backend.session: use pkg-config to find logind lib

Introduce the `backend_session_elogind` cargo feature which pulls
`backend_session_logind` and makes the logind session backend seek
`libelogind.so` instead of `libsystemd.so`.

Fixes #127

.github/workflows/ci.yml

@@ -65,7 +65,7 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: test
-          args: --all-features
+          args: --features "test_all_features"
   
   anvil-ci:
     strategy:
@@ -111,7 +111,7 @@ jobs:
       - name: Test all
         if: matrix.features == 'all'
         working-directory: ./anvil
-        run: cargo test --all-features
+        run: cargo test --features "test_all_features"
 
 
   lint:
@@ -135,8 +135,8 @@ jobs:
         run: cargo fmt --all -- --check
       
       - name: Clippy Smithay
-        run: cargo clippy --all-features -- -D warnings
+        run: cargo clippy --features "test_all_features" -- -D warnings
 
       - name: Clippy Anvil
         working-directory: ./anvil
-        run: cargo clippy --all-features -- -D warnings
+        run: cargo clippy --features "test_all_features" -- -D warnings

.github/workflows/docs.yml

@@ -33,7 +33,7 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: doc
-          args: --no-deps --all-features
+          args: --no-deps --features "test_all_features"
 
       - name: Setup index
         run: cp ./doc_index.html ./target/doc/index.html

Cargo.toml

@@ -20,11 +20,11 @@ glium = { version = "0.27.0", optional = true, default-features = false }
 image = { version = "0.23.0", optional = true }
 input = { version = "0.5", default-features = false, optional = true }
 lazy_static = "1"
+libc = "0.2.70"
 libloading = "0.6.0"
 nix = "0.17"
 slog = "2"
 slog-stdlog = "4"
-systemd = { version = "0.4.0", optional = true }
 tempfile = "3.0"
 thiserror = "1"
 udev = { version = "0.4", optional = true }
@@ -43,6 +43,7 @@ slog-term = "2.3"
 
 [build-dependencies]
 gl_generator = { version = "0.14", optional = true }
+pkg-config = { version = "0.3.17", optional = true }
 
 [features]
 default = ["backend_winit", "backend_drm_legacy", "backend_drm_atomic", "backend_drm_gbm", "backend_drm_eglstream", "backend_drm_egl", "backend_libinput", "backend_udev", "backend_session_logind", "renderer_glium", "xwayland", "wayland_frontend"]
@@ -57,12 +58,14 @@ backend_egl = ["gl_generator"]
 backend_libinput = ["input"]
 backend_session = []
 backend_udev = ["udev"]
-backend_session_logind = ["dbus", "systemd", "backend_session"]
+backend_session_logind = ["dbus", "backend_session", "pkg-config"]
+backend_session_elogind = ["backend_session_logind"]
 renderer_gl = ["gl_generator"]
 renderer_glium = ["renderer_gl", "glium"]
 use_system_lib = ["wayland_frontend", "wayland-sys", "wayland-server/use_system_lib"]
 wayland_frontend = ["wayland-server", "wayland-commons", "wayland-protocols"]
 xwayland = ["wayland_frontend"]
+test_all_features = ["default"]
 
 [[example]]
 name = "raw_legacy_drm"

anvil/Cargo.toml

@@ -31,3 +31,5 @@ egl = [ "smithay/use_system_lib" ]
 winit = [ "smithay/backend_winit" ]
 udev = [ "smithay/backend_libinput", "smithay/backend_udev", "smithay/backend_drm_atomic", "smithay/backend_drm_legacy", "smithay/backend_drm_gbm", "smithay/backend_drm_eglstream", "smithay/backend_drm_egl", "smithay/backend_session", "input" ]
 logind = [ "smithay/backend_session_logind" ]
+elogind = ["logind", "smithay/backend_session_elogind" ]
+test_all_features = ["default"]

build.rs

@@ -1,12 +1,8 @@
 #[cfg(any(feature = "backend_egl", feature = "renderer_gl"))]
-extern crate gl_generator;
-
-#[cfg(any(feature = "backend_egl", feature = "renderer_gl"))]
+fn gl_generate() {
     use gl_generator::{Api, Fallbacks, Profile, Registry};
     use std::{env, fs::File, path::PathBuf};
 
-#[cfg(any(feature = "backend_egl", feature = "renderer_gl"))]
-fn main() {
     let dest = PathBuf::from(&env::var("OUT_DIR").unwrap());
 
     println!("cargo:rerun-if-changed=build.rs");
@@ -63,5 +59,42 @@ fn main() {
     }
 }
 
