Re: plain 2.6.21-rc5 (1) vs amanda (0)

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 04 Apr 2007 14:17:13 -0400
Dave Dillow <dave@thedillows.org> wrote:

> On Wed, 2007-04-04 at 10:42 -0700, Andrew Morton wrote:
> > On Wed, 4 Apr 2007 10:45:30 +0200 Ingo Molnar <mingo@elte.hu> wrote:
> > 
> > > 
> > > * Dave Dillow <dave@thedillows.org> wrote:
> > > 
> > > > > Then it is a matter of figuring out why the device number changed -- 
> > > > > I'm thinking it is device-mapper, but will look closer tomorrow.
> > > > 
> > > > This commit is the one that changed it:
> > > > 
> > > > commit fdf892be32d84a1745fa0aee5fc60517421b8038
> > > > Author: Andrew Morton <akpm@osdl.org>
> > > > Date:   Mon Feb 12 00:51:44 2007 -0800
> > > > 
> > > >     [PATCH] register_blkdev(): don't hand out the LOCAL/EXPERIMENTAL majors
> > > >     
> > > >     As pointed out in http://bugzilla.kernel.org/show_bug.cgi?id=7922, 
> > > >     dynamic blockdev major allocation can hand out majors which LANANA 
> > > >     has defined as being for local/experimental use.
> > > 
> > > i dont think we should break backwards compatibility with a system that 
> > > has not changed any hardware. Andrew, should we revert this?
> > 
> > Well that's an odd thing for a backup program to be doing - there are any
> > number of things which could cause a dynamically-allocated major to change.
> > 
> > ho hum, yes, I guess it needs to go.
> 
> The thing is, it's been broken for a long time -- this change just
> highlighted it. This isn't the first time that device-mapper has moved
> -- the introduction of mdp (before git, so haven't tracked down
> timeframe) also moved it around. The dynamic major is not stable, so
> should we be concerned if it moves for 2.6.21?
> 
> I don't like the effect it has on the backups, but I don't think we
> should hand out LOCAL/EXP majors to dynamic devices, either. There is a
> module option to make the device-mapper and mdp majors stable, so
> perhaps a compromise is possible? Revert for 2.6.21, and schedule the
> patch for later addition, which gives distros time to use the DM major
> option?

hm, good points.

Overall, the patch helps kernel developers and hurts the userbase.  I tend
to prefer to hurt kernel developers than our users ;)

I don't think the protect-lanana-numbers thing is very important, really. 
If some kernel developer or someone who is maintaining an unofficial
out-of-tree driver hits the problem, they are presumably able to handle
it.  Preferably by switching to a dynamically-assigned major.