ceph/doc/rbd/api/librbdpy.rst

   1 ================
   2  Librbd (Python)
   3 ================
   4
   5 .. highlight:: python
   6
   7 The `rbd` python module provides file-like access to RBD images.
   8
   9
  10 Example: Creating and writing to an image
  11 =========================================
  12
  13 To use `rbd`, you must first connect to RADOS and open an IO
  14 context::
  15
  16     cluster = rados.Rados(conffile='my_ceph.conf')
  17     cluster.connect()
  18     ioctx = cluster.open_ioctx('mypool')
  19
  20 Then you instantiate an :class:rbd.RBD object, which you use to create the
  21 image::
  22
  23     rbd_inst = rbd.RBD()
  24     size = 4 * 1024**3  # 4 GiB
  25     rbd_inst.create(ioctx, 'myimage', size)
  26
  27 To perform I/O on the image, you instantiate an :class:rbd.Image object::
  28
  29     image = rbd.Image(ioctx, 'myimage')
  30     data = 'foo' * 200
  31     image.write(data, 0)
  32
  33 This writes 'foo' to the first 600 bytes of the image. Note that data
  34 cannot be :type:unicode - `Librbd` does not know how to deal with
  35 characters wider than a :c:type:char.
  36
  37 In the end, you will want to close the image, the IO context and the connection to RADOS::
  38
  39     image.close()
  40     ioctx.close()
  41     cluster.shutdown()
  42
  43 To be safe, each of these calls would need to be in a separate :finally
  44 block::
  45
  46     cluster = rados.Rados(conffile='my_ceph_conf')
  47     try:
  48         ioctx = cluster.open_ioctx('my_pool')
  49         try:
  50             rbd_inst = rbd.RBD()
  51             size = 4 * 1024**3  # 4 GiB
  52             rbd_inst.create(ioctx, 'myimage', size)
  53             image = rbd.Image(ioctx, 'myimage')
  54             try:
  55                 data = 'foo' * 200
  56                 image.write(data, 0)
  57             finally:
  58                 image.close()
  59         finally:
  60             ioctx.close()
  61     finally:
  62         cluster.shutdown()
  63
  64 This can be cumbersome, so the :class:`Rados`, :class:`Ioctx`, and
  65 :class:`Image` classes can be used as context managers that close/shutdown
  66 automatically (see :pep:`343`). Using them as context managers, the
  67 above example becomes::
  68
  69     with rados.Rados(conffile='my_ceph.conf') as cluster:
  70         with cluster.open_ioctx('mypool') as ioctx:
  71             rbd_inst = rbd.RBD()
  72             size = 4 * 1024**3  # 4 GiB
  73             rbd_inst.create(ioctx, 'myimage', size)
  74             with rbd.Image(ioctx, 'myimage') as image:
  75                 data = 'foo' * 200
  76                 image.write(data, 0)
  77
  78 API Reference
  79 =============
  80
  81 .. automodule:: rbd
  82     :members: RBD, Image, SnapIterator