-#[cfg(not(any(feature = "backend_egl", feature = "renderer_gl")))]
-fn main() {}
+#[cfg(feature = "backend_session_logind")]
+fn find_logind() {
+    // We should allow only dynamic linkage due to libsystemd and libelogind LICENSE.
+
+    #[cfg(feature = "backend_session_elogind")]
+    {
+        if pkg_config::Config::new()
+            .statik(false)
+            .probe("libelogind")
+            .is_err()
+        {
+            println!("cargo:warning=Could not find `libelogind.so`.");
+            println!("cargo:warning=If your system is systemd-based, you should only enable the `backend_session_logind` feature, not `backend_session_elogind`.");
+            std::process::exit(1);
+        }
+    }
+
+    #[cfg(not(feature = "backend_session_elogind"))]
+    {
+        if pkg_config::Config::new()
+            .statik(false)
+            .probe("libsystemd")
+            .is_err()
+        {
+            println!("cargo:warning=Could not find `libsystemd.so`.");
+            println!("cargo:warning=If your system uses elogind, please enable the `backend_session_elogind` feature.");
+            println!("cargo:warning=Otherwise, you may need to disable the `backend_session_logind` feature as your system does not support it.");
+            std::process::exit(1);
+        }
+    }
+}
+
+fn main() {
+    #[cfg(any(feature = "backend_egl", feature = "renderer_gl"))]
+    gl_generate();
+
+    #[cfg(feature = "backend_session_logind")]
+    find_logind();
+}

src/backend/session/dbus/logind.rs

@@ -52,7 +52,6 @@ use std::{
     rc::{Rc, Weak},
     sync::atomic::{AtomicBool, Ordering},
 };
-use systemd::login;
 
 use calloop::{EventSource, Poll, Readiness, Token};
 
@@ -91,9 +90,7 @@ impl LogindSession {
             .new(o!("smithay_module" => "backend_session", "session_type" => "logind"));
 
         // Acquire session_id, seat and vt (if any) via libsystemd
-        let session_id = login::get_session(None).map_err(Error::FailedToGetSession)?;
-        let seat = login::get_seat(session_id.clone()).map_err(Error::FailedToGetSeat)?;
-        let vt = login::get_vt(session_id.clone()).ok();
+        let (session_id, seat, vt) = ffi::get_login_state()?;
 
         // Create dbus connection
         let conn = DBusConnection::new_system().map_err(Error::FailedDbusConnection)?;
@@ -558,3 +555,61 @@ impl AsErrno for Error {
         None
     }
 }
+
+/*
+ * FFI routines to retrieve the session state from logind or elogind
+ */
+
+mod ffi {
+    use libc::pid_t;
+    use std::{
+        ffi::CString,
+        os::raw::{c_char, c_int, c_uint},
+    };
+
+    pub fn get_login_state() -> Result<(String, String, Option<u32>), super::Error> {
+        let session_name = unsafe {
+            let mut session_name: *mut c_char = std::ptr::null_mut();
+            let ret = sd_pid_get_session(0, &mut session_name);
+            if ret < 0 {
+                return Err(super::Error::FailedToGetSession(
+                    std::io::Error::from_raw_os_error(-ret),
+                ));
+            }
+            CString::from_raw(session_name)
+        };
+
+        let seat_name = unsafe {
+            let mut seat_name: *mut c_char = std::ptr::null_mut();
+            let ret = sd_session_get_seat(session_name.as_ptr(), &mut seat_name);
+            if ret < 0 {
+                return Err(super::Error::FailedToGetSeat(std::io::Error::from_raw_os_error(
+                    -ret,
+                )));
+            }
+            CString::from_raw(seat_name)
+        };
+
+        let vt_num = unsafe {
+            let mut vt_num = 0;
+            let ret = sd_session_get_vt(session_name.as_ptr(), &mut vt_num);
+            if ret < 0 {
+                None
+            } else {
+                Some(vt_num)
+            }
+        };
+
+        Ok((
+            session_name.into_string().unwrap(),
+            seat_name.into_string().unwrap(),
+            vt_num,
+        ))
+    }
+
+    extern "C" {
+        fn sd_pid_get_session(pid: pid_t, out_session: *mut *mut c_char) -> c_int;
+        fn sd_session_get_seat(session: *const c_char, out_seat: *mut *mut c_char) -> c_int;
+        fn sd_session_get_vt(session: *const c_char, out_vt: *mut c_uint) -> c_int;
+    }
+}

src/reexports.rs

@@ -13,8 +13,6 @@ pub use image;
 pub use input;
 #[cfg(any(feature = "backend_udev", feature = "backend_drm"))]
 pub use nix;
-#[cfg(feature = "backend_session_logind")]
-pub use systemd;
 #[cfg(feature = "backend_udev")]
 pub use udev;
 #[cfg(feature = "wayland_frontend")]