-host" abstraction to the processes running inside Sysbox containers.

Main Features

As of today, Sysbox-fs supports the (partial) emulation of the following components:

• procfs & sysfs emulation: The goal here is to expose and emulate resources that are not yet namespaced by the Linux kernel, or that are only reachable within the initial user-namespace.

  Sysbox-fs achieves this by mounting a FUSE file-system over specific sections of the /proc and /sys virtual file-systems, so that I/O requests targeting those resources are handled by Sysbox-fs in user-space.

• Syscall emulation: Sysbox-fs traps and emulate a small set of syscalls inside a system container. The main purpose here is to provide processes inside the system container with a more complete and consistent view of the resources that are reachable within a system container. We rely on the Linux kernel's seccomp BPF features to achieve this.

  For example, inside a system container we trap the mount system call in order to ensure that such mounts always result in the Sysbox-fs' emulated procfs being mounted, rather than the kernel's procfs.

  Another example is the umount syscall, which we trap to ensure that Sysbox-fs' emulated components cannot be unmounted to expose the kernel's version of the corresponding FS node.

Build & Usage

Sysbox-fs is built through the Makefile targets exposed in the Sysbox repository. Refer to its README file for details.

Testing

Sysbox-fs' repository incorporates unit-tests to verify the basic operation of its main packages. You can manually execute these unit-tests through the usual go test ./... instruction.

For a more thorough verification of Sysbox-fs features, refer to the integration-testsuites hosted in the Sysbox repository and executed as part of the testing Makefile targets (e.g. make test).