Move last_bytes into the path module

The last_bytes function is not libvirt specific and this patch moves it
into the path module. Now other virt drivers can use it without assuming
they depend on libvirt.

Change-Id: Ieb7fef9d054efef6bdb44b1d438ec703752be8b4

5 files changed, 43 insertions, 43 deletions

diff --git a/nova/privsep/libvirt.py b/nova/privsep/libvirt.py
index 05bd124518..8d87012c84 100644
--- a/nova/privsep/libvirt.py
+++ b/nova/privsep/libvirt.py
@@ -18,7 +18,6 @@ libvirt specific routines.
 """
 
 import binascii
-import errno
 import os
 import stat
 
@@ -34,39 +33,6 @@ LOG = logging.getLogger(__name__)
 
 
 @nova.privsep.sys_admin_pctxt.entrypoint
-def last_bytes(path, num):
-    # NOTE(mikal): this is implemented in this contrived manner because you
-    # can't mock a decorator in python (they're loaded at file parse time,
-    # and the mock happens later).
-    with open(path, 'rb') as f:
-        return _last_bytes_inner(f, num)
-
-
-def _last_bytes_inner(file_like_object, num):
-    """Return num bytes from the end of the file, and remaining byte count.
-
-    :param file_like_object: The file to read
-    :param num: The number of bytes to return
-
-    :returns: (data, remaining)
-    """
-
-    try:
-        file_like_object.seek(-num, os.SEEK_END)
-    except IOError as e:
-        # seek() fails with EINVAL when trying to go before the start of
-        # the file. It means that num is larger than the file size, so
-        # just go to the start.
-        if e.errno == errno.EINVAL:
-            file_like_object.seek(0, os.SEEK_SET)
-        else:
-            raise
-
-    remaining = file_like_object.tell()
-    return (file_like_object.read(), remaining)
-
-
-@nova.privsep.sys_admin_pctxt.entrypoint
 def dmcrypt_create_volume(target, device, cipher, key_size, key):
     """Sets up a dmcrypt mapping
 
diff --git a/nova/privsep/path.py b/nova/privsep/path.py
index e2864b2faa..c35e32ce54 100644
--- a/nova/privsep/path.py
+++ b/nova/privsep/path.py
@@ -15,6 +15,7 @@
 
 """Routines that bypass file-system checks."""
 
+import errno
 import os
 
 from oslo_utils import fileutils
@@ -89,3 +90,36 @@ class path(object):
     @nova.privsep.sys_admin_pctxt.entrypoint
     def exists(path):
         return os.path.exists(path)
+
+
+@nova.privsep.sys_admin_pctxt.entrypoint
+def last_bytes(path, num):
+    # NOTE(mikal): this is implemented in this contrived manner because you
+    # can't mock a decorator in python (they're loaded at file parse time,
+    # and the mock happens later).
+    with open(path, 'rb') as f:
+        return _last_bytes_inner(f, num)
+
+
+def _last_bytes_inner(file_like_object, num):
+    """Return num bytes from the end of the file, and remaining byte count.
+
+    :param file_like_object: The file to read
+    :param num: The number of bytes to return
+
+    :returns: (data, remaining)
+    """
+
+    try:
+        file_like_object.seek(-num, os.SEEK_END)
+    except IOError as e:
+        # seek() fails with EINVAL when trying to go before the start of
+        # the file. It means that num is larger than the file size, so
+        # just go to the start.
+        if e.errno == errno.EINVAL:
+            file_like_object.seek(0, os.SEEK_SET)
+        else:
+            raise
+
+    remaining = file_like_object.tell()
+    return (file_like_object.read(), remaining)
diff --git a/nova/tests/unit/privsep/test_libvirt.py b/nova/tests/unit/privsep/test_path.py
index af8bb5a7ce..cacbebd0e9 100644
--- a/nova/tests/unit/privsep/test_libvirt.py
+++ b/nova/tests/unit/privsep/test_path.py
@@ -17,7 +17,7 @@ import os
 import six
 import tempfile
 
