logd: regression in handling watermark boundary.

Deal with a regression introduced in commit
5a34d6ea43d28f3b5d27bf6dd5b9fa31ec033531 (logd: drop mSequence from
LogBufferElement) where log_time was compared against nsec() time
miscalculating the watermark boundary.  When dealing with logcat
-t/-T, or any tail reading, add a margin to prune to back off by a
period of 3 seconds (pruneMargin).

Test: gTest liblog-unit-tests logcat-unit-tests and logd-unit-tests
Bug: 37378309
Change-Id: I72ea858e4e7b5fa91741ea84c40d2e7c3c4aa031

1 files changed, 1 insertions, 0 deletions

diff --git a/logd/LogBuffer.h b/logd/LogBuffer.h
index 19d11cb7f..1272c20f6 100644
--- a/logd/LogBuffer.h
+++ b/logd/LogBuffer.h
@@ -174,6 +174,7 @@ class LogBuffer {
    private:
     static constexpr size_t minPrune = 4;
     static constexpr size_t maxPrune = 256;
+    static const log_time pruneMargin;
 
     void maybePrune(log_id_t id);
     bool prune(log_id_t id, unsigned long pruneRows, uid_t uid = AID_ROOT);