Message-ID: <4EF27CDD.9060801@am.sony.com>
Date:	Wed, 21 Dec 2011 16:42:05 -0800
From:	Tim Bird <tim.bird@...sony.com>
To:	john stultz <johnstul@...ibm.com>
CC:	Greg KH <gregkh@...e.de>,
	linux-embedded <linux-embedded@...r.kernel.org>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Brian Swetland <swetland@...gle.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Lennart Poettering <lennart@...ttering.net>
Subject: Re: RFC: android logger feedback request

On 12/21/2011 04:18 PM, john stultz wrote:
> On Wed, 2011-12-21 at 15:19 -0800, Greg KH wrote:
>> On Wed, Dec 21, 2011 at 02:59:15PM -0800, Tim Bird wrote:
>>> Hi all,
>>>
>>> I'm looking for feedback on the Android logger code, to see what
>>> it would take to make this code acceptable for inclusion in
>>> the mainline kernel.
>>>
>>> Information about the features of Android logging system
>>> can be found at: http://elinux.org/Android_Logging_System
>>>
>>> This system creates a new system-wide logging service, in
>>> the kernel, for user-space message.  It is more comparable
>>> to syslog than to the kernel log buffer, as it holds only
>>> user-space messages.  It is optimized for write
>>> performance, since most of the time the log is written to
>>> and never read.  It creates multiple log channels, to prevent
>>> an abundance of log messages in one channel from overwriting
>>> messages in another channel.  The log channels have sizes
>>> fixed at kernel compile-time.
>>>
>>> Log messages are stored in very simple in-kernel buffers, that
>>> overflow old messages upon wrapping.  A fixed set of attributes
>>> (pid, tid, timestamp and message), is kept for each message.
>>> By convention, Android puts a message priority and context tag
>>> into each message.
>>>
>>> In Android, this system uses a fixed set of device nodes with
>>> well-known names: /dev/log/main, /dev/log/events, /dev/log/radio
>>> and /dev/log/system.
>>>
>>> Operations on the log are done via a character device, using
>>> standard file operations and some ioctls.
>>>
>>> The code for this is below (I've moved it from linux-next
>>> drivers/staging/android for my own testing).
>>>
>>> Please let me know what issues you see with this code.
>>
>> That all describes the current code, but you haven't described what's
>> wrong with the existing syslog interface that requires this new driver
>> to be written.  And why can't the existing interface be fixed to address
>> these (potential) shortcomings?
>>
>>> One specific question I have is where is the most appropriate
>>> place for this code to live, in the kernel source tree?
>>> Other embedded systems might want to use this system (it
>>> is simpler than syslog, and superior in some ways), so I don't
>>> think it should remain in an android-specific directory.
>>
>> What way is it superior?  Again, why not extend syslog?  Why not "fix"
>> syslog if this really is a superior thing?  How does this tie into Kay
>> and Lennard's proposal for work in this area?
> 
> There is also some overlap functionality wise with pstore as well, as I
> believe the logger is used as a known location in memory where messages
> can be fetched from after a kernel panic or crash.

I don't know if that's true or not.  I think you may be thinking
of Android's RAM console feature.  If there's a way to save
application messages over a reboot using the logger buffers, I'm
unfamiliar with it.
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Workgroup of the Linux Foundation
Senior Staff Engineer, Sony Network Entertainment
=============================

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