[dm-devel] Re: [PATCH] Allow multipath devices to be created for readonly devices

[Alasdair G Kergon]

On Wed, Jul 08, 2009 at 02:17:59PM +0530, Nikanth Karthikesan wrote:
> Currently we cannot create device-mapper tables for multipath devices
> whenever they are read-only.This patch modifies the device-mapper to
> set the 'READ-ONLY' flag automatically whenever a read-only is added
> to the table.
 
I recall discussing this before:

1) Contrary to the assertion above, you can already create such dm
tables, by marking them explicitly as read-only.

2) The distinction between read-only and read-write device-mapper
devices is currently clear and simple.  This proposal replaces the
definitions with far-less-intuitive ones and that is why I ignored it
first time around.

If you believe the existing interface and behaviour is inadequate,
think about some alternatives:
  - What is the heart of the problem here?  Give a specific example
to show why we need improvements: Is the patch really about
optimisation, arguing that to achieve the desired result through the
current interface involves avoidable effort?
  - Consider whether adding another clearly-defined state to the system 
or extending the userspace interface would be a better approach.

Alasdair