Adding upstream version 5.3.1.upstream/5.3.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 71 insertions, 0 deletions

diff --git a/modules/detect_time_jump/.packaging/test.config b/modules/detect_time_jump/.packaging/test.config
new file mode 100644
index 0000000..7ed0e60
--- /dev/null
+++ b/modules/detect_time_jump/.packaging/test.config
@@ -0,0 +1,4 @@
+-- SPDX-License-Identifier: GPL-3.0-or-later
+modules.load('detect_time_jump')
+assert(detect_time_jump)
+quit()
diff --git a/modules/detect_time_jump/README.rst b/modules/detect_time_jump/README.rst
new file mode 100644
index 0000000..066f5a3
--- /dev/null
+++ b/modules/detect_time_jump/README.rst
@@ -0,0 +1,22 @@
+.. SPDX-License-Identifier: GPL-3.0-or-later
+
+.. _mod-detect_time_jump:
+
+Detect discontinuous jumps in the system time
+=============================================
+
+This module detect discontinuous jumps in the system time when resolver
+is running.  It clears cache when a significant backward time jumps occurs.
+
+Time jumps are usually created by NTP time change or by admin intervention.
+These change can affect cache records as they store timestamp and TTL in real
+time.
+
+If you want to preserve cache during time travel you should disable
+this module by ``modules.unload('detect_time_jump')``.
+
+Due to the way monotonic system time works on typical systems,
+suspend-resume cycles will be perceived as forward time jumps,
+but this direction of shift does not have the risk of using records
+beyond their intended TTL, so forward jumps do not cause erasing the cache.
+
diff --git a/modules/detect_time_jump/detect_time_jump.lua b/modules/detect_time_jump/detect_time_jump.lua
new file mode 100644
index 0000000..ab099e8
--- /dev/null
+++ b/modules/detect_time_jump/detect_time_jump.lua
@@ -0,0 +1,45 @@
+-- SPDX-License-Identifier: GPL-3.0-or-later
+-- Module interface
+local ffi = require('ffi')
+
+local mod = {}
+mod.threshold = 10 * min
+local event_id = nil
+
+-- Get time of last cache clear. Compute difference between realtime
+-- and monotonic time. Compute difference of actual realtime and monotonic
+-- time. In ideal case these differences should be almost same.
+-- If they differ more than mod.threshold value then clear cache.
+local function check_time()
+	local checkpoint = cache.checkpoint()
+	local cache_timeshift = checkpoint.walltime.sec * 1000 - checkpoint.monotime
+	local actual_timeshift = os.time() * 1000 - tonumber(ffi.C.kr_now())
+	local jump_backward = cache_timeshift - actual_timeshift
+	if jump_backward > mod.threshold then
+		log("Detected backwards time jump, clearing cache.\n" ..
+		"But what does that mean? It means your future hasn't been written yet."
+		)
+		cache.clear()
+	elseif -jump_backward > mod.threshold then
+		-- On Linux 4.17+ this shouldn't happen anymore: https://lwn.net/Articles/751482/
+		log("Detected forward time jump.  (Suspend-resume, possibly.)")
+		cache.checkpoint(true)
+	end
+end
+
+function mod.init()
+	if event_id then
+		error("Module is already loaded.")
+	else
+		event_id = event.recurrent(1 * min , check_time)
+	end
+end
+
+function mod.deinit()
+	if event_id then
+		event.cancel(event_id)
+		event_id = nil
+	end
+end
+
+return mod