X-Git-Url: https://code.grnet.gr/git/ganeti-local/blobdiff_plain/2a52a064ad9411c5f5b45d69955a6a861a767d4b..29921401f2fb372efac3d5e022a4622b37c8e07e:/lib/backend.py

diff --git a/lib/backend.py b/lib/backend.py
index 10ddcf5..c8d5c85 100644
--- a/lib/backend.py
+++ b/lib/backend.py
@@ -68,10 +68,11 @@ def _Fail(msg, *args, **kwargs):
   """
   if args:
     msg = msg % args
-  if "exc" in kwargs and kwargs["exc"]:
-    logging.exception(msg)
-  else:
-    logging.error(msg)
+  if "log" not in kwargs or kwargs["log"]: # if we should log this error
+    if "exc" in kwargs and kwargs["exc"]:
+      logging.exception(msg)
+    else:
+      logging.error(msg)
   raise RPCFail(msg)
 
 
@@ -147,7 +148,8 @@ def _CleanDirectory(path, exclude=None):
 def JobQueuePurge():
   """Removes job queue files and archived jobs.
 
-  @rtype: None
+  @rtype: tuple
+  @return: True, None
 
   """
   _CleanDirectory(constants.QUEUE_DIR, exclude=[constants.JOB_QUEUE_LOCK_FILE])
@@ -161,7 +163,7 @@ def GetMasterInfo():
   for consumption here or from the node daemon.
 
   @rtype: tuple
-  @return: True, (master_netdev, master_ip, master_name) in case of success
+  @return: master_netdev, master_ip, master_name
   @raise RPCFail: in case of errors
 
   """
@@ -171,8 +173,8 @@ def GetMasterInfo():
     master_ip = cfg.GetMasterIP()
     master_node = cfg.GetMasterNode()
   except errors.ConfigurationError, err:
-    _Fail("Cluster configuration incomplete", exc=True)
-  return True, (master_netdev, master_ip, master_node)
+    _Fail("Cluster configuration incomplete: %s", err, exc=True)
+  return master_netdev, master_ip, master_node
 
 
 def StartMaster(start_daemons):
@@ -183,13 +185,13 @@ def StartMaster(start_daemons):
   based on the start_daemons parameter.
 
   @type start_daemons: boolean
-  @param start_daemons: whther to also start the master
+  @param start_daemons: whether to also start the master
       daemons (ganeti-masterd and ganeti-rapi)
   @rtype: None
 
   """
   # GetMasterInfo will raise an exception if not able to return data
-  master_netdev, master_ip, _ = GetMasterInfo()[1]
+  master_netdev, master_ip, _ = GetMasterInfo()
 
   payload = []
   if utils.TcpPing(master_ip, constants.DEFAULT_NODED_PORT):
@@ -222,7 +224,8 @@ def StartMaster(start_daemons):
         logging.error(msg)
         payload.append(msg)
 
-  return not payload, "; ".join(payload)
+  if payload:
+    _Fail("; ".join(payload))
 
 
 def StopMaster(stop_daemons):
@@ -242,7 +245,7 @@ def StopMaster(stop_daemons):
   # need to decide in which case we fail the RPC for this
 
   # GetMasterInfo will raise an exception if not able to return data
-  master_netdev, master_ip, _ = GetMasterInfo()[1]
+  master_netdev, master_ip, _ = GetMasterInfo()
 
   result = utils.RunCmd(["ip", "address", "del", "%s/32" % master_ip,
                          "dev", master_netdev])
@@ -255,8 +258,6 @@ def StopMaster(stop_daemons):
     for daemon in constants.RAPI_PID, constants.MASTERD_PID:
       utils.KillProcess(utils.ReadPidFile(utils.DaemonPidFileName(daemon)))
 
-  return True, None
-
 
 def AddNode(dsa, dsapub, rsa, rsapub, sshkey, sshpub):
   """Joins this node to the cluster.
@@ -302,8 +303,6 @@ def AddNode(dsa, dsapub, rsa, rsapub, sshkey, sshpub):
 
   utils.RunCmd([constants.SSH_INITD_SCRIPT, "restart"])
 
-  return (True, "Node added successfully")
-
 
 def LeaveCluster():
   """Cleans up and remove the current node.
@@ -370,7 +369,7 @@ def GetNodeInfo(vgname, hypervisor_type):
   finally:
     f.close()
 
-  return True, outputarray
+  return outputarray
 
 
 def VerifyNode(what, cluster_name):
@@ -472,7 +471,7 @@ def VerifyNode(what, cluster_name):
       used_minors = str(err)
     result[constants.NV_DRBDLIST] = used_minors
 
-  return True, result
+  return result
 
 
 def GetVolumeList(vg_name):
@@ -522,7 +521,7 @@ def ListVolumeGroups():
       size of the volume
 
   """
-  return True, utils.ListVolumeGroups()
+  return utils.ListVolumeGroups()
 
 
 def NodeVolumes():
@@ -565,9 +564,8 @@ def NodeVolumes():
       'vg': line[3].strip(),
     }
 
-  return True, [map_line(line.split('|'))
-                for line in result.stdout.splitlines()
-                if line.count('|') >= 3]
+  return [map_line(line.split('|')) for line in result.stdout.splitlines()
+          if line.count('|') >= 3]
 
 
 def BridgesExist(bridges_list):
@@ -583,9 +581,7 @@ def BridgesExist(bridges_list):
       missing.append(bridge)
 
   if missing:
-    return False, "Missing bridges %s" % (", ".join(missing),)
-
-  return True, None
+    _Fail("Missing bridges %s", ", ".join(missing))
 
 
 def GetInstanceList(hypervisor_list):
@@ -635,7 +631,7 @@ def GetInstanceInfo(instance, hname):
     output['state'] = iinfo[4]
     output['time'] = iinfo[5]
 
-  return True, output
+  return output
 
 
 def GetInstanceMigratable(instance):
@@ -651,15 +647,14 @@ def GetInstanceMigratable(instance):
 
