Ability to specify Host Devices during container start

The command line and daemon started supporting --device
parameter during docker start a while ago in the following commit:
docker/docker@e855c4b

Since the command line looks like this,
--device=[] Add a host device to the container (e.g. --device=/dev/sdc:/dev/xvdc)
This patch allows a list of strings to be passed into the start() method
and we parse out the 3 components just like in the above mentioned commit

README.md

@@ -385,6 +385,23 @@ c.start(container_id, binds={
 })
 ```
 
+
+Access to devices on the host
+=============================
+
+If you need to directly expose some host devices to a container, you can use
+the devices parameter in the `Client.start` method as shown below
+
+```python
+c.start(container_id, devices=['/dev/sda:/dev/xvda:rwm'])
+```
+
+Each string is a single mapping using the colon (':') as the separator. So the
+above example essentially allow the container to have read write permissions to
+access the host's /dev/sda via a node named /dev/xvda in the container. The
+devices parameter is a list to allow multiple devices to be mapped.
+
+
 Connection to daemon using HTTPS
 ================================
 

docker/client.py

@@ -827,7 +827,7 @@ class Client(requests.Session):
     def start(self, container, binds=None, port_bindings=None, lxc_conf=None,
               publish_all_ports=False, links=None, privileged=False,
               dns=None, dns_search=None, volumes_from=None, network_mode=None,
-              restart_policy=None, cap_add=None, cap_drop=None):
+              restart_policy=None, cap_add=None, cap_drop=None, devices=None):
         if isinstance(container, dict):
             container = container.get('Id')
 
@@ -895,6 +895,9 @@ class Client(requests.Session):
         if cap_drop:
             start_config['CapDrop'] = cap_drop
 
+        if devices:
+            start_config['Devices'] = utils.parse_devices(devices)
+
         url = self._url("/containers/{0}/start".format(container))
         res = self._post_json(url, data=start_config)
         self._raise_for_status(res)

docker/utils/utils.py

@@ -233,3 +233,23 @@ def parse_host(addr):
     if proto == "http+unix":
         return "%s://%s" % (proto, host)
     return "%s://%s:%d" % (proto, host, port)
+
+
+def parse_devices(devices):
+    device_list = []
+    for device in devices:
+        device_mapping = device.split(",")
+        if device_mapping:
+            path_on_host = device_mapping[0]
+            if len(device_mapping) > 1:
+                path_in_container = device_mapping[1]
+            else:
+                path_in_container = path_on_host
+            if len(device_mapping) > 2:
+                permissions = device_mapping[2]
+            else:
+                permissions = 'rwm'
+            device_list.append({"PathOnHost": path_on_host,
+                                "PathInContainer": path_in_container,
+                                "CgroupPermissions": permissions})
+    return device_list

tests/test.py

@@ -891,6 +891,41 @@ class DockerClientTest(Cleanup, unittest.TestCase):
             docker.client.DEFAULT_TIMEOUT_SECONDS
         )
 
+    def test_start_container_with_devices(self):
+        try:
+            self.client.start(fake_api.FAKE_CONTAINER_ID,
+                              devices=['/dev/sda:/dev/xvda:rwm',
+                                       '/dev/sdb:/dev/xvdb',
+                                       '/dev/sdc'])
+        except Exception as e:
+            self.fail('Command should not raise exception: {0}'.format(e))
+        args = fake_request.call_args
+        self.assertEqual(
+            args[0][0],
+            url_prefix + 'containers/3cc2351ab11b/start'
+        )
+        self.assertEqual(
+            json.loads(args[1]['data']),
+            {"PublishAllPorts": False, "Privileged": False,
+             "Devices": [{'CgroupPermissions': 'rwm',
+                          'PathInContainer': '/dev/sda:/dev/xvda:rwm',
+                          'PathOnHost': '/dev/sda:/dev/xvda:rwm'},
+                         {'CgroupPermissions': 'rwm',
+                          'PathInContainer': '/dev/sdb:/dev/xvdb',
+                          'PathOnHost': '/dev/sdb:/dev/xvdb'},
+                         {'CgroupPermissions': 'rwm',
+                          'PathInContainer': '/dev/sdc',
+                          'PathOnHost': '/dev/sdc'}]}
+        )
+        self.assertEqual(
+            args[1]['headers'],
+            {'Content-Type': 'application/json'}
+        )
+        self.assertEqual(
+            args[1]['timeout'],
+            docker.client.DEFAULT_TIMEOUT_SECONDS
+        )
+
     def test_resize_container(self):
         try:
             self.client.resize(