Index: sys/cam/cam_compat.c
===================================================================
--- sys/cam/cam_compat.c
+++ sys/cam/cam_compat.c
@@ -54,6 +54,12 @@
 
 #include "opt_cam.h"
 
+/*
+ * Note: struct cdev *dev parameter here is simply passed through. For cdioctl
+ * we need to pass down a struct periph * which has been cast to a cdev and that
+ * is cast back again in cdioctl_dev().
+ */
+
 static int cam_compat_handle_0x17(struct cdev *dev, u_long cmd, caddr_t addr,
     int flag, struct thread *td, d_ioctl_t *cbfnp);
 static int cam_compat_handle_0x18(struct cdev *dev, u_long cmd, caddr_t addr,
Index: sys/cam/scsi/scsi_cd.c
===================================================================
--- sys/cam/scsi/scsi_cd.c
+++ sys/cam/scsi/scsi_cd.c
@@ -76,6 +76,7 @@
 #include <cam/cam_xpt_periph.h>
 #include <cam/cam_queue.h>
 #include <cam/cam_sim.h>
+#include <cam/cam_compat.h>
 
 #include <cam/scsi/scsi_message.h>
 #include <cam/scsi/scsi_da.h>
@@ -1752,6 +1753,20 @@
 	}
 }
 
+static int
+cdioctl_dev(struct cdev *dev, u_long cmd, caddr_t addr, int flag, struct thread *td)
+{
+	struct cam_periph *periph;
+
+	/*
+	 * For compat, we need to cast struct periph * into struct cdev *dev and
+	 * then back again.
+	 */
+	periph = (struct cam_periph *)(void *)dev;
+	cam_periph_assert(periph, MA_OWNED);
+	return (cam_periph_ioctl(periph, cmd, addr, cderror));
+}
+
 static int
 cdioctl(struct disk *dp, u_long cmd, void *addr, int flag, struct thread *td)
 {
@@ -2608,6 +2623,15 @@
 	default:
 		cam_periph_lock(periph);
 		error = cam_periph_ioctl(periph, cmd, addr, cderror);
+		if (error == ENOTTY) {
+			/*
+			 * We assume that the compat layer doesn't care about
+			 * the dev parameter. It just passes it through, so
+			 * cheat a little.
+			 */
+			error = cam_compat_ioctl((struct cdev *)(void *)periph,
+			    cmd, addr, flag, td, cdioctl_dev);
+		}
 		cam_periph_unlock(periph);
 		break;
 	}