Mainline Android logger project

Revision as of 07:51, 24 May 2011 by Tim Bird (Talk | contribs) (Features)

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Android logger issues

This section describes some attributes of the Android logger code, which are relevant for mainlining the code into Linux. Let's use a modified SWOT (Strengths, Weaknesses, Opportunities, Threats) analysis for strategic planning to mainline this code.

To find the logger's strengths and weaknesses, lets research and provide information and hard numbers for how it compares with existing logging alternatives.

Competition (Threats)

What are the alternatives to the Android logger?

  • logbuf (the kernel log buffer)
  • syslog

What are the pros and cons of each system (see feature matrix below)


How much overhead does each logging system have?

How long does it take to write 1 million messages, for each of the above systems?


What are the space requirements for each logging system?


How much does each system need to be maintained?


What things can be configured at compile-time and run-time for each system?


What features does each of the log systems have?

[Create a feature matrix here]

Attribute logger logbuf syslog Notes
multiple channels yes no no? allows for separation of data to prevent overrun
can limit space used yes yes ?
cost to write 1M messages ? ? ? need to benchmark
average cost to write a message ? ? ? need to measure
average message size ? ? ? need to measure
RAM required for complete logger system ? ? ? need to measure
flash or disk required for complete logger system ? ? ? need to measure
number of context switches per message ? ? ? need to measure
logs both kernel and user messages? no no yes? klogd puts logbuf messages into syslog?
ability to store messages persistently on target no no* yes klogd puts logbuf messages into syslog?
ability to store messages persistently on host yes* no
integrated into existing debug tools yes no? no? I don't know of anything but target-side tools (dmesg, cat /var/log) that "know" about logbuf and syslog
ability to filter messages by tag yes no ? does syslog require tagging, is grep used for syslog tagging?

What features *could* each log system have, if extended? Would extension to an existing system interfere with it's current primary purpose? For each change contemplated, can it be implemented to minimize the impact to existing code?

Barriers to entry as is (Weaknesses)

Does logger duplicate functionality that exists elsewhere? Does it make sense to extend an existing system, rather than implement a new system?

What are barriers to entry:

  • use of ioctl?
  • hardcoded number of log channels
  • other style issues?
  • longterm maintainer?

Attractive features of logger as is (Strengths)

What are the differentiating features of logger, compared to alternatives?

  • minimal context switches for logging
  • use of ring buffer automatically limits log size
  • log is in memory (no cost to store unused log messages)
  • all messages are tagged
  • all messages have priority
  • all messages have timestamp
  • user-space program to filter messages by tag
  • channel selection by user-space policy

Project task list

  • Get needed hardware
  • Make sure contractors have all required source code:
    • AOSP, Android kernels, and logger code
  • Identify and review code before submission
    • identify possible mainline objections to code, and plan how to respond
    • compare with alternatives
      • compare and contrast logger code with kernel log buffer (e.g. dmesg vs. logcat)
        • performance, features, size,
      • compare and contrast logger code with syslog (syslogd, /var/log)
  • Submit code to LKML
  • Respond to feedback received
  • Add logger code to busybox?
    • Should this be done first?
    • log
    • logwrapper
    • logsync
    • What about logd_write.c code
      • included in bionic - should be included in busybox directly, because it's missing in glibc?
  • what about udev?
    • should mainline Linux automatically create logger devices nodes?
    • they are created by 'init' in Android systems