Source Code for Module ganeti.utils.bitarrays

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29   
30  """Utility functions for managing bitarrays. 
31   
32  """ 
33   
34   
35  from bitarray import bitarray 
36   
37  from ganeti import errors 
38   
39  # Constant bitarray that reflects to a free slot 
40  # Use it with bitarray.search() 
41  _AVAILABLE_SLOT = bitarray("0") 
42   
43   
44 -def GetFreeSlot(slots, slot=None, reserve=False): 
45    """Helper method to get first available slot in a bitarray 
46   
47    @type slots: bitarray 
48    @param slots: the bitarray to operate on 
49    @type slot: integer 
50    @param slot: if given we check whether the slot is free 
51    @type reserve: boolean 
52    @param reserve: whether to reserve the first available slot or not 
53    @return: the idx of the (first) available slot 
54    @raise errors.OpPrereqError: If all slots in a bitarray are occupied 
55      or the given slot is not free. 
56   
57    """ 
58    if slot is not None: 
59      assert slot < len(slots) 
60      if slots[slot]: 
61        raise errors.GenericError("Slot %d occupied" % slot) 
62   
63    else: 
64      avail = slots.search(_AVAILABLE_SLOT, 1) 
65      if not avail: 
66        raise errors.GenericError("All slots occupied") 
67   
68      slot = int(avail[0]) 
69   
70    if reserve: 
71      slots[slot] = True 
72   
73    return slot 
74