For Linux, the Composefs file system has been proposed

Alexander Larsson, the creator of Flatpak working at Red Hat, introduced a preliminary version of patches implementing the Composefs file system for the Linux kernel. The proposed file system resembles Squashfs and is also suitable for mounting images in read-only mode. The differences hinge on how Composefs provides efficient shared storage of the contents across multiple mounted disk images and supports authenticity checks of the readable data. Areas where Composefs may be in demand include mounting container images and using it for Git-like OSTree repositories.

Composefs uses a content-addressable storage model, meaning the primary identifier is not the file name, but rather a hash of the file's content. This model ensures deduplication and allows only a single copy of identical files to be stored across different mounted partitions. For example, container images contain many standard system files, and when using Composefs, each of these files will be shared among all mounted images without applying tricks like hard link passing. Thus, shared files not only take up a single copy on disk, but also occupy a single entry in the page cache, helping to save both disk and RAM.

To conserve disk space, data and metadata in mounted images are separated. When mounting, the following are specified:

• A binary index containing all the metadata of the file system, including file names, access rights, and other information, except for the actual content of the files.
• The base directory that stores the content of all mounted images. Files are stored linked to a hash of their content.

En binær indeks opprettes for hver av bilde-FS-ene, mens basisbiblioteket er felles for alle bilder. For verifisering av innholdet i individuelle filer og hele bilde i delt lagring kan mekanismen fs-verity brukes, som ved tilgang til filer kontrollerer samsvaret mellom de angitte hashene i den binære indeksen og det faktiske innholdet (dvs. hvis en angriper endrer en fil i basisbiblioteket eller data blir skadet som følge av et sammenbrudd, vil slik sjekk avdekke avvik).

Kilde: opennet.ru