linux-kernel - Re: Unified tracing buffer

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Message-ID: <33307c790809231127w274be5b9lba7931f2e6c4ef73@mail.gmail.com>
Date:	Tue, 23 Sep 2008 11:27:37 -0700
From:	"Martin Bligh" <mbligh@...gle.com>
To:	prasad@...ux.vnet.ibm.com
Cc:	"Tom Zanussi" <zanussi@...cast.net>,
	"Mathieu Desnoyers" <mathieu.desnoyers@...ymtl.ca>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Mathieu Desnoyers" <compudj@...stal.dyndns.org>,
	"Steven Rostedt" <rostedt@...dmis.org>, od@...e.com,
	"Frank Ch. Eigler" <fche@...hat.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>, hch@....de,
	"David Wilder" <dwilder@...ibm.com>
Subject: Re: Unified tracing buffer

On Tue, Sep 23, 2008 at 10:55 AM, K.Prasad <prasad@...ux.vnet.ibm.com> wrote:
> On Tue, Sep 23, 2008 at 07:00:38AM -0700, Martin Bligh wrote:
>> > - get rid of anything having to do with padding, nobody needs it and its
>> > only affect has been to horribly distort and complicate a lot of the
>> > code
>> > - get rid of sub-buffers, they just cause confusion
>> > - get rid of mmap, nobody uses it
>> > - no sub-buffers and no mmap support means we can get rid of most of the
>> > callbacks, and a lot of API confusion along with them
>> > - add relay flags - they probably should have been used from the
>> > beginning and options made explicit instead of being shoehorned into the
>> > callback functions.
>>
>> Actually, I think if you did all that, it'd be pretty close to what we
>> want anyway ...
>
> In the perspective of having a layered infrastructure, can we consider
> the interfaces later added over relay (to be used as a wrapper), namely
> relay_printk() and relay_dump()?

Might well work, but let's see what relayfs comes out looking like.
If it's heavily simplfiied, hopefully people will like it.

> - Very minimal work required to log data using the interfaces. Usage is
> made simple to resemble the printk(). Like
>
>        struct relay_printk_data *tpk;
>        tpk->parent_dir = "PARENT";
>        tpk->dir = "DIR";
>        relay_printk(tpk, <String to be output>);
>        relay_dump(tpk, <Some binary data to output>);

You really don't want to store strings in the buffer, it's horribly
inefficient. I think the intent was to store binary data from tagged
events, along with the format strings, and do all the expansion later.
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