libudev-zero

Drop-in replacement for libudev that enables you to use any device manager you like without worrying about the udev dependency at all!

Why?

Because udev sucks, it is bloated and overengineered. udev is just like systemd, it locks you into using non-portable crap that you can't avoid because multiple programs depend on it. Look, even FreeBSD was forced to rewrite[1] this crappy library because libinput hard-depends on udev. Without libinput you can't use wayland and many other cool stuff.

Michael Forney (author of cproc, samurai, Oasis Linux, ...) decided to fork[2] libinput and remove the hard dependency on udev. Is this a solution? Yes. Is this a complete solution? No. This fork has a lot of disadvantages like requiring patching applications to use libinput_netlink instead of the libinput_udev API in order to use the automatic detection of input devices and hotplugging. Static configuration is also required for anything other than input devices (e.g drm devices). Moreover hotplugging is vulnerable to race conditions when libinput handles the uevent faster than the device manager which can lead to file permission issues. libudev-zero prevents these race conditions by design.

Thankfully udev has stable API and hopefully no changes will be made to it the future. On this basis I decided to create this clean-room implementation of libudev which can be used with any or without a device manager.

[1] https://github.com/FreeBSDDesktop/libudev-devd
[2] https://github.com/oasislinux/libinput

What Works

• xorg-server
• dosfstools - need to implement udev_enumerate_add_match_parent()
• libinput
• usbutils
• wlroots
• weston
• libusb
• kwin - fix
• ???

Dependencies

• C99 compiler (build time)
• POSIX make (build time)
• POSIX & XSI libc
• epoll & inotify
• Linux >= 2.6.39

Installation

make
make PREFIX=/usr install # this will overwrite udev libraries if they exist
# rebuild all the packages that depend on libudev, and you're ready to go.

Hotplugging

Note that hotplugging support is fully optional! You can skip this step if you don't have a need for the hotplugging capability.

Hotplugging is fairly uncomplicated and not overengineered at all. Everything is portable as much as possible. To use hotplugging the only thing you need is a uevent receiver (like a device manager, busybox's uevent, CONFIG_UEVENT_HELPER, ...). I will explain only the mdev and CONFIG_UEVENT_HELPER methods because their usage is fairly basic. For busybox's uevent you need to write your own parser which is kinda, well, complex.

UDEV_MONITOR_DIR is an arbitrary directory where the uevent files are stored. The default is /tmp/.libudev-zero. You can change it at build time by appending -DUDEV_MONITOR_DIR=<dir> to CFLAGS. I don't recommend setting UDEV_MONITOR_DIR to regular filesystems (i.e non-tmpfs) because temporary files aren't automatically discarded after reboot or termination (yet).

a) the mdev method

1. merge mdev.conf with your mdev.conf
2. restart the mdev daemon

b) the CONFIG_UEVENT_HELPER method

1. ensure that CONFIG_UEVENT_HELPER is enabled in your kernel configuration
2. add the directory containing helper.sh after marking it as executable or helper.c after compiling it, to /proc/sys/kernel/hotplug

example:

echo "/full/path/to/helper"       > /proc/sys/kernel/hotplug # will use the default UDEV_MONITOR_DIR
OR
echo "/full/path/to/helper <dir>" > /proc/sys/kernel/hotplug # change <dir> to your UDEV_MONITOR_DIR

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Then you can run an application that uses hotplugging like xorg-server to see if it's working by unplugging and plugging something back. If you face any problems while trying out any of these methods, please create an issue.

TODO

• speed up performance
• extend device support
• implement hotplugging support

Donate

You can send a donation to BTC: 1BwrcsgtWZeLVvNeEQSg4A28a3yrGN3FpK if you like this project.

Thank you very much!