Setup composite USB-gadget in a breeze !

xg_multi stands for Extended g_multi (Multifunction Composite USB-gadget) -- or -- Cross(-hosts OS) g_multi.
xg_multi seemlessly interoperates with Linux, macOS and Windows hosts (unlike g_multi).

This Extended Multifunction Composite USB-gadget is built upon libcomposite configfs system.
It is a shell script to run on device in order to enable features, rather than a driver to load (like for its sibling).

Features:

xg_multi does create the following gadgets on any device originaly in OTG-peripheral mode:

• serial (ACM): ttyGS0 on device side
• ethernet (ECM for Linux/macOS, RNDIS for Windows - switches gracefully): usb0 on device side
• mass-storage

Benefits:

• Works across most host OS computers (Linux/macOS/Windows) without additional host-side drivers or configuration required.
• Should work on any linux device supporting OTG-peripheral mode (including Raspberry Pis).
• Does necessary sanity-checks on ports beforehand and returns clean if not relevant.

Note: application-specific ports configurations (i.e. serial options, console bring-up, networking adresses, ...) are not in the scope of this project: user shall take care of this once ports are created.
(i.e: on Alpine Linux, after running xg_multi, port setup can be done during setup-alpine)

Setup procedure:

Make sure dwc2 (or dwc3) driver is previously loaded on device, and configuration is set to OTG peripheral mode: this may be driven by hardware (including cable) and/or software.
(on supporting Pi devices, just add dtoverlay=dwc2,dr_mode=peripheral in config.txt to force both by software)

Then run xg_multi on device as described:

usage: xg_multi [-D <MAC address>>] [-H <MAC address>] [-V <file path>]
       xg_multi -r

Setup (or remove) Extended Multifunction USB-gadget: serial, ethernet (ECM/RNDIS),
and mass-storage (if valid path is specified).
Ports are just created and are left unconfigured (i.e console, networking,...)

Options: -D|--Device <MAC address>  Specify MAC address for device
         -H|--Host <MAC address>    Specify MAC address for host
         -V|--Volume <file path>    Path to device/LUN file to use as mass-storage
         -r|--remove                Remove gadgets
         -h|--help                  help information and usage

Main execution steps are logged: cat /var/log/messages | grep xg_multi.

OpenRC files are also available to run xg_multi as a boot service; an Alpine Linux package is also available.

Note:

• xg_multi is intended to run on ash shell within busybox. It may work within other environments (bash,...), but has not been tested (yet).
• on Linux host featuring Modem Manager, user may need to be part of dialout group, and create some filtering rule to avoid spurious AT commands on serial line.

  cat /etc/udev/rules.d/99-ttyacms-gadget.rules
  ATTRS{idVendor}=="0x1d6b" ATTRS{idProduct}=="0x0104", ENV{ID_MM_DEVICE_IGNORE}="1"

Credits

Kudos for various snippets from @geekman, @Leo-PL and many others trying to solve various MS particularites...