rublk: compress: don't call db.flush() in case of readonly when exiting

Signed-off-by: Ming Lei <tom.leiming@gmail.com>

Author: ming1

src/compress.rs

@@ -491,11 +491,13 @@ pub(crate) fn ublk_add_compress(
         comm.send_dev_id(dev.dev_info().dev_id).unwrap();
     });
 
-    log::info!("ublk device stopped, flushing RocksDB before exit...");
-    db_arc.flush()?;
-    log::info!("Final RocksDB flush successful.");
+    if !read_only {
+        log::info!("ublk device stopped, flushing RocksDB before exit...");
+        db_arc.flush()?;
+        log::info!("Final RocksDB flush successful.");
+    }
 
     run_result.unwrap();
 
     Ok(0)
-}
+}