umockdev 0.3: record and replay of tty devices

I’m happy to announce a new release 0.3 of umockdev.

The big new feature is the ability to fake character devices and provide recording and replaying of communications on them. This work is driven by our need to create automatic tests for the Ubuntu phone stack, i. e. pretending that we have a 3G or phone driver and ensuring that the higher level stacks behaves as expected without actually having to have a particular modem. I don’t currently have a phone capable of running Ubuntu, so I tested this against the standard ModemManager daemon which we use in the desktop. But the principle is the same, it’s “just” capturing and replaying read() and write() calls from/to a device node.

In principle it ought to work in just the same way for other device nodes than tty, e. g. input devices or DRI control; but that will require some slight tweaks in how the fake device nodes are set up; please let me know if you are intested in a particular use case (preferably as a bug report).

With just using the command line tools, this is how you would capture ModemManager’s talking to an USB 3G stick which creates /dev/ttyUSB{0,1,2}. The communication gets recorded into a text file, which umockdev calls “script” (yay my lack of imagination for names!):

# Dump the sysfs device and udev properties
$ umockdev-record /dev/ttyUSB* > huawei.umockdev

# Record the communication
$ umockdev-record -s /dev/ttyUSB0=0.script -s /dev/ttyUSB1=1.script \
     -s /dev/ttyUSB2=2.script -- modem-manager --debug

The –debug option for ModemManager is not necessary, but it’s nice to see what’s going on. Note that you should shut down the running system instance for that, or run this on a private D-BUS.

Now you can disconnect the stick (not necessary, just to clearly prove that the following does not actually talk to the stick), and replay in a test bed:

$ umockdev-run -d huawei.umockdev -s /dev/ttyUSB0=0.script -s /dev/ttyUSB1=1.script \
    -s /dev/ttyUSB2=2.script -- modem-manager --debug

Please note that the CLI options of umockdev-record and umockdev-run changed to be more consistent and fit the new features.

If you use the API, you can do the same with the new umockdev_testbed_load_script() method, which will spawn a thread that replays the script on the faked device node (which is just a PTY underneath).

If you want full control, you can also do all the communication from your test cases manually: umockdev_testbed_get_fd("/dev/mydevice") will give you a (bidirectional) file descriptor of the “master” end, so that whenever your program under test connects to /dev/mydevice you can directly talk to it and pretend that you are an actual device driver. You can look at the t_tty_data() test case for how this looks like (that’s the test for the Vala binding, but it works in just the same way in C or the GI bindings).

I’m sure that there are lots of open ends here still, but as usual this work is use case driven; so if you want to do something with this, please let me know and we can talk about fine-tuning this.

In other news, with this release you can also cleanly remove mocked devices (umockdev_testbed_remove_device()), a feature requested by the Mir developers. Finally there are a couple of bug fixes; see the release notes for details.

I’ll upload this to Saucy today. If you need it for earlier Ubuntu releases, you can have a look into my daily builds PPA.

Let’s test!

Martin Pitt