Available Experimental release of the file system Composefs 0.1.4 , designed to jointly store the contents of several admonished disk images. The project is developed by Alexander Larsson, the creator of Flatpak, in order to increase the efficiency of mounting container images and placing the GIT-like Ostree repository. The project code is written in SI and is distributed under the GPLV2 license.
Initially, the first version of Composefs was a separate FS, implemented in the form of a Linux nucleus module. In the release of 0.1.4, approach to development completely revised and Support for work in the form of the nucleus module is stopped. Since in many ways Composefs intersects with an existing code in the nucleus, it was decided that it would be easier to develop composefs in the form of a superstructure over the FS Overlayfs and Erofs.
A similar approach will make it possible to obtain the necessary functionality through inclusion in the core of a number of patches to Overlayfs, without the need to undergo a long process of reviewing and coordinating the inclusion of a separate file system in the main composition of the nucleus. In the current form, all the capabilities required from EROFS are already present in the Linux nucleus, starting with the release of 5.15. Overlafs requires the addition of support for the Data-ALY mode for the lower-level catalogs and the possibility of preserving FS-Verity Hashi in an extended attribute (XATTR) Overlay.metacopy. The first change is already accepted into the branch of the nucleus 6.5-RC1, and the second is added to the Overlayfs-Next branch and expects to include 6.6. Moreover, if the user does not need to check integrity, then you can already use COMPOSEFS with the standard Linux nuclei, without waiting for the paths to turn on to Overlayfs.
In addition to a set of changes to Overlayfs, the Composefs project is developing a fuse module of the Fuse Module Composefs-Fuse, tools for creating and mounting fs from the user space (MKCOMPOSEFS, MUUNT.COMPOSEFS) and the format of images (used Montained Erofs and extensions. Overlayfs attributes ). Since the project is based on the already finished components of the nucleus, its stability is evaluated as a bustle – the first stable release is planned to be released after the adoption of the remaining patches for Overlayfs.