Logind fallback support for unprivileged users (#83)

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - run: sudo apt-get update
-      - run: sudo apt-get -y install v4l-utils libv4l-dev libudev-dev libvulkan-dev
+      - run: sudo apt-get -y install v4l-utils libv4l-dev libudev-dev libvulkan-dev libdbus-1-dev
       - run: make test
 
   lint:
@@ -21,5 +21,5 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - run: sudo apt-get update
-      - run: sudo apt-get -y install v4l-utils libv4l-dev libudev-dev libvulkan-dev
+      - run: sudo apt-get -y install v4l-utils libv4l-dev libudev-dev libvulkan-dev libdbus-1-dev
       - run: make lint

Cargo.toml

@@ -20,6 +20,7 @@ env_logger = "0.9"
 inotify = "0.10"
 lazy_static = "1.4"
 xdg = "2.4.1"
+dbus = "0.9.7"
 
 [dev-dependencies]
 mockall = "0.11.4"

README.md

@@ -36,13 +36,17 @@ Use one of the available packages and methods below:
 
 [![CI](https://github.com/maximbaz/wluma/actions/workflows/ci.yml/badge.svg)](https://github.com/maximbaz/wluma/actions/workflows/ci.yml)
 
-If you want to build the app yourself, make sure you use latest stable Rust, otherwise you might get compilation errors! Using `rustup` is perhaps the easiest. Ubuntu needs the following dependencies: `sudo apt-get -y install v4l-utils libv4l-dev libudev-dev libvulkan-dev`.
+If you want to build the app yourself, make sure you use latest stable Rust, otherwise you might get compilation errors! Using `rustup` is perhaps the easiest. Ubuntu needs the following dependencies: `sudo apt-get -y install v4l-utils libv4l-dev libudev-dev libvulkan-dev libdbus-1-dev`.
 
 Then simply run `make build`.
 
 ## Permissions
 
-In order to access backlight devices, `wluma` must either run as `root`, or preferrably instead you should add your user to `video` group in combination with installing the supplied `90-wluma-backlight.rules` udev rule (don't forget to reboot thereafter).
+In order to access backlight devices, `wluma` must either:
+
+- have direct driver access: install the supplied `90-wluma-backlight.rules` udev rule, add your user to the `video` group and reboot (fastest)
+- run on a system that uses `elogind` or `systemd-logind` (they provide a safe interface for unprivileged users to control device's brightness through `dbus`, no configuration necessary)
+- run as `root` (not recommended)
 
 ## Configuration
 

src/brightness/backlight.rs

@@ -1,26 +1,62 @@
 use crate::device_file::{read, write};
+use dbus::channel::Sender;
+use dbus::{self, blocking::Connection, Message};
 use inotify::{Inotify, WatchMask};
 use std::error::Error;
 use std::fs;
 use std::fs::{File, OpenOptions};
 use std::io::ErrorKind;
 use std::path::Path;
 
+struct Dbus {
+    connection: Connection,
+    message: Message,
+}
+
 pub struct Backlight {
     file: File,
     min_brightness: u64,
     max_brightness: u64,
     inotify: Inotify,
     current: Option<u64>,
+    dbus: Option<Dbus>,
+    has_write_permission: bool,
 }
 
 impl Backlight {
     pub fn new(path: &str, min_brightness: u64) -> Result<Self, Box<dyn Error>> {
         let brightness_path = Path::new(path).join("brightness");
-        let file = OpenOptions::new()
+        let mut file = OpenOptions::new()
             .read(true)
             .write(true)
             .open(&brightness_path)?;
+        let current_brightness = read(&mut file)?;
+        let has_write_permission = write(&mut file, current_brightness).is_ok();
+
+        let dbus = if has_write_permission {
+            None
+        } else {
+            let id = Path::new(path)
+                .file_name()
+                .and_then(|x| x.to_str())
+                .ok_or("Unable to identify backlight ID")?;
+
+            let message = Message::new_method_call(
+                "org.freedesktop.login1",
+                "/org/freedesktop/login1/session/auto",
+                "org.freedesktop.login1.Session",
+                "SetBrightness",
+            )
+            .ok()
+            .map(|m| m.append2("backlight", id));
+
+            Connection::new_system().ok().and_then(|connection| {
+                message.map(|message| Dbus {
+                    connection,
+                    message,
+                })
+            })
+        };
 
         let max_brightness = fs::read_to_string(Path::new(path).join("max_brightness"))?
             .trim()
@@ -40,6 +76,8 @@ impl Backlight {
             max_brightness,
             inotify,
             current: None,
+            dbus,
+            has_write_permission,
         })
     }
 }
@@ -70,7 +108,16 @@ impl super::Brightness for Backlight {
     fn set(&mut self, value: u64) -> Result<u64, Box<dyn Error>> {
         let value = value.clamp(self.min_brightness, self.max_brightness);
 
-        write(&mut self.file, value as f64)?;
+        if self.has_write_permission {
+            write(&mut self.file, value as f64)?;
+        } else if let Some(dbus) = &self.dbus {
+            dbus.connection
+                .send(dbus.message.duplicate()?.append1(value as u32))
+                .map_err(|_| "Unable to send brightness change message via dbus")?;
+        } else {
+            Err(std::io::Error::from(ErrorKind::PermissionDenied))?
+        }
+
         self.current = Some(value);
 
         // Consume file events to not trigger get() update

src/brightness/controller.rs

@@ -103,7 +103,7 @@ impl Controller {
                 if target.reached(current) {
                     self.target = None;
                 } else {
-                    let new_value = (current as i64 + target.step).max(0) as u64;
+                    let new_value = current.saturating_add_signed(target.step);
                     match self.brightness.set(new_value) {
                         Ok(new_value) => self.current = Some(new_value),
                         Err(err) => log::error!(