bionic_systrace.cpp revision 9e87f2f876243225deef37645ddceaa5d225cb41 
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 <fcntl.h>
19#include <stdio.h>
20#include <stdlib.h>
21
22#include "private/bionic_systrace.h"
23#include "private/libc_logging.h"
24
25#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
26#include <sys/_system_properties.h>
27
28#define WRITE_OFFSET   32
29
30static const prop_info* g_pinfo = NULL;
31static uint32_t g_serial = -1;
32static uint64_t g_tags = 0;
33static int g_trace_marker_fd = -1;
34
35static bool should_trace() {
36  // If g_pinfo is null, this means that systrace hasn't been run and it's safe to
37  // assume that no trace writing will need to take place.  However, to avoid running
38  // this costly find check each time, we set it to a non-tracing value so that next
39  // time, it will just check the serial to see if the value has been changed.
40  // this function also deals with the bootup case, during which the call to property
41  // set will fail if the property server hasn't yet started.
42  if (g_pinfo == NULL) {
43    g_pinfo = __system_property_find("debug.atrace.tags.enableflags");
44    if (g_pinfo == NULL) {
45      __system_property_set("debug.atrace.tags.enableflags", "0");
46      g_pinfo = __system_property_find("debug.atrace.tags.enableflags");
47      if (g_pinfo == NULL) {
48        return false;
49      }
50    }
51  }
52
53  // Find out which tags have been enabled on the command line and set
54  // the value of tags accordingly.  If the value of the property changes,
55  // the serial will also change, so the costly system_property_read function
56  // can be avoided by calling the much cheaper system_property_serial
57  // first.  The values within pinfo may change, but its location is guaranteed
58  // not to move.
59  const uint32_t cur_serial = __system_property_serial(g_pinfo);
60  if (cur_serial != g_serial) {
61    g_serial = cur_serial;
62    char value[PROP_VALUE_MAX];
63    __system_property_read(g_pinfo, 0, value);
64    g_tags = strtoull(value, NULL, 0);
65  }
66
67  // Finally, verify that this tag value enables bionic tracing.
68  return ((g_tags & ATRACE_TAG_BIONIC) != 0);
69}
70
71ScopedTrace::ScopedTrace(const char* message) {
72  if (!should_trace()) {
73    return;
74  }
75
76  if (g_trace_marker_fd == -1) {
77    g_trace_marker_fd = open("/sys/kernel/debug/tracing/trace_marker", O_WRONLY | O_CLOEXEC);
78    if (g_trace_marker_fd == -1) {
79      __libc_fatal("Could not open kernel trace file: %s\n", strerror(errno));
80    }
81  }
82
83  // If bionic tracing has been enabled, then write the message to the
84  // kernel trace_marker.
85  int length = strlen(message);
86  char buf[length + WRITE_OFFSET];
87  size_t len = snprintf(buf, length + WRITE_OFFSET, "B|%d|%s", getpid(), message);
88  ssize_t wbytes = TEMP_FAILURE_RETRY(write(g_trace_marker_fd, buf, len));
89
90  // Error while writing
91  if (static_cast<size_t>(wbytes) != len) {
92    __libc_fatal("Could not write to kernel trace file: %s\n", strerror(errno));
93  }
94}
95
96ScopedTrace::~ScopedTrace() {
97  if (!should_trace()) {
98    return;
99  }
100
101  ssize_t wbytes = TEMP_FAILURE_RETRY(write(g_trace_marker_fd, "E", 1));
102
103  // Error while writing
104  if (static_cast<size_t>(wbytes) != 1) {
105    __libc_fatal("Could not write to kernel trace file: %s\n", strerror(errno));
106  }
107}
108