linux-kernel - Problem w/ CONFIG_DEBUG_BLOCK_EXT

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Message-ID: <48BD173B.3090600@hp.com>
Date:	Tue, 02 Sep 2008 06:36:43 -0400
From:	"Alan D. Brunelle" <Alan.Brunelle@...com>
To:	device-mapper development <dm-devel@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>, tj@...nel.org
Subject: Problem w/ CONFIG_DEBUG_BLOCK_EXT_DEVT

I have found two problems in LVM2/DM w/ a potential new "experimental
feature" in 2.6.28: CONFIG_DEBUG_BLOCK_EXT_DEVT (this is from Jens
Axboe's origin/for-2.6.28 git branch)

"Conventionally, block device numbers are allocated from predetermined
contiguous area.  However, extended block area may introduce
non-contiguous block device numbers.  This option forces most block
device numbers to be allocated from the extended space and spreads them
to discover kernel or userland code paths which assume predetermined
contiguous device number allocation."

W/ LVM2 & DM there are (at least) two issues:

(1) Device major numbers for some reason are /not/ being entered
correctly into /proc/devices -- w/ CONFIG_DEBUG_BLOCK_EXT_DEVT=y I am
seeing some devices w/ major "259" (a SATA controller) but no entry in
/proc/devices. LVM2/DM will not find the entry in /proc/devices, and not
allow any device w/ that major to be used with LVM commands.

(2) Device minor numbers can be quite large, and the 10-character limits
in dm/lib/libdm-deptree.c are too small.

Alan
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