   """
   hyper = hypervisor.GetHypervisor(instance.hypervisor)
-  if instance.name not in hyper.ListInstances():
-    return (False, 'not running')
+  iname = instance.name
+  if iname not in hyper.ListInstances():
+    _Fail("Instance %s is not running", iname)
 
   for idx in range(len(instance.disks)):
-    link_name = _GetBlockDevSymlinkPath(instance.name, idx)
+    link_name = _GetBlockDevSymlinkPath(iname, idx)
     if not os.path.islink(link_name):
-      return (False, 'not restarted since ganeti 1.2.5')
-
-  return (True, '')
+      _Fail("Instance %s was not restarted since ganeti 1.2.5", iname)
 
 
 def GetAllInstancesInfo(hypervisor_list):
@@ -685,7 +680,7 @@ def GetAllInstancesInfo(hypervisor_list):
   for hname in hypervisor_list:
     iinfo = hypervisor.GetHypervisor(hname).GetAllInstancesInfo()
     if iinfo:
-      for name, inst_id, memory, vcpus, state, times in iinfo:
+      for name, _, memory, vcpus, state, times in iinfo:
         value = {
           'memory': memory,
           'vcpus': vcpus,
@@ -702,7 +697,7 @@ def GetAllInstancesInfo(hypervisor_list):
                     " with different parameters", name)
         output[name] = value
 
-  return True, output
+  return output
 
 
 def InstanceOsAdd(instance, reinstall):
@@ -712,19 +707,10 @@ def InstanceOsAdd(instance, reinstall):
   @param instance: Instance whose OS is to be installed
   @type reinstall: boolean
   @param reinstall: whether this is an instance reinstall
-  @rtype: boolean
-  @return: the success of the operation
+  @rtype: None
 
   """
-  try:
-    inst_os = OSFromDisk(instance.os)
-  except errors.InvalidOS, err:
-    os_name, os_dir, os_err = err.args
-    if os_dir is None:
-      return (False, "Can't find OS '%s': %s" % (os_name, os_err))
-    else:
-      return (False, "Error parsing OS '%s' in directory %s: %s" %
-              (os_name, os_dir, os_err))
+  inst_os = OSFromDisk(instance.os)
 
   create_env = OSEnvironment(instance)
   if reinstall:
@@ -741,10 +727,8 @@ def InstanceOsAdd(instance, reinstall):
                   result.output)
     lines = [utils.SafeEncode(val)
              for val in utils.TailFile(logfile, lines=20)]
-    return (False, "OS create script failed (%s), last lines in the"
-            " log file:\n%s" % (result.fail_reason, "\n".join(lines)))
-
-  return (True, "Successfully installed")
+    _Fail("OS create script failed (%s), last lines in the"
+          " log file:\n%s", result.fail_reason, "\n".join(lines), log=False)
 
 
 def RunRenameInstance(instance, old_name):
@@ -775,10 +759,8 @@ def RunRenameInstance(instance, old_name):
                   result.cmd, result.fail_reason, result.output)
     lines = [utils.SafeEncode(val)
              for val in utils.TailFile(logfile, lines=20)]
-    return (False, "OS rename script failed (%s), last lines in the"
-            " log file:\n%s" % (result.fail_reason, "\n".join(lines)))
-
-  return (True, "Rename successful")
+    _Fail("OS rename script failed (%s), last lines in the"
+          " log file:\n%s", result.fail_reason, "\n".join(lines), log=False)
 
 
 def _GetVGInfo(vg_name):
@@ -814,7 +796,7 @@ def _GetVGInfo(vg_name):
         "pv_count": int(valarr[2]),
         }
     except ValueError, err:
-      logging.exception("Fail to parse vgs output")
+      logging.exception("Fail to parse vgs output: %s", err)
   else:
     logging.error("vgs output has the wrong number of fields (expected"
                   " three): %s", str(valarr))
@@ -858,7 +840,7 @@ def _RemoveBlockDevLinks(instance_name, disks):
   """Remove the block device symlinks belonging to the given instance.
 
   """
-  for idx, disk in enumerate(disks):
+  for idx, _ in enumerate(disks):
     link_name = _GetBlockDevSymlinkPath(instance_name, idx)
     if os.path.islink(link_name):
       try:
@@ -902,14 +884,14 @@ def StartInstance(instance):
 
   @type instance: L{objects.Instance}
   @param instance: the instance object
-  @rtype: boolean
-  @return: whether the startup was successful or not
+  @rtype: None
 
   """
   running_instances = GetInstanceList([instance.hypervisor])
 
   if instance.name in running_instances:
-    return (True, "Already running")
+    logging.info("Instance %s already running, not starting", instance.name)
+    return
 
   try:
     block_devices = _GatherAndLinkBlockDevs(instance)
@@ -921,8 +903,6 @@ def StartInstance(instance):
     _RemoveBlockDevLinks(instance.name, instance.disks)
     _Fail("Hypervisor error: %s", err, exc=True)
 
-  return (True, "Instance started successfully")
-
 
 def InstanceShutdown(instance):
   """Shut an instance down.
@@ -931,21 +911,22 @@ def InstanceShutdown(instance):
 
   @type instance: L{objects.Instance}
   @param instance: the instance object
-  @rtype: boolean
-  @return: whether the startup was successful or not
+  @rtype: None
 
   """
   hv_name = instance.hypervisor
   running_instances = GetInstanceList([hv_name])
+  iname = instance.name
 
-  if instance.name not in running_instances:
-    return (True, "Instance already stopped")
+  if iname not in running_instances:
+    logging.info("Instance %s not running, doing nothing", iname)
+    return
 
   hyper = hypervisor.GetHypervisor(hv_name)
   try:
     hyper.StopInstance(instance)
   except errors.HypervisorError, err:
-    _Fail("Failed to stop instance %s: %s", instance.name, err)
+    _Fail("Failed to stop instance %s: %s", iname, err)
 
   # test every 10secs for 2min
 
@@ -956,21 +937,18 @@ def InstanceShutdown(instance):
     time.sleep(10)
   else:
     # the shutdown did not succeed
-    logging.error("Shutdown of '%s' unsuccessful, using destroy",
-                  instance.name)
+    logging.error("Shutdown of '%s' unsuccessful, using destroy", iname)
 
     try:
       hyper.StopInstance(instance, force=True)
     except errors.HypervisorError, err:
-      _Fail("Failed to force stop instance %s: %s", instance.name, err)
+      _Fail("Failed to force stop instance %s: %s", iname, err)
 
     time.sleep(1)
     if instance.name in GetInstanceList([hv_name]):
-      _Fail("Could not shutdown instance %s even by destroy", instance.name)
+      _Fail("Could not shutdown instance %s even by destroy", iname)
 
-  _RemoveBlockDevLinks(instance.name, instance.disks)
-
-  return (True, "Instance has been shutdown successfully")
+  _RemoveBlockDevLinks(iname, instance.disks)
 
 
 def InstanceReboot(instance, reboot_type):
@@ -988,8 +966,7 @@ def InstanceReboot(instance, reboot_type):
       - the other reboot type (L{constants.INSTANCE_REBOOT_HARD})
         is not accepted here, since that mode is handled
         differently
-  @rtype: boolean
-  @return: the success of the operation
+  @rtype: None
 
