virtinst: Add support for fs write policy

This introduces new attribute wrpolicy with only supported
value as immediate. This helps specify whether to skip the
host page cache.

When wrpolicy is specified, meaning when wrpolicy=immediate
a writeback is explicitly initiated for the dirty pages in
the host page cache as part of the guest file write operation.

Signed-off-by: Deepak C Shetty <deepakcs@linux.vnet.ibm.com>

Author: Deepak C Shetty

tests/xmlparse-xml/change-filesystems-in.xml

@@ -33,6 +33,11 @@
       <target dir='/bar/baz'/>
     </filesystem>
     <filesystem type='mount' accessmode='squash'>
+      <driver type='path' wrpolicy='immediate'/>
+      <source dir='/foo/bar'/>
+      <target dir='/bar/baz'/>
+    </filesystem>
+    <filesystem type='mount' accessmode='mapped'>
       <driver type='path'/>
       <source dir='/foo/bar'/>
       <target dir='/bar/baz'/>

tests/xmlparse-xml/change-filesystems-out.xml

@@ -37,5 +37,11 @@
       <target dir="/bar/baz"/>
       <readonly/>
     </filesystem>
+    <filesystem>
+      <driver type="handle" wrpolicy="immediate"/>
+      <source dir="/foo/bar"/>
+      <target dir="/bar/baz"/>
+      <readonly/>
+    </filesystem>
   </devices>
 </domain>

tests/xmlparse.py

@@ -577,11 +577,13 @@ def testAlterFilesystems(self):
         dev1 = guest.get_devices(devtype)[0]
         dev2 = guest.get_devices(devtype)[1]
         dev3 = guest.get_devices(devtype)[2]
+        dev4 = guest.get_devices(devtype)[3]
 
         check = self._make_checker(dev1)
         check("type", None, "mount")
         check("mode", None, "passthrough")
         check("driver", "handle", None)
+        check("wrpolicy", None, None)
         check("source", "/foo/bar", "/new/path")
         check("target", "/bar/baz", "/new/target")
 
@@ -595,6 +597,14 @@ def testAlterFilesystems(self):
         check("type", "mount", None)
         check("mode", "squash", None)
         check("driver", "path", "handle")
+        check("wrpolicy", "immediate", None)
+        check("readonly", False, True)
+
+        check = self._make_checker(dev4)
+        check("type", "mount", None)
+        check("mode", "mapped", None)
+        check("driver", "path", "handle")
+        check("wrpolicy", None, "immediate")
         check("readonly", False, True)
 
         self._alter_compare(guest.get_config_xml(), outfile)

virtinst/VirtualFilesystem.py

@@ -42,6 +42,10 @@ class VirtualFilesystem(VirtualDevice.VirtualDevice):
     MODE_DEFAULT = "default"
     MOUNT_MODES = [MODE_PASSTHROUGH, MODE_MAPPED, MODE_SQUASH, MODE_DEFAULT]
 
+    WRPOLICY_IMM = "immediate"
+    WRPOLICY_DEFAULT = "default"
+    WRPOLICIES = [WRPOLICY_IMM, WRPOLICY_DEFAULT]
+
     DRIVER_PATH = "path"
     DRIVER_HANDLE = "handle"
     DRIVER_DEFAULT = "default"
@@ -75,13 +79,15 @@ def __init__(self, conn, parsexml=None, parsexmlnode=None, caps=None):
         self._target = None
         self._source = None
         self._readonly = None
+        self._wrpolicy = None
 
         if self._is_parse():
             return
 
         self.mode = self.MODE_DEFAULT
         self.type = self.TYPE_DEFAULT
         self.driver = self.DRIVER_DEFAULT
+        self.wrpolicy = self.WRPOLICY_DEFAULT
 
     def _get_type(self):
         return self._type
@@ -99,6 +105,14 @@ def _set_mode(self, val):
         self._mode = val
     mode = _xml_property(_get_mode, _set_mode, xpath="./@accessmode")
 
+    def _get_wrpolicy(self):
+        return self._wrpolicy
+    def _set_wrpolicy(self, val):
+        if val is not None and not self.WRPOLICIES.count(val):
+            raise ValueError(_("Unsupported filesystem write policy '%s'" % val))
+        self._wrpolicy = val
+    wrpolicy = _xml_property(_get_wrpolicy, _set_wrpolicy, xpath="./driver/@wrpolicy")
+
     def _get_readonly(self):
         return self._readonly
     def _set_readonly(self, val):
@@ -162,13 +176,17 @@ def _get_xml_config(self):
         source = self.source
         target = self.target
         readonly = self.readonly
+        wrpolicy = self.wrpolicy
 
         if mode == self.MODE_DEFAULT:
             mode = None
         if ftype == self.TYPE_DEFAULT:
             ftype = None
         if driver == self.DRIVER_DEFAULT:
             driver = None
+            wrpolicy = None
+        if wrpolicy == self.WRPOLICY_DEFAULT:
+            wrpolicy = None
 
         if not source or not target:
             raise ValueError(
@@ -182,7 +200,12 @@ def _get_xml_config(self):
         fsxml += ">\n"
 
         if driver:
-            fsxml += "      <driver type='%s'/>\n" % driver
+            if not wrpolicy:
+                fsxml += "      <driver type='%s'/>\n" % driver
+            else:
+                fsxml += "      <driver type='%s' wrpolicy='%s' />\n" % (
+                                                                    driver,
+                                                                    wrpolicy)
 
         fsxml += "      <source %s='%s'/>\n" % (
                                             self.type_to_source_prop(ftype),