1 LIBLOG(3) Android Internal NDK Programming Manual LIBLOG(3) 2 3 4 5 NAME 6 liblog - Android Internal NDK logger interfaces 7 8 SYNOPSIS 9 /* 10 * Please limit to 24 characters for runtime is loggable, 11 * 16 characters for persist is loggable, and logcat pretty 12 * alignment with limit of 7 characters. 13 */ 14 #define LOG_TAG "yourtag" 15 #include <log/log.h> 16 17 ALOG(android_priority, tag, format, ...) 18 IF_ALOG(android_priority, tag) 19 LOG_PRI(priority, tag, format, ...) 20 LOG_PRI_VA(priority, tag, format, args) 21 #define LOG_TAG NULL 22 ALOGV(format, ...) 23 SLOGV(format, ...) 24 RLOGV(format, ...) 25 ALOGV_IF(cond, format, ...) 26 SLOGV_IF(cond, format, ...) 27 RLOGV_IF(cond, format, ...) 28 IF_ALOGC() 29 ALOGD(format, ...) 30 SLOGD(format, ...) 31 RLOGD(format, ...) 32 ALOGD_IF(cond, format, ...) 33 SLOGD_IF(cond, format, ...) 34 RLOGD_IF(cond, format, ...) 35 IF_ALOGD() 36 ALOGI(format, ...) 37 SLOGI(format, ...) 38 RLOGI(format, ...) 39 ALOGI_IF(cond, format, ...) 40 SLOGI_IF(cond, format, ...) 41 RLOGI_IF(cond, format, ...) 42 IF_ALOGI() 43 ALOGW(format, ...) 44 SLOGW(format, ...) 45 RLOGW(format, ...) 46 ALOGW_IF(cond, format, ...) 47 SLOGW_IF(cond, format, ...) 48 RLOGW_IF(cond, format, ...) 49 IF_ALOGW() 50 ALOGE(format, ...) 51 SLOGE(format, ...) 52 RLOGE(format, ...) 53 ALOGE_IF(cond, format, ...) 54 SLOGE_IF(cond, format, ...) 55 RLOGE_IF(cond, format, ...) 56 IF_ALOGE() 57 LOG_FATAL(format, ...) 58 LOG_ALWAYS_FATAL(format, ...) 59 LOG_FATAL_IF(cond, format, ...) 60 LOG_ALWAYS_FATAL_IF(cond, format, ...) 61 ALOG_ASSERT(cond, format, ...) 62 LOG_EVENT_INT(tag, value) 63 LOG_EVENT_LONG(tag, value) 64 65 clockid_t android_log_clockid() 66 67 log_id_t android_logger_get_id(struct logger *logger) 68 int android_logger_clear(struct logger *logger) 69 int android_logger_get_log_size(struct logger *logger) 70 int android_logger_get_log_readable_size(struct logger *logger) 71 int android_logger_get_log_version(struct logger *logger) 72 73 struct logger_list *android_logger_list_alloc(int mode, 74 unsigned int tail, 75 pid_t pid) 76 struct logger *android_logger_open(struct logger_list *logger_list, 77 log_id_t id) 78 struct logger_list *android_logger_list_open(log_id_t id, int mode, 79 unsigned int tail, 80 pid_t pid) 81 int android_logger_list_read(struct logger_list *logger_list, 82 struct log_msg *log_msg) 83 void android_logger_list_free(struct logger_list *logger_list) 84 85 log_id_t android_name_to_log_id(const char *logName) 86 const char *android_log_id_to_name(log_id_t log_id) 87 88 android_log_context create_android_logger(uint32_t tag) 89 90 int android_log_write_list_begin(android_log_context ctx) 91 int android_log_write_list_end(android_log_context ctx) 92 93 int android_log_write_int32(android_log_context ctx, int32_t value) 94 int android_log_write_int64(android_log_context ctx, int64_t value) 95 int android_log_write_string8(android_log_context ctx, 96 const char *value) 97 int android_log_write_string8_len(android_log_context ctx, 98 const char *value, size_t maxlen) 99 int android_log_write_float32(android_log_context ctx, float value) 100 101 int android_log_write_list(android_log_context ctx, 102 log_id_t id = LOG_ID_EVENTS) 103 104 android_log_context create_android_log_parser(const char *msg, 105 size_t len) 106 android_log_list_element android_log_read_next(android_log_context ctx) 107 android_log_list_element android_log_peek_next(android_log_context ctx) 108 109 int android_log_destroy(android_log_context *ctx) 110 111 #include <log/log_transport.h> 112 113 int android_set_log_transport(int transport_flag) 114 int android_get_log_transport() 115 116 Link with -llog 117 118 DESCRIPTION 119 liblog represents an interface to the volatile Android Logging system 120 for NDK (Native) applications and libraries. Interfaces for either 121 writing or reading logs. The log buffers are divided up in Main, Sys 122 tem, Radio and Events sub-logs. 123 124 The logging interfaces are a series of macros, all of which can be 125 overridden individually in order to control the verbosity of the appli 126 cation or library. [ASR]LOG[VDIWE] calls are used to log to BAsic, 127 System or Radio sub-logs in either the Verbose, Debug, Info, Warning or 128 Error priorities. [ASR]LOG[VDIWE]_IF calls are used to perform thus 129 based on a condition being true. IF_ALOG[VDIWE] calls are true if the 130 current LOG_TAG is enabled at the specified priority. LOG_ALWAYS_FATAL 131 is used to ALOG a message, then kill the process. LOG_FATAL call is a 132 variant of LOG_ALWAYS_FATAL, only enabled in engineering, and not 133 release builds. ALOG_ASSERT is used to ALOG a message if the condition 134 is false; the condition is part of the logged message. 