Re: [dm-devel] linux-next - WARNING: at fs/block_dev.c:824 bd_link_disk_holder+0x92/0x1ac()

Karel Zak
2011-01-13T12:27:33Z

On Thu, Jan 13, 2011 at 12:26:14PM +0100, Milan Broz wrote:
> On 01/13/2011 12:06 PM, Tejun Heo wrote:
> > Urgh... gees, so there actually was a user using all that cruft.
> > Sorry about the breakage, I'll see how multiple symlinks can be
> > restored. I'm curious why this was added at all tho. What was the
> > rationalization? It's not like two subsystems can share the same
> > block device so marking the currently owning subsystem should have
> > been enough at the block layer. There is no reason for block devices
> > to present information which is of no use to itself. All that's
> > necessary is "this is taken by dm or md for more information, query
> > those". dm and md need their own conf/representation layer anyway.
>
> I am not sure if I understand it correctly, but multiple holders/slaves
> links are very useful in userspace to present device dependences.
>
> We just implemented lsblk command in util-linux which simple prints
> tree according to these links, so dependendes of DM/MD/whatever devices
> can be printed without using any system specific callbacks, just using
> sysfs. See http://karelzak.blogspot.com/2010/12/lsblk8.html

We also use holders/slaves links in libblkid to evaluate dependencies
between devices (since 2008).

> Whatever changes are needed, please keep this functionality, it can be useful.

Definitely.

Karel

--
Karel Zak <kzak@redhat.com>