wayland.seat: send keymaps in individual tempfiles

Send keymaps to client using a new tempfile for each client, rather than
a single shared tempfile. Doing so prevents a client from tempering with
the contents of the tempfile, which would then cause other clients to
read a corrupted keymap.

See this bug report for details:
https://bugs.freedesktop.org/show_bug.cgi?id=101595

src/wayland/seat/keyboard.rs

@@ -237,23 +237,12 @@ pub(crate) fn create_keyboard_handler(
 
     info!(log, "Loaded Keymap"; "name" => internal.keymap.layouts().next());
 
-    // prepare a tempfile with the keymap, to send it to clients
+    let keymap = internal.keymap.get_as_string(xkb::KEYMAP_FORMAT_TEXT_V1);
-    let mut keymap_file = tempfile().map_err(Error::IoError)?;
-    let keymap_data = internal.keymap.get_as_string(xkb::KEYMAP_FORMAT_TEXT_V1);
-    keymap_file
-        .write_all(keymap_data.as_bytes())
-        .map_err(Error::IoError)?;
-    keymap_file.flush().map_err(Error::IoError)?;
-
-    trace!(log, "Keymap loaded and copied to tempfile.";
-        "fd" => keymap_file.as_raw_fd(), "len" => keymap_data.as_bytes().len()
-    );
 
     Ok(KeyboardHandle {
         arc: Arc::new(KbdArc {
             internal: Mutex::new(internal),
-            keymap_file,
+            keymap,
-            keymap_len: keymap_data.as_bytes().len() as u32,
             logger: log,
         }),
     })
@@ -261,8 +250,7 @@ pub(crate) fn create_keyboard_handler(
 
 struct KbdArc {
     internal: Mutex<KbdInternal>,
-    keymap_file: ::std::fs::File,
+    keymap: String,
-    keymap_len: u32,
     logger: ::slog::Logger,
 }
 
@@ -411,11 +399,27 @@ impl KeyboardHandle {
     /// This should be done first, before anything else is done with this keyboard.
     pub(crate) fn new_kbd(&self, kbd: Resource<WlKeyboard>) {
         trace!(self.arc.logger, "Sending keymap to client");
+
+        // prepare a tempfile with the keymap, to send it to the client
+        let ret = tempfile().and_then(|mut f| {
+            f.write_all(self.arc.keymap.as_bytes())?;
+            f.flush()?;
             kbd.send(Event::Keymap {
                 format: KeymapFormat::XkbV1,
-            fd: self.arc.keymap_file.as_raw_fd(),
+                fd: f.as_raw_fd(),
-            size: self.arc.keymap_len,
+                size: self.arc.keymap.as_bytes().len() as u32,
             });
+            Ok(())
+        });
+
+        if let Err(e) = ret {
+            warn!(self.arc.logger,
+                "Failed write keymap to client in a tempfile";
+                "err" => format!("{:?}", e)
+            );
+            return;
+        };
+
         let mut guard = self.arc.internal.lock().unwrap();
         if kbd.version() >= 4 {
             kbd.send(Event::RepeatInfo {