[dm-devel] [PATCH] multipath devices are not getting created for readonly devices

[Alasdair G Kergon]

On Wed, Mar 12, 2014 at 12:34:54PM +0100, Hannes Reinecke wrote:
> Currently we cannot create device-mapper tables for multipath devices
> whenever the underlying devices are read-only.

Userspace can specify a read-only table when creating it.

> This patch modifies the device-mapper to set the 'READ-ONLY' flag
> automatically whenever a read-only device is added to the table.
 
I don't know if it's working properly at the moment, but some targets
(like dm-delay) are meant to work with a combination of read-only and
read-write devices. 

I don't think the table mode should get changed quite like this: I
think this problem needs wider review, perhaps overlapping with the
problem of checking on the I/O path not just at device open time.

Alasdair