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4
.gitignore
vendored
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4
.gitignore
vendored
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build
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udev-filter
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*.vimspector.json
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*.clangd
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67
readme.md
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67
readme.md
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# 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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56
src/Makefile
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56
src/Makefile
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CXX = /usr/bin/g++
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CXXFLAGS = -std=c++23 -MMD -MP -Wall -Wpedantic -Wextra
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LDFLAGS =
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OBJECT_DIR = ../build
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EXEC = ../udev-filter
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SRC = $(wildcard *.cpp) $(wildcard */*.cpp)
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OBJECTS = $($(notdir SRC):%.cpp=$(OBJECT_DIR)/%.o)
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OBJECT_DIRS = $(OBJECT_DIR) $(foreach dir,$(SRCDIRS), $(OBJECT_DIR)/$(dir))
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DEPENDS = ${OBJECTS:.o=.d}
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CXXFLAGS += $(IFLAGS)
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default: $(EXEC)
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echo $(OBJECTS)
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.PHONY: release
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release: CXXFLAGS += -O3
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release : default
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# rule for the executable
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$(EXEC): $(OBJECT_DIRS) $(OBJECTS)
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$(CXX) $(OBJECTS) -o $@ $(CXXFLAGS) $(LDFLAGS) $(LDLIBS)
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# include the makefiles generated by the -M flag
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-include $(DEPENDS)
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# rule for all ../build/*.o files
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$(OBJECT_DIR)/%.o: $(shell echo $<) %.cpp
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$(CXX) -c $< -o $@ $(CXXFLAGS) $(LDFLAGS)
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$(OBJECT_DIRS):
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mkdir -p $@
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#
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# Extra Options
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#
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# with debug flags
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.PHONY += install debug run clean clean_all docs
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debug: CXXFLAGS += -g # -DDEBUG
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debug: default
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# make with debug flags and run afterwards
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run: CXXFLAGS += -g
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run: default
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$(CXX) $(OBJECTS) -o $(EXEC) $(CXXFLAGS) $(LDFLAGS) $(LDLIBS)
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./$(EXEC)
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# remove all object and dependecy files
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clean:
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-rm -r $(OBJECT_DIR)
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-rm $(EXEC)
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223
src/main.cpp
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223
src/main.cpp
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#include <cstdio>
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#include <iostream>
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#include <stdexcept>
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#include <streambuf>
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#include <string>
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#include <print>
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#include <unordered_map>
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#include <vector>
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#include <ranges>
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/**
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* @brief Filter udev events
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* @details
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* Watches udevadm monitor -p and prints the name of a defined event when it occurs.
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* You can define an event with a name and a list of properties.
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* All of the properties must occur in the udev event for the defined event to occur.
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* You can find out which properties you need by running `udevadm monitor -p`.
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* Each property is full match of a line in one event block, for example `DRIVER=usb`, `ACTION=add` or `ID_USB_VENDOR=Company_Inc.`
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*/
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template<typename T, class CharT=char>
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concept FormatableRange = std::ranges::forward_range<T> && std::formattable<std::ranges::range_value_t<T>, CharT>;
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/**
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* @brief Format ranges
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* @details
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* Format string accepts c = {curly brackets}, b = [box brackets], a = <angle brackets>, r = (round brackets)
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*/
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template<typename U, class CharT> requires FormatableRange<U, CharT>
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struct std::formatter<U, CharT> {
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using T = std::ranges::range_value_t<U>;
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constexpr auto parse(std::format_parse_context& ctx){
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auto pos = ctx.begin();
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while (pos != ctx.end() && *pos != '}') {
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if (*pos == 'a') { useChar = 0; } // <a>ngle
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else if (*pos == 'b') { useChar = 1; } // [b]ox
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else if (*pos == 'c') { useChar = 2; } // {c}urly
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else if (*pos == 'p') { useChar = 3; } // (r)ound
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else {
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throw std::format_error("Invalid format args for forward range.");
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}
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++pos;
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}
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return pos; // expect `}` at this position, otherwise its an error
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}
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auto format(const U& v, auto& ctx) const {
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auto out = ctx.out();
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char c = openChars.at(useChar);
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out = std::format_to(out, "{}", c);
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auto it = v.begin();
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if (it != v.end()) {
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out = std::format_to(out, "{}", *it);
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}
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it++;
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for (; it != v.end(); it++) {
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out = std::format_to(out, ", {}", *it);
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}
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c = closeChars.at(useChar);
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return std::format_to(out, "{}", c);
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// return out;
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}
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public:
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size_t useChar = 2;
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static constexpr std::string_view openChars = "<[{()";
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static constexpr std::string_view closeChars{">]})"};
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};
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const char* help =
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"udev-filter [--help] [--debug] [--command-add=FLAGS] {--event=EVENT PROPERTIES...}\n\n"
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"Example:\n"
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"udev-filter --command-add=\"-s usb\" --event=USB_REMOVED ACTION=remove\n"
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"udev-filter --command-add=\"-s usb\" --event=YUBIKEY_ADDED ACTION=add ID_USB_VENDOR=Yubico"
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;
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/**
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* @brief Wrap the output of a command in a streambuffer
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*/
