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

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Message-ID: <20110114150736.GJ16523@nb.net.home>
Date:	Fri, 14 Jan 2011 16:07:36 +0100
From:	Karel Zak <kzak@...hat.com>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Tejun Heo <tj@...nel.org>, Milan Broz <mbroz@...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
Subject: Re: [dm-devel] linux-next - WARNING: at fs/block_dev.c:824
	bd_link_disk_holder+0x92/0x1ac()

On Thu, Jan 13, 2011 at 05:10:02PM +0100, Kay Sievers wrote:
> On Thu, Jan 13, 2011 at 16:59, Karel Zak <kzak@...hat.com> wrote:
> > On Thu, Jan 13, 2011 at 03:43:38PM +0100, Kay Sievers wrote:
> >> On Thu, Jan 13, 2011 at 15:30, Tejun Heo <tj@...nel.org> wrote:
> >> > On Thu, Jan 13, 2011 at 3:25 PM, Milan Broz <mbroz@...hat.com> wrote:
> >> >> Maybe, but this was not invented in DM/MD camp:-)
> >> >> Probably Kay or Greg can answer why it was done this way?
> >>
> >> It's not from Greg or Kay. It just appeared some day in the context of dm. :)
> >>
> >> And yes, symlinks *look* nice and simple for the outside, but they are
> >> not, and have all sorts of problems like non-atomic updates, make it
> >
> >  Sounds like sysfs implementation problem, right?
> 
> It's a normal multi-file problem. It can by-definition not be atomic
> without doing really weird locking things.

 BTW, lsblk(8) and libblkid don't depend on the fact that slaves/holders 
 files are symlinks.
 
 The important thing is the filename (/sys/block/.../slaves/<name>) 
 only. We don't follow the symlinks and we don't use readlink() there.
 
 It means that you can replace the symlinks with regular files where
 in the file contents is for example maj:min, etc.

    Karel

-- 
 Karel Zak  <kzak@...hat.com>
 http://karelzak.blogspot.com
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