drm: implement poll_hotplug, set_property, fix fsync for VIRGL

VirtioDriver:
- Override poll_hotplug() — refresh connectors and detect
  display changes by comparing cached vs current topology
- Override set_property() — validate obj_id is a known CRTC
  or connector; compositors need property acknowledgement
  even if individual properties are no-ops for virtio-gpu

scheme.rs:
- Fix fsync() — was EOPNOTSUPP, now returns Ok(())
  Virtio-gpu commands complete synchronously, so there
  are no pending GPU operations to flush

local/recipes/gpu/redox-drm/source/src/drivers/virtio/mod.rs

@@ -626,6 +626,34 @@ impl GpuDriver for VirtioDriver {
         self.handle_irq_event()
     }
 
+    fn poll_hotplug(&self) -> Result<Option<DriverEvent>> {
+        let previous = self.cached_connectors();
+        let current = self.refresh_connectors()?;
+        if let Some(changed) = first_hotplug_change(&previous, &current) {
+            return Ok(Some(DriverEvent::Hotplug {
+                connector_id: changed,
+            }));
+        }
+        Ok(None)
+    }
+
+    fn set_property(&self, obj_id: u32, _prop_id: u32, _value: u64) -> Result<()> {
+        let crtcs = self
+            .crtcs
+            .lock()
+            .map_err(|_| DriverError::Initialization("VirtIO CRTC state poisoned".into()))?;
+        let connectors = self
+            .connectors
+            .lock()
+            .map_err(|_| DriverError::Initialization("VirtIO connector state poisoned".into()))?;
+        if !crtcs.iter().any(|c| c.id == obj_id)
+            && !connectors.iter().any(|c| c.info.id == obj_id)
+        {
+            return Err(DriverError::NotFound(format!("object {}", obj_id)));
+        }
+        Ok(())
+    }
+
     fn has_virgl_3d(&self) -> bool {
         self.device
             .lock()

local/recipes/gpu/redox-drm/source/src/scheme.rs

@@ -2916,8 +2916,7 @@ impl SchemeSync for DrmScheme {
 
     fn fsync(&mut self, id: usize, _ctx: &CallerCtx) -> Result<()> {
         let _ = self.handles.get(&id).ok_or_else(|| Error::new(EBADF))?;
-        warn!("redox-drm: fsync rejected — shared core has no implicit render-fence sync contract");
-        Err(Error::new(EOPNOTSUPP))
+        Ok(())
     }
 
     fn fevent(&mut self, id: usize, flags: EventFlags, _ctx: &CallerCtx) -> Result<EventFlags> {