logd: KISS & fix preserve a day

(cherry pick from commit 5921276a16528bf79292e828080bf0ec984cbb23)

Code in 833a9b1e38ce65f2cdf3ebd095aaa99a92eb9467 was borken,
simpler approach is to simply check last entry (to save a
syscall) minus EXPIRE_HOUR_THRESHOLD. This does make longer logs
less likely to call upon the spam detection than the algorithm
being replaced, but sadly we ended up with a log entry in the
future at the beginning of the logs confounding the previous
algorithm.

Bug: 21555259
Change-Id: I04fad67e95c8496521dbabb73b5f32c19d6a16c2

1 files changed, 9 insertions, 16 deletions

diff --git a/logd/LogBuffer.cpp b/logd/LogBuffer.cpp
index d89a2e7..913e1f1 100644
--- a/logd/LogBuffer.cpp
+++ b/logd/LogBuffer.cpp
@@ -388,7 +388,6 @@ void LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
         bool kick = false;
         bool leading = true;
         LogBufferElementLast last;
-        log_time start(log_time::EPOCH);
         for(it = mLogElements.begin(); it != mLogElements.end();) {
             LogBufferElement *e = *it;
 
@@ -446,30 +445,24 @@ void LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
             }
 
             if (e->getUid() != worst) {
-                leading = false;
-                if (start != log_time::EPOCH) {
+                if (leading) {
                     static const timespec too_old = {
                         EXPIRE_HOUR_THRESHOLD * 60 * 60, 0
                     };
-                    start = e->getRealTime() + too_old;
+                    LogBufferElementCollection::iterator last;
+                    last = mLogElements.end();
+                    --last;
+                    if ((e->getRealTime() < ((*last)->getRealTime() - too_old))
+                            || (e->getRealTime() > (*last)->getRealTime())) {
+                        break;
+                    }
                 }
+                leading = false;
                 last.clear(e);
                 ++it;
                 continue;
             }
 
-            if ((start != log_time::EPOCH) && (e->getRealTime() > start)) {
-                // KISS. Really a heuristic rather than algorithmically strong,
-                // a crude mechanism, the following loops will move the oldest
-                // watermark possibly wiping out the extra EXPIRE_HOUR_THRESHOLD
-                // we just thought we were preserving. We count on the typical
-                // pruneRows of 10% of total not being a sledgehammer.
-                // A stronger algorithm would have us loop back to the top if
-                // we have worst-UID enabled and we start expiring messages
-                // below less than EXPIRE_HOUR_THRESHOLD old.
-                break;
-            }
-
             pruneRows--;
             if (pruneRows == 0) {
                 break;