deprecate eventlet monkey patching within oslo.privsep.daemon

Change-Id: I26ed6b42fc6eeeef23ad37e74631f372de6daf2c

oslo_privsep/daemon.py

@@ -55,6 +55,7 @@ import sys
 import tempfile
 import threading
 
+import debtcollector
 import eventlet
 from eventlet import patcher
 from oslo_config import cfg
@@ -83,7 +84,10 @@ def _null():
     return []
 
 
+_MONKEY_PATCHED = False
 for module in EVENTLET_MODULES:
+    if eventlet.patcher.is_monkey_patched(module):
+        _MONKEY_PATCHED = True
     if hasattr(patcher, '_green_%s_modules' % module):
         method = getattr(patcher, '_green_%s_modules' % module)
     elif hasattr(patcher, '_green_%s' % module):
@@ -92,6 +96,10 @@ for module in EVENTLET_MODULES:
         method = _null()
     EVENTLET_LIBRARIES.append((module, method))
 
+if _MONKEY_PATCHED:
+    debtcollector.deprecate(
+        "Eventlet support is deprecated and will be removed")
+
 
 @enum.unique
 class StdioFd(enum.IntEnum):

releasenotes/notes/deprecate-eventlet-monkey-patching-c37fea982471c01c.yaml

@@ -0,0 +1,11 @@
+---
+deprecations:
+  - |
+    Eventlet usages are deprecated and the removal of Eventlet from
+    OpenStack `is planned <https://governance.openstack.org/tc//goals/proposed/remove-eventlet.html>`_,
+    for this reason, using the ``daemon`` module of oslo.privsep in a monkey
+    patched environment is now deprecated. The support of Eventlet will be
+    soon removed from oslo.privsep.
+
+    Please start considering removing your internal Eventlet usages and
+    start migrating your stack.

requirements.txt

@@ -10,3 +10,4 @@ cffi>=1.14.0 # MIT
 eventlet>=0.21.0 # MIT
 greenlet>=0.4.14 # MIT
 msgpack>=0.6.0 # Apache-2.0
+debtcollector>=3.0.0 # Apache-2.0