logd can record and replay log messages for offline analysis.
logd has a
RecordingLogBuffer buffer that records messages to /data/misc/logd/recorded-messages. It stores messages in memory until that file is accessible, in order to capture all messages since the beginning of boot. It is only meant for logging developers to use and must be manually enabled in by adding
Android.bp and setting
log_buffer = new SimpleLogBuffer(&reader_list, &log_tags, &log_statistics); in
Recording messages may delay the Log() function from completing and it is highly recommended to make the logd socket in
liblog blocking, by removing
SOCK_NONBLOCK from the
socket() call in
Recorded messages can be replayed offline with the
replay_messages tool. It runs on host and device and supports the following options:
interesting- this prints ‘interesting’ statistics for each of the log buffer types (simple, chatty, serialized). The statistics are:
memory_usage BUFFER_TYPE- this prints the memory usage (sum of private dirty pages of the
replay_messagesprocess). Note that the input file is mmap()'ed as RO/Shared so it does not appear in these dirty pages, and a baseline is taken before allocating the log buffers, so only their contributions are measured. The tool outputs the memory usage every 100,000 messages.
latency BUFFER_TYPE- this prints statistics of the latency of the Log() function for the given buffer type. It specifically prints the 1st, 2nd, and 3rd quartiles; the 95th, 99th, and 99.99th percentiles; and the maximum latency.
print_logs BUFFER_TYPE [buffers] [print_point]- this prints the logs as processed by the given buffer_type from the buffers specified by
buffersstarting after the number of logs specified by
print_pointhave been logged. This acts as if a user called
logcatimmediately after the specified logs have been logged, which is particularly useful since it will show the chatty pruning messages at that point. It additionally prints the statistics from
logcat -Safter the logs.
buffersis a comma separated list of the numeric buffer id values from
<android/log.h>. For example,
0,1,3represents the main, radio, and system buffers. It can can also be
print_pointis an positive integer. If it is unspecified, logs are printed after the entire input file is consumed.
nothing BUFFER_TYPE- this does nothing other than read the input file and call Log() for the given buffer type. This is used for profiling CPU usage of strictly the log buffer.