Android logger - Revision history

Tim Bird at 00:12, 15 January 2011

2011-01-15T00:12:33Z

Tim Bird: /* Overview */ add system logger information

2011-01-15T00:10:55Z

‎Overview: add system logger information

Tim Bird: /* Device Nodes */

2011-01-14T21:16:43Z

‎Device Nodes

Tim Bird: redo section levels, add to category:android

2009-11-12T00:03:06Z

redo section levels, add to category:android

Tim Bird: /* Reading */

2009-11-12T00:01:54Z

‎Reading

Tim Bird: /* Overview */ Add more information

2009-11-11T23:59:41Z

‎Overview: Add more information

Tim Bird: create page

2009-11-11T23:45:17Z

create page

New page

Here is some information on the Android logger:

== Overview ==
General system-wide logging is supported by a kernel device driver call 'logger'.
The code for the driver is in 'drivers/android/logger.c'.

The code supports 3 logging buffers, named "main", "events", and "radio", for different
types of events.

== Device Nodes ==
The driver is activated when a user-space program opens a device node with the appropriate
major and minor number.

These nodes are located in /dev/log, as shown below:
# ls -l /dev/log
crw-rw--w- 1 0 1007 10, 50 Nov 5 02:00 events
crw-rw--w- 1 0 1007 10, 51 Nov 5 02:00 main
crw-rw--w- 1 0 1007 10, 49 Nov 5 02:00 radio

== Logcat command ==
You can use the 'logcat' command to read the log. This command is located in /system/bin
in the local filesystem, or you can access the functionality using the 'adb logcat' command.

Documentation on the use of this command is at:
http://developer.android.com/guide/developing/tools/adb.html

Some quick notes:
* Log messages each have a tag and log level.
** You can filter the messages by tag and log level, with a different level per tag.
* You can specify (using a system property) that various programs emit their stdout or stderr to the log.

@@ Line 8: / Line 8: @@
 types of events.
-=== Driver Features ===
+== Driver Features ==
 Log reading and writing is done via normal Linux file reads and writes.
@@ Line 14: / Line 14: @@
 very quickly, to avoid logging having too much overhead in the system.
-==== Reading ====
+=== Reading ===
 From user-space, a normal 'read' operation is used to read an entry from
 the log.  Each read() returns one log entry, or blocks waiting for the next entry.
@@ Line 22: / Line 22: @@
 request.
-==== Writing ====
+=== Writing ===
 The system performs writes to the log.  The driver saves the pid, tgid and timestamp for each log entry.
 It appears that the level, tag and message are provided by user-space.
-==== ioctls ====
+=== ioctls ===
 The following ioctl's are supported, which pretty much do what you would expect:
@@ Line 55: / Line 55: @@
 ** You can filter the messages by tag and log level, with a different level per tag.
 * You can specify (using a system property) that various programs emit their stdout or stderr to the log.

@@ Line 15: / Line 15: @@
 ==== Reading ====
-From user-space, use a normal 'read' operation to read an entry from
+From user-space, a normal 'read' operation is used to read an entry from
-the log.
+the log.  Each read() returns one log entry, or blocks waiting for the next entry.
 At least LOGGER_ENTRY_MAX_LEN (4096) should be used as the amount of data to read from the log on a read

@@ Line 46: / Line 46: @@
 /dev/log/system was added in Feb, 2010
-== Logcat command ==
+== Android Logging System ==
-You can use the 'logcat' command to read the log.  This command is located in /system/bin
+See [[Android Logging System]] for information about the complete android logging system, including tools which access this driver.
-in the local filesystem, or you can access the functionality using the 'adb logcat' command.
-−
-Documentation on the use of this command is at:
-http://developer.android.com/guide/developing/tools/adb.html
-−
-Some quick notes:
-* Log messages each have a tag and log level.
-** You can filter the messages by tag and log level, with a different level per tag.
-* You can specify (using a system property) that various programs emit their stdout or stderr to the log.
 [[Category:Android]]

@@ Line 5: / Line 5: @@
 The code for the driver is in 'drivers/android/logger.c'.
-The code supports 3 logging buffers, named "main", "events", and "radio", for different
+The code supports 4 logging buffers, named "main", "events", "radio", and "system" for different
 types of events.

@@ Line 43: / Line 43: @@
   crw-rw--w-    1 0        1007      10,  51 Nov  5 02:00 main
   crw-rw--w-    1 0        1007      10,  49 Nov  5 02:00 radio
 == Logcat command ==