ivanorlov2206/virtualalsa

The virtual ALSA driver for api testing

Virtual ALSA driver

How it works?

This small driver uses platform_driver and platform_device interfaces to make the DMA buffer allocation possible, as well as ALSA snd_* api to actually generate some sound. You can probably use this driver as an example of virtual ALSA driver for your own purposes, or for some userspace applications testing/fuzzing.

It creates the virtual sound card called "pcmtest". After inserting the module you will be able to find it in aplay -L list.

What can it do?

It can:

• Simulate capture and playback modes
• Generate random or pattern-based capture data
• Simulate up to 8 substreams, 4 channels
• Support interleaved and non-interleaved access modes
• Inject errors into the PCM callbacks
• Inject delays into the capturing process

arecord -D hw:CARD=pcmtest,DEV=0 -c 1 -f S16_LE --duration=3 out.wav

And you have 3 seconds of beautiful white noise...

The driver itself has two modes for capture data generating:

0. The random sequence of bytes
1. The pattern repeating mode

To change the module mode, write the corresponding option to the module parameter:

echo 1 > /sys/module/pcmtest/parameters/fill_mode

The most interesting is the second mode, where you can specify the pattern to repeat:

echo some_pattern > /sys/kernel/debug/pcmtest/fill_pattern

The pattern can be up to 4096 bytes long.

Also, it can be used for checking the playback functionality. If the playback buffer contains the looped pattern (which you set in fill_pattern) the test will success, and the

/sys/kernel/debug/pcmtest/pc_test

file will contain '1' after the pcm closing. Otherwise, if the buffer is corrupted somehow, this debugfs file will contain '0'.

If you want to test the playback functionality as mentioned above, the pattern must not contain zeros - otherwise the test results will be incorrect.

Reset IOCTL redefinition

This driver can be used to test the 'RESET' ioctl redefinition through ALSA API. To test it, reset the pcm (for example, with snd_pcm_reset call), and check this debugfs file (in case if the new IOCTL triggers, it will contain '1', otherwise - '0').

Errors and delays injecting

The module has several parameters, which can help you to inject errors into the PCM callbacks and inject delays into the playback and capturing processes.

See module parameters inside pcmtest.c