nvme: support NVME_VOLATILE_WRITE_CACHE feature

The SCSI emulation in the Linux NVMe driver really wants to know
if a device has a volatile write cache.  Given that qemu has moved
away from a model where we report the backing store WCE bit to
one where the WCE bit is supposed to be part of the migratable
guest-visible state we always return 1 here.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/block/nvme.c

diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index ad988d7..4b6d5e6 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -479,6 +479,9 @@
         req->cqe.result =
             cpu_to_le32((n->num_queues - 1) | ((n->num_queues - 1) << 16));
         break;
+    case NVME_VOLATILE_WRITE_CACHE:
+        req->cqe.result = cpu_to_le32(1);
+        break;
     default:
         return NVME_INVALID_FIELD | NVME_DNR;
     }