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_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
134ERRORS
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
161SEE ALSO
162 syslogd(8)
163
164
165
166 24 Jan 2014 LIBLOG(3)
167