| LIBLOG(3) Android Internal NDK Programming Manual LIBLOG(3) |
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| NAME |
| liblog - Android Internal NDK logger interfaces |
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| SYNOPSIS |
| /* |
| * Please limit to 24 characters for runtime is loggable, |
| * 16 characters for persist is loggable, and logcat pretty |
| * alignment with limit of 7 characters. |
| */ |
| #define LOG_TAG "yourtag" |
| #include <log/log.h> |
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| ALOG(android_priority, tag, format, ...) |
| IF_ALOG(android_priority, tag) |
| LOG_PRI(priority, tag, format, ...) |
| LOG_PRI_VA(priority, tag, format, args) |
| #define LOG_TAG NULL |
| ALOGV(format, ...) |
| SLOGV(format, ...) |
| RLOGV(format, ...) |
| ALOGV_IF(cond, format, ...) |
| SLOGV_IF(cond, format, ...) |
| RLOGV_IF(cond, format, ...) |
| IF_ALOGC() |
| ALOGD(format, ...) |
| SLOGD(format, ...) |
| RLOGD(format, ...) |
| ALOGD_IF(cond, format, ...) |
| SLOGD_IF(cond, format, ...) |
| RLOGD_IF(cond, format, ...) |
| IF_ALOGD() |
| ALOGI(format, ...) |
| SLOGI(format, ...) |
| RLOGI(format, ...) |
| ALOGI_IF(cond, format, ...) |
| SLOGI_IF(cond, format, ...) |
| RLOGI_IF(cond, format, ...) |
| IF_ALOGI() |
| ALOGW(format, ...) |
| SLOGW(format, ...) |
| RLOGW(format, ...) |
| ALOGW_IF(cond, format, ...) |
| SLOGW_IF(cond, format, ...) |
| RLOGW_IF(cond, format, ...) |
| IF_ALOGW() |
| ALOGE(format, ...) |
| SLOGE(format, ...) |
| RLOGE(format, ...) |
| ALOGE_IF(cond, format, ...) |
| SLOGE_IF(cond, format, ...) |
| RLOGE_IF(cond, format, ...) |
| IF_ALOGE() |
| LOG_FATAL(format, ...) |
| LOG_ALWAYS_FATAL(format, ...) |
| LOG_FATAL_IF(cond, format, ...) |
| LOG_ALWAYS_FATAL_IF(cond, format, ...) |
| ALOG_ASSERT(cond, format, ...) |
| LOG_EVENT_INT(tag, value) |
| LOG_EVENT_LONG(tag, value) |
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| clockid_t android_log_clockid() |
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| log_id_t android_logger_get_id(struct logger *logger) |
| int android_logger_clear(struct logger *logger) |
| int android_logger_get_log_size(struct logger *logger) |
| int android_logger_get_log_readable_size(struct logger *logger) |
| int android_logger_get_log_version(struct logger *logger) |
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| struct logger_list *android_logger_list_alloc(int mode, |
| unsigned int tail, |
| pid_t pid) |
| struct logger *android_logger_open(struct logger_list *logger_list, |
| log_id_t id) |
| struct logger_list *android_logger_list_open(log_id_t id, int mode, |
| unsigned int tail, |
| pid_t pid) |
| int android_logger_list_read(struct logger_list *logger_list, |
| struct log_msg *log_msg) |
| void android_logger_list_free(struct logger_list *logger_list) |
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| log_id_t android_name_to_log_id(const char *logName) |
| const char *android_log_id_to_name(log_id_t log_id) |
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| android_log_context create_android_logger(uint32_t tag) |
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| int android_log_write_list_begin(android_log_context ctx) |
| int android_log_write_list_end(android_log_context ctx) |
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| int android_log_write_int32(android_log_context ctx, int32_t value) |
| int android_log_write_int64(android_log_context ctx, int64_t value) |
| int android_log_write_string8(android_log_context ctx, |
| const char *value) |
| int android_log_write_string8_len(android_log_context ctx, |
| const char *value, size_t maxlen) |
| int android_log_write_float32(android_log_context ctx, float value) |
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| int android_log_write_list(android_log_context ctx, |
| log_id_t id = LOG_ID_EVENTS) |
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| android_log_context create_android_log_parser(const char *msg, |
| size_t len) |
| android_log_list_element android_log_read_next(android_log_context ctx) |
| android_log_list_element android_log_peek_next(android_log_context ctx) |
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| int android_log_destroy(android_log_context *ctx) |
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| #include <log/log_transport.h> |
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| int android_set_log_transport(int transport_flag) |
| int android_get_log_transport() |
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| Link with -llog |
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| DESCRIPTION |
| liblog represents an interface to the volatile Android Logging system |
| for NDK (Native) applications and libraries. Interfaces for either |
| writing or reading logs. The log buffers are divided up in Main, Sys‐ |
| tem, Radio and Events sub-logs. |
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| The logging interfaces are a series of macros, all of which can be |
| overridden individually in order to control the verbosity of the appli‐ |
| cation or library. [ASR]LOG[VDIWE] calls are used to log to BAsic, |
