Merge "libvirt:driver:Disallow AIO=native when 'O_DIRECT' is not available" into stable/ussuri

3 files changed, 75 insertions, 0 deletions

diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py
index 30b8f3ea7d..b25fca8fd5 100644
--- a/nova/tests/unit/virt/libvirt/test_driver.py
+++ b/nova/tests/unit/virt/libvirt/test_driver.py
@@ -18102,6 +18102,51 @@ class LibvirtConnTestCase(test.NoDBTestCase,
         drvr._set_cache_mode(fake_conf)
         self.assertEqual('none', fake_conf.driver_cache)
 
+    def _make_fake_conf(self, cache=None):
+        if cache:
+            self.flags(disk_cachemodes=['block=' + cache], group='libvirt')
+        else:
+            self.flags(group='libvirt')
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
+        fake_conf = FakeConfigGuestDisk()
+        fake_conf.source_type = 'block'
+        fake_conf.driver_io = 'native'
+        drvr._set_cache_mode(fake_conf)
+        return fake_conf
+
+    def test_set_cache_mode_driver_io_writeback(self):
+        """Tests that when conf.driver_io is 'native' and driver_cache is
+        'writeback', then conf.driver_io is forced to 'threads'
+        """
+        fake_conf = self._make_fake_conf('writeback')
+        self.assertEqual('writeback', fake_conf.driver_cache)
+        self.assertEqual('threads', fake_conf.driver_io)
+
+    def test_set_cache_mode_driver_io_writethrough(self):
+        """Tests that when conf.driver_io is 'native' and driver_cache is
+        'writethrough', then conf.driver_io is forced to 'threads'
+        """
+        fake_conf = self._make_fake_conf('writethrough')
+        self.assertEqual('writethrough', fake_conf.driver_cache)
+        self.assertEqual('threads', fake_conf.driver_io)
+
+    def test_set_cache_mode_driver_io_unsafe(self):
+        """Tests that when conf.driver_io is 'native' and driver_cache is
+        'unsafe', then conf.driver_io is forced to 'threads'
+        """
+        fake_conf = self._make_fake_conf('unsafe')
+        self.assertEqual('unsafe', fake_conf.driver_cache)
+        self.assertEqual('threads', fake_conf.driver_io)
+
+    def test_without_set_cache_mode_driver_io(self):
+        """Tests that when conf.driver_io is 'native' and driver_cache is
+        not set(this is default settings), then conf.driver_io is kept as
+        'native'
+        """
+        fake_conf = self._make_fake_conf()
+        self.assertIsNone(fake_conf.driver_cache)
+        self.assertEqual('native', fake_conf.driver_io)
+
     def test_set_cache_mode_invalid_mode(self):
         self.flags(disk_cachemodes=['file=FAKE'], group='libvirt')
         drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index 320f3503ad..012906b5f6 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -592,6 +592,22 @@ class LibvirtDriver(driver.ComputeDriver):
                                                   driver_cache)
             conf.driver_cache = cache_mode
 
+        # NOTE(acewit): If the [libvirt]disk_cachemodes is set as
+        # `block=writeback` or `block=writethrough` or `block=unsafe`,
+        # whose correponding Linux's IO semantic is not O_DIRECT in
+        # file nova.conf, then it will result in an attachment failure
+        # because of the libvirt bug
+        # (https://bugzilla.redhat.com/show_bug.cgi?id=1086704)
+        if ((getattr(conf, 'driver_io', None) == "native") and
+                conf.driver_cache not in [None, 'none', 'directsync']):
+            conf.driver_io = "threads"
+            LOG.warning("The guest disk driver io mode has fallen back "
+                        "from 'native' to 'threads' because the "
+                        "disk cache mode is set as %(cachemode)s, which does"
+                        "not use O_DIRECT. See the following bug report "
+                        "for more details: https://launchpad.net/bugs/1841363",
+                        {'cachemode': conf.driver_cache})
+
     def _do_quality_warnings(self):
         """Warn about potential configuration issues.
 
diff --git a/releasenotes/notes/bug-1841363-fallback-to-threaded-io-when-native-io-is-not-supported-fe56014e9648a518.yaml b/releasenotes/notes/bug-1841363-fallback-to-threaded-io-when-native-io-is-not-supported-fe56014e9648a518.yaml
new file mode 100644
index 0000000000..8ea68c9741
--- /dev/null
+++ b/releasenotes/notes/bug-1841363-fallback-to-threaded-io-when-native-io-is-not-supported-fe56014e9648a518.yaml
@@ -0,0 +1,14 @@
+---
+fixes:
+  - |
+    Since Libvirt v.1.12.0 and the introduction of the `libvirt issue`_ ,
+    there is a fact that if we set cache mode whose write semantic is not
+    O_DIRECT (i.e. "unsafe", "writeback" or "writethrough"), there will
+    be a problem with the volume drivers (i.e. LibvirtISCSIVolumeDriver,
+    LibvirtNFSVolumeDriver and so on), which designate native io explicitly.
+
+    When the driver_cache (default is none) has been configured as neither
+    "none" nor "directsync", the libvirt driver will ensure the driver_io
+    to be "threads" to avoid an instance spawning failure.
+
+    .. _`libvirt issue`: https://bugzilla.redhat.com/show_bug.cgi?id=1086704