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Python bindings for device-mapper

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# `dmpy` - python bindings for device-mapper

The `dmpy` package exposes the interfaces declared in `libdevmapper.h`
to python programs. It implements a native module named `dmpy` which
provides classes and functions for interacting with the device-mapper:
most function and parameter names are exactly the same as their
`libdevmapper` counterparts, with the exception that type prefixes like
`dm_task_` are dropped where the function is a method of a class, for
e.g.:

```
  dm_task_set_name() -> dmpy.DmTask.set_name()
```

The dmpy project is [hosted on GitHub][0].

## Reporting bugs
Bugs can be reported at the [GitHub Issue Tracker][1], or via the
[dm-devel mailing list][2].

## Building dmpy
To build the module, from the top-level directory, run:

```
$ python setup.py build
```

To build the module for a specific version of the python interpreter
(either 2 or 3), use the command name provided by your distribution
to select the version, for example:

`$ python3 setup.py build`
  `$ python2.7 setup.py build`
  `$ /usr/python2.7/bin/python setup.py build`

You can set `PYTHONPATH`, or just cd into the build directory to load
the module:

```
  # python3
  [...]
  >>> import dmpy as dm
  >>>
```

Or use the `setup.py` `install` command to install the package.

## dmpy types
Device-mapper functions are exposed as module functions and class
methods. The following dmpy classes are implemented:

* `DmCookie` Cookie used for `UDEV` synchronisation (experimental)
  * `DmError`  Generic device-mapper error class
  * `DmTask`,  Represents a `dm_task` object and its methods
  * `DmTimestamp` Represents the device-mapper `dm_timestamp`
  * `DmInfo`   A `dm_info` struct as returned by `DM_DEVICE_INFO`
  * `DmStats`  Represents a `dm_stats` handle and the objects it contains
  * `DmStatsRegion`  Represents one region and the areas it contains.

All of these (except `DmInfo` and `DmStatsRegion`) expose a class-name
constructor in the module: `DmInfo` objects can only be constructed by
retrieving one from a `DmTask` object that has executed a
`DM_DEVICE_INFO` ioctl. Similarly, `DmStatsRegion` objects should only
be obtained by accessing the members of a containing `DmStats` object.`

See the [HACKING.md][3] file for information on `dmpy` internals.

## Getting help
All classes, methods, and module functions have an associated `__doc__`
string, which can be displayed using Python's builtin `help()`:

```python
>>> help(dm.DmTask.get_uuid)
Help on method_descriptor:

get_uuid(...)
    Get the dm device's UUID based on the value of the mangling mode
    set during preceding `DmTask.run()` call.
    
    To force either mangled or unmangled output, set the `mangle` kwarg
    to '1' or '0' respectively.
```

## Examples

* Import `dmpy` and get the device-mapper versions:

```python
>>> import dmpy as dm
>>> dm.get_library_version()
'1.02.122 (2016-04-09)'
>>> dm.driver_version()
'4.34.0'
>>>
```

* List all device-mapper devices and their major and minor numbers
```python
>>> import dmpy as dm
>>> dmt = dm.DmTask(dm.DM_DEVICE_LIST)
>>> dmt.run()
>>> for d in dmt.get_names():
...     print("Device: %s (%d, %d)" % d)
...
Device: vg_hex-lv_home (253, 2)
Device: vg_hex-lv_root (253, 0)
Device: souflé (253, 8)
Device: home (253, 15)
Device: vg_hex-lv_images (253, 1)
>>>
```

* List all target versions

```python
>>> dmt = dm.DmTask(dm.DM_DEVICE_LIST_VERSIONS)
>>> dmt.run()
>>> versions = dmt.get_versions()
>>> for t in versions.keys():
...     v = versions[t]
...     print("%s (%d.%d.%d)" % (t, v[0], v[1], v[2]))
...
thin (1.19.0)
error (1.4.0)
snapshot (1.15.0)
snapshot-merge (1.4.0)
crypt (1.14.1)
snapshot-origin (1.9.0)
thin-pool (1.19.0)
striped (1.5.1)
mirror (1.14.0)
linear (1.2.1)
zero (1.1.0)

```

* Send a `DM_DEVICE_TARGET_MSG` and retrieve the response

```python
>>> dmt = dm.DmTask(dm.DM_DEVICE_TARGET_MSG)
>>> dmt.set_name("vg_hex/lv_root")
>>> dmt.set_message("@stats_list")
<dmpy.DmTask object at 0x7f8de2a21f30>
>>> dmt.set_sector(0)
True
>>> dmt.run()
>>> print(dmt.get_message_response().strip())
0: 0+16777216 16777216 dmioscope -
1: 16777216+16777216 16777216 dmioscope -
2: 33554432+16777216 16777216 dmioscope -
3: 50331648+16777216 16777216 dmioscope -
4: 0+16777216 16777216 dmioscope -
5: 0+67108864 67108864 dmstats -
9: 16777216+16777216 16777216 dmioscope -
10: 33554432+16777216 16777216 dmioscope -
11: 50331648+16777216 16777216 dmioscope -
>>>
```

[0]: https://github.com/bmr-cymru/dmpy
 [1]: https://github.com/bmr-cymru/dmpy/issues
 [2]: https://www.redhat.com/mailman/listinfo/dm-devel
 [3]: https://github.com/bmr-cymru/dmpy/blob/master/HACKING.md

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