Index: head/sys/dev/nvme/nvme.h
===================================================================
--- head/sys/dev/nvme/nvme.h
+++ head/sys/dev/nvme/nvme.h
@@ -41,6 +41,7 @@
 #define	NVME_PASSTHROUGH_CMD		_IOWR('n', 0, struct nvme_pt_command)
 #define	NVME_RESET_CONTROLLER		_IO('n', 1)
 #define	NVME_GET_NSID			_IOR('n', 2, struct nvme_get_nsid)
+#define	NVME_GET_MAX_XFER_SIZE		_IOR('n', 3, uint64_t)
 
 #define	NVME_IO_TEST			_IOWR('n', 100, struct nvme_io_test)
 #define	NVME_BIO_TEST			_IOWR('n', 101, struct nvme_io_test)
Index: head/sys/dev/nvme/nvme_ctrlr.c
===================================================================
--- head/sys/dev/nvme/nvme_ctrlr.c
+++ head/sys/dev/nvme/nvme_ctrlr.c
@@ -1345,6 +1345,9 @@
 		gnsid->nsid = 0;
 		break;
 	}
+	case NVME_GET_MAX_XFER_SIZE:
+		*(uint64_t *)arg = ctrlr->max_xfer_size;
+		break;
 	default:
 		return (ENOTTY);
 	}