wayland.shm: allow buffer access to return a value

src/wayland/shm/mod.rs

@@ -145,24 +145,26 @@ pub enum BufferAccessError {
 ///
 /// If the buffer is not managed by the provided `ShmGlobal`, the closure is not called
 /// and this method will return `Err(())` (this will be the case for an EGL buffer for example).
-pub fn with_buffer_contents<F>(buffer: &Resource<wl_buffer::WlBuffer>, f: F) -> Result<(), BufferAccessError>
+pub fn with_buffer_contents<F, T>(
+    buffer: &Resource<wl_buffer::WlBuffer>,
+    f: F,
+) -> Result<T, BufferAccessError>
 where
-    F: FnOnce(&[u8], BufferData),
+    F: FnOnce(&[u8], BufferData) -> T,
 {
     if !buffer.is_implemented_with::<ShmGlobalData>() {
         return Err(BufferAccessError::NotManaged);
     }
     let data = unsafe { &*(buffer.get_user_data() as *mut InternalBufferData) };
 
-    if data.pool
-        .with_data_slice(|slice| f(slice, data.data))
-        .is_err()
-    {
+    match data.pool.with_data_slice(|slice| f(slice, data.data)) {
+        Ok(t) => Ok(t),
+        Err(()) => {
             // SIGBUS error occured
             buffer.post_error(wl_shm::Error::InvalidFd as u32, "Bad pool size.".into());
-        return Err(BufferAccessError::BadMap);
+            Err(BufferAccessError::BadMap)
+        }
     }
-    Ok(())
 }
 
 impl Implementation<Resource<wl_shm::WlShm>, wl_shm::Request> for ShmGlobalData {

src/wayland/shm/pool.rs

@@ -46,7 +46,7 @@ impl Pool {
         })
     }
 
-    pub fn with_data_slice<F: FnOnce(&[u8])>(&self, f: F) -> Result<(), ()> {
+    pub fn with_data_slice<T, F: FnOnce(&[u8]) -> T>(&self, f: F) -> Result<T, ()> {
         // Place the sigbus handler
         SIGBUS_INIT.call_once(|| unsafe {
             place_sigbus_handler();
@@ -67,7 +67,7 @@ impl Pool {
         });
 
         let slice = pool_guard.get_slice();
-        f(slice);
+        let t = f(slice);
 
         // Cleanup Post-access
         SIGBUS_GUARD.with(|guard| {
@@ -77,7 +77,7 @@ impl Pool {
                 debug!(self.log, "SIGBUS caught on access on shm pool"; "fd" => self.fd);
                 Err(())
             } else {
-                Ok(())
+                Ok(t)
             }
         })
     }