Temporarily suspending automount on a device

This is part of a series of posts on the design and technical steps of creating Himblick, a digital signage box based on the Raspberry Pi 4.

After seeing lots of automatic mount/umount notifications during provisioning, we wondered if it would be possibile to temporarily disable them while we're working on the SD card.

It turns out that it's possible, and here's a convenient python context manager to do it cleanly, based on /usr/lib/udisks2/udisks2-inhibit, but adding the possibility of inhibiting automounting only on one specific device:

    @contextmanager
    def pause_automounting(self, dev: Dict[str, Any]):
        """
        Pause automounting on the device for the duration of this context
        manager
        """
        # See /usr/lib/udisks2/udisks2-inhibit
        devpath = dev["path"]
        rules_dir = "/run/udev/rules.d"
        os.makedirs(rules_dir, exist_ok=True)
        rule_file = os.path.join(rules_dir, "90-udisks-inhibit-" + devpath.replace("/", "_") + ".rules")
        with open(rule_file, "wt") as fd:
            print('SUBSYSTEM=="block", ENV{DEVNAME}=="' + devpath + '*", ENV{UDISKS_IGNORE}="1"', file=fd)
            fd.flush()
            os.fsync(fd.fileno())
        run(["udevadm", "control", "--reload"])
        run(["udevadm", "trigger", "--settle", "--subsystem-match=block"])
        try:
            yield
        finally:
            os.unlink(rule_file)
            run(["udevadm", "control", "--reload"])
            run(["udevadm", "trigger", "--settle", "--subsystem-match=block"])