-import nova.privsep.libvirt
+import nova.privsep.path
 from nova import test
 
 
@@ -30,13 +30,13 @@ class LastBytesTestCase(test.NoDBTestCase):
 
     def test_truncated(self):
         self.f.seek(0, os.SEEK_SET)
-        out, remaining = nova.privsep.libvirt._last_bytes_inner(self.f, 5)
+        out, remaining = nova.privsep.path._last_bytes_inner(self.f, 5)
         self.assertEqual(out, b'67890')
         self.assertGreater(remaining, 0)
 
     def test_read_all(self):
         self.f.seek(0, os.SEEK_SET)
-        out, remaining = nova.privsep.libvirt._last_bytes_inner(self.f, 1000)
+        out, remaining = nova.privsep.path._last_bytes_inner(self.f, 1000)
         self.assertEqual(out, b'1234567890')
         self.assertFalse(remaining > 0)
 
@@ -47,4 +47,4 @@ class LastBytesTestCase(test.NoDBTestCase):
             flo.write(content)
             self.assertEqual(
                 (content, 0),
-                nova.privsep.libvirt._last_bytes_inner(flo, 1000))
+                nova.privsep.path._last_bytes_inner(flo, 1000))
diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py
index 6415e8cbbb..526d01704e 100755
--- a/nova/tests/unit/virt/libvirt/test_driver.py
+++ b/nova/tests/unit/virt/libvirt/test_driver.py
@@ -11493,7 +11493,7 @@ class LibvirtConnTestCase(test.NoDBTestCase,
                 drvr._ensure_console_log_for_instance,
                 mock.ANY)
 
-    @mock.patch('nova.privsep.libvirt.last_bytes',
+    @mock.patch('nova.privsep.path.last_bytes',
                 return_value=(b'67890', 0))
     def test_get_console_output_file(self, mock_last_bytes):
         with utils.tempdir() as tmpdir:
@@ -11575,7 +11575,7 @@ class LibvirtConnTestCase(test.NoDBTestCase,
             self.assertEqual('', output)
 
     @mock.patch('os.path.exists', return_value=True)
-    @mock.patch('nova.privsep.libvirt.last_bytes',
+    @mock.patch('nova.privsep.path.last_bytes',
                 return_value=(b'67890', 0))
     @mock.patch('nova.privsep.path.writefile')
     @mock.patch('nova.privsep.libvirt.readpty')
@@ -11682,7 +11682,7 @@ class LibvirtConnTestCase(test.NoDBTestCase,
 
         def mock_last_bytes(path, count):
             with fake_libvirt_utils.file_open(path) as flo:
-                return nova.privsep.libvirt._last_bytes_inner(flo, count)
+                return nova.privsep.path._last_bytes_inner(flo, count)
 
         xml = """
         <domain type='kvm'>
@@ -11712,7 +11712,7 @@ class LibvirtConnTestCase(test.NoDBTestCase,
                     libvirt_driver.MAX_CONSOLE_BYTES = bytes_to_read
                     with mock.patch('os.path.exists',
                                     side_effect=mock_path_exists):
-                        with mock.patch('nova.privsep.libvirt.last_bytes',
+                        with mock.patch('nova.privsep.path.last_bytes',
                                         side_effect=mock_last_bytes):
                             log_data = drvr.get_console_output(self.context,
                                                                instance)
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index 99a30059a8..eb9aa23b11 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -2839,7 +2839,7 @@ class LibvirtDriver(driver.ComputeDriver):
         path = console_log
 
         while bytes_to_read > 0 and os.path.exists(path):
-            read_log_data, remaining = nova.privsep.libvirt.last_bytes(
+            read_log_data, remaining = nova.privsep.path.last_bytes(
                                         path, bytes_to_read)
             # We need the log file content in chronological order,
             # that's why we *prepend* the log data.