Move _get_agent_params() to a common place

The function _get_agent_params() parse the parameters passed to the agent
via kernel cmdline or vmedia. Other parts of the code needs to access
these parameters as well, so this patch is moving _get_agent_params()
and the related functions to a common place (utils.py).

Change-Id: I860f84d1d13511fff56d4aa56358ee597a9760d5

ironic_python_agent/utils.py

@@ -13,9 +13,12 @@
 # limitations under the License.
 
 import collections
+import glob
+import os
 
 from oslo_concurrency import processutils
 
+from ironic_python_agent import errors
 from ironic_python_agent.openstack.common import _i18n as gtu
 from ironic_python_agent.openstack.common import log as logging
 
@@ -39,3 +42,101 @@ def execute(*cmd, **kwargs):
     LOG.debug(gtu._('Command stdout is: "%s"') % result[0])
     LOG.debug(gtu._('Command stderr is: "%s"') % result[1])
     return result
+
+
+def _read_params_from_file(filepath):
+    """Extract key=value pairs from a file.
+
+    :param filepath: path to a file containing key=value pairs separated by
+                     whitespace or newlines.
+    :returns: a dictionary representing the content of the file
+    """
+    with open(filepath) as f:
+        cmdline = f.read()
+
+    options = cmdline.split()
+    params = {}
+    for option in options:
+        if '=' not in option:
+            continue
+        k, v = option.split('=', 1)
+        params[k] = v
+
+    return params
+
+
+def _get_vmedia_device():
+    """Finds the device filename of the virtual media device using sysfs.
+
+    :returns: a string containing the filename of the virtual media device
+    """
+    sysfs_device_models = glob.glob("/sys/class/block/*/device/model")
+    vmedia_device_model = "virtual media"
+    for model_file in sysfs_device_models:
+        try:
+            with open(model_file) as model_file_fobj:
+                if vmedia_device_model in model_file_fobj.read().lower():
+                    vmedia_device = model_file.split('/')[4]
+                    return vmedia_device
+        except Exception:
+            pass
+
+
+def _get_vmedia_params():
+    """This method returns the parameters passed to the agent through virtual
+    media floppy.
+
+    :returns: a partial dict of potential agent configuration parameters
+    :raises: VirtualMediaBootError when it cannot find the virtual media device
+    """
+    vmedia_mount_point = "/vmedia_mnt"
+    parameters_file = "parameters.txt"
+
+    vmedia_device = _get_vmedia_device()
+    if not vmedia_device:
+        msg = "Unable to find virtual media device"
+        raise errors.VirtualMediaBootError(msg)
+
+    vmedia_device_file = os.path.join("/dev", vmedia_device)
+    os.mkdir(vmedia_mount_point)
+
+    try:
+        stdout, stderr = execute("mount", vmedia_device_file,
+                                 vmedia_mount_point)
+    except processutils.ProcessExecutionError as e:
+        msg = ("Unable to mount virtual media device %(device)s: %(error)s" %
+              {'device': vmedia_device_file, 'error': e})
+        raise errors.VirtualMediaBootError(msg)
+
+    parameters_file_path = os.path.join(vmedia_mount_point, parameters_file)
+    params = _read_params_from_file(parameters_file_path)
+
+    try:
+        stdout, stderr = execute("umount", vmedia_mount_point)
+    except processutils.ProcessExecutionError as e:
+        pass
+
+    return params
+
+
+def get_agent_params():
+    """Gets parameters passed to the agent via kernel cmdline or vmedia.
+
+    Parameters can be passed using either the kernel commandline or through
+    virtual media. If boot_method is vmedia, merge params provided via vmedia
+    with those read from the kernel command line.
+
+    Although it should never happen, if a variable is both set by vmedia and
+    kernel command line, the setting in vmedia will take precedence.
+
+    :returns: a dict of potential configuration parameters for the agent
+    """
+    params = _read_params_from_file('/proc/cmdline')
+
+    # If the node booted over virtual media, the parameters are passed
+    # in a text file within the virtual media floppy.
+    if params.get('boot_method', None) == 'vmedia':
+        vmedia_params = _get_vmedia_params()
+        params.update(vmedia_params)
+
+    return params