test: add test for mds drop cache command

Fixes: http://tracker.ceph.com/issues/23362
Signed-off-by: Venky Shankar <vshankar@redhat.com>

qa/tasks/cephfs/test_misc.py

@@ -207,3 +207,46 @@ def test_dump_inode(self):
         info = self.fs.mds_asok(['dump', 'inode', '1'])
         assert(info['path'] == "/")
 
+    def test_drop_cache_command(self):
+        """
+        Basic test for checking drop cache command. Note that the cache size
+        post trimming is not checked here.
+        """
+
+        self.mount_b.umount_wait()
+        ls_data = self.fs.mds_asok(['session', 'ls'])
+        self.assert_session_count(1, ls_data)
+
+        # create some files
+        self.mount_a.create_n_files("dc-dir/dc-file", 1000)
+
+        # drop cache
+        drop_res = self.fs.mds_asok(['cache', 'drop', '10'])
+        self.assertTrue(drop_res['client_recall']['return_code'] == 0)
+        self.assertTrue(drop_res['flush_journal']['return_code'] == 0)
+
+    def test_drop_cache_command_timeout(self):
+        """
+        Check drop cache command with non-responding client. Note that the
+        cache size post trimming is not checked here.
+        """
+
+        self.mount_b.umount_wait()
+        ls_data = self.fs.mds_asok(['session', 'ls'])
+        self.assert_session_count(1, ls_data)
+
+        # create some files
+        self.mount_a.create_n_files("dc-dir/dc-file-t", 1000)
+
+        # simulate client death
+        self.mount_a.kill()
+
+        # drop cache
+        drop_res = self.fs.mds_asok(['cache', 'drop', '5'])
+
+        self.assertTrue(drop_res['client_recall']['return_code'] == errno.ETIMEDOUT)
+        self.assertTrue(drop_res['flush_journal']['return_code'] == 0)
+
+        self.mount_a.kill_cleanup()
+        self.mount_a.mount()
+        self.mount_a.wait_until_mounted()