vdfs4

Samsung's VDFS4 filesystem — the kernel driver and the mkfs.vdfs userspace tools — patched to build and run on a modern Linux kernel.

The original driver targets Linux 5.4. This repo fixes the build against a much newer kernel (folio-based page cache, mnt_idmap, fs_context, modern block layer, etc.) and fixes a few real bugs found by mounting, reading, and writing actual firmware images:

• A deadlock and a data-corruption bug in the compressed-file read path.
• A NULL-pointer crash on writeback (dirty_folio was never wired up for this kernel).

Full history of every change, with rationale, is in git log.

Requirements

sudo apt-get install build-essential linux-headers-$(uname -r) perl patch

linux-headers-$(uname -r) must match the running kernel exactly. zlib, zstd, lzo, and OpenSSL are vendored and built from source inside vdfs-tools, so no -dev packages are needed for those.

Build

Kernel module:

cd linux/fs/vdfs4
make
sudo insmod vdfs4.ko
sudo mount -t vdfs -o dncs /dev/<device-or-loop> <mountpoint>

dncs (do-not-check-signature) is required unless the volume is signed with Samsung's private key — none of ours are.

Userspace tools (mkfs.vdfs):

cd vdfs-tools
make mkfs
truncate -s 256M image.vdfs4
./mkfs.vdfs --root-dir <some-dir> image.vdfs4

Known limitations

• -c <algo> (mkfs compression) is broken for non---read-only images — the on-disk file descriptor comes back zeroed on read. Looks like a gap in Samsung's own tooling rather than anything in the kernel driver: every real firmware image we found pairs compression exclusively with --read-only.
• Authenticated/signed volumes need Samsung's actual private key; testing here used -o dncs to skip signature checks on unsigned synthetic images.

License

GPL-2.0-or-later, inherited from Samsung's original source (see LICENSE).