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https://github.com/ceph/ceph
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83 lines
2.3 KiB
ReStructuredText
83 lines
2.3 KiB
ReStructuredText
================
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Librbd (Python)
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================
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.. highlight:: python
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The `rbd` python module provides file-like access to RBD images.
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Example: Creating and writing to an image
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=========================================
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To use `rbd`, you must first connect to RADOS and open an IO
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context::
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cluster = rados.Rados(conffile='my_ceph.conf')
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cluster.connect()
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ioctx = cluster.open_ioctx('mypool')
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Then you instantiate an :class:rbd.RBD object, which you use to create the
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image::
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rbd_inst = rbd.RBD()
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size = 4 * 1024**3 # 4 GiB
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rbd_inst.create(ioctx, 'myimage', size)
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To perform I/O on the image, you instantiate an :class:rbd.Image object::
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image = rbd.Image(ioctx, 'myimage')
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data = 'foo' * 200
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image.write(data, 0)
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This writes 'foo' to the first 600 bytes of the image. Note that data
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cannot be :type:unicode - `Librbd` does not know how to deal with
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characters wider than a :c:type:char.
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In the end, you will want to close the image, the IO context and the connection to RADOS::
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image.close()
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ioctx.close()
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cluster.shutdown()
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To be safe, each of these calls would need to be in a separate :finally
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block::
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cluster = rados.Rados(conffile='my_ceph_conf')
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try:
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ioctx = cluster.open_ioctx('my_pool')
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try:
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rbd_inst = rbd.RBD()
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size = 4 * 1024**3 # 4 GiB
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rbd_inst.create(ioctx, 'myimage', size)
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image = rbd.Image(ioctx, 'myimage')
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try:
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data = 'foo' * 200
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image.write(data, 0)
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finally:
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image.close()
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finally:
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ioctx.close()
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finally:
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cluster.shutdown()
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This can be cumbersome, so the :class:`Rados`, :class:`Ioctx`, and
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:class:`Image` classes can be used as context managers that close/shutdown
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automatically (see :pep:`343`). Using them as context managers, the
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above example becomes::
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with rados.Rados(conffile='my_ceph.conf') as cluster:
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with cluster.open_ioctx('mypool') as ioctx:
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rbd_inst = rbd.RBD()
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size = 4 * 1024**3 # 4 GiB
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rbd_inst.create(ioctx, 'myimage', size)
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with rbd.Image(ioctx, 'myimage') as image:
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data = 'foo' * 200
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image.write(data, 0)
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API Reference
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=============
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.. automodule:: rbd
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:members: RBD, Image, SnapIterator
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