LogReader.cpp revision 2ee4371cb73cd23a8615593956de2e4f0cea4a98 
1/*
2 * Copyright (C) 2017 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 "logd/LogReader.h"
18
19#include <utils/Errors.h>
20
21#include <time.h>
22#include <unistd.h>
23
24using namespace android;
25using namespace std;
26
27namespace android {
28namespace os {
29namespace statsd {
30
31#define SNOOZE_INITIAL_MS 100
32#define SNOOZE_MAX_MS (10 * 60 * 1000)  // Ten minutes
33
34LogReader::LogReader(const sp<LogListener>& listener) : mListener(listener) {
35}
36
37LogReader::~LogReader() {
38}
39
40void LogReader::Run() {
41    int nextSnoozeMs = SNOOZE_INITIAL_MS;
42
43    // In an ideal world, this outer loop will only ever run one iteration, but it
44    // exists to handle crashes in logd.  The inner loop inside connect_and_read()
45    // reads from logd forever, but if that read fails, we fall out to the outer
46    // loop, do the backoff (resetting the backoff timeout if we successfully read
47    // something), and then try again.
48    while (true) {
49        // Connect and read
50        int lineCount = connect_and_read();
51
52        // Figure out how long to sleep.
53        if (lineCount > 0) {
54            // If we managed to read at least one line, reset the backoff
55            nextSnoozeMs = SNOOZE_INITIAL_MS;
56        } else {
57            // Otherwise, expontial backoff
58            nextSnoozeMs *= 1.5f;
59            if (nextSnoozeMs > 10 * 60 * 1000) {
60                // Don't wait for toooo long.
61                nextSnoozeMs = SNOOZE_MAX_MS;
62            }
63        }
64
65        // Sleep
66        timespec ts;
67        timespec rem;
68        ts.tv_sec = nextSnoozeMs / 1000;
69        ts.tv_nsec = (nextSnoozeMs % 1000) * 1000000L;
70        while (nanosleep(&ts, &rem) == -1) {
71            if (errno == EINTR) {
72                ts = rem;
73            }
74            // other errors are basically impossible
75        }
76    }
77}
78
79int LogReader::connect_and_read() {
80    int lineCount = 0;
81    status_t err;
82    logger_list* loggers;
83    logger* eventLogger;
84
85    // Prepare the logging context
86    loggers = android_logger_list_alloc(ANDROID_LOG_RDONLY,
87                                        /* don't stop after N lines */ 0,
88                                        /* no pid restriction */ 0);
89
90    // Open the buffer(s)
91    eventLogger = android_logger_open(loggers, LOG_ID_STATS);
92
93    // Read forever
94    if (eventLogger) {
95
96        while (true) {
97            log_msg msg;
98
99            // Read a message
100            err = android_logger_list_read(loggers, &msg);
101            // err = 0 - no content, unexpected connection drop or EOF.
102            // err = +ive number - size of retrieved data from logger
103            // err = -ive number, OS supplied error _except_ for -EAGAIN
104            if (err <= 0) {
105                fprintf(stderr, "logcat read failure: %s\n", strerror(err));
106                break;
107            }
108
109            // Record that we read one (used above to know how to snooze).
110            lineCount++;
111
112            // Wrap it in a LogEvent object
113            LogEvent event(msg);
114
115            // Call the listener
116            mListener->OnLogEvent(&event);
117        }
118    }
119
120    // Free the logger list and close the individual loggers
121    android_logger_list_free(loggers);
122
123    return lineCount;
124}
125
126}  // namespace statsd
127}  // namespace os
128}  // namespace android
129