Merge "Fix launching of guests where instances_path is on GlusterFS"

2 files changed, 54 insertions, 7 deletions

diff --git a/nova/virt/libvirt.xml.template b/nova/virt/libvirt.xml.template
index b3cc75580..225133eb5 100644
--- a/nova/virt/libvirt.xml.template
+++ b/nova/virt/libvirt.xml.template
@@ -66,40 +66,40 @@
 #else
     #if $getVar('rescue', False)
         <disk type='file'>
-            <driver type='${driver_type}' cache='none'/>
+            <driver type='${driver_type}' cache='${cachemode}'/>
             <source file='${basepath}/disk.rescue'/>
             <target dev='${disk_prefix}a' bus='${ephemeral_disk_bus}'/>
         </disk>
         <disk type='file'>
-            <driver type='${driver_type}' cache='none'/>
+            <driver type='${driver_type}' cache='${cachemode}'/>
             <source file='${basepath}/disk'/>
             <target dev='${disk_prefix}b' bus='${ephemeral_disk_bus}'/>
         </disk>
     #else
         #if not ($getVar('ebs_root', False))
         <disk type='file' device='${root_device_type}'>
-            <driver type='${driver_type}' cache='none'/>
+            <driver type='${driver_type}' cache='${cachemode}'/>
             <source file='${basepath}/disk'/>
             <target dev='${root_device}' bus='${root_disk_bus}'/>
         </disk>
         #end if
         #if $getVar('ephemeral_device', False)
             <disk type='file'>
-                <driver type='${driver_type}' cache='none'/>
+                <driver type='${driver_type}' cache='${cachemode}'/>
                 <source file='${basepath}/disk.local'/>
                 <target dev='${ephemeral_device}' bus='${ephemeral_disk_bus}'/>
             </disk>
         #end if
         #for $eph in $ephemerals
          <disk type='block'>
-                <driver type='${driver_type}' cache='none'/>
+                <driver type='${driver_type}' cache='${cachemode}'/>
                 <source dev='${basepath}/${eph.device_path}'/>
                 <target dev='${eph.device}' bus='${ephemeral_disk_bus}'/>
          </disk>
         #end for
         #if $getVar('swap_device', False)
             <disk type='file'>
-                <driver type='${driver_type}' cache='none'/>
+                <driver type='${driver_type}' cache='${cachemode}'/>
                 <source file='${basepath}/disk.swap'/>
                 <target dev='${swap_device}' bus='${ephemeral_disk_bus}'/>
             </disk>
@@ -110,7 +110,7 @@
     #end if
     #if $getVar('config_drive', False)
         <disk type='file'>
-            <driver type='raw' />
+            <driver type='raw' cache='${cachemode}'/>
             <source file='${basepath}/disk.config' />
             <target dev='${disk_prefix}z' bus='${ephemeral_disk_bus}' />
         </disk>
diff --git a/nova/virt/libvirt/connection.py b/nova/virt/libvirt/connection.py
index 3aabfde13..f1e04d3f9 100644
--- a/nova/virt/libvirt/connection.py
+++ b/nova/virt/libvirt/connection.py
@@ -225,9 +225,25 @@ class LibvirtConnection(driver.ComputeDriver):
         self.default_second_device = self._disk_prefix + 'b'
         self.default_third_device = self._disk_prefix + 'c'
 
+        self._disk_cachemode = None
         self.image_cache_manager = imagecache.ImageCacheManager()
 
     @property
+    def disk_cachemode(self):
+        if self._disk_cachemode is None:
+            # We prefer 'none' for consistent performance, host crash
+            # safety & migration correctness by avoiding host page cache.
+            # Some filesystems (eg GlusterFS via FUSE) don't support
+            # O_DIRECT though. For those we fallback to 'writethrough'
+            # which gives host crash safety, and is safe for migration
+            # provided the filesystem is cache coherant (cluster filesystems
+            # typically are, but things like NFS are not).
+            self._disk_cachemode = "none"
+            if not self._supports_direct_io(FLAGS.instances_path):
+                self._disk_cachemode = "writethrough"
+        return self._disk_cachemode
+
+    @property
     def host_state(self):
         if not self._host_state:
             self._host_state = HostState(self.read_only)
@@ -996,6 +1012,36 @@ class LibvirtConnection(driver.ComputeDriver):
         return {'host': host, 'port': port, 'internal_access_path': None}
 
     @staticmethod
+    def _supports_direct_io(dirpath):
+        testfile = os.path.join(dirpath, ".directio.test")
+        hasDirectIO = True
+        try:
+            f = os.open(testfile, os.O_CREAT | os.O_WRONLY | os.O_DIRECT)
+            os.close(f)
+            LOG.debug(_("Path '%(path)s' supports direct I/O") %
+                      {'path': dirpath})
+        except OSError, e:
+            if e.errno == errno.EINVAL:
+                LOG.debug(_("Path '%(path)s' does not support direct I/O: "
+                            "'%(ex)s'") % {'path': dirpath, 'ex': str(e)})
+                hasDirectIO = False
+            else:
+                LOG.error(_("Error on '%(path)s' while checking direct I/O: "
+                            "'%(ex)s'") % {'path': dirpath, 'ex': str(e)})
+                raise e
+        except Exception, e:
+            LOG.error(_("Error on '%(path)s' while checking direct I/O: "
+                        "'%(ex)s'") % {'path': dirpath, 'ex': str(e)})
+            raise e
+        finally:
+            try:
+                os.unlink(testfile)
+            except:
+                pass
+
+        return hasDirectIO
+
+    @staticmethod
     def _cache_image(fn, target, fname, cow=False, size=None, *args, **kwargs):
         """Wrapper for a method that creates an image that caches the image.
 
@@ -1374,6 +1420,7 @@ class LibvirtConnection(driver.ComputeDriver):
         xml_info = {'type': FLAGS.libvirt_type,
                     'name': instance['name'],
                     'uuid': instance['uuid'],
+                    'cachemode': self.disk_cachemode,
                     'basepath': os.path.join(FLAGS.instances_path,
                                              instance['name']),
                     'memory_kb': inst_type['memory_mb'] * 1024,