   """
   running_instances = GetInstanceList([instance.hypervisor])
@@ -1005,17 +982,13 @@ def InstanceReboot(instance, reboot_type):
       _Fail("Failed to soft reboot instance %s: %s", instance.name, err)
   elif reboot_type == constants.INSTANCE_REBOOT_HARD:
     try:
-      stop_result = InstanceShutdown(instance)
-      if not stop_result[0]:
-        return stop_result
+      InstanceShutdown(instance)
       return StartInstance(instance)
     except errors.HypervisorError, err:
       _Fail("Failed to hard reboot instance %s: %s", instance.name, err)
   else:
     _Fail("Invalid reboot_type received: %s", reboot_type)
 
-  return (True, "Reboot successful")
-
 
 def MigrationInfo(instance):
   """Gather information about an instance to be migrated.
@@ -1029,7 +1002,7 @@ def MigrationInfo(instance):
     info = hyper.MigrationInfo(instance)
   except errors.HypervisorError, err:
     _Fail("Failed to fetch migration information: %s", err, exc=True)
-  return (True, info)
+  return info
 
 
 def AcceptInstance(instance, info, target):
@@ -1048,7 +1021,6 @@ def AcceptInstance(instance, info, target):
     hyper.AcceptInstance(instance, info, target)
   except errors.HypervisorError, err:
     _Fail("Failed to accept instance: %s", err, exc=True)
-  return (True, "Accept successfull")
 
 
 def FinalizeMigration(instance, info, success):
@@ -1067,7 +1039,6 @@ def FinalizeMigration(instance, info, success):
     hyper.FinalizeMigration(instance, info, success)
   except errors.HypervisorError, err:
     _Fail("Failed to finalize migration: %s", err, exc=True)
-  return (True, "Migration Finalized")
 
 
 def MigrateInstance(instance, target, live):
@@ -1092,7 +1063,6 @@ def MigrateInstance(instance, target, live):
     hyper.MigrateInstance(instance.name, target, live)
   except errors.HypervisorError, err:
     _Fail("Failed to migrate instance: %s", err, exc=True)
-  return (True, "Migration successfull")
 
 
 def BlockdevCreate(disk, size, owner, on_primary, info):
@@ -1133,7 +1103,7 @@ def BlockdevCreate(disk, size, owner, on_primary, info):
       clist.append(crdev)
 
   try:
-    device = bdev.Create(disk.dev_type, disk.physical_id, clist, size)
+    device = bdev.Create(disk.dev_type, disk.physical_id, clist, disk.size)
   except errors.BlockDeviceError, err:
     _Fail("Can't create block device: %s", err)
 
@@ -1153,8 +1123,7 @@ def BlockdevCreate(disk, size, owner, on_primary, info):
 
   device.SetInfo(info)
 
-  physical_id = device.unique_id
-  return True, physical_id
+  return device.unique_id
 
 
 def BlockdevRemove(disk):
@@ -1169,7 +1138,6 @@ def BlockdevRemove(disk):
 
   """
   msgs = []
-  result = True
   try:
     rdev = _RecursiveFindBD(disk)
   except errors.BlockDeviceError, err:
@@ -1182,18 +1150,18 @@ def BlockdevRemove(disk):
       rdev.Remove()
     except errors.BlockDeviceError, err:
       msgs.append(str(err))
-      result = False
-    if result:
+    if not msgs:
       DevCacheManager.RemoveCache(r_path)
 
   if disk.children:
     for child in disk.children:
-      c_status, c_msg = BlockdevRemove(child)
-      result = result and c_status
-      if c_msg: # not an empty message
-        msgs.append(c_msg)
+      try:
+        BlockdevRemove(child)
+      except RPCFail, err:
+        msgs.append(str(err))
 
-  return (result, "; ".join(msgs))
+  if msgs:
+    _Fail("; ".join(msgs))
 
 
 def _RecursiveAssembleBD(disk, owner, as_primary):
@@ -1237,7 +1205,7 @@ def _RecursiveAssembleBD(disk, owner, as_primary):
       children.append(cdev)
 
   if as_primary or disk.AssembleOnSecondary():
-    r_dev = bdev.Assemble(disk.dev_type, disk.physical_id, children)
+    r_dev = bdev.Assemble(disk.dev_type, disk.physical_id, children, disk.size)
     r_dev.SetSyncSpeed(constants.SYNC_SPEED)
     result = r_dev
     if as_primary or disk.OpenOnSecondary():
@@ -1260,16 +1228,14 @@ def BlockdevAssemble(disk, owner, as_primary):
       C{True} for secondary nodes
 
   """
-  status = True
-  result = "no error information"
   try:
     result = _RecursiveAssembleBD(disk, owner, as_primary)
     if isinstance(result, bdev.BlockDev):
       result = result.dev_path
   except errors.BlockDeviceError, err:
-    result = "Error while assembling disk: %s" % str(err)
-    status = False
-  return (status, result)
+    _Fail("Error while assembling disk: %s", err, exc=True)
+
+  return result
 
 
 def BlockdevShutdown(disk):
@@ -1286,12 +1252,10 @@ def BlockdevShutdown(disk):
   @type disk: L{objects.Disk}
   @param disk: the description of the disk we should
       shutdown
-  @rtype: boolean
-  @return: the success of the operation
+  @rtype: None
 
   """
   msgs = []
-  result = True
   r_dev = _RecursiveFindBD(disk)
   if r_dev is not None:
     r_path = r_dev.dev_path
@@ -1300,16 +1264,16 @@ def BlockdevShutdown(disk):
       DevCacheManager.RemoveCache(r_path)
     except errors.BlockDeviceError, err:
       msgs.append(str(err))
-      result = False
 
   if disk.children:
     for child in disk.children:
-      c_status, c_msg = BlockdevShutdown(child)
-      result = result and c_status
-      if c_msg: # not an empty message
-        msgs.append(c_msg)
+      try:
+        BlockdevShutdown(child)
+      except RPCFail, err:
+        msgs.append(str(err))
 
-  return (result, "; ".join(msgs))
+  if msgs:
+    _Fail("; ".join(msgs))
 
 
 def BlockdevAddchildren(parent_cdev, new_cdevs):
@@ -1319,8 +1283,7 @@ def BlockdevAddchildren(parent_cdev, new_cdevs):
   @param parent_cdev: the disk to which we should add children
   @type new_cdevs: list of L{objects.Disk}
   @param new_cdevs: the list of children which we should add
-  @rtype: boolean
-  @return: the success of the operation
+  @rtype: None
 
