smoo is an inverted mass‑storage USB protocol. The device sees a block device whose data comes from the host.

It uses the ublk driver and FunctionFS to implement the device side of the protocol in user-space. It can make use of FunctionFS DMA-BUF support for a (nearly) zero-copy data path.

The host implementation supports rusb (for CLI and desktop apps) and WebUSB (for WASM + web targets).

It is implemented in async-first Rust, mostly by robots.

"UMS" backwards is "SMU". Which sounds like smoo. So there you go.

# This project does not yet have a tagged release.
# You must build it from source. Twice.
# Once on the host computer, and once on the device connected over USB.
# (you might be missing some dependencies, see below)
cargo build

# On the device side:
sudo modprobe ublk-drv
sudo ./target/debug/smoo-gadget-cli --no-dma-buf

# on the host side
dd if=/dev/urandom of=random.img bs=4096 count=512
sudo ./target/debug/smoo-host-cli --file random.img

# the device will now see a /dev/ublkb0 device
# it will return data matching the contents of random.img on the host.
# you can confirm this easily:
# from host: sha256sum random.img
# from gadget: dd if=/dev/ublkb0 | sha256sum

• Alpine: apk add linux-headers clang-dev
• Debian: sudo apt build-dep ./
• Fedora: sudo dnf build-dep --spec ./smoo.spec
• Others: idk pls expand here

This is an early prototype. It requires a recent Linux kernel with FunctionFS, and ublk support enabled. It should work on any device with a UDC, and is tested primarily on SDM670/SDM845 pocket computers.

See HACKING.md for architecture and implementation details.