evdev

Note: This is work in progress. Use at your own risk.

evdev is a pure Go implementation of the Linux evdev API. It allows a Go application to track events from any devices mapped to /dev/input/event[X].

TODO

• Better error handling. The Device type now mostly ignores ioctl errors once the device has been successfuly opened. This is done to simplify the API. Some of the SetXXX methods do return a boolean value to indicate success/failure, but this is not consistently applied. Some of them work by sending an Event struct to the device by queueing it in the Device.Outbox channel. Which in turn is processed in a separate goroutine (see Device.pollOutbox).

  We can currently not receive any return values from such an operation. This includes possible errors. Should we implement some sort of synchronous call mechanism for these kind of writes? Ideally we do want to keep all of the writes confined to the same goroutine.

  We do not necessarily need an actual error value, just a boolean indicating success or failure. ioctl errors are usually very non-descriptive anyway, so there is little point in passing them around.

Known issues

Permissions

Opening nodes in /dev/input may require root access. This means that our client applications do as well. To solve this, there are a couple of options.

The most sensible one is to use a udev rule to give device access to anyone in the input group. Then add yourself to this group. This hinges on the question whether or not your system uses udev. For Arch Linux, udev comes pre-installed as a part of systemd.

Here is a short listing of the steps to undertake to make this work, but we strongly advise that you read through the appropriate documentation on what udev rules are and how to safely create or edit them.

As root, perform the following steps:

$ mkdir -p /etc/udev/rules.d
$ nano /etc/udev/rules.d/99-input.rules

Put this in the file:

KERNEL=="event*", NAME="input/%k", MODE="660", GROUP="input"

Save and exit nano. Then create the input group and add yourself to it:

$ groupadd -f input
$ gpasswd -a <YOURUSERNAME> input

This will add any input devices to the input group. Only users who are in this group, will be able to read from them. Reboot your machine to make these changes take effect.

`/dev/input' should now list someting like this:

$ ls -l /dev/input/
total 0
drwxr-xr-x 2 root root     120 Sep  7 18:10 by-id
drwxr-xr-x 2 root root     140 Sep  7 18:10 by-path
crw-rw---- 1 root input 13, 64 Sep  7 18:10 event0
crw-rw---- 1 root input 13, 65 Sep  7 18:10 event1
crw-rw---- 1 root input 13, 74 Sep  7 18:10 event10
crw-rw---- 1 root input 13, 75 Sep  7 18:10 event11
crw-rw---- 1 root input 13, 76 Sep  7 18:10 event12
crw-rw---- 1 root input 13, 77 Sep  7 18:10 event13
crw-rw---- 1 root input 13, 78 Sep  7 18:10 event14
crw-rw---- 1 root input 13, 66 Sep  7 18:10 event2
crw-rw---- 1 root input 13, 67 Sep  7 18:10 event3
crw-rw---- 1 root input 13, 68 Sep  7 18:10 event4
crw-rw---- 1 root input 13, 69 Sep  7 18:10 event5
crw-rw---- 1 root input 13, 70 Sep  7 18:10 event6
crw-rw---- 1 root input 13, 71 Sep  7 18:10 event7
crw-rw---- 1 root input 13, 72 Sep  7 18:10 event8
crw-rw---- 1 root input 13, 73 Sep  7 18:10 event9
crw-r----- 1 root root  13, 63 Sep  7 18:10 mice
crw-r----- 1 root root  13, 32 Sep  7 18:10 mouse0

Usage

go get github.com/jteeuwen/evdev

References

• linuxjournal.com
• Documentation/input/event-codes.txt
• Documentation/input/ff.txt

License

Unless otherwise stated, all of the work in this project is subject to a 1-clause BSD license. Its contents can be found in the enclosed LICENSE file.