   """
   parent_bdev = _RecursiveFindBD(parent_cdev)
@@ -1330,7 +1293,6 @@ def BlockdevAddchildren(parent_cdev, new_cdevs):
   if new_bdevs.count(None) > 0:
     _Fail("Can't find new device(s) to add: %s:%s", new_bdevs, new_cdevs)
   parent_bdev.AddChildren(new_bdevs)
-  return (True, None)
 
 
 def BlockdevRemovechildren(parent_cdev, new_cdevs):
@@ -1340,8 +1302,7 @@ def BlockdevRemovechildren(parent_cdev, new_cdevs):
   @param parent_cdev: the disk from which we should remove children
   @type new_cdevs: list of L{objects.Disk}
   @param new_cdevs: the list of children which we should remove
-  @rtype: boolean
-  @return: the success of the operation
+  @rtype: None
 
   """
   parent_bdev = _RecursiveFindBD(parent_cdev)
@@ -1359,7 +1320,6 @@ def BlockdevRemovechildren(parent_cdev, new_cdevs):
     else:
       devs.append(rpath)
   parent_bdev.RemoveChildren(devs)
-  return (True, None)
 
 
 def BlockdevGetmirrorstatus(disks):
@@ -1381,7 +1341,7 @@ def BlockdevGetmirrorstatus(disks):
     if rbd is None:
       _Fail("Can't find device %s", dsk)
     stats.append(rbd.CombinedSyncStatus())
-  return True, stats
+  return stats
 
 
 def _RecursiveFindBD(disk):
@@ -1401,7 +1361,7 @@ def _RecursiveFindBD(disk):
     for chdisk in disk.children:
       children.append(_RecursiveFindBD(chdisk))
 
-  return bdev.FindDevice(disk.dev_type, disk.physical_id, children)
+  return bdev.FindDevice(disk.dev_type, disk.physical_id, children, disk.size)
 
 
 def BlockdevFind(disk):
@@ -1422,8 +1382,8 @@ def BlockdevFind(disk):
   except errors.BlockDeviceError, err:
     _Fail("Failed to find device: %s", err, exc=True)
   if rbd is None:
-    return (True, None)
-  return (True, (rbd.dev_path, rbd.major, rbd.minor) + rbd.GetSyncStatus())
+    return None
+  return (rbd.dev_path, rbd.major, rbd.minor) + rbd.GetSyncStatus()
 
 
 def UploadFile(file_name, data, mode, uid, gid, atime, mtime):
@@ -1446,9 +1406,7 @@ def UploadFile(file_name, data, mode, uid, gid, atime, mtime):
   @param atime: the atime to set on the file (can be None)
   @type mtime: float
   @param mtime: the mtime to set on the file (can be None)
-  @rtype: boolean
-  @return: the success of the operation; errors are logged
-      in the node daemon log
+  @rtype: None
 
   """
   if not os.path.isabs(file_name):
@@ -1475,7 +1433,6 @@ def UploadFile(file_name, data, mode, uid, gid, atime, mtime):
 
   utils.WriteFile(file_name, data=raw_data, mode=mode, uid=uid, gid=gid,
                   atime=atime, mtime=mtime)
-  return (True, "success")
 
 
 def WriteSsconfFiles(values):
@@ -1515,11 +1472,9 @@ def _OSOndiskVersion(name, os_dir):
   @param name: the OS name we should look for
   @type os_dir: str
   @param os_dir: the directory inwhich we should look for the OS
-  @rtype: int or None
-  @return:
-      Either an integer denoting the version or None in the
-      case when this is not a valid OS name.
-  @raise errors.InvalidOS: if the OS cannot be found
+  @rtype: tuple
+  @return: tuple (status, data) with status denoting the validity and
+      data holding either the vaid versions or an error message
 
   """
   api_file = os.path.sep.join([os_dir, "ganeti_api_version"])
@@ -1527,12 +1482,12 @@ def _OSOndiskVersion(name, os_dir):
   try:
     st = os.stat(api_file)
   except EnvironmentError, err:
-    raise errors.InvalidOS(name, os_dir, "'ganeti_api_version' file not"
-                           " found (%s)" % _ErrnoOrStr(err))
+    return False, ("Required file 'ganeti_api_version' file not"
+                   " found under path %s: %s" % (os_dir, _ErrnoOrStr(err)))
 
   if not stat.S_ISREG(stat.S_IFMT(st.st_mode)):
-    raise errors.InvalidOS(name, os_dir, "'ganeti_api_version' file is not"
-                           " a regular file")
+    return False, ("File 'ganeti_api_version' file at %s is not"
+                   " a regular file" % os_dir)
 
   try:
     f = open(api_file)
@@ -1541,17 +1496,17 @@ def _OSOndiskVersion(name, os_dir):
     finally:
       f.close()
   except EnvironmentError, err:
-    raise errors.InvalidOS(name, os_dir, "error while reading the"
-                           " API version (%s)" % _ErrnoOrStr(err))
+    return False, ("Error while reading the API version file at %s: %s" %
+                   (api_file, _ErrnoOrStr(err)))
 
   api_versions = [version.strip() for version in api_versions]
   try:
     api_versions = [int(version) for version in api_versions]
   except (TypeError, ValueError), err:
-    raise errors.InvalidOS(name, os_dir,
-                           "API version is not integer (%s)" % str(err))
+    return False, ("API version(s) can't be converted to integer: %s" %
+                   str(err))
 
-  return api_versions
+  return True, api_versions
 
 
 def DiagnoseOS(top_dirs=None):
@@ -1562,8 +1517,12 @@ def DiagnoseOS(top_dirs=None):
       search (if not given defaults to
       L{constants.OS_SEARCH_PATH})
   @rtype: list of L{objects.OS}
-  @return: an OS object for each name in all the given
-      directories
+  @return: a list of tuples (name, path, status, diagnose)
+      for all (potential) OSes under all search paths, where:
+          - name is the (potential) OS name
+          - path is the full path to the OS
+          - status True/False is the validity of the OS
+          - diagnose is the error message for an invalid OS, otherwise empty
 
   """
   if top_dirs is None:
@@ -1575,46 +1534,49 @@ def DiagnoseOS(top_dirs=None):
       try:
         f_names = utils.ListVisibleFiles(dir_name)
       except EnvironmentError, err:
-        logging.exception("Can't list the OS directory %s", dir_name)
+        logging.exception("Can't list the OS directory %s: %s", dir_name, err)
         break
       for name in f_names:
-        try:
-          os_inst = OSFromDisk(name, base_dir=dir_name)
-          result.append(os_inst)
-        except errors.InvalidOS, err:
-          result.append(objects.OS.FromInvalidOS(err))
+        os_path = os.path.sep.join([dir_name, name])
+        status, os_inst = _TryOSFromDisk(name, base_dir=dir_name)
+        if status:
+          diagnose = ""
+        else:
+          diagnose = os_inst
+        result.append((name, os_path, status, diagnose))
 
   return result
 
 
-def OSFromDisk(name, base_dir=None):
+def _TryOSFromDisk(name, base_dir=None):
   """Create an OS instance from disk.
 
