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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #include <errno.h>
     18 #include <fcntl.h>
     19 #include <stdio.h>
     20 #include <stdlib.h>
     21 #include <string.h>
     22 
     23 #include "private/bionic_lock.h"
     24 #include "private/bionic_systrace.h"
     25 #include "private/CachedProperty.h"
     26 
     27 #include <cutils/trace.h> // For ATRACE_TAG_BIONIC.
     28 
     29 #define WRITE_OFFSET   32
     30 
     31 static Lock g_lock;
     32 static CachedProperty g_debug_atrace_tags_enableflags("debug.atrace.tags.enableflags");
     33 static uint64_t g_tags;
     34 static int g_trace_marker_fd = -1;
     35 
     36 static bool should_trace() {
     37   g_lock.lock();
     38   if (g_debug_atrace_tags_enableflags.DidChange()) {
     39     g_tags = strtoull(g_debug_atrace_tags_enableflags.Get(), nullptr, 0);
     40   }
     41   g_lock.unlock();
     42   return ((g_tags & ATRACE_TAG_BIONIC) != 0);
     43 }
     44 
     45 static int get_trace_marker_fd() {
     46   g_lock.lock();
     47   if (g_trace_marker_fd == -1) {
     48     g_trace_marker_fd = open("/sys/kernel/debug/tracing/trace_marker", O_CLOEXEC | O_WRONLY);
     49   }
     50   g_lock.unlock();
     51   return g_trace_marker_fd;
     52 }
     53 
     54 void bionic_trace_begin(const char* message) {
     55   if (!should_trace()) {
     56     return;
     57   }
     58 
     59   int trace_marker_fd = get_trace_marker_fd();
     60   if (trace_marker_fd == -1) {
     61     return;
     62   }
     63 
     64   // If bionic tracing has been enabled, then write the message to the
     65   // kernel trace_marker.
     66   int length = strlen(message);
     67   char buf[length + WRITE_OFFSET];
     68   size_t len = snprintf(buf, length + WRITE_OFFSET, "B|%d|%s", getpid(), message);
     69 
     70   // Tracing may stop just after checking property and before writing the message.
     71   // So the write is acceptable to fail. See b/20666100.
     72   TEMP_FAILURE_RETRY(write(trace_marker_fd, buf, len));
     73 }
     74 
     75 void bionic_trace_end() {
     76   if (!should_trace()) {
     77     return;
     78   }
     79 
     80   int trace_marker_fd = get_trace_marker_fd();
     81   if (trace_marker_fd == -1) {
     82     return;
     83   }
     84 
     85   TEMP_FAILURE_RETRY(write(trace_marker_fd, "E", 1));
     86 }
     87 
     88 ScopedTrace::ScopedTrace(const char* message) : called_end_(false) {
     89   bionic_trace_begin(message);
     90 }
     91 
     92 ScopedTrace::~ScopedTrace() {
     93   End();
     94 }
     95 
     96 void ScopedTrace::End() {
     97   if (!called_end_) {
     98     bionic_trace_end();
     99     called_end_ = true;
    100   }
    101 }
    102