ModemManager in OpenWRT (take #2)
I’ve been lately working on integrating ModemManager in OpenWRT , in order to provide a unique and consolidated way to configure and manage mobile broadband modems (2G, 3G, 4G, Iridium…), all workingwith netifd .
OpenWRT already has some support for a lot of the devices that ModemManager is able to manage (e.g. through the uqmi , umbim or wwan packages), but unlike the current solutions, ModemManager doesn’t require protocol-specific configurations or setups for the different devices; i.e. the configuration for a modem running in MBIM mode may be the same one as the configuration for a modem requiring AT commands and a PPP session.
Currently the OpenWRT package prepared is based on ModemManager git master, and therefore it supports: QMI modems (including the new MC74XX series which are raw-ip only and don’t support DMS UIM operations), MBIM modems, devices requiring QMI over MBIM operations (e.g. FCC auth), and of course generic AT+PPP based modems, Cinterion , Huawei (both AT+PPP and AT+NDISDUP), Icera , Haier , Linktop , Longcheer , Ericsson MBM, Motorola , Nokia , Novatel , Option (AT+PPP and HSO), Pantech , Samsung , Sierra Wireless (AT+PPP and DirectIP), Simtech , Telit , u-blox , Wavecom , ZTE … and even Iridium and Thuraya satellite modems. All with the same configuration.
Along with ModemManager itself, the OpenWRT feed also contains libqmi and libmbim , which provide the qmicli , mbimcli , and soon the qmi-firmware-update utilities. Note that you can also use these command line tools, even if ModemManager is running, via the qmi-proxy and mbim-proxy setups (i.e. just adding -p to the qmicli or mbimcli commands).
This is not thefirst time I’ve tried to do this; but this time I believe it is a much more complete setup and likely ready for others to play with it. You can jump to the modemmanager-openwrt bitbucket repository and follow the instructions to include it in your OpenWRT builds:
The following sections try to get into a bit more detail of which were the changes required to make all this work.
And of course, thanks to VeloCloud for sponsoringthe development of the latest ModemManager features that made this integrationpossibleudev vs hotplug
One of the latest biggest featuresmerged in ModemManager was the possibility to run without udev support; i.e. without automatically monitoring the device addition and removals happening in the system.
Instead of using udev , the mmcli command line tool ended up with a new --report-kernel-event that can be used to report the device addition and removals manually, e.g.:$ mmcli --report-kernel-event="action=add,subsystem=tty,name=ttyUSB0" $ mmcli --report-kernel-event="action=add,subsystem=net,name=wwan0"
This new way of notifying device events made it very easy to integrate the automatic device discovery supported in ModemManager directly via tty and net hotplug scripts (see mm_report_event() ).
With the integration in the hotplug scripts, ModemManager will automatically detect and probe the different ports exposed by the broadband modem devices.udev rules
ModemManager relies on udev rules for different things:Blacklisting devices : E.g. we don’t want ModemManager to claim and probe the TTYs exposed by Arduinos or braille displays. The package includes a USB vid:pid based blacklist of devices that expose TTY ports and are not modems to be managed by ModemManager. Blacklisting ports: There are cases where we don’t want the automatic logic selection to grab and use some specific modem ports, so the package also provides a much shorter list of ports blacklisted from actual modem devices. E.g. the QMI implementation in some ZTE devices is so poor that we decided to completely skip it and fallback to AT+PPP. Greylisting USB serial adapters : The TTY ports exposed by USB serial adapters aren’t probed automatically, as we don’t know what’s connected in the serial side. If we want to have a serial modem, though, the mmcli --scan-modems operation may be executed, which will include the probing of these greylisted devices. Specifying port type hints : Some devices expose multiple AT ports, but with different purposes. E.g. a modem may expose a port for AT control and another port for the actual PPP session, and choosing the wrong one will not work. ModemManager includes a list of port type hints so that the automatic selection of which port is for what purpose is done transparently.
As we’re not using udev when running in OpenWRT, ModemManager includes now a custom generic udev rules parser that uses sysfs properties to process and apply the rules.procd based startup
The ModemManager daemon is setup to be started and controlled via procd . The init script controlling the startup will also take care of scheduling the re-play of the hotplug events that had earlier triggered --report-kernel-event actions (they’re cached in /tmp ); e.g. to cope with events coming before the daemon started or to handle daemon restarts gracefully .DBus
Well, no, I didn’t port ModemManager to use ubus If you want to run ModemManager under OpenWRT you’ll also need to have the DBus daemon running.netifd protocol handler When using ModemManager, the user shouldn’t need to know the peculiarities of the modem being used : all modems and protocols (QMI, MBIM, Generic AT, vendor-specific AT…) are all managed via the same single DBus interfaces. All the modem control commands are internal to ModemManager, an
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