   This function will return an OS instance if the given name is a
-  valid OS name. Otherwise, it will raise an appropriate
-  L{errors.InvalidOS} exception, detailing why this is not a valid OS.
+  valid OS name.
 
   @type base_dir: string
   @keyword base_dir: Base directory containing OS installations.
                      Defaults to a search in all the OS_SEARCH_PATH dirs.
-  @rtype: L{objects.OS}
-  @return: the OS instance if we find a valid one
-  @raise errors.InvalidOS: if we don't find a valid OS
+  @rtype: tuple
+  @return: success and either the OS instance if we find a valid one,
+      or error message
 
   """
   if base_dir is None:
     os_dir = utils.FindFile(name, constants.OS_SEARCH_PATH, os.path.isdir)
     if os_dir is None:
-      raise errors.InvalidOS(name, None, "OS dir not found in search path")
+      return False, "Directory for OS %s not found in search path" % name
   else:
     os_dir = os.path.sep.join([base_dir, name])
 
-  api_versions = _OSOndiskVersion(name, os_dir)
+  status, api_versions = _OSOndiskVersion(name, os_dir)
+  if not status:
+    # push the error up
+    return status, api_versions
 
   if constants.OS_API_VERSION not in api_versions:
-    raise errors.InvalidOS(name, os_dir, "API version mismatch"
-                           " (found %s want %s)"
-                           % (api_versions, constants.OS_API_VERSION))
+    return False, ("API version mismatch for path '%s': found %s, want %s." %
+                   (os_dir, api_versions, constants.OS_API_VERSION))
 
   # OS Scripts dictionary, we will populate it with the actual script names
   os_scripts = dict.fromkeys(constants.OS_SCRIPTS)
@@ -1625,24 +1587,51 @@ def OSFromDisk(name, base_dir=None):
     try:
       st = os.stat(os_scripts[script])
     except EnvironmentError, err:
-      raise errors.InvalidOS(name, os_dir, "'%s' script missing (%s)" %
-                             (script, _ErrnoOrStr(err)))
+      return False, ("Script '%s' under path '%s' is missing (%s)" %
+                     (script, os_dir, _ErrnoOrStr(err)))
 
     if stat.S_IMODE(st.st_mode) & stat.S_IXUSR != stat.S_IXUSR:
-      raise errors.InvalidOS(name, os_dir, "'%s' script not executable" %
-                             script)
+      return False, ("Script '%s' under path '%s' is not executable" %
+                     (script, os_dir))
 
     if not stat.S_ISREG(stat.S_IFMT(st.st_mode)):
-      raise errors.InvalidOS(name, os_dir, "'%s' is not a regular file" %
-                             script)
+      return False, ("Script '%s' under path '%s' is not a regular file" %
+                     (script, os_dir))
+
+  os_obj = objects.OS(name=name, path=os_dir,
+                      create_script=os_scripts[constants.OS_SCRIPT_CREATE],
+                      export_script=os_scripts[constants.OS_SCRIPT_EXPORT],
+                      import_script=os_scripts[constants.OS_SCRIPT_IMPORT],
+                      rename_script=os_scripts[constants.OS_SCRIPT_RENAME],
+                      api_versions=api_versions)
+  return True, os_obj
+
+
+def OSFromDisk(name, base_dir=None):
+  """Create an OS instance from disk.
+
+  This function will return an OS instance if the given name is a
+  valid OS name. Otherwise, it will raise an appropriate
+  L{RPCFail} exception, detailing why this is not a valid OS.
+
+  This is just a wrapper over L{_TryOSFromDisk}, which doesn't raise
+  an exception but returns true/false status data.
+
+  @type base_dir: string
+  @keyword base_dir: Base directory containing OS installations.
+                     Defaults to a search in all the OS_SEARCH_PATH dirs.
+  @rtype: L{objects.OS}
+  @return: the OS instance if we find a valid one
+  @raise RPCFail: if we don't find a valid OS
+
+  """
+  status, payload = _TryOSFromDisk(name, base_dir)
+
+  if not status:
+    _Fail(payload)
 
+  return payload
 
-  return objects.OS(name=name, path=os_dir, status=constants.OS_VALID_STATUS,
-                    create_script=os_scripts[constants.OS_SCRIPT_CREATE],
-                    export_script=os_scripts[constants.OS_SCRIPT_EXPORT],
-                    import_script=os_scripts[constants.OS_SCRIPT_IMPORT],
-                    rename_script=os_scripts[constants.OS_SCRIPT_RENAME],
-                    api_versions=api_versions)
 
 def OSEnvironment(instance, debug=0):
   """Calculate the environment for an os script.
@@ -1694,6 +1683,10 @@ def OSEnvironment(instance, debug=0):
       result['NIC_%d_FRONTEND_TYPE' % idx] = \
         instance.hvparams[constants.HV_NIC_TYPE]
 
+  for source, kind in [(instance.beparams, "BE"), (instance.hvparams, "HV")]:
+    for key, value in source.items():
+      result["INSTANCE_%s_%s" % (kind, key)] = str(value)
+
   return result
 
 def BlockdevGrow(disk, amount):
@@ -1712,15 +1705,13 @@ def BlockdevGrow(disk, amount):
   """
   r_dev = _RecursiveFindBD(disk)
   if r_dev is None:
-    return False, "Cannot find block device %s" % (disk,)
+    _Fail("Cannot find block device %s", disk)
 
   try:
     r_dev.Grow(amount)
   except errors.BlockDeviceError, err:
     _Fail("Failed to grow block device: %s", err, exc=True)
 
-  return True, None
-
 
 def BlockdevSnapshot(disk):
   """Create a snapshot copy of a block device.
@@ -1748,7 +1739,7 @@ def BlockdevSnapshot(disk):
     r_dev = _RecursiveFindBD(disk)
     if r_dev is not None:
       # let's stay on the safe side and ask for the full size, for now
-      return True, r_dev.Snapshot(disk.size)
+      return r_dev.Snapshot(disk.size)
     else:
       _Fail("Cannot find block device %s", disk)
   else:
@@ -1770,8 +1761,7 @@ def ExportSnapshot(disk, dest_node, instance, cluster_name, idx):
   @type idx: int
   @param idx: the index of the disk in the instance's disk list,
       used to export to the OS scripts environment
-  @rtype: boolean
-  @return: the success of the operation
+  @rtype: None
 