| System or Radio sub-logs in either the Verbose, Debug, Info, Warning or |
| Error priorities. [ASR]LOG[VDIWE]_IF calls are used to perform thus |
| based on a condition being true. IF_ALOG[VDIWE] calls are true if the |
| current LOG_TAG is enabled at the specified priority. LOG_ALWAYS_FATAL |
| is used to ALOG a message, then kill the process. LOG_FATAL call is a |
| variant of LOG_ALWAYS_FATAL, only enabled in engineering, and not |
| release builds. ALOG_ASSERT is used to ALOG a message if the condition |
| is false; the condition is part of the logged message. |
| LOG_EVENT_(INT|LONG) is used to drop binary content into the Events |
| sub-log. |
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| The log reading interfaces permit opening the logs either singly or |
| multiply, retrieving a log entry at a time in time sorted order, |
| optionally limited to a specific pid and tail of the log(s) and finally |
| a call closing the logs. A single log can be opened with android_log‐ |
| ger_list_open; or multiple logs can be opened with android_log‐ |
| ger_list_alloc, calling in turn the android_logger_open for each log |
| id. Each entry can be retrieved with android_logger_list_read. The |
| log(s) can be closed with android_logger_list_free. The logs should be |
| opened with an ANDROID_LOG_RDONLY mode. ANDROID_LOG_NONBLOCK mode |
| will report when the log reading is done with an EAGAIN error return |
| code, otherwise the android_logger_list_read call will block for new |
| entries. |
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| The ANDROID_LOG_WRAP mode flag to the android_logger_list_alloc_time |
| signals logd to quiesce the reader until the buffer is about to prune |
| at the start time then proceed to dumping content. |
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| The ANDROID_LOG_PSTORE mode flag to the android_logger_open is used to |
| switch from the active logs to the persistent logs from before the last |
| reboot. |
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| The value returned by android_logger_open can be used as a parameter to |
| the android_logger_clear function to empty the sub-log. It is recom‐ |
| mended to only open log ANDROID_LOG_WRONLY in that case. |
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| The value returned by android_logger_open can be used as a parameter to |
| the android_logger_get_log_(size|readable_size|version) to retrieve the |
| sub-log maximum size, readable size and log buffer format protocol ver‐ |
| sion respectively. android_logger_get_id returns the id that was used |
| when opening the sub-log. It is recommended to open the log |
| ANDROID_LOG_RDONLY in these cases. |
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| android_set_log_transport() selects transport filters. Argument is |
| either LOGGER_DEFAULT, LOGGER_LOGD, LOGGER_NULL or LOGGER_LOCAL. Log to |
| logger daemon for default or logd, drop contents on floor, or log into |
| local memory respectively. Both android_set_log_transport() |
| and android_get_log_transport() return the current transport mask, or |
| a negative errno for any problems. |
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| ERRORS |
| If messages fail, a negative error code will be returned to the caller. |
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| The -ENOTCONN return code indicates that the logger daemon is stopped. |
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| The -EBADF return code indicates that the log access point can not be |
| opened, or the log buffer id is out of range. |
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| For the -EAGAIN return code, this means that the logging message was |
| temporarily backed-up either because of Denial Of Service (DOS) logging |
| pressure from some chatty application or service in the Android system, |
| or if too small of a value is set in /proc/sys/net/unix/max_dgram_qlen. |
| To aid in diagnosing the occurence of this, a binary event from liblog |
| will be sent to the log daemon once a new message can get through |
| indicating how many messages were dropped as a result. Please take |
| action to resolve the structural problems at the source. |
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| It is generally not advised for the caller to retry the -EAGAIN return |
| code as this will only make the problem(s) worse and cause your |
| application to temporarily drop to the logger daemon priority, BATCH |
| scheduling policy and background task cgroup. If you require a group of |
| messages to be passed atomically, merge them into one message with |
| embedded newlines to the maximum length LOGGER_ENTRY_MAX_PAYLOAD. |
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| Other return codes from writing operation can be returned. Since the |
| library retries on EINTR, -EINTR should never be returned. |
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| SEE ALSO |
| syslogd(8), klogd, auditd(8) |
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| 08 Feb 2017 LIBLOG(3) |