Fix trying to become drm master on logind session

src/backend/drm/mod.rs

@@ -251,6 +251,7 @@ pub struct DrmDevice<A: ControlDevice + 'static> {
     device_id: dev_t,
     backends: HashMap<crtc::Handle, Weak<DrmBackendInternal<A>>>,
     active: bool,
+    priviledged: bool,
     logger: ::slog::Logger,
 }
 
@@ -319,13 +320,17 @@ impl<A: ControlDevice + 'static> DrmDevice<A> {
             device_id,
             old_state: HashMap::new(),
             active: true,
+            priviledged: true,
             logger: log.clone(),
         };
 
         info!(log, "DrmDevice initializing");
 
-        // we want to mode-set, so we better be the master
-        drm.set_master().chain_err(|| ErrorKind::DrmMasterFailed)?;
+        // we want to mode-set, so we better be the master, if we run via a tty session
+        if let Err(_) = drm.set_master() {
+            warn!(log, "Unable to become drm master, assuming unpriviledged mode");
+            drm.priviledged = false;
+        };
 
         let res_handles = drm.resource_handles().chain_err(|| {
             ErrorKind::DrmDev(format!(
@@ -506,6 +511,7 @@ impl<A: ControlDevice + 'static> Drop for DrmDevice<A> {
                 );
             }
         }
+        if self.priviledged {
             if let Err(err) = self.drop_master() {
                 error!(
                     self.logger,
@@ -513,6 +519,7 @@ impl<A: ControlDevice + 'static> Drop for DrmDevice<A> {
                 );
             }
         }
+    }
 }
 
 /// Handler for drm node events
@@ -606,6 +613,7 @@ impl<A: ControlDevice + 'static> SessionObserver for StateToken<DrmDevice<A>> {
                }
         }
         device.active = false;
+        if device.priviledged {
             if let Err(err) = device.drop_master() {
                 error!(
                     device.logger,
@@ -613,6 +621,7 @@ impl<A: ControlDevice + 'static> SessionObserver for StateToken<DrmDevice<A>> {
                 );
             }
         }
+    }
 
     fn activate<'a>(&mut self, state: &mut StateProxy<'a>, devnum: Option<(u32, u32, Option<RawFd>)>) {
         let device = state.get_mut(self);
@@ -622,10 +631,12 @@ impl<A: ControlDevice + 'static> SessionObserver for StateToken<DrmDevice<A>> {
             {
                return;
            } else if let Some(fd) = fd {
+               info!(device.logger, "Replacing fd");
                nix::unistd::dup2(device.as_raw_fd(), fd).expect("Failed to replace file descriptor of drm device");
            }
         }
         device.active = true;
+        if device.priviledged {
             if let Err(err) = device.set_master() {
                 crit!(
                     device.logger,
@@ -633,6 +644,7 @@ impl<A: ControlDevice + 'static> SessionObserver for StateToken<DrmDevice<A>> {
                     err
                 );
             }
+        }
         let mut crtcs = Vec::new();
         for (crtc, backend) in device.backends.iter() {
             if let Some(backend) = backend.upgrade() {