1 LIBLOG(3) Android NDK Programming Manual LIBLOG(3) 2 3 4 5 NAME 6 liblog - Android NDK logger interfaces 7 8 SYNOPSIS 9 #include <log/log.h> 10 11 ALOG(android_priority, tag, format, ...) 12 IF_ALOG(android_priority, tag) 13 LOG_PRI(priority, tag, format, ...) 14 LOG_PRI_VA(priority, tag, format, args) 15 #define LOG_TAG NULL 16 ALOGV(format, ...) 17 SLOGV(format, ...) 18 RLOGV(format, ...) 19 ALOGV_IF(cond, format, ...) 20 SLOGV_IF(cond, format, ...) 21 RLOGV_IF(cond, format, ...) 22 IF_ALOGC() 23 ALOGD(format, ...) 24 SLOGD(format, ...) 25 RLOGD(format, ...) 26 ALOGD_IF(cond, format, ...) 27 SLOGD_IF(cond, format, ...) 28 RLOGD_IF(cond, format, ...) 29 IF_ALOGD() 30 ALOGI(format, ...) 31 SLOGI(format, ...) 32 RLOGI(format, ...) 33 ALOGI_IF(cond, format, ...) 34 SLOGI_IF(cond, format, ...) 35 RLOGI_IF(cond, format, ...) 36 IF_ALOGI() 37 ALOGW(format, ...) 38 SLOGW(format, ...) 39 RLOGW(format, ...) 40 ALOGW_IF(cond, format, ...) 41 SLOGW_IF(cond, format, ...) 42 RLOGW_IF(cond, format, ...) 43 IF_ALOGW() 44 ALOGE(format, ...) 45 SLOGE(format, ...) 46 RLOGE(format, ...) 47 ALOGE_IF(cond, format, ...) 48 SLOGE_IF(cond, format, ...) 49 RLOGE_IF(cond, format, ...) 50 IF_ALOGE() 51 LOG_FATAL(format, ...) 52 LOG_ALWAYS_FATAL(format, ...) 53 LOG_FATAL_IF(cond, format, ...) 54 LOG_ALWAYS_FATAL_IF(cond, format, ...) 55 ALOG_ASSERT(cond, format, ...) 56 LOG_EVENT_INT(tag, value) 57 LOG_EVENT_LONG(tag, value) 58 59 Link with -llog 60 61 #include <log/logger.h> 62 63 log_id_t android_logger_get_id(struct logger *logger) 64 int android_logger_clear(struct logger *logger) 65 int android_logger_get_log_size(struct logger *logger) 66 int android_logger_get_log_readable_size(struct logger *logger) 67 int android_logger_get_log_version(struct logger *logger) 68 69 struct logger_list *android_logger_list_alloc(int mode, unsigned int 70 tail, pid_t pid) 71 struct logger *android_logger_open(struct logger_list *logger_list, 72 log_id_t id) 73 struct logger_list *android_logger_list_open(log_id_t id, int mode, 74 unsigned int tail, pid_t pid) 75 76 int android_logger_list_read(struct logger_list *logger_list, struct 77 log_msg *log_msg 78 79 void android_logger_list_free(struct logger_list *logger_list) 80 81 log_id_t android_name_to_log_id(const char *logName) 82 const char *android_log_id_to_name(log_id_t log_id) 83 84 Link with -llog 85 86 DESCRIPTION 87 liblog represents an interface to the volatile Android Logging system 88 for NDK (Native) applications and libraries. Interfaces for either 89 writing or reading logs. The log buffers are divided up in Main, Sys 90 tem, Radio and Events sub-logs. 91 92 The logging interfaces are a series of macros, all of which can be 93 overridden individually in order to control the verbosity of the appli 94 cation or library. [ASR]LOG[VDIWE] calls are used to log to BAsic, 95 System or Radio sub-logs in either the Verbose, Debug, Info, Warning or 96 Error priorities. [ASR]LOG[VDIWE]_IF calls are used to perform thus 97 based on a condition being true. IF_ALOG[VDIWE] calls are true if the 98 current LOG_TAG is enabled at the specified priority. LOG_ALWAYS_FATAL 99 is used to ALOG a message, then kill the process. LOG_FATAL call is a 100 variant of LOG_ALWAYS_FATAL, only enabled in engineering, and not 101 release builds. ALOG_ASSERT is used to ALOG a message if the condition 102 is false; the condition is part of the logged message. 103 LOG_EVENT_(INT|LONG) is used to drop binary content into the Events 104 sub-log. 105 106 The log reading interfaces permit opening the logs either singly or 107 multiply, retrieving a log entry at a time in time sorted order, 108 optionally limited to a specific pid and tail of the log(s) and finally 109 a call closing the logs. A single log can be opened with android_log 110 ger_list_open; or multiple logs can be opened with android_log 111 ger_list_alloc, calling in turn the android_logger_open for each log 112 id. Each entry can be retrieved with android_logger_list_read. The 113 log(s) can be closed with android_logger_list_free. The logs should be 114 opened with an ANDROID_LOG_RDONLY mode. ANDROID_LOG_NONBLOCK mode 115 will report when the log reading is done with an EAGAIN error return 116 code, otherwise the android_logger_list_read call will block for new 117 entries. 118 119 The ANDROID_LOG_PSTORE mode flag to the android_logger_open is used to 120 switch from the active logs to the persistent logs from before the last 121 reboot. 122 123 The value returned by android_logger_open can be used as a parameter to 124 the android_logger_clear function to empty the sub-log. It is recom 125 mended to only open log ANDROID_LOG_WRONLY in that case. 126 127 The value returned by android_logger_open can be used as a parameter to 128 the android_logger_get_log_(size|readable_size|version) to retrieve the 129 sub-log maximum size, readable size and log buffer format protocol ver 130 sion respectively. android_logger_get_id returns the id that was used 131 when opening the sub-log. It is recommended to open the log 132 ANDROID_LOG_RDONLY in these cases. 133 134 ERRORS 135 If messages fail, a negative error code will be returned to the caller. 136 137 The -ENOTCONN return code indicates that the logger daemon is stopped. 138 139 The -EBADF return code indicates that the log access point can not be 140 opened, or the log buffer id is out of range. 141 142 For the -EAGAIN return code, this means that the logging message was 143 temporarily backed-up either because of Denial Of Service (DOS) logging 144 pressure from some chatty application or service in the Android system, 145 or if too small of a value is set in /proc/sys/net/unix/max_dgram_qlen. 146 To aid in diagnosing the occurence of this, a binary event from liblog 147 will be sent to the log daemon once a new message can get through 148 indicating how many messages were dropped as a result. Please take 149 action to resolve the structural problems at the source. 150 151 It is generally not advised for the caller to retry the -EAGAIN return 152 code as this will only make the problem(s) worse and cause your 153 application to temporarily drop to the logger daemon priority, BATCH 154 scheduling policy and background task cgroup. If you require a group of 155 messages to be passed atomically, merge them into one message with 156 embedded newlines to the maximum length LOGGER_ENTRY_MAX_PAYLOAD. 157 158 Other return codes from writing operation can be returned. Since the 159 library retries on EINTR, -EINTR should never be returned. 160 161 SEE ALSO 162 syslogd(8) 163 164 165 166 24 Jan 2014 LIBLOG(3) 167
