Description of problem:

isBlockDevice() throws an error if device doesn't exist`.

running getDeviceList, vdsm scans all paths under /sys/block, and in case one of the paths are missing, it throws and exception.


Thread-401::ERROR::2011-07-27 10:21:40,478::dispatcher::106::Storage.Dispatcher.Protect::(run) [Errno 2]
 No such multipath device `sdfs`
Thread-401::ERROR::2011-07-27 10:21:40,479::dispatcher::107::Storage.Dispatcher.Protect::(run) Traceback
 (most recent call last):
  File "/usr/share/vdsm/storage/dispatcher.py", line 96, in run
    result = ctask.prepare(self.func, *args, **kwargs)
  File "/usr/share/vdsm/storage/task.py", line 1184, in prepare
    raise self.error
OSError: [Errno 2] No such multipath device `sdfs`

MainProcess|Thread-401::DEBUG::2011-07-27 10:21:40,416::multipath::159::Storage.Misc.excCmd::(getScsiSer
ial) FAILED: <err> = ''; <rc> = 1
Thread-401::ERROR::2011-07-27 10:21:40,469::task::865::TaskManager.Task::(_setError) Unexpected error
Traceback (most recent call last):
  File "/usr/share/vdsm/storage/task.py", line 873, in _run
    return fn(*args, **kargs)
  File "/usr/share/vdsm/storage/hsm.py", line 686, in public_getDeviceList
    devices = self._getDeviceList(storageType)
  File "/usr/share/vdsm/storage/hsm.py", line 714, in _getDeviceList
    for dev in multipath.pathListIter(guids):
  File "/usr/share/vdsm/storage/multipath.py", line 223, in pathListIter
    if not devicemapper.isBlockDevice(slave):
  File "/usr/share/vdsm/storage/devicemapper.py", line 80, in isBlockDevice
    devName = resolveDevName(devName)
  File "/usr/share/vdsm/storage/devicemapper.py", line 73, in resolveDevName
    raise OSError(errno.ENOENT, "No such multipath device `%s`" % devName)
OSError: [Errno 2] No such multipath device `sdfs`