   """
   export_env = OSEnvironment(instance)
@@ -1818,8 +1808,6 @@ def ExportSnapshot(disk, dest_node, instance, cluster_name, idx):
     _Fail("OS snapshot export command '%s' returned error: %s"
           " output: %s", command, result.fail_reason, result.output)
 
-  return (True, None)
-
 
 def FinalizeExport(instance, snap_disks):
   """Write out the export configuration information.
@@ -1831,8 +1819,7 @@ def FinalizeExport(instance, snap_disks):
   @param snap_disks: list of snapshot block devices, which
       will be used to get the actual name of the dump file
 
-  @rtype: boolean
-  @return: the success of the operation
+  @rtype: None
 
   """
   destdir = os.path.join(constants.EXPORT_DIR, instance.name + ".new")
@@ -1884,8 +1871,6 @@ def FinalizeExport(instance, snap_disks):
   shutil.rmtree(finaldestdir, True)
   shutil.move(destdir, finaldestdir)
 
-  return True, None
-
 
 def ExportInfo(dest):
   """Get export configuration information.
@@ -1907,7 +1892,7 @@ def ExportInfo(dest):
       not config.has_section(constants.INISECT_INS)):
     _Fail("Export info file doesn't have the required fields")
 
-  return True, config.Dumps()
+  return config.Dumps()
 
 
 def ImportOSIntoInstance(instance, src_node, src_images, cluster_name):
@@ -1955,8 +1940,7 @@ def ImportOSIntoInstance(instance, src_node, src_images, cluster_name):
                             (idx, result.fail_reason, result.output[-100]))
 
   if final_result:
-    return False, "; ".join(final_result)
-  return True, None
+    _Fail("; ".join(final_result), log=False)
 
 
 def ListExports():
@@ -1967,9 +1951,9 @@ def ListExports():
 
   """
   if os.path.isdir(constants.EXPORT_DIR):
-    return True, utils.ListVisibleFiles(constants.EXPORT_DIR)
+    return utils.ListVisibleFiles(constants.EXPORT_DIR)
   else:
-    return False, "No exports directory"
+    _Fail("No exports directory")
 
 
 def RemoveExport(export):
@@ -1977,8 +1961,7 @@ def RemoveExport(export):
 
   @type export: str
   @param export: the name of the export to remove
-  @rtype: boolean
-  @return: the success of the operation
+  @rtype: None
 
   """
   target = os.path.join(constants.EXPORT_DIR, export)
@@ -1988,8 +1971,6 @@ def RemoveExport(export):
   except EnvironmentError, err:
     _Fail("Error while removing the export: %s", err, exc=True)
 
-  return True, None
-
 
 def BlockdevRename(devlist):
   """Rename a list of block devices.
@@ -2028,7 +2009,8 @@ def BlockdevRename(devlist):
                   (dev, unique_id, err))
       logging.exception("Can't rename device '%s' to '%s'", dev, unique_id)
       result = False
-  return (result, "; ".join(msgs))
+  if not result:
+    _Fail("; ".join(msgs))
 
 
 def _TransformFileStorageDir(file_storage_dir):
@@ -2049,10 +2031,8 @@ def _TransformFileStorageDir(file_storage_dir):
   base_file_storage_dir = cfg.GetFileStorageDir()
   if (not os.path.commonprefix([file_storage_dir, base_file_storage_dir]) ==
       base_file_storage_dir):
-    logging.error("file storage directory '%s' is not under base file"
-                  " storage directory '%s'",
-                  file_storage_dir, base_file_storage_dir)
-    return None
+    _Fail("File storage directory '%s' is not under base file"
+          " storage directory '%s'", file_storage_dir, base_file_storage_dir)
   return file_storage_dir
 
 
@@ -2068,22 +2048,16 @@ def CreateFileStorageDir(file_storage_dir):
 
   """
   file_storage_dir = _TransformFileStorageDir(file_storage_dir)
-  result = True,
-  if not file_storage_dir:
-    result = False,
+  if os.path.exists(file_storage_dir):
+    if not os.path.isdir(file_storage_dir):
+      _Fail("Specified storage dir '%s' is not a directory",
+            file_storage_dir)
   else:
-    if os.path.exists(file_storage_dir):
-      if not os.path.isdir(file_storage_dir):
-        logging.error("'%s' is not a directory", file_storage_dir)
-        result = False,
-    else:
-      try:
-        os.makedirs(file_storage_dir, 0750)
-      except OSError, err:
-        logging.error("Cannot create file storage directory '%s': %s",
-                      file_storage_dir, err)
-        result = False,
-  return result
+    try:
+      os.makedirs(file_storage_dir, 0750)
+    except OSError, err:
+      _Fail("Cannot create file storage directory '%s': %s",
+            file_storage_dir, err, exc=True)
 
 
 def RemoveFileStorageDir(file_storage_dir):
@@ -2099,22 +2073,16 @@ def RemoveFileStorageDir(file_storage_dir):
 
   """
   file_storage_dir = _TransformFileStorageDir(file_storage_dir)
-  result = True,
-  if not file_storage_dir:
-    result = False,
-  else:
-    if os.path.exists(file_storage_dir):
-      if not os.path.isdir(file_storage_dir):
-        logging.error("'%s' is not a directory", file_storage_dir)
-        result = False,
-      # deletes dir only if empty, otherwise we want to return False
-      try:
-        os.rmdir(file_storage_dir)
-      except OSError, err:
-        logging.exception("Cannot remove file storage directory '%s'",
-                          file_storage_dir)
-        result = False,
-  return result
+  if os.path.exists(file_storage_dir):
+    if not os.path.isdir(file_storage_dir):
+      _Fail("Specified Storage directory '%s' is not a directory",
+            file_storage_dir)
+    # deletes dir only if empty, otherwise we want to fail the rpc call
+    try:
+      os.rmdir(file_storage_dir)
+    except OSError, err:
+      _Fail("Cannot remove file storage directory '%s': %s",
+            file_storage_dir, err)
 
