Add execd_preinstall support to ceilometer charm

Reabase of https://code.launchpad.net/~moon127/charms/trusty/ceilometer/add-execd-preinstall/+merge/224077

charm-helpers-hooks.yaml

@@ -9,3 +9,4 @@ include:
     - contrib.network.ip
     - contrib.python.packages
     - contrib.charmsupport
+    - payload.execd

hooks/ceilometer_hooks.py

@@ -55,6 +55,7 @@ from charmhelpers.contrib.hahelpers.cluster import (
     get_hacluster_config,
     is_elected_leader
 )
+from charmhelpers.payload.execd import execd_preinstall
 
 hooks = Hooks()
 CONFIGS = register_configs()
@@ -62,6 +63,7 @@ CONFIGS = register_configs()
 
 @hooks.hook()
 def install():
+    execd_preinstall()
     origin = config('openstack-origin')
     if (lsb_release()['DISTRIB_CODENAME'] == 'precise'
             and origin == 'distro'):

hooks/charmhelpers/payload/__init__.py

@@ -0,0 +1 @@
+"Tools for working with files injected into a charm just before deployment."

hooks/charmhelpers/payload/execd.py

@@ -0,0 +1,50 @@
+#!/usr/bin/env python
+
+import os
+import sys
+import subprocess
+from charmhelpers.core import hookenv
+
+
+def default_execd_dir():
+    return os.path.join(os.environ['CHARM_DIR'], 'exec.d')
+
+
+def execd_module_paths(execd_dir=None):
+    """Generate a list of full paths to modules within execd_dir."""
+    if not execd_dir:
+        execd_dir = default_execd_dir()
+
+    if not os.path.exists(execd_dir):
+        return
+
+    for subpath in os.listdir(execd_dir):
+        module = os.path.join(execd_dir, subpath)
+        if os.path.isdir(module):
+            yield module
+
+
+def execd_submodule_paths(command, execd_dir=None):
+    """Generate a list of full paths to the specified command within exec_dir.
+    """
+    for module_path in execd_module_paths(execd_dir):
+        path = os.path.join(module_path, command)
+        if os.access(path, os.X_OK) and os.path.isfile(path):
+            yield path
+
+
+def execd_run(command, execd_dir=None, die_on_error=False, stderr=None):
+    """Run command for each module within execd_dir which defines it."""
+    for submodule_path in execd_submodule_paths(command, execd_dir):
+        try:
+            subprocess.check_call(submodule_path, shell=True, stderr=stderr)
+        except subprocess.CalledProcessError as e:
+            hookenv.log("Error ({}) running  {}. Output: {}".format(
+                e.returncode, e.cmd, e.output))
+            if die_on_error:
+                sys.exit(e.returncode)
+
+
+def execd_preinstall(execd_dir=None):
+    """Run charm-pre-install for each module within execd_dir."""
+    execd_run('charm-pre-install', execd_dir=execd_dir)