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class procbuf : public std::streambuf {
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public:
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procbuf(const std::string& cmd) {
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file = popen(cmd.c_str(), "r");
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if (!file) {
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throw std::runtime_error("Failed to run");
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}
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setg(&ch, &ch+1, &ch+1); // point to end of area
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}
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~procbuf() {
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pclose(file);
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}
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private:
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int_type underflow() override {
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if (feof(file) || ferror(file)) {
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return traits_type::eof();
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}
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int c = fgetc(file);
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if (c == EOF) {
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return traits_type::eof();
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}
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// now you could apply transforms on the char
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/*if (static_cast<char>(c) == '=') {*/
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/* c = static_cast<int>('B');*/
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/*}*/
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ch = static_cast<char>(c);
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setg(&ch, &ch, &ch+1); // point to area
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return traits_type::to_int_type(static_cast<char>(ch));
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}
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private:
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FILE* file;
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char ch;
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};
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int main(int argc, const char** argv) {
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bool debug=false;
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// parse args
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std::unordered_map<std::string_view, std::vector<unsigned>> properties;
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// name and how many properties need to match
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std::vector<std::pair<std::string_view, unsigned>> events;
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std::string command("udevadm monitor -p");
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for (int i = 1; i < argc; ++i) {
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std::string_view arg(argv[i]);
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if (arg.starts_with("--command-add=")) {
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int cmdbeg = arg.find('=')+1;
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std::string_view cmd(arg.begin()+cmdbeg, arg.end());
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command += " ";
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command += cmd;
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}
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else if (arg.starts_with("--event=")) {
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int eventbeg = arg.find('=')+1;
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std::string_view event(arg.begin()+eventbeg, arg.end());
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if (event.size() == 0) {
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throw std::invalid_argument("An event must be at least one character long");
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}
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events.push_back({event, 0});
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}
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else if (arg == "--help") {
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std::println("{}", help);
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return 0;
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}
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else if (arg == "--debug") {
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debug=true;
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}
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else {
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// property, must come after a --event=<event>
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if (events.empty()) {
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throw std::invalid_argument(std::format("Properties must come after a '--event=<event name>', but '{}' does not.", arg));
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}
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unsigned eventIndex = events.size() - 1;
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events.at(eventIndex).second += 1;
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if (properties.contains(arg)) {
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properties.at(arg).push_back(eventIndex);
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} else {
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properties.emplace(arg, std::vector<unsigned>{eventIndex});
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}
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}
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}
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if (events.size() == 0) {
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throw std::invalid_argument("At least one event must be given");
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}
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if (properties.size() == 0) {
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throw std::invalid_argument("At least one property must be given");
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}
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// events without any properties are now technically allowed
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if (debug) {
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int i = 0;
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for (auto& [name, nRequired] : events) {
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std::println("Event {}: {} ({})", i, name, nRequired);
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i += 1;
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}
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for (auto& [prop, eventIdx] : properties) {
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std::println("Property of {:c}: {}", eventIdx, prop); // TODO
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}
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std::println("Command: {}", command);
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}
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// testing
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/*properties = {*/
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/* {"EVENT=remove", 0},*/
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/* {"ID_MODEL=Flipper_Hediago", 0},*/
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/* {"EVENT=add", 1}*/
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/*};*/
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/*events = {{"FLIPPER REMOVED", 1}};*/
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// index into events and how many properties were found
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std::unordered_map<unsigned, unsigned> foundEvents;
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procbuf buf(command);
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std::istream stream(&buf);
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std::string line;
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while (stream) {
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std::getline(stream, line);
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/*std::println("{}", line);*/
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if (properties.contains(line)) {
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for (unsigned eventIndex : properties.at(line)) {
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unsigned& nFound = foundEvents[eventIndex];
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nFound += 1;
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}
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/*std::println("Event={}, found nr. {} = {}", eventIndex, nFound, line);*/
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}
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// With -p, one udev event ends with two newlines
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// -> event end
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if (line.size() == 0) {
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// print all event names for which all properties were found
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for (const auto& [index, nFound] : foundEvents) {
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unsigned nRequired = events.at(index).second;
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if (nFound == nRequired) {
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std::println("{}", events.at(index).first);
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}
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}
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foundEvents.clear();
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}
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}
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return 0;
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}
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