block: Add blk_dev_has_tray()

Pull out the check whether a block device has a tray from
blk_dev_is_tray_open() into its own function so both attributes (whether
there is a tray vs. whether that tray is open) can be queried
independently.

Cc: qemu-stable <qemu-stable@nongnu.org>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 1454096953-31773-2-git-send-email-mreitz@redhat.com

block/block-backend.c

@@ -458,6 +458,14 @@ bool blk_dev_has_removable_media(BlockBackend *blk)
     return !blk->dev || (blk->dev_ops && blk->dev_ops->change_media_cb);
 }
 
+/*
+ * Does @blk's attached device model have a tray?
+ */
+bool blk_dev_has_tray(BlockBackend *blk)
+{
+    return blk->dev_ops && blk->dev_ops->is_tray_open;
+}
+
 /*
  * Notify @blk's attached device model of a media eject request.
  * If @force is true, the medium is about to be yanked out forcefully.
@@ -474,7 +482,7 @@ void blk_dev_eject_request(BlockBackend *blk, bool force)
  */
 bool blk_dev_is_tray_open(BlockBackend *blk)
 {
-    if (blk->dev_ops && blk->dev_ops->is_tray_open) {
+    if (blk_dev_has_tray(blk)) {
         return blk->dev_ops->is_tray_open(blk->dev_opaque);
     }
     return false;

include/block/block_int.h

@@ -695,6 +695,7 @@ void blk_set_bs(BlockBackend *blk, BlockDriverState *bs);
 
 void blk_dev_change_media_cb(BlockBackend *blk, bool load);
 bool blk_dev_has_removable_media(BlockBackend *blk);
+bool blk_dev_has_tray(BlockBackend *blk);
 void blk_dev_eject_request(BlockBackend *blk, bool force);
 bool blk_dev_is_tray_open(BlockBackend *blk);
 bool blk_dev_is_medium_locked(BlockBackend *blk);