68 lines
2.5 KiB
Markdown
68 lines
2.5 KiB
Markdown
# udev-filter
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Super fast and efficient way of only getting udev events you desire.
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It provides an efficient way to perform automatic tasks when any device related event occurs,
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entirely in userspace and *without adding any udev rules*!
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**udev-filter** listens to events via `udevadm monitor -p`.
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It matches the udev events to event properties that are passed as command arguments.
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When all properties of an event are registered, the program ouputs the name of the event, as defined by the user.
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## Examples
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```shell
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udev-filter --event=USB_REMOVED ACTION=remove
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USB_REMOVED
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USB_REMOVED
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...
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```
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prints `USB_REMOVED` any time a USB device is removed.
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The name after --event can be freely chosen.
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Another, more useful example might be:
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```shell
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udev-filter --event=YUBIKEY_ADDED ACTION=add ID_USB_VENDOR=Yubico
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```
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prints `YUBIKEY_ADDED` every time a device with vendor id "Yubico" is added.
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You can, of course, also listen to many events add once. To combine the previous two:
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```shell
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udev-filter \
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--event=USB_REMOVED ACTION=remove SUBSYSTEM=USB \
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--event=YUBIKEY_ADDED ACTION=add ID_USB_VENDOR=Yubico"
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```
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### Performing actions on events
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To automatically open yubico-authenticator every time a yubikey is connected, create
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this shell script and run it in the background:
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```shell
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# stdbuf is necessary to force buffer flushing on newlines
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stdbuf -oL ./udev-filter --command-add="-s usb" \
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--event=YUBIKEY_ADDED ACTION=add ID_USB_VENDOR=Yubico | \
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while read EVENT; do
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# in this example the only possible event is YUBIKEY_ADDED, so the switch-case is not necessary,
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# but it is useful for further expansion
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case $EVENT in
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YUBIKEY_ADDED)
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notify-send "Yubikey Added!"
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{ pgrep yubico || yubico-authenticator & }
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;;
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*)
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notify-send "Unhandled event: $EVENT"
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;;
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esac
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done
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```
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Because **udev-filter** relies on events instead of polling, this script will consume near zero resources.
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It will only do something whenever a udev event occurs.
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To find out which properties you need to query, run `udevadm monitor -p`.
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To limit the events to a certain subsystem, add `-s <subsystem>` to udevadm, and later `--command-add="-s <subsystem>"` to `udev-filter`.
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## Installation
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gcc, with glibc++ for C++23 and GNU make are required, which will be available in most modern Linux distributions already.
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```
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cd src
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make release
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```
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will create `../udev-filter`. Copy it anywhere you want, for example `~/.local/bin`
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