Quote from Figure 106 in NVMe 1.3a:

  The Identify Namespace data structure is returned to the host for the
  namespace specified in the Namespace Identifier (CDW1.NSID) field if it
  is an active NSID. If the specified namespace is not an active NSID,
  then the controller returns a zero filled data structure.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NSagi Grimberg <sagi@rimberg.me>
Reviewed-by: NMax Gurtovoy <maxg@mellanox.com>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>