Za Linux je ponuđen datotečni sustav Composefs

Alexander Larsson, creator of Flatpak and working at Red Hat, presented a preliminary version of patches implementing the Composefs file system for the Linux kernel. The proposed file system is similar to Squashfs and is also suitable for mounting images in read-only mode. The differences boil down to providing effective shared storage of content from multiple mounted disk images in Composefs and supporting the verification of readable data authenticity. Areas of application that may find the Composefs file system in demand include mounting container images and using it for Git-like OSTree repositories.

Composefs uses a content-addressable storage model, meaning that the primary identifier is not the file name but the hash of the file's content. This model ensures deduplication and allows for essentially storing only one copy of identical files found 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 tricks like hard links. Moreover, shared files are stored as a single copy on disk and are handled with a single entry in the page cache, saving both disk and RAM.

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

• A binary index that contains all the metadata of the file system, including file names, access permissions, and other information, except the actual content of the files.
• The base directory where the contents of all mounted images are stored. Files are stored linked to the hash of their content.

Binarni indeks se stvara za svaku sliku FS, dok je osnovni katalog zajednički za sve slike. Za verifikaciju sadržaja pojedinih datoteka i cijele slike u uvjetima zajedničkog pohranjivanja može se koristiti mehanizam fs-verity, koji prilikom pristupa datotekama provjerava usklađenost navedene u binarnom indeksu hash vrijednosti s stvarnim sadržajem (tj. ako napadač promijeni datoteku u osnovnom katalogu ili se podaci oštete zbog kvara, tada će se takva provjera otkriti neslaganje).

Izvor: opennet.ru