1LIBLOG(3) Android NDK Programming Manual LIBLOG(3)
2
3
4
5NAME
6 liblog - Android NDK logger interfaces
7
8SYNOPSIS
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
86DESCRIPTION
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_WRAP mode flag to the android_logger_list_alloc_time
120 signals logd to quiesce the reader until the buffer is about to prune
121 at the start time then proceed to dumping content.
122
123 The ANDROID_LOG_PSTORE mode flag to the android_logger_open is used to
124 switch from the active logs to the persistent logs from before the last
125 reboot.
126
127 The value returned by android_logger_open can be used as a parameter to
128 the android_logger_clear function to empty the sub-log. It is recom‐
129 mended to only open log ANDROID_LOG_WRONLY in that case.
130
131 The value returned by android_logger_open can be used as a parameter to
132 the android_logger_get_log_(size|readable_size|version) to retrieve the
133 sub-log maximum size, readable size and log buffer format protocol ver‐
134 sion respectively. android_logger_get_id returns the id that was used
135 when opening the sub-log. It is recommended to open the log
136 ANDROID_LOG_RDONLY in these cases.
137
138ERRORS
139 If messages fail, a negative error code will be returned to the caller.
140
141 The -ENOTCONN return code indicates that the logger daemon is stopped.
142
143 The -EBADF return code indicates that the log access point can not be
144 opened, or the log buffer id is out of range.
145
146 For the -EAGAIN return code, this means that the logging message was
147 temporarily backed-up either because of Denial Of Service (DOS) logging
148 pressure from some chatty application or service in the Android system,
149 or if too small of a value is set in /proc/sys/net/unix/max_dgram_qlen.
150 To aid in diagnosing the occurence of this, a binary event from liblog
151 will be sent to the log daemon once a new message can get through
152 indicating how many messages were dropped as a result. Please take
153 action to resolve the structural problems at the source.
154
155 It is generally not advised for the caller to retry the -EAGAIN return
156 code as this will only make the problem(s) worse and cause your
157 application to temporarily drop to the logger daemon priority, BATCH
158 scheduling policy and background task cgroup. If you require a group of
159 messages to be passed atomically, merge them into one message with
160 embedded newlines to the maximum length LOGGER_ENTRY_MAX_PAYLOAD.
161
162 Other return codes from writing operation can be returned. Since the
163 library retries on EINTR, -EINTR should never be returned.
164
165SEE ALSO
166 syslogd(8)
167
168
169
170 24 Jan 2014 LIBLOG(3)
171