linux-kernel - Re: [PATCH][v3] blktrace: conversion to tracepoints

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Message-ID: <20081103172112.GB32603@ghostprotocols.net>
Date:	Mon, 3 Nov 2008 15:21:12 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][v3] blktrace: conversion to tracepoints

Em Thu, Oct 30, 2008 at 12:11:45PM +0100, Jens Axboe escreveu:
> On Thu, Oct 30 2008, Arnaldo Carvalho de Melo wrote:
> > Yes, I tested it, run 'btrace /dev/sda' several times, while doing a
> > 45 GB backup using rsync over NFS, etc. So it should have exercised the
> > tracepoints use and repeated registrater/unregister cycles.
> 
> Awesome, just wanted to know what level of testing you had done (from
> "none" to "doesn't crash" to "actually works"), so thanks for that.

Jens,

	Now I'm working on the marker glue code for systemtap to use
these tracepoints and I noticed that one important piece of information
is not available unless one first uses blk_trace_ioctl to fill in
request_queue->blk_trace, that is request_queue->blk_trace->dev, i.e.
the device associated with the request_queue.

	Is there a way to, from the request_queue, get the dev? I guess
not, as if there would be you wouldn't have added it to struct
blk_trace...

	Would it be sane to add get struct block_device->bd_dev dev_t
info into struct request_queue at sd_probe time or most probably at some
more suitable routine in the device/disk registration sequence of
events?

	I am certainly missing lots of connections here, there are many
objects and relationships among these objects that may make the
association of a block_device with a request_queue not to be fixed all
the time, thus requiring the struct blk_trace ->dev field to be set up
at ioctl time, but I'm just trying to figure out how to remove the
requirement of a setup routine for the tracepoints to know what is the
dev_t associated with the request_queue they are getting as a parameter.

Best Regards,

- Arnaldo
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