Re: [PATCH 0/5] target/rbd: distributed lun reset support

[Christoph Hellwig <hch@infradead.org>]

On Fri, May 08, 2015 at 01:04:05AM -0500, Mike Christie wrote:
> > All of them.  It's just another consumer of the in-kernel block devices
> > interface.
> 
> Will users use lio with what you are working on?

It's the other way around.  The pNFS block device uses a block device
it wants to use persistent reservations on.  If we do have a proper
in-kernel API for that it could also work on say RBD and NVMe as long as
they provide a mapping for SCSI3 PRs.  For NVMe that exists as a spec,
and for RBD it seems like you're about to deliver one.

> I ask because I am thinking it might be better to implement my own
> se_subsystem_api and sbc_ops structs and in my backend just make libceph
> calls directly for callouts like sbc_ops->execute_rw. So I would not have
> a block_device or request_queue if I went that route.
> 
> If I do my own backend, for reset support (PR support will be similar
> with callouts added to the se_subsystem_api) I would just need the patch
> below.

It's defintively simpler, so for prototyping it might be the way to go.
I think in the long run going for a general block device API will be
more useful for everyone involved.