From 7620bcb54c86628fba8c017e0aa8ca4ec2100f29 Mon Sep 17 00:00:00 2001
From: Alex Buynytskyy <alexbuy@google.com>
Date: Fri, 5 Mar 2021 21:35:50 -0800
Subject: [PATCH] Better error message for missing page reads.

>missing reads count 15, timestamp delta 10ms

Bug: 181876064
Test: atest PackageManagerShellCommandIncrementalTest
Change-Id: I9c5a7ef62d10feee3512d934f7ad3ba9f402448c
---
 ..._pm_PackageManagerShellCommandDataLoader.cpp | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/services/core/jni/com_android_server_pm_PackageManagerShellCommandDataLoader.cpp b/services/core/jni/com_android_server_pm_PackageManagerShellCommandDataLoader.cpp
index 8efbaf577134d..f0210eeb80e8c 100644
--- a/services/core/jni/com_android_server_pm_PackageManagerShellCommandDataLoader.cpp
+++ b/services/core/jni/com_android_server_pm_PackageManagerShellCommandDataLoader.cpp
@@ -643,7 +643,7 @@ private:
         }
 
         TracedRead last = {};
-        auto lastSerialNo = mLastSerialNo;
+        auto lastSerialNo = mLastSerialNo < 0 ? pageReads[0].serialNo : mLastSerialNo;
         for (auto&& read : pageReads) {
             const auto expectedSerialNo = lastSerialNo + last.count;
 #ifdef VERBOSE_READ_LOGS
@@ -676,8 +676,7 @@ private:
 
             // Second, report missing reads, if any.
             if (read.serialNo != expectedSerialNo) {
-                const auto readsMissing = read.serialNo - expectedSerialNo;
-                traceMissingReads(readsMissing);
+                traceMissingReads(expectedSerialNo, read.serialNo);
             }
 
             last = TracedRead{
@@ -721,9 +720,13 @@ private:
         ATRACE_END();
     }
 
-    void traceMissingReads(int64_t count) {
-        const auto trace = android::base::StringPrintf("missing_page_reads: count=%lld",
-                                                       static_cast<long long>(count));
+    void traceMissingReads(int64_t expectedSerialNo, int64_t readSerialNo) {
+        const auto readsMissing = readSerialNo - expectedSerialNo;
+        const auto trace =
+                android::base::StringPrintf("missing_page_reads: count=%lld, range [%lld,%lld)",
+                                            static_cast<long long>(readsMissing),
+                                            static_cast<long long>(expectedSerialNo),
+                                            static_cast<long long>(readSerialNo));
         ATRACE_BEGIN(trace.c_str());
         ATRACE_END();
     }
@@ -874,7 +877,7 @@ private:
     std::atomic<bool> mStopReceiving = false;
     std::atomic<bool> mReadLogsEnabled = false;
     std::chrono::milliseconds mWaitOnEofInterval{WaitOnEofMinInterval};
-    int64_t mLastSerialNo{1};
+    int64_t mLastSerialNo{-1};
     /** Tracks which files have been requested */
     std::unordered_set<FileIdx> mRequestedFiles;
 };