Add func to salt.utils.systemd to tell if scopes are available

salt/utils/systemd.py

@@ -15,22 +15,34 @@ import salt.utils
 log = logging.getLogger(__name__)
 
 
-def booted(context):
+def booted(context=None):
     '''
     Return True if the system was booted with systemd, False otherwise.
     Pass in the loader context "__context__", this function will set the
     systemd.sd_booted key to represent if systemd is running
     '''
-    # We can cache this for as long as the minion runs.
-    if 'systemd.sd_booted' not in context:
-        try:
-            # This check does the same as sd_booted() from libsystemd-daemon:
-            # http://www.freedesktop.org/software/systemd/man/sd_booted.html
-            if os.stat('/run/systemd/system'):
-                context['systemd.sd_booted'] = True
-        except OSError:
-            context['systemd.sd_booted'] = False
-    return context['systemd.sd_booted']
+    contextkey = 'salt.utils.systemd.booted'
+    if isinstance(context, dict):
+        # Can't put this if block on the same line as the above if block,
+        # because it willl break the elif below.
+        if contextkey in context:
+            return context[contextkey]
+    elif context is not None:
+        raise SaltInvocationError('context must be a dictionary if passed')
+
+    try:
+        # This check does the same as sd_booted() from libsystemd-daemon:
+        # http://www.freedesktop.org/software/systemd/man/sd_booted.html
+        ret = bool(os.stat('/run/systemd/system'))
+    except OSError:
+        ret = False
+
+    try:
+        context[contextkey] = ret
+    except TypeError:
+        pass
+
+    return ret
 
 
 def version(context=None):
@@ -38,11 +50,14 @@ def version(context=None):
     Attempts to run systemctl --version. Returns None if unable to determine
     version.
     '''
+    contextkey = 'salt.utils.systemd.version'
     if isinstance(context, dict):
-        if 'systemd.version' in context:
-            return context['systemd.version']
+        # Can't put this if block on the same line as the above if block,
+        # because it willl break the elif below.
+        if contextkey in context:
+            return context[contextkey]
     elif context is not None:
-        raise SaltInvocationError('context must be a dictionary or None')
+        raise SaltInvocationError('context must be a dictionary if passed')
     stdout = subprocess.Popen(
         ['systemctl', '--version'],
         close_fds=True,
@@ -58,7 +73,20 @@ def version(context=None):
         return None
     else:
         try:
-            context['systemd.version'] = ret
+            context[contextkey] = ret
         except TypeError:
             pass
         return ret
+
+
+def has_scope(context=None):
+    '''
+    Scopes were introduced in systemd 205, this function returns a boolean
+    which is true when the minion is systemd-booted and running systemd>=205.
+    '''
+    if not booted(context):
+        return False
+    _sd_version = version(context)
+    if _sd_version is None:
+        return False
+    return _sd_version >= 205