[dm-devel] Extending DM w/ new target type

[Alasdair G Kergon]

On Thu, Aug 01, 2013 at 11:04:37AM -0600, John Strange wrote:
> 1. I'd like to use DM with a new target type.  I'm porting our virtualized
> storage solution from Windows.  I've been able to register my target and
> get callbacks working, but in looking at the dm-raid code, I'm concerned
> with how tightly coupled it is with the routines in md.c (multiple devices
> implementation).  Is there an expectation that a DM target use the md_xxxx
> routines?
 
If you need that sort of raid functionality, then yes (and you should
look into using the external metadata support if you have a new format).

> 2. I used dmsetup to create a mapping for a device that my target
> controls.  Is there a way to make the underlying device (e.g. /dev/sdb) not
> visible to the system?  

No and this is by design: all layers of the device stack are addressable from
userspace.

> I'm paranoid about external accesses to a LUN that
> I'm using.

Utilities should detect the device is in use.
 
Alasdair