BLK_FEAT_DAX
QUEUE_SYSFS_FEATURE_SHOW(dax, BLK_FEAT_DAX);
limits->features |= BLK_FEAT_DAX;
limits->features &= ~BLK_FEAT_DAX;
lim.features |= BLK_FEAT_DAX;
.features = BLK_FEAT_DAX,
#define blk_queue_dax(q) ((q)->limits.features & BLK_FEAT_DAX)