Persistent Reservation API V2

[Christoph Hellwig]

On Thu, Aug 20, 2015 at 11:56:36PM +0000, Keith Busch wrote:

> NVMe can also specify
> if whether or not a reservation should persist through power-loss.

SCSI does as well, it's the APTPL flag.  However reservations not persistent
through a power loss are basically useless, so I decided to force them on
in the API.  From the documentation:

"All implementations are expected to ensure the reservations survive
 a power loss"

So I would prefer not to add it, or if we really have to as a negative flag
to specifically opt out of the APTPL behavior.

> with it. For example, NVMe can ignore existing keys when acquiring a
> reservation in addition to registering a new key.

This sounds like a sensible addition to me, and I wouldn't be surprised
if future SPC versions will add this flag.