VirtualDisk: Handle the blktap default

And cache the blktap lookup once for the localhost

virtManager/addhardware.py

@@ -27,7 +27,6 @@ from gi.repository import Gdk
 # pylint: enable=E0611
 
 import virtinst
-from virtinst import util
 from virtinst import (VirtualChannelDevice, VirtualParallelDevice,
                       VirtualSerialDevice, VirtualConsoleDevice,
                       VirtualVideoDevice, VirtualWatchdog,
@@ -1374,7 +1373,7 @@ class vmmAddHardware(vmmGObjectUI):
     def validate(self, page_num):
         ret = self._validate(page_num)
         if ret is not False and self._dev:
-            self._dev.set_defaults()
+            self._dev.set_defaults(self.vm.get_xmlobj())
             self._dev.validate()
         return ret
 
@@ -1413,7 +1412,8 @@ class vmmAddHardware(vmmGObjectUI):
             disk.bus = bus
             disk.set_create_storage(size=disksize, sparse=sparse,
                                     fmt=fmt or None)
-            disk.driver_cache = cache
+            if cache:
+                disk.driver_cache = cache
 
             if not fmt:
                 fmt = self.conn.get_default_storage_format()
@@ -1422,11 +1422,6 @@ class vmmAddHardware(vmmGObjectUI):
                     fmt in disk.get_vol_install().list_formats()):
                     logging.debug("Setting disk format from prefs: %s", fmt)
                     disk.get_vol_install().format = fmt
-
-            if (disk.type == virtinst.VirtualDisk.TYPE_FILE and
-                not self.vm.is_hvm() and
-                util.is_blktap_capable(self.conn.get_backend())):
-                disk.driver_name = virtinst.VirtualDisk.DRIVER_TAP
         except Exception, e:
             return self.err.val_err(_("Storage parameter error."), e)
 

virtinst/devicedisk.py

@@ -744,10 +744,16 @@ class VirtualDisk(VirtualDevice):
         if volobj:
             self._change_backend(None, volobj)
 
-    def set_defaults(self):
+    def set_defaults(self, guest):
         if self.is_cdrom():
             self.read_only = True
 
+        if (guest.os.is_xenpv() and
+            self.type == VirtualDisk.TYPE_FILE and
+            self.driver_name is None and
+            util.is_blktap_capable(self.conn)):
+            self.driver_name = VirtualDisk.DRIVER_TAP
+
         if not self.conn.is_qemu():
             return
         if not self.is_disk():

virtinst/guest.py

@@ -30,7 +30,6 @@ import virtinst
 from virtinst import util
 from virtinst import support
 from virtinst import OSXML
-from virtinst import VirtualDisk
 from virtinst import VirtualDevice
 from virtinst import Clock
 from virtinst import Seclabel
@@ -209,7 +208,6 @@ class Guest(XMLBuilder):
         Add the passed device to the guest's device list.
 
         @param dev: VirtualDevice instance to attach to guest
-        @param set_defaults: Whether to set defaults for the device
         """
         self._add_child(dev)
 
@@ -605,7 +603,7 @@ class Guest(XMLBuilder):
         self._set_feature_defaults()
 
         for dev in self.get_all_devices():
-            dev.set_defaults()
+            dev.set_defaults(self)
         self._add_implied_controllers()
         self._check_address_multi()
         self._set_disk_defaults()
@@ -790,13 +788,6 @@ class Guest(XMLBuilder):
             if not disk.bus:
                 set_disk_bus(disk)
 
-            # Default file backed PV guests to tap driver
-            if (self.os.is_xenpv() and
-                disk.type == VirtualDisk.TYPE_FILE and
-                disk.driver_name is None and
-                util.is_blktap_capable(self.conn)):
-                disk.driver_name = VirtualDisk.DRIVER_TAP
-
             # Generate disk targets
             if disk.target:
                 used_targets.append(disk.target)

virtinst/util.py

@@ -28,6 +28,9 @@ import libvirt
 import libxml2
 
 
+_host_blktap_capable = None
+
+
 def listify(l):
     if l is None:
         return []
@@ -348,13 +351,19 @@ def is_blktap_capable(conn):
     if conn.is_remote():
         return False
 
-    f = open("/proc/modules")
+    global _host_blktap_capable
-    lines = f.readlines()
+    if _host_blktap_capable is not None:
-    f.close()
+        return _host_blktap_capable
+
+    lines = file("/proc/modules").readlines()
     for line in lines:
         if line.startswith("blktap ") or line.startswith("xenblktap "):
-            return True
+            _host_blktap_capable = True
-    return False
+            break
+
+    if not _host_blktap_capable:
+        _host_blktap_capable = False
+    return _host_blktap_capable
 
 
 def randomUUID(conn):

virtinst/xmlbuilder.py

@@ -864,11 +864,11 @@ class XMLBuilder(object):
         """
         pass
 
-    def set_defaults(self):
+    def set_defaults(self, guest):
         """
         Encode any default values if needed
         """
-        pass
+        ignore = guest
 
 
     ###################