Dynamically generates mountpoints based on the active RAUC bootslot (barebox version)

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README.md

bootslot-mounts

This is a shell script that runs as a systemd generator very early in the boot process. It is intended to be used on a device with an A/B partition scheme, in coordination with RAUC. Because RAUC does not handle mounting additional slots into the filesystem tree, this script's job is to automatically select and mount additional partitions using generated systemd .mount files.

Installation

Install bootslot-mounts to /usr/lib/systemd/system-generators. Ensure it is executable. Then, write a configuration file; see below.

Configuration file

The configuration file is an INI-formatted file placed at /etc/bootslot-mounts.conf. This has three sections, as follows.

  • The [mountpoints] section specifies names for mountpoints referred to in slot sections. The key of each entry is a "friendly name" of the mountpoint, and the value is the absolute path in the filesystem.
  • Each [slot] section has heading format [slot_BOOTNAME], where BOOTNAME is the value of the rauc.slot string passed on the kernel command line. The key of each entry in these sections is the friendly name of each mountpoint in the mountpoints section, and the value is the name of the block device to mount.

Other mount functionality, such as manually specifying mount options, is not supported at this time.

Specifying the root filesystem device is not supported (although this would not be difficult). But typically this is passed in by the bootloader.

Example

The following configuration file defines two mountpoints, boot and var, and three slots, A, B, and recovery. The boot mountpoint has an A/B scheme and is backed by either /dev/mmcblk0p1 or /dev/mmcblk0p2, depending on the active boot slot. Likewise, var is mounted at /dev/mmcblk0p5 or /dev/mmcblk0p6. The recovery partition only mounts its special var and does not mount boot at all.

[mountpoints]
boot=/boot
var=/var

[slot_A]
boot=/dev/mmcblk0p1
var=/dev/mmcblk0p5

[slot_B]
boot=/dev/mmcblk0p2
var=/dev/mmcblk0p6

[slot_recovery]
var=/dev/mmcblk0p7