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