Remove redundant syscalls

This will optimize the first GET on files added from file interface.
More info: https://gist.github.com/prashanthpai/62e0bec770421561ea79

Change-Id: I3f0fd897eedf1413c3e7d5dca0f6196c62549fcb
Signed-off-by: Prashanth Pai <ppai@redhat.com>

swiftonfile/swift/common/utils.py

@@ -292,18 +292,19 @@ def _get_etag(path_or_fd):
     return etag
 
 
-def get_object_metadata(obj_path_or_fd):
+def get_object_metadata(obj_path_or_fd, stats=None):
     """
     Return metadata of object.
     """
-    if isinstance(obj_path_or_fd, int):
-        # We are given a file descriptor, so this is an invocation from the
-        # DiskFile.open() method.
-        stats = do_fstat(obj_path_or_fd)
-    else:
-        # We are given a path to the object when the DiskDir.list_objects_iter
-        # method invokes us.
-        stats = do_stat(obj_path_or_fd)
+    if not stats:
+        if isinstance(obj_path_or_fd, int):
+            # We are given a file descriptor, so this is an invocation from the
+            # DiskFile.open() method.
+            stats = do_fstat(obj_path_or_fd)
+        else:
+            # We are given a path to the object when the
+            # DiskDir.list_objects_iter method invokes us.
+            stats = do_stat(obj_path_or_fd)
 
     if not stats:
         metadata = {}
@@ -320,8 +321,7 @@ def get_object_metadata(obj_path_or_fd):
     return metadata
 
 
-def restore_metadata(path, metadata):
-    meta_orig = read_metadata(path)
+def restore_metadata(path, metadata, meta_orig):
     if meta_orig:
         meta_new = meta_orig.copy()
         meta_new.update(metadata)
@@ -332,12 +332,12 @@ def restore_metadata(path, metadata):
     return meta_new
 
 
-def create_object_metadata(obj_path_or_fd):
+def create_object_metadata(obj_path_or_fd, stats=None, existing_meta={}):
     # We must accept either a path or a file descriptor as an argument to this
     # method, as the diskfile modules uses a file descriptior and the DiskDir
     # module (for container operations) uses a path.
-    metadata = get_object_metadata(obj_path_or_fd)
-    return restore_metadata(obj_path_or_fd, metadata)
+    metadata_from_stat = get_object_metadata(obj_path_or_fd, stats)
+    return restore_metadata(obj_path_or_fd, metadata_from_stat, existing_meta)
 
 
 # The following dir_xxx calls should definitely be replaced

swiftonfile/swift/obj/diskfile.py

@@ -636,8 +636,8 @@ class DiskFile(object):
 
             self._metadata = read_metadata(self._fd)
             if not validate_object(self._metadata, self._stat):
-                create_object_metadata(self._fd)
-                self._metadata = read_metadata(self._fd)
+                self._metadata = create_object_metadata(self._fd, self._stat,
+                                                        self._metadata)
             assert self._metadata is not None
             self._filter_metadata()
 

test/unit/common/test_utils.py

@@ -320,10 +320,9 @@ class TestUtils(unittest.TestCase):
     def test_restore_metadata_none(self):
         # No initial metadata
         path = "/tmp/foo/i"
-        res_d = utils.restore_metadata(path, {'b': 'y'})
+        res_d = utils.restore_metadata(path, {'b': 'y'}, {})
         expected_d = {'b': 'y'}
         assert res_d == expected_d, "Expected %r, result %r" % (expected_d, res_d)
-        assert _xattr_op_cnt['get'] == 1, "%r" % _xattr_op_cnt
         assert _xattr_op_cnt['set'] == 1, "%r" % _xattr_op_cnt
 
     def test_restore_metadata(self):
@@ -332,10 +331,9 @@ class TestUtils(unittest.TestCase):
         initial_d = {'a': 'z'}
         xkey = _xkey(path, utils.METADATA_KEY)
         _xattrs[xkey] = serialize_metadata(initial_d)
-        res_d = utils.restore_metadata(path, {'b': 'y'})
+        res_d = utils.restore_metadata(path, {'b': 'y'}, initial_d)
         expected_d = {'a': 'z', 'b': 'y'}
         assert res_d == expected_d, "Expected %r, result %r" % (expected_d, res_d)
-        assert _xattr_op_cnt['get'] == 1, "%r" % _xattr_op_cnt
         assert _xattr_op_cnt['set'] == 1, "%r" % _xattr_op_cnt
 
     def test_restore_metadata_nochange(self):
@@ -344,10 +342,9 @@ class TestUtils(unittest.TestCase):
         initial_d = {'a': 'z'}
         xkey = _xkey(path, utils.METADATA_KEY)
         _xattrs[xkey] = serialize_metadata(initial_d)
-        res_d = utils.restore_metadata(path, {})
+        res_d = utils.restore_metadata(path, {}, initial_d)
         expected_d = {'a': 'z'}
         assert res_d == expected_d, "Expected %r, result %r" % (expected_d, res_d)
-        assert _xattr_op_cnt['get'] == 1, "%r" % _xattr_op_cnt
         assert _xattr_op_cnt['set'] == 0, "%r" % _xattr_op_cnt
 
     def test_deserialize_metadata_pickle(self):
@@ -460,7 +457,6 @@ class TestUtils(unittest.TestCase):
         xkey = _xkey(tf.name, utils.METADATA_KEY)
         assert len(_xattrs.keys()) == 1
         assert xkey in _xattrs
-        assert _xattr_op_cnt['get'] == 1
         assert _xattr_op_cnt['set'] == 1
         md = deserialize_metadata(_xattrs[xkey])
         assert r_md == md
@@ -482,7 +478,6 @@ class TestUtils(unittest.TestCase):
             xkey = _xkey(td, utils.METADATA_KEY)
             assert len(_xattrs.keys()) == 1
             assert xkey in _xattrs
-            assert _xattr_op_cnt['get'] == 1
             assert _xattr_op_cnt['set'] == 1
             md = deserialize_metadata(_xattrs[xkey])
             assert r_md == md