Modify hypervisor to support file backend

The driver in the xen config file needs to be changed when dealing with
files rather then bdevs.

This patch does two things:
- Add _GetConfigFileDiskData to XenHypervisor which returns the correct
  disk xen config line. This function checks the logical disk type of
  every given block device, such that also hybrid (e.g. mixed drbd and
  file VBDs) are possible
- Make Xen[Pvm|Hvm]Hypervisor._WriteConfigFile() a classmethod to be
  able to call the helper function _GetConfigFileDiskData() in their
  parent XenHypervisor

Reviewed-by: iustinp

lib/hypervisor.py

@@ -310,12 +310,45 @@ class XenHypervisor(BaseHypervisor):
     if not utils.CheckDaemonAlive('/var/run/xend.pid', 'xend'):
       return "xend daemon is not running"
 
+  @staticmethod
+  def _GetConfigFileDiskData(disk_template, block_devices):
+    """Get disk directive for xen config file.
+
+    This method builds the xen config disk directive according to the
+    given disk_template and block_devices.
+
+    Args:
+      disk_template: String containing instance disk template
+      block_devices: List[tuple1,tuple2,...]
+        tuple: (cfdev, rldev)
+          cfdev: dict containing ganeti config disk part
+          rldev: ganeti.bdev.BlockDev object
+
+    Returns:
+      String containing disk directive for xen instance config file
+
+    """
+    FILE_DRIVER_MAP = {
+      constants.FD_LOOP: "file",
+      constants.FD_BLKTAP: "tap:aio",
+      }
+    disk_data = []
+    for cfdev, rldev in block_devices:
+      if cfdev.dev_type == constants.LD_FILE:
+        line = "'%s:%s,%s,w'" % (FILE_DRIVER_MAP[cfdev.physical_id[0]],
+                                 rldev.dev_path, cfdev.iv_name)
+      else:
+        line = "'phy:%s,%s,w'" % (rldev.dev_path, cfdev.iv_name)
+      disk_data.append(line)
+
+    return disk_data
+
 
 class XenPvmHypervisor(XenHypervisor):
   """Xen PVM hypervisor interface"""
 
-  @staticmethod
-  def _WriteConfigFile(instance, block_devices, extra_args):
+  @classmethod
+  def _WriteConfigFile(cls, instance, block_devices, extra_args):
     """Write the Xen config file for the instance.
 
     """
@@ -365,11 +398,9 @@ class XenPvmHypervisor(XenHypervisor):
       vif_data.append("'%s'" % nic_str)
 
     config.write("vif = [%s]\n" % ",".join(vif_data))
-
-    disk_data = ["'phy:%s,%s,w'" % (rldev.dev_path, cfdev.iv_name)
-                 for cfdev, rldev in block_devices]
-    config.write("disk = [%s]\n" % ",".join(disk_data))
-
+    config.write("disk = [%s]\n" % ",".join(
+                 cls._GetConfigFileDiskData(instance.disk_template,
+                                            block_devices)))
     config.write("root = '/dev/sda ro'\n")
     config.write("on_poweroff = 'destroy'\n")
     config.write("on_reboot = 'restart'\n")
@@ -576,8 +607,8 @@ class FakeHypervisor(BaseHypervisor):
 class XenHvmHypervisor(XenHypervisor):
   """Xen HVM hypervisor interface"""
 
-  @staticmethod
-  def _WriteConfigFile(instance, block_devices, extra_args):
+  @classmethod
+  def _WriteConfigFile(cls, instance, block_devices, extra_args):
     """Create a Xen 3.1 HVM config file.
 
     """
@@ -638,13 +669,10 @@ class XenHvmHypervisor(XenHypervisor):
       vif_data.append("'%s'" % nic_str)
 
     config.write("vif = [%s]\n" % ",".join(vif_data))
-
-    disk_data = ["'phy:%s,%s,w'" %
-                 (rldev.dev_path, cfdev.iv_name.replace("sd", "ioemu:hd"))
-                 for cfdev, rldev in block_devices]
     iso = "'file:/srv/ganeti/iso/hvm-install.iso,hdc:cdrom,r'"
-    config.write("disk = [%s, %s]\n" % (",".join(disk_data), iso) )
-
+    config.write("disk = [%s, %s]\n" % (",".join(
+                 cls._GetConfigFileDiskData(instance.disk_template,
+                                            block_devices)), iso))
     config.write("on_poweroff = 'destroy'\n")
     config.write("on_reboot = 'restart'\n")
     config.write("on_crash = 'restart'\n")