d45d36e011
- If logger system is prostrated, send an event message with the liblog tag from the associated UID and PID with a count of dropped messages once logging is resumed. - Added to the README a description of the error return values. - Describe in the README the appropriate mitigations for dropped messages. - If the caller sees this message, then /proc/sys/net/unix/max_dgram_qlen is likely too small Change-Id: Iaf387b9e5e1b6aa93bebc7481f9e8353732e3229
166 lines
7.1 KiB
Text
166 lines
7.1 KiB
Text
LIBLOG(3) Android NDK Programming Manual LIBLOG(3)
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NAME
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liblog - Android NDK logger interfaces
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SYNOPSIS
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#include <log/log.h>
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ALOG(android_priority, tag, format, ...)
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IF_ALOG(android_priority, tag)
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LOG_PRI(priority, tag, format, ...)
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LOG_PRI_VA(priority, tag, format, args)
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#define LOG_TAG NULL
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ALOGV(format, ...)
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SLOGV(format, ...)
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RLOGV(format, ...)
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ALOGV_IF(cond, format, ...)
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SLOGV_IF(cond, format, ...)
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RLOGV_IF(cond, format, ...)
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IF_ALOGC()
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ALOGD(format, ...)
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SLOGD(format, ...)
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RLOGD(format, ...)
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ALOGD_IF(cond, format, ...)
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SLOGD_IF(cond, format, ...)
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RLOGD_IF(cond, format, ...)
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IF_ALOGD()
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ALOGI(format, ...)
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SLOGI(format, ...)
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RLOGI(format, ...)
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ALOGI_IF(cond, format, ...)
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SLOGI_IF(cond, format, ...)
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RLOGI_IF(cond, format, ...)
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IF_ALOGI()
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ALOGW(format, ...)
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SLOGW(format, ...)
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RLOGW(format, ...)
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ALOGW_IF(cond, format, ...)
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SLOGW_IF(cond, format, ...)
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RLOGW_IF(cond, format, ...)
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IF_ALOGW()
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ALOGE(format, ...)
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SLOGE(format, ...)
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RLOGE(format, ...)
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ALOGE_IF(cond, format, ...)
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SLOGE_IF(cond, format, ...)
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RLOGE_IF(cond, format, ...)
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IF_ALOGE()
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LOG_FATAL(format, ...)
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LOG_ALWAYS_FATAL(format, ...)
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LOG_FATAL_IF(cond, format, ...)
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LOG_ALWAYS_FATAL_IF(cond, format, ...)
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ALOG_ASSERT(cond, format, ...)
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LOG_EVENT_INT(tag, value)
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LOG_EVENT_LONG(tag, value)
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Link with -llog
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#include <log/logger.h>
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log_id_t android_logger_get_id(struct logger *logger)
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int android_logger_clear(struct logger *logger)
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int android_logger_get_log_size(struct logger *logger)
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int android_logger_get_log_readable_size(struct logger *logger)
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int android_logger_get_log_version(struct logger *logger)
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struct logger_list *android_logger_list_alloc(int mode, unsigned int
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tail, pid_t pid)
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struct logger *android_logger_open(struct logger_list *logger_list,
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log_id_t id)
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struct logger_list *android_logger_list_open(log_id_t id, int mode,
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unsigned int tail, pid_t pid)
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int android_logger_list_read(struct logger_list *logger_list, struct
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log_msg *log_msg
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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)
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const char *android_log_id_to_name(log_id_t log_id)
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Link with -llog
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DESCRIPTION
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liblog represents an interface to the volatile Android Logging system
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for NDK (Native) applications and libraries. Interfaces for either
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writing or reading logs. The log buffers are divided up in Main, Sys‐
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tem, Radio and Events sub-logs.
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The logging interfaces are a series of macros, all of which can be
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overridden individually in order to control the verbosity of the appli‐
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cation or library. [ASR]LOG[VDIWE] calls are used to log to BAsic,
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System or Radio sub-logs in either the Verbose, Debug, Info, Warning or
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Error priorities. [ASR]LOG[VDIWE]_IF calls are used to perform thus
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based on a condition being true. IF_ALOG[VDIWE] calls are true if the
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current LOG_TAG is enabled at the specified priority. LOG_ALWAYS_FATAL
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is used to ALOG a message, then kill the process. LOG_FATAL call is a
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variant of LOG_ALWAYS_FATAL, only enabled in engineering, and not
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release builds. ALOG_ASSERT is used to ALOG a message if the condition
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is false; the condition is part of the logged message.
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LOG_EVENT_(INT|LONG) is used to drop binary content into the Events
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sub-log.
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The log reading interfaces permit opening the logs either singly or
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multiply, retrieving a log entry at a time in time sorted order,
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optionally limited to a specific pid and tail of the log(s) and finally
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a call closing the logs. A single log can be opened with android_log‐
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ger_list_open; or multiple logs can be opened with android_log‐
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ger_list_alloc, calling in turn the android_logger_open for each log
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id. Each entry can be retrieved with android_logger_list_read. The
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log(s) can be closed with android_logger_list_free. The logs should be
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opened with an ANDROID_LOG_RDONLY mode. ANDROID_LOG_NONBLOCK mode
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will report when the log reading is done with an EAGAIN error return
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code, otherwise the android_logger_list_read call will block for new
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entries.
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The ANDROID_LOG_PSTORE mode flag to the android_logger_open is used to
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switch from the active logs to the persistent logs from before the last
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reboot.
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The value returned by android_logger_open can be used as a parameter to
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the android_logger_clear function to empty the sub-log. It is recom‐
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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
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the android_logger_get_log_(size|readable_size|version) to retrieve the
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sub-log maximum size, readable size and log buffer format protocol ver‐
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sion respectively. android_logger_get_id returns the id that was used
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when opening the sub-log. It is recommended to open the log
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ANDROID_LOG_RDONLY in these cases.
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ERRORS
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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
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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
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temporarily backed-up either because of Denial Of Service (DOS) logging
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pressure from some chatty application or service in the Android system,
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or if too small of a value is set in /proc/sys/net/unix/max_dgram_qlen.
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To aid in diagnosing the occurence of this, a binary event from liblog
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will be sent to the log daemon once a new message can get through
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indicating how many messages were dropped as a result. Please take
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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
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code as this will only make the problem(s) worse and cause your
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application to temporarily drop to the logger daemon priority, BATCH
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scheduling policy and background task cgroup. If you require a group of
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messages to be passed atomically, merge them into one message with
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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
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library retries on EINTR, -EINTR should never be returned.
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SEE ALSO
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syslogd(8)
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24 Jan 2014 LIBLOG(3)
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