135 LOG_EVENT_(INT|LONG) is used to drop binary content into the Events 136 sub-log. 137 138 The log reading interfaces permit opening the logs either singly or 139 multiply, retrieving a log entry at a time in time sorted order, 140 optionally limited to a specific pid and tail of the log(s) and finally 141 a call closing the logs. A single log can be opened with android_log 142 ger_list_open; or multiple logs can be opened with android_log 143 ger_list_alloc, calling in turn the android_logger_open for each log 144 id. Each entry can be retrieved with android_logger_list_read. The 145 log(s) can be closed with android_logger_list_free. The logs should be 146 opened with an ANDROID_LOG_RDONLY mode. ANDROID_LOG_NONBLOCK mode 147 will report when the log reading is done with an EAGAIN error return 148 code, otherwise the android_logger_list_read call will block for new 149 entries. 150 151 The ANDROID_LOG_WRAP mode flag to the android_logger_list_alloc_time 152 signals logd to quiesce the reader until the buffer is about to prune 153 at the start time then proceed to dumping content. 154 155 The ANDROID_LOG_PSTORE mode flag to the android_logger_open is used to 156 switch from the active logs to the persistent logs from before the last 157 reboot. 158 159 The value returned by android_logger_open can be used as a parameter to 160 the android_logger_clear function to empty the sub-log. It is recom 161 mended to only open log ANDROID_LOG_WRONLY in that case. 162 163 The value returned by android_logger_open can be used as a parameter to 164 the android_logger_get_log_(size|readable_size|version) to retrieve the 165 sub-log maximum size, readable size and log buffer format protocol ver 166 sion respectively. android_logger_get_id returns the id that was used 167 when opening the sub-log. It is recommended to open the log 168 ANDROID_LOG_RDONLY in these cases. 169 170 android_set_log_transport() selects transport filters. Argument is 171 either LOGGER_DEFAULT, LOGGER_LOGD, LOGGER_NULL or LOGGER_LOCAL. Log to 172 logger daemon for default or logd, drop contents on floor, or log into 173 local memory respectively. Both android_set_log_transport() 174 and android_get_log_transport() return the current transport mask, or 175 a negative errno for any problems. 176 177 ERRORS 178 If messages fail, a negative error code will be returned to the caller. 179 180 The -ENOTCONN return code indicates that the logger daemon is stopped. 181 182 The -EBADF return code indicates that the log access point can not be 183 opened, or the log buffer id is out of range. 184 185 For the -EAGAIN return code, this means that the logging message was 186 temporarily backed-up either because of Denial Of Service (DOS) logging 187 pressure from some chatty application or service in the Android system, 188 or if too small of a value is set in /proc/sys/net/unix/max_dgram_qlen. 189 To aid in diagnosing the occurence of this, a binary event from liblog 190 will be sent to the log daemon once a new message can get through 191 indicating how many messages were dropped as a result. Please take 192 action to resolve the structural problems at the source. 193 194 It is generally not advised for the caller to retry the -EAGAIN return 195 code as this will only make the problem(s) worse and cause your 196 application to temporarily drop to the logger daemon priority, BATCH 197 scheduling policy and background task cgroup. If you require a group of 198 messages to be passed atomically, merge them into one message with 199 embedded newlines to the maximum length LOGGER_ENTRY_MAX_PAYLOAD. 200 201 Other return codes from writing operation can be returned. Since the 202 library retries on EINTR, -EINTR should never be returned. 203 204 SEE ALSO 205 syslogd(8), klogd, auditd(8) 206 207 208 209 08 Feb 2017 LIBLOG(3) 210
