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

Karel Zak
2011-01-13T16:01:42Z

On Thu, Jan 13, 2011 at 03:43:38PM +0100, Kay Sievers wrote:
> On Thu, Jan 13, 2011 at 15:30, Tejun Heo <tj@kernel.org> wrote:
> > On Thu, Jan 13, 2011 at 3:25 PM, Milan Broz <mbroz@redhat.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?

If there is noway to fix sysfs then we can add a generic ioctl or
/sys/block/<device>/{slave,holder}_list files with list of
holders/slaves.

But please, don't force userspace to use *claimer-specific*
methods to answer *generic questions* like slave/holder dependencies
between devices.

> impossible to ever rename a device (as long as they copy the device
> name), and and and .... we should not add more of this.
>
> >> If btrfs internally creates some virtual _block_ device for its pool, it should
> >> present it here too with slaves/holders. If not, why it should create any links there?
> >
> > Yeah, that's the most bothering part for me.  The biggest customers of
> > bd_claim are filesystems and all these custom symlinkeries don't do
> > nothing for them.  It just doesn't make a whole lot of sense to me.
>
> Btrfs does not use any blockdev as the master for good reason, and it
> can never map its slaves inside of /sys/block.

Yep, expected and correct response :-)

Karel

--
Karel Zak <kzak@redhat.com>