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-rw-r--r--modules/detect_time_jump/detect_time_jump.lua45
1 files changed, 45 insertions, 0 deletions
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