proxy to allow programs such as qmicli (libqmi), uqmi, and oFono to work with qmuxd
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qmiserial2qmuxd.c

README.md

qmiserial2qmuxd

This is a Linux/Android program to allow programs such as qmicli (libqmi), uqmi, and oFono to work with qmuxd. Usually such programs talk directly to a serial Qualcomm QMI interface (typically something like /dev/cdc-wdm1 provided by qmi_wwan on Linux.) Some devices or configurations only have QMI access through qmuxd, a properietary Qualcomm daemon that provides a different protocol over local Unix socket. So, qmiserial2qmuxd emulates the serial interface and proxies requests/responses to qmuxd, so that the standard opensource QMI tools can work in this configuration too.

I've tested several requests successfully on my Android phone (Samsung Galaxy S4 Mini) with qmicli and uqmi. I expect other requests and devices to work as well, but haven't tested, and haven't done heavy-duty or "real-world" use yet. The code probably needs to be made more robust, safe, and convenient to use, but I think the basic function is feature-complete. The concept is simple enough that I hope there's little room for bugs.

Building for Android

You may need to first edit the SOCKPATH define in qmiserial2qmuxd.c to match your qmuxd.

You can get an Android toolchain using the NDK, e.g.:

$ ~/android-ndk/build/tools/make-standalone-toolchain.sh --arch=arm --install-dir=./android-toolchain --platform=android-21
$ export PATH $PATH:$PWD/android-toolchain
$ make qmiserial2qmuxd.android

Usage (Android over adb)

Requires socat tool on the host system ("socat" package on Ubuntu.) You also need a relatively new adb version that supports proper piping of stdin/out. I've tested with adb 1.0.39 from the Android SDK (check version with adb version). From my glance at the Ubuntu sources, I think all current Ubuntu adb packages are too old!

Paths and privilege escalation may need adjustment for your environment. If your adbd is running as root, you can leave out the su radio part.

$ socat PTY,link=/tmp/qmiserial2qmuxd.pty,cfmakeraw EXEC:"adb shell su radio /data/local/tmp/qmiserial2qmuxd"
$ qmicli -d /tmp/qmiserial2qmuxd.pty --dms-get-msisdn
[/dev/pts/5] Device MSISDN retrieved:
	MSISDN: 'XXXXXXX'

Debug logs will be written to the Android log with tag "qmiserial2qmuxd" (view with adb logcat -s qmiserial2qmuxd:D)

Note: in some tests I saw adb output about starting/killing its daemon getting into the pty and causing "QMI framing error detected" from qmicli. I think this final version of the command with latest adb doesn't have that issue, but in case it pops up for you, be aware.

Design

There are two threads. One takes a message from the serial interface and immediately writes the translated form to the qmuxd socket, then waits for the next message again. The other reads from the qmuxd socket and writes to the serial device. We don't track any state about the messages (like transaction IDs) or much about what they mean, we just pass them through.

Issues and Development

Please let me know by Github issue or email if you have any questions or problems -- it's only been tested on my one device after all. Code review and improvement suggestions by pull request or email are welcome!

Resources on the interface and protocol

License

Copyright (C) 2017 Joey Hewitt joey@joeyhewitt.com

qmiserial2qmuxd is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

qmiserial2qmuxd is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with qmiserial2qmuxd. If not, see http://www.gnu.org/licenses/.

TODO

  • Make qmuxd socket path configurable - maybe follow GobiAPI's naming convention. In the source right now it is defined for Android.
  • Check if indications/unsolicited messages work
  • Does anything bad happen if multiple programs access us at once? (Is this one of the reasons for the existence of qmuxd and libqmi's proxy mode?) We could set the pty to exclusive mode if needed.
  • Do endianness conversions, so we'll work on a big-endian system (assuming the wire protocols are always little-endian)
  • Write an implementation in something like Python? I've started with C because it's probably best for my needs, but a higher-level language might make it clearer how this works, and have less possibility of memory bugs and crashes.
  • Is there a good reason qmuxd wants you to do control operations through it? (e.g. eQMUXD_MSG_ALLOC_QMI_CLIENT_ID and eQMUXD_MSG_RELEASE_QMI_CLIENT_ID in GobiAPI, several others I see in libqmi_client_qmux.so.) I found a way to do raw control requests for simplicity, but maybe qmuxd wants us to use its extra layer so it can manage something important...