From e0a754a0a608e1eb9021cf847b83e72165219de2 Mon Sep 17 00:00:00 2001
From: Daniil Baturin <daniil@vyos.io>
Date: Sun, 4 Jul 2021 14:10:22 -0500
Subject: T3663: prerequisites for inotify-based watching implementations.

---
 debian/control      |  1 +
 python/vyos/util.py | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/debian/control b/debian/control
index aed1a3b2d..5a434bfc6 100644
--- a/debian/control
+++ b/debian/control
@@ -24,6 +24,7 @@ Build-Depends:
   python3-setuptools,
   python3-sphinx,
   python3-xmltodict,
+  python3-inotify,
   quilt,
   whois
 Standards-Version: 3.9.6
diff --git a/python/vyos/util.py b/python/vyos/util.py
index cf90dc74f..630fb1dcc 100644
--- a/python/vyos/util.py
+++ b/python/vyos/util.py
@@ -16,6 +16,9 @@
 import os
 import re
 import sys
+import time
+
+import inotify.adapters
 
 #
 # NOTE: Do not import full classes here, move your import to the function
@@ -506,6 +509,36 @@ def file_is_persistent(path):
     absolute = os.path.abspath(os.path.dirname(path))
     return re.match(location,absolute)
 
+def wait_for_inotify(file_path, event_type=None, timeout=None, sleep_interval=0.1):
+    """ Waits for an inotify event to occur """
+    if not os.path.dirname(file_path):
+        raise ValueError(
+          "File path {} does not have a directory part (required for inotify watching)".format(file_path))
+    if not os.path.basename(file_path):
+        raise ValueError(
+          "File path {} does not have a file part, do not know what to watch for".format(file_path))
+
+    time_start = time.time()
+
+    i = inotify.adapters.Inotify()
+    i.add_watch(os.path.dirname(file_path))
+
+    for event in i.event_gen(yield_nones=True):
+        if (timeout is not None) and ((time.time() - time_start) > timeout):
+            # If the function didn't return until this point,
+            # the file failed to have been written to and closed within the timeout
+            raise OSError("Waiting for file {} to be written has failed".format(file_path))
+
+        if event is not None:
+            (_, type_names, path, filename) = event
+            if filename == os.path.basename(file_path):
+                if event_type in type_names:
+                    return
+
+def wait_for_file_write_complete(file_path, timeout=None, sleep_interval=0.1):
+    """ Waits for a process to close a file after opening it in write mode. """
+    wait_for_inotify(file_path,
+      event_type='IN_CLOSE_WRITE', timeout=timeout, sleep_interval=sleep_interval)
 
 def commit_in_progress():
     """ Not to be used in normal op mode scripts! """
-- 
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