Re: [PATCH 3/3] dm: allow error target to replace immutable target

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Aug 29 2013 at  1:07pm -0400,
Mikulas Patocka <mpatocka@redhat.com> wrote:

> 
> 
> On Thu, 29 Aug 2013, Mike Snitzer wrote:
> 
> > On Thu, Aug 29 2013 at 10:37am -0400,
> > Mikulas Patocka <mpatocka@redhat.com> wrote:
> > 
> > > As I said - I think it would be better to remove the immutable flag than 
> > > to create more flags to bypass it.
> > 
> > Immutable was introduced to prevent dangerous scenarios that weren't
> > accounted for in original design, etc.  It solved your crash when you
> > rep;aced a thin-pool with an empty table.
> > 
> > immutable is staying for now.  And as it turns out allowing error target
> > to override an immutable target was always held to be a logical/possible
> > future relaxation of the immutable constraint.
> > 
> > Mike
> 
> If you can replace a thin-pool target with an error target - so why can't 
> you replace a thin-pool target with linear (or any other) target?
> 
> I don't see why the error target should be special.

error target gives us the ability to disconnect the thin-pool from the
underlying devices.  It is practical for testing, etc.

What use-case are you saying will be valid to switch a thin-pool target
to linear?