From 5836379b2114f47c53485b42ab157104c29b2c4e Mon Sep 17 00:00:00 2001
From: Mark Salyzyn <salyzyn@google.com>
Date: Mon, 17 Apr 2017 12:46:12 -0700
Subject: [PATCH] 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
---
 logd/LogBuffer.cpp | 18 ++++++++++++------
 logd/LogBuffer.h   |  1 +
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/logd/LogBuffer.cpp b/logd/LogBuffer.cpp
index 0c7019ad8..4a790c9f5 100644
--- a/logd/LogBuffer.cpp
+++ b/logd/LogBuffer.cpp
@@ -43,6 +43,8 @@
 // Default
 #define log_buffer_size(id) mMaxSize[id]
 
+const log_time LogBuffer::pruneMargin(3, 0);
+
 void LogBuffer::init() {
     log_id_for_each(i) {
         mLastSet[i] = false;
@@ -672,6 +674,8 @@ bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
         }
         times++;
     }
+    log_time watermark(log_time::tv_sec_max, log_time::tv_nsec_max);
+    if (oldest) watermark = oldest->mStart - pruneMargin;
 
     LogBufferElementCollection::iterator it;
 
@@ -693,7 +697,7 @@ bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
                 mLastSet[id] = true;
             }
 
-            if (oldest && (oldest->mStart <= element->getRealTime().nsec())) {
+            if (oldest && (watermark <= element->getRealTime())) {
                 busy = true;
                 if (oldest->mTimeout.tv_sec || oldest->mTimeout.tv_nsec) {
                     oldest->triggerReader_Locked();
@@ -785,7 +789,7 @@ bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
         while (it != mLogElements.end()) {
             LogBufferElement* element = *it;
 
-            if (oldest && (oldest->mStart <= element->getRealTime().nsec())) {
+            if (oldest && (watermark <= element->getRealTime())) {
                 busy = true;
                 if (oldest->mTimeout.tv_sec || oldest->mTimeout.tv_nsec) {
                     oldest->triggerReader_Locked();
@@ -939,7 +943,7 @@ bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
             mLastSet[id] = true;
         }
 
-        if (oldest && (oldest->mStart <= element->getRealTime().nsec())) {
+        if (oldest && (watermark <= element->getRealTime())) {
             busy = true;
             if (whitelist) {
                 break;
@@ -983,7 +987,7 @@ bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
                 mLastSet[id] = true;
             }
 
-            if (oldest && (oldest->mStart <= element->getRealTime().nsec())) {
+            if (oldest && (watermark <= element->getRealTime())) {
                 busy = true;
                 if (stats.sizes(id) > (2 * log_buffer_size(id))) {
                     // kick a misbehaving log reader client off the island
@@ -1090,13 +1094,15 @@ log_time LogBuffer::flushTo(SocketClient* reader, const log_time& start,
         // client wants to start from the beginning
         it = mLogElements.begin();
     } else {
-        LogBufferElementCollection::iterator last;
         // 3 second limit to continue search for out-of-order entries.
-        log_time min = start - log_time(3, 0);
+        log_time min = start - pruneMargin;
+
         // Cap to 300 iterations we look back for out-of-order entries.
         size_t count = 300;
+
         // Client wants to start from some specified time. Chances are
         // we are better off starting from the end of the time sorted list.
+        LogBufferElementCollection::iterator last;
         for (last = it = mLogElements.end(); it != mLogElements.begin();
              /* do nothing */) {
             --it;
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);