bionic_systrace.cpp revision 166112531558a1d4ea179c29147f27db7045db22 
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 <cutils/trace.h>
18#include <errno.h>
19#include <fcntl.h>
20#include <stdio.h>
21#include <stdlib.h>
22#include <string.h>
23
24#include "private/bionic_lock.h"
25#include "private/bionic_systrace.h"
26#include "private/libc_logging.h"
27
28#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
29#include <sys/_system_properties.h>
30
31#define WRITE_OFFSET   32
32
33constexpr char SYSTRACE_PROPERTY_NAME[] = "debug.atrace.tags.enableflags";
34
35static Lock g_lock;
36static const prop_info* g_pinfo;
37static uint32_t g_serial = -1;
38static uint64_t g_tags;
39static int g_trace_marker_fd = -1;
40
41static bool should_trace() {
42  bool result = false;
43  g_lock.lock();
44  // If g_pinfo is null, this means that systrace hasn't been run and it's safe to
45  // assume that no trace writing will need to take place.  However, to avoid running
46  // this costly find check each time, we set it to a non-tracing value so that next
47  // time, it will just check the serial to see if the value has been changed.
48  // this function also deals with the bootup case, during which the call to property
49  // set will fail if the property server hasn't yet started.
50  if (g_pinfo == NULL) {
51    g_pinfo = __system_property_find(SYSTRACE_PROPERTY_NAME);
52    if (g_pinfo == NULL) {
53      __system_property_set(SYSTRACE_PROPERTY_NAME, "0");
54      g_pinfo = __system_property_find(SYSTRACE_PROPERTY_NAME);
55    }
56  }
57  if (g_pinfo != NULL) {
58    // Find out which tags have been enabled on the command line and set
59    // the value of tags accordingly.  If the value of the property changes,
60    // the serial will also change, so the costly system_property_read function
61    // can be avoided by calling the much cheaper system_property_serial
62    // first.  The values within pinfo may change, but its location is guaranteed
63    // not to move.
64    uint32_t cur_serial = __system_property_serial(g_pinfo);
65    if (cur_serial != g_serial) {
66      g_serial = cur_serial;
67      char value[PROP_VALUE_MAX];
68      __system_property_read(g_pinfo, 0, value);
69      g_tags = strtoull(value, NULL, 0);
70    }
71    result = ((g_tags & ATRACE_TAG_BIONIC) != 0);
72  }
73  g_lock.unlock();
74  return result;
75}
76
77static int get_trace_marker_fd() {
78  g_lock.lock();
79  if (g_trace_marker_fd == -1) {
80    g_trace_marker_fd = open("/sys/kernel/debug/tracing/trace_marker", O_CLOEXEC | O_WRONLY);
81  }
82  g_lock.unlock();
83  return g_trace_marker_fd;
84}
85
86ScopedTrace::ScopedTrace(const char* message) {
87  if (!should_trace()) {
88    return;
89  }
90
91  int trace_marker_fd = get_trace_marker_fd();
92  if (trace_marker_fd == -1) {
93    return;
94  }
95
96  // If bionic tracing has been enabled, then write the message to the
97  // kernel trace_marker.
98  int length = strlen(message);
99  char buf[length + WRITE_OFFSET];
100  size_t len = snprintf(buf, length + WRITE_OFFSET, "B|%d|%s", getpid(), message);
101
102  // Tracing may stop just after checking property and before writing the message.
103  // So the write is acceptable to fail. See b/20666100.
104  TEMP_FAILURE_RETRY(write(trace_marker_fd, buf, len));
105}
106
107ScopedTrace::~ScopedTrace() {
108  if (!should_trace()) {
109    return;
110  }
111
112  int trace_marker_fd = get_trace_marker_fd();
113  if (trace_marker_fd == -1) {
114    return;
115  }
116
117  TEMP_FAILURE_RETRY(write(trace_marker_fd, "E", 1));
118}
119