From f2ef1a2a0479ccd57bad69b3314516a0148ff764 Mon Sep 17 00:00:00 2001
From: Matthieu Baerts <matttbe@kernel.org>
Date: Wed, 22 Jul 2026 16:59:11 +0200
Subject: [PATCH] logger: rotate log at startup

Before this modification, the log files were truncated at startup: the
last log messages were then lost in case of restart, e.g. a service
failed, restarted because the crashed seemed to be caused by a transient
error, then ... arf, too late to understand why.

Now, the log files, if any and not empty, are rotated at startup.
Another solution could be to modify _log_open_init() to open the log
files with 'a+' to avoid the truncation. It seems cleaner to do a
rotation. The drawback is that it can create many small files in case of
frequent restarts, but that shouldn't be that frequent.

Signed-off-by: Matthieu Baerts <matttbe@kernel.org>
---
 core/logger.py | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/core/logger.py b/core/logger.py
index 166b9645..766dc5fb 100644
--- a/core/logger.py
+++ b/core/logger.py
@@ -78,6 +78,17 @@ def log(self, header, data):
         self.end_sec()
         self._log_flush()
 
+    def _rotate_log(self):
+        # copy the data in to a compressed file now
+        name = self._path + '-' + datetime.datetime.now().isoformat() + '.xz'
+
+        with open(self._path, "rb") as f:
+            with lzma.open(name, "w") as zf:
+                data = f.read()
+                while data:
+                    zf.write(data)
+                    data = f.read()
+
     def _maybe_close(self):
         if self._level:
             return
@@ -90,21 +101,16 @@ def _maybe_close(self):
         self._log_file.close()
         self._log_file = None
 
-        # copy the data in to a compressed file now
-        name = self._path + '-' + datetime.datetime.now().isoformat() + '.xz'
-
-        with open(self._path, "rb") as f:
-            with lzma.open(name, "w") as zf:
-                data = f.read()
-                while data:
-                    zf.write(data)
-                    data = f.read()
+        self._rotate_log(self)
 
         # truncate the main log by re-opening
         self._log_file = open(self._path, "w+")
         self._log_open()
 
     def _log_open_init(self):
+        if os.path.isfile(self._path) and os.path.getsize(self._path) > 0:
+            self._rotate_log(self)
+
         self._log_file = open(self._path, "w+")
 
     def _log_open(self):