Index: sbin/camcontrol/camcontrol.c
===================================================================
--- sbin/camcontrol/camcontrol.c
+++ sbin/camcontrol/camcontrol.c
@@ -7788,11 +7788,10 @@
 		flags |= CAM_DIR_IN;
 		mmc_data = malloc(mmc_data_len);
 		memset(mmc_data, 0, mmc_data_len);
+		memset(&mmc_d, 0, sizeof(mmc_d));
 		mmc_d.len = mmc_data_len;
 		mmc_d.data = mmc_data;
 		mmc_d.flags = MMC_DATA_READ;
-		mmc_d.block_size = 0;
-		mmc_d.block_count = 0;
 	} else flags |= CAM_DIR_NONE;
 
 	cam_fill_mmcio(&ccb->mmcio,
Index: sys/cam/mmc/mmc_da.c
===================================================================
--- sys/cam/mmc/mmc_da.c
+++ sys/cam/mmc/mmc_da.c
@@ -791,6 +791,11 @@
 	softc->state = SDDA_STATE_INIT;
 	softc->mmcdata =
 		(struct mmc_data *)malloc(sizeof(struct mmc_data), M_DEVBUF, M_NOWAIT|M_ZERO);
+	if (softc->mmcdata == NULL) {
+		printf("sddaregister: Unable to probe new device. "
+		    "Unable to allocate mmcdata\n");
+		return (CAM_REQ_CMP_ERR);
+	}
 	periph->softc = softc;
 	softc->periph = periph;
 
@@ -1806,10 +1811,10 @@
 
 		mmcio->cmd.flags = MMC_RSP_R1 | MMC_CMD_ADTC;
 		mmcio->cmd.data = softc->mmcdata;
+		memset(mmcio->cmd.data, 0, sizeof(struct mmc_data));
 		mmcio->cmd.data->data = bp->bio_data;
 		mmcio->cmd.data->len = 512 * count;
 		mmcio->cmd.data->flags = (bp->bio_cmd == BIO_READ ? MMC_DATA_READ : MMC_DATA_WRITE);
-		mmcio->cmd.data->block_count = mmcio->cmd.data->block_size = 0;
 		/* Direct h/w to issue CMD12 upon completion */
 		if (count > 1) {
 			mmcio->cmd.data->flags |= MMC_DATA_MULTI;
Index: sys/dev/mmc/mmcreg.h
===================================================================
--- sys/dev/mmc/mmcreg.h
+++ sys/dev/mmc/mmcreg.h
@@ -199,6 +199,7 @@
 #define	MMC_DATA_READ	(1UL << 1)
 #define	MMC_DATA_STREAM	(1UL << 2)
 #define	MMC_DATA_MULTI	(1UL << 3)
+#define MMC_DATA_BLOCK_SIZE (1UL << 4)
 	struct mmc_request *mrq;
 };