 
 def RenameFileStorageDir(old_file_storage_dir, new_file_storage_dir):
@@ -2131,46 +2099,37 @@ def RenameFileStorageDir(old_file_storage_dir, new_file_storage_dir):
   """
   old_file_storage_dir = _TransformFileStorageDir(old_file_storage_dir)
   new_file_storage_dir = _TransformFileStorageDir(new_file_storage_dir)
-  result = True,
-  if not old_file_storage_dir or not new_file_storage_dir:
-    result = False,
-  else:
-    if not os.path.exists(new_file_storage_dir):
-      if os.path.isdir(old_file_storage_dir):
-        try:
-          os.rename(old_file_storage_dir, new_file_storage_dir)
-        except OSError, err:
-          logging.exception("Cannot rename '%s' to '%s'",
-                            old_file_storage_dir, new_file_storage_dir)
-          result =  False,
-      else:
-        logging.error("'%s' is not a directory", old_file_storage_dir)
-        result = False,
+  if not os.path.exists(new_file_storage_dir):
+    if os.path.isdir(old_file_storage_dir):
+      try:
+        os.rename(old_file_storage_dir, new_file_storage_dir)
+      except OSError, err:
+        _Fail("Cannot rename '%s' to '%s': %s",
+              old_file_storage_dir, new_file_storage_dir, err)
     else:
-      if os.path.exists(old_file_storage_dir):
-        logging.error("Cannot rename '%s' to '%s'. Both locations exist.",
-                      old_file_storage_dir, new_file_storage_dir)
-        result = False,
-  return result
+      _Fail("Specified storage dir '%s' is not a directory",
+            old_file_storage_dir)
+  else:
+    if os.path.exists(old_file_storage_dir):
+      _Fail("Cannot rename '%s' to '%s': both locations exist",
+            old_file_storage_dir, new_file_storage_dir)
 
 
-def _IsJobQueueFile(file_name):
+def _EnsureJobQueueFile(file_name):
   """Checks whether the given filename is in the queue directory.
 
   @type file_name: str
   @param file_name: the file name we should check
-  @rtype: boolean
-  @return: whether the file is under the queue directory
+  @rtype: None
+  @raises RPCFail: if the file is not valid
 
   """
   queue_dir = os.path.normpath(constants.QUEUE_DIR)
   result = (os.path.commonprefix([queue_dir, file_name]) == queue_dir)
 
   if not result:
-    logging.error("'%s' is not a file in the queue directory",
-                  file_name)
-
-  return result
+    _Fail("Passed job queue file '%s' does not belong to"
+          " the queue directory '%s'", file_name, queue_dir)
 
 
 def JobQueueUpdate(file_name, content):
@@ -2187,14 +2146,11 @@ def JobQueueUpdate(file_name, content):
   @return: the success of the operation
 
   """
-  if not _IsJobQueueFile(file_name):
-    return False
+  _EnsureJobQueueFile(file_name)
 
   # Write and replace the file atomically
   utils.WriteFile(file_name, data=_Decompress(content))
 
-  return True
-
 
 def JobQueueRename(old, new):
   """Renames a job queue file.
@@ -2205,17 +2161,15 @@ def JobQueueRename(old, new):
   @param old: the old (actual) file name
   @type new: str
   @param new: the desired file name
-  @rtype: boolean
-  @return: the success of the operation
+  @rtype: tuple
+  @return: the success of the operation and payload
 
   """
-  if not (_IsJobQueueFile(old) and _IsJobQueueFile(new)):
-    return False
+  _EnsureJobQueueFile(old)
+  _EnsureJobQueueFile(new)
 
   utils.RenameFile(old, new, mkdir=True)
 
-  return True
-
 
 def JobQueueSetDrainFlag(drain_flag):
   """Set the drain flag for the queue.
@@ -2224,8 +2178,8 @@ def JobQueueSetDrainFlag(drain_flag):
 
   @type drain_flag: boolean
   @param drain_flag: if True, will set the drain flag, otherwise reset it.
-  @rtype: boolean
-  @return: always True
+  @rtype: truple
+  @return: always True, None
   @warning: the function always returns True
 
   """
@@ -2234,8 +2188,6 @@ def JobQueueSetDrainFlag(drain_flag):
   else:
     utils.RemoveFile(constants.JOB_QUEUE_DRAIN_FILE)
 
-  return True
-
 
 def BlockdevClose(instance_name, disks):
   """Closes the given block devices.
@@ -2268,11 +2220,10 @@ def BlockdevClose(instance_name, disks):
     except errors.BlockDeviceError, err:
       msg.append(str(err))
   if msg:
-    return (False, "Can't make devices secondary: %s" % ",".join(msg))
+    _Fail("Can't make devices secondary: %s", ",".join(msg))
   else:
     if instance_name:
       _RemoveBlockDevLinks(instance_name, disks)
-    return (True, "All devices secondary")
 
 
 def ValidateHVParams(hvname, hvparams):
@@ -2282,19 +2233,14 @@ def ValidateHVParams(hvname, hvparams):
   @param hvname: the hypervisor name
   @type hvparams: dict
   @param hvparams: the hypervisor parameters to be validated
-  @rtype: tuple (success, message)
-  @return: a tuple of success and message, where success
-      indicates the succes of the operation, and message
-      which will contain the error details in case we
-      failed
+  @rtype: None
 
   """
   try:
     hv_type = hypervisor.GetHypervisor(hvname)
     hv_type.ValidateParameters(hvparams)
-    return (True, "Validation passed")
   except errors.HypervisorError, err:
-    return (False, str(err))
+    _Fail(str(err), log=False)
 
 
 def DemoteFromMC():
@@ -2304,17 +2250,16 @@ def DemoteFromMC():
   # try to ensure we're not the master by mistake
   master, myself = ssconf.GetMasterAndMyself()
   if master == myself:
-    return (False, "ssconf status shows I'm the master node, will not demote")
+    _Fail("ssconf status shows I'm the master node, will not demote")
   pid_file = utils.DaemonPidFileName(constants.MASTERD_PID)
   if utils.IsProcessAlive(utils.ReadPidFile(pid_file)):
-    return (False, "The master daemon is running, will not demote")
+    _Fail("The master daemon is running, will not demote")
   try:
     utils.CreateBackup(constants.CLUSTER_CONF_FILE)
   except EnvironmentError, err:
     if err.errno != errno.ENOENT:
-      return (False, "Error while backing up cluster file: %s" % str(err))
+      _Fail("Error while backing up cluster file: %s", err, exc=True)
   utils.RemoveFile(constants.CLUSTER_CONF_FILE)
-  return (True, "Done")
 
 
 def _FindDisks(nodes_ip, disks):
@@ -2331,18 +2276,16 @@ def _FindDisks(nodes_ip, disks):
   for cf in disks:
     rd = _RecursiveFindBD(cf)
     if rd is None:
-      return (False, "Can't find device %s" % cf)
+      _Fail("Can't find device %s", cf)
     bdevs.append(rd)
-  return (True, bdevs)
+  return bdevs
 
 
 def DrbdDisconnectNet(nodes_ip, disks):
   """Disconnects the network on a list of drbd devices.
 
