libvirt: read rotated "console.log" files

A libvirt guest can output its console into a "console.log" file.
This change enhances the reading of this file in case there is log
rotation on this file. This will be the case in a following change
which make use of the "virtlogd" deamon of libvirt 1.3.0 and beyond.
If no log-rotation is used, the method will behave as before. This
change makes the later virtlogd change easier to review.

Change-Id: Ica2c91ad309df8e66433fe0c7fe2b799a23c0096

nova/tests/unit/virt/libvirt/test_driver.py

@@ -10798,7 +10798,8 @@ class LibvirtConnTestCase(test.NoDBTestCase):
 
             self.assertEqual('', output)
 
-    def test_get_console_output_pty(self):
+    @mock.patch('os.path.exists', return_value=True)
+    def test_get_console_output_pty(self, mocked_path_exists):
         fake_libvirt_utils.files['pty'] = '01234567890'
 
         with utils.tempdir() as tmpdir:
@@ -10872,6 +10873,66 @@ class LibvirtConnTestCase(test.NoDBTestCase):
         self.assertRaises(exception.ConsoleNotAvailable,
                           drvr.get_console_output, self.context, instance)
 
+    @mock.patch('nova.virt.libvirt.host.Host.get_domain')
+    @mock.patch.object(libvirt_guest.Guest, "get_xml_desc")
+    def test_get_console_output_logrotate(self, mock_get_xml, get_domain):
+        fake_libvirt_utils.files['console.log'] = 'uvwxyz'
+        fake_libvirt_utils.files['console.log.0'] = 'klmnopqrst'
+        fake_libvirt_utils.files['console.log.1'] = 'abcdefghij'
+
+        def mock_path_exists(path):
+            return os.path.basename(path) in fake_libvirt_utils.files
+
+        xml = """
+        <domain type='kvm'>
+            <devices>
+                <disk type='file'>
+                    <source file='filename'/>
+                </disk>
+                <console type='file'>
+                    <source path='console.log'/>
+                    <target port='0'/>
+                </console>
+            </devices>
+        </domain>
+        """
+        mock_get_xml.return_value = xml
+        get_domain.return_value = mock.MagicMock()
+
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
+        instance = objects.Instance(**self.test_instance)
+
+        def _get_logd_output(bytes_to_read):
+            with utils.tempdir() as tmp_dir:
+                self.flags(instances_path=tmp_dir)
+                log_data = ""
+                try:
+                    prev_max = libvirt_driver.MAX_CONSOLE_BYTES
+                    libvirt_driver.MAX_CONSOLE_BYTES = bytes_to_read
+                    with mock.patch('os.path.exists',
+                                    side_effect=mock_path_exists):
+                        log_data = drvr.get_console_output(self.context,
+                                                           instance)
+                finally:
+                    libvirt_driver.MAX_CONSOLE_BYTES = prev_max
+                return log_data
+
+        # span across only 1 file (with remaining bytes)
+        self.assertEqual('wxyz', _get_logd_output(4))
+        # span across only 1 file (exact bytes)
+        self.assertEqual('uvwxyz', _get_logd_output(6))
+        # span across 2 files (with remaining bytes)
+        self.assertEqual('opqrstuvwxyz', _get_logd_output(12))
+        # span across all files (exact bytes)
+        self.assertEqual('abcdefghijklmnopqrstuvwxyz', _get_logd_output(26))
+        # span across all files with more bytes than available
+        self.assertEqual('abcdefghijklmnopqrstuvwxyz', _get_logd_output(30))
+        # files are not available
+        fake_libvirt_utils.files = {}
+        self.assertEqual('', _get_logd_output(30))
+        # reset the file for other tests
+        fake_libvirt_utils.files['console.log'] = '01234567890'
+
     def test_get_host_ip_addr(self):
         drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
         ip = drvr.get_host_ip_addr()

nova/virt/libvirt/driver.py

@@ -2646,12 +2646,21 @@ class LibvirtDriver(driver.ComputeDriver):
 
         return fpath
 
-    def _get_console_output_file(self, instance, path):
+    def _get_console_output_file(self, instance, console_log):
+        bytes_to_read = MAX_CONSOLE_BYTES
+        log_data = ""  # The last N read bytes
+        i = 0  # in case there is a log rotation (like "virtlogd")
+        path = console_log
+        while bytes_to_read > 0 and os.path.exists(path):
             libvirt_utils.chown(path, os.getuid())
-
             with libvirt_utils.file_open(path, 'rb') as fp:
-            log_data, remaining = utils.last_bytes(fp,
-                                                   MAX_CONSOLE_BYTES)
+                read_log_data, remaining = utils.last_bytes(fp, bytes_to_read)
+                # We need the log file content in chronological order,
+                # that's why we *prepend* the log data.
+                log_data = read_log_data + log_data
+                bytes_to_read -= len(read_log_data)
+                path = console_log + "." + str(i)
+                i += 1
             if remaining > 0:
                 LOG.info(_LI('Truncated console log returned, '
                              '%d bytes ignored'), remaining,