linux-kernel - Re: [for-next][PATCH 0/8] tracing: Addition of multiple buffers

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Date:	Wed, 27 Feb 2013 14:41:57 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Sharp <dhsharp@...gle.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
	hcochran@...mark.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [for-next][PATCH 0/8] tracing: Addition of multiple buffers

On Wed, 2013-02-27 at 11:37 -0800, David Sharp wrote:
> On Wed, Feb 27, 2013 at 9:22 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> > With this patch set, a new directory is created in the debug/tracing
> > directory called "instances". Here you can mkdir/rmdir a new directory
> > that will contain some of the files in the debug/tracing directory.
> > Note, this is not totally finished, but it's at a point were it is
> > functional and useful.
> >
> > To add mkdir/rmdir in debugfs, as debugfs does not support these operations,
> 
> Is there some reason not to extend debugfs to support mkdir/rmdir?

Yeah, Greg KH NACK'd the idea, and he's the debugfs maintainer.

He also suggested the tracefs addition, which I do intend on doing, but
until then this is going to be the work around.

-- Steve

> 
> > I had to have the instances' inode use its own inode_operations and add a
> > mkdir and rmdir method. As the instances directory can not be renamed
> > or removed, or modified in any other way, it has the inode mutex released
> > in order to call back to create or remove the debugfs directories.
> > It has its own mutex to protect against multiple instances of this,
> > and I've run many stress tests to make sure it can't crash. I haven't
> > found were it can. The alternative is to have a "new" and "free" file
> > to create and remove directories and it will basically do the exact
> > same thing that the mkdir/rmdir does now, with the exact same protection.
> > I do eventually want to make a tracefs, but that requires a lot of
> > design planning and wont be in the near future (too many other things
> > to do).


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