   """
-  status, bdevs = _FindDisks(nodes_ip, disks)
-  if not status:
-    return status, bdevs
+  bdevs = _FindDisks(nodes_ip, disks)
 
   # disconnect disks
   for rd in bdevs:
@@ -2351,16 +2294,13 @@ def DrbdDisconnectNet(nodes_ip, disks):
     except errors.BlockDeviceError, err:
       _Fail("Can't change network configuration to standalone mode: %s",
             err, exc=True)
-  return (True, "All disks are now disconnected")
 
 
 def DrbdAttachNet(nodes_ip, disks, instance_name, multimaster):
   """Attaches the network on a list of drbd devices.
 
   """
-  status, bdevs = _FindDisks(nodes_ip, disks)
-  if not status:
-    return status, bdevs
+  bdevs = _FindDisks(nodes_ip, disks)
 
   if multimaster:
     for idx, rd in enumerate(bdevs):
@@ -2394,7 +2334,7 @@ def DrbdAttachNet(nodes_ip, disks, instance_name, multimaster):
         # standalone, even though this should not happen with the
         # new staged way of changing disk configs
         try:
-          rd.ReAttachNet(multimaster)
+          rd.AttachNet(multimaster)
         except errors.BlockDeviceError, err:
           _Fail("Can't change network configuration: %s", err)
     if all_connected:
@@ -2402,7 +2342,7 @@ def DrbdAttachNet(nodes_ip, disks, instance_name, multimaster):
     time.sleep(sleep_time)
     sleep_time = min(5, sleep_time * 1.5)
   if not all_connected:
-    return (False, "Timeout in disk reconnecting")
+    _Fail("Timeout in disk reconnecting")
   if multimaster:
     # change to primary mode
     for rd in bdevs:
@@ -2410,33 +2350,25 @@ def DrbdAttachNet(nodes_ip, disks, instance_name, multimaster):
         rd.Open()
       except errors.BlockDeviceError, err:
         _Fail("Can't change to primary mode: %s", err)
-  if multimaster:
-    msg = "multi-master and primary"
-  else:
-    msg = "single-master"
-  return (True, "Disks are now configured as %s" % msg)
 
 
 def DrbdWaitSync(nodes_ip, disks):
   """Wait until DRBDs have synchronized.
 
   """
-  status, bdevs = _FindDisks(nodes_ip, disks)
-  if not status:
-    return status, bdevs
+  bdevs = _FindDisks(nodes_ip, disks)
 
   min_resync = 100
   alldone = True
-  failure = False
   for rd in bdevs:
     stats = rd.GetProcStatus()
     if not (stats.is_connected or stats.is_in_resync):
-      failure = True
-      break
+      _Fail("DRBD device %s is not in sync: stats=%s", rd, stats)
     alldone = alldone and (not stats.is_in_resync)
     if stats.sync_percent is not None:
       min_resync = min(min_resync, stats.sync_percent)
-  return (not failure, (alldone, min_resync))
+
+  return (alldone, min_resync)
 
 
 def PowercycleNode(hypervisor_type):
@@ -2449,11 +2381,11 @@ def PowercycleNode(hypervisor_type):
   hyper = hypervisor.GetHypervisor(hypervisor_type)
   try:
     pid = os.fork()
-  except OSError, err:
+  except OSError:
     # if we can't fork, we'll pretend that we're in the child process
     pid = 0
   if pid > 0:
-    return (True, "Reboot scheduled in 5 seconds")
+    return "Reboot scheduled in 5 seconds"
   time.sleep(5)
   hyper.PowercycleNode()
 
@@ -2556,14 +2488,15 @@ class HooksRunner(object):
     elif phase == constants.HOOKS_PHASE_POST:
       suffix = "post"
     else:
-      raise errors.ProgrammerError("Unknown hooks phase: '%s'" % phase)
+      _Fail("Unknown hooks phase '%s'", phase)
+
     rr = []
 
     subdir = "%s-%s.d" % (hpath, suffix)
     dir_name = "%s/%s" % (self._BASE_DIR, subdir)
     try:
       dir_contents = utils.ListVisibleFiles(dir_name)
-    except OSError, err:
+    except OSError:
       # FIXME: must log output in case of failures
       return rr
 
@@ -2603,17 +2536,15 @@ class IAllocatorRunner(object):
     @param idata: the allocator input data
 
     @rtype: tuple
-    @return: four element tuple of:
-       - run status (one of the IARUN_ constants)
-       - stdout
-       - stderr
-       - fail reason (as from L{utils.RunResult})
+    @return: two element tuple of:
+       - status
+       - either error message or stdout of allocator (for success)
 
     """
     alloc_script = utils.FindFile(name, constants.IALLOCATOR_SEARCH_PATH,
                                   os.path.isfile)
     if alloc_script is None:
-      return (constants.IARUN_NOTFOUND, None, None, None)
+      _Fail("iallocator module '%s' not found in the search path", name)
 
     fd, fin_name = tempfile.mkstemp(prefix="ganeti-iallocator.")
     try:
@@ -2621,12 +2552,12 @@ class IAllocatorRunner(object):
       os.close(fd)
       result = utils.RunCmd([alloc_script, fin_name])
       if result.failed:
-        return (constants.IARUN_FAILURE, result.stdout, result.stderr,
-                result.fail_reason)
+        _Fail("iallocator module '%s' failed: %s, output '%s'",
+              name, result.fail_reason, result.output)
     finally:
       os.unlink(fin_name)
 
-    return (constants.IARUN_SUCCESS, result.stdout, result.stderr, None)
+    return result.stdout
 
 
 class DevCacheManager(object):
@@ -2687,7 +2618,7 @@ class DevCacheManager(object):
     try:
       utils.WriteFile(fpath, data=fdata)
     except EnvironmentError, err:
-      logging.exception("Can't update bdev cache for %s", dev_path)
+      logging.exception("Can't update bdev cache for %s: %s", dev_path, err)
 
   @classmethod
   def RemoveCache(cls, dev_path):
@@ -2709,4 +2640,4 @@ class DevCacheManager(object):
     try:
       utils.RemoveFile(fpath)
     except EnvironmentError, err:
-      logging.exception("Can't update bdev cache for %s", dev_path)
+      logging.exception("Can't update bdev cache for %s: %s", dev_path, err)