linux-kernel - Re: [dm-devel] linux-next - WARNING: at fs/block_dev.c:824 bd_link_disk

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Date:	Thu, 13 Jan 2011 15:11:07 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Milan Broz <mbroz@...hat.com>
Cc:	Karel Zak <kzak@...hat.com>,
	device-mapper development <dm-devel@...hat.com>,
	Jun'ichi Nomura <j-nomura@...jp.nec.com>,
	Valdis.Kletnieks@...edu, linux-kernel@...r.kernel.org,
	linux-raid@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>
Subject: Re: [dm-devel] linux-next - WARNING: at fs/block_dev.c:824
 bd_link_disk_holder+0x92/0x1ac()

Hello,

On Thu, Jan 13, 2011 at 02:58:23PM +0100, Milan Broz wrote:
> On 01/13/2011 02:37 PM, Tejun Heo wrote:
> 
> > So, just don't do it.  Sysfs is for device hierarchy.  Don't try to
> > shove pretty looking things there (unless it's something widely agreed
> > on and necessary, of course).
> 
> I think that it is exactly what holders/slaves do - displaying device
> hierarchy. So application can check which underlying device are related
> and ask them for more info if needed (=> with system specific call,
> it can be simple sysfs attribute, ioctl, whatever).

Yeah, sure but in a completely unrestrained and non-standard way.
First of all, it wasn't even necessary to begin with and I don't
really see anyone else other than md/dm using it.  I mean, where are
you gonna you put that slaves directory?  Sure you can put it
somewhere but really it would be just that - somewhere.  All this
doesn't even matter.  It wasn't even necessary to begin with.

> So the only request here is to keep these symlinks correct, nothing more.
> Or am I missing anything?

Yeah, I'm fixing that.  Don't worry.  I just wanna say it wasn't such
a brilliant idea to add it in the first place and hope that people
would restrain from doing similar things in the future.

So, as a general rule, when in doubt, just create an attribute.  Let's
refrain from custom symlinkery in sysfs, please.  In this case too, a
holder attribute containing strings like ext[3|4], md, dm or whatnot
would have been _much_ simpler and actually more useful.

Thank you.

-- 
tejun
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