linux-kernel - Re: RFC: android logger feedback request

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Date:	Wed, 21 Dec 2011 17:00:47 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Tim Bird <tim.bird@...sony.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 Wed, 2011-12-21 at 16:49 -0800, john stultz wrote:
> On Wed, 2011-12-21 at 16:42 -0800, Tim Bird wrote:
> > 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.
> 
> I may very well be confusing things. I had thought apanic pulled the
> logger data, but maybe I'm wrong.

Looks like I am wrong. Apologies. Thanks for pointing my error out.
-john

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