From 2980f57f2c3da88139342b394f685c2c505c96c5 Mon Sep 17 00:00:00 2001
From: Luis Hector Chavez <lhchavez@google.com>
Date: Wed, 11 Apr 2018 15:35:44 -0700
Subject: [PATCH] init: Use android::base::boot_clock instead of /proc/uptime

/proc/uptime internally uses whatever would be returned by
clock_gettime(CLOCK_BOOTTIME), so use android::base::boot_clock instead
which avoids parsing strings and rounding errors.

Bug: 77273909
Test: CtsBootStatsTestCases
Change-Id: Ic162eefcf226073949a18cca55db3c2324b98749
---
 init/bootchart.cpp | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/init/bootchart.cpp b/init/bootchart.cpp
index 379b4fa84..c2cf57399 100644
--- a/init/bootchart.cpp
+++ b/init/bootchart.cpp
@@ -32,12 +32,14 @@
 #include <mutex>
 #include <thread>
 
+#include <android-base/chrono_utils.h>
 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
 
 using android::base::StringPrintf;
+using android::base::boot_clock;
 using namespace std::chrono_literals;
 
 namespace android {
@@ -50,9 +52,9 @@ static std::condition_variable g_bootcharting_finished_cv;
 static bool g_bootcharting_finished;
 
 static long long get_uptime_jiffies() {
-  std::string uptime;
-  if (!android::base::ReadFileToString("/proc/uptime", &uptime)) return 0;
-  return 100LL * strtod(uptime.c_str(), NULL);
+    constexpr int64_t kNanosecondsPerJiffy = 10000000;
+    boot_clock::time_point uptime = boot_clock::now();
+    return uptime.time_since_epoch().count() / kNanosecondsPerJiffy;
 }
 
 static std::unique_ptr<FILE, decltype(&fclose)> fopen_unique(const char* filename,