Message-ID: <20111222002719.GA18361@suse.de>
Date:	Wed, 21 Dec 2011 16:27:19 -0800
From:	Greg KH <gregkh@...e.de>
To:	john stultz <johnstul@...ibm.com>
Cc:	Tim Bird <tim.bird@...sony.com>,
	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, Dec 21, 2011 at 04:18:11PM -0800, 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.

That sounds like a major overlap, can't pstore be used for this
functionality today instead of the logger code?

greg k-h
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