diff --git a/mars.h b/mars.h
index feb7565b..a14884ec 100644
--- a/mars.h
+++ b/mars.h
@@ -194,7 +194,7 @@ static const struct generic_aspect_type *BRICK##_aspect_types[BRICK_OBJ_NR] = {
 		int test = atomic_read(atom);				\
 		if (test OP (minval)) {					\
 			atomic_set(atom, minval);			\
-			MARS_ERR("line %d atomic " #atom " " #OP " " #minval "\n", __LINE__); \
+			MARS_ERR("%d: atomic " #atom " " #OP " " #minval "\n", __LINE__); \
 		}							\
 	} while (0)
 
@@ -219,19 +219,19 @@ static inline void mars_ref_attach_bio(struct mars_ref_object *mref, struct bio
 #define CHECK_HEAD_EMPTY(head)						\
 	if (unlikely(!list_empty(head))) {				\
 		INIT_LIST_HEAD(head);					\
-		MARS_ERR("list_head " #head " (%p) not empty\n", head);	\
+		MARS_ERR("%d: list_head " #head " (%p) not empty\n", __LINE__, head); \
 	}								\
 
 #endif
 
 #define CHECK_PTR(ptr,label)						\
 	if (unlikely(!(ptr))) {						\
-		MARS_FAT("ptr " #ptr " is NULL\n");			\
+		MARS_FAT("%d: ptr " #ptr " is NULL\n", __LINE__);	\
 		goto label;						\
 	}
 
 #define _CHECK(ptr,label)						\
 	if (unlikely(!(ptr))) {						\
-		MARS_FAT("condition " #ptr " is VIOLATED\n");		\
+		MARS_FAT("%d: condition " #ptr " is VIOLATED\n", __LINE__); \
 		goto label;						\
 	}
diff --git a/mars_buf.c b/mars_buf.c
index 364929bd..cd989370 100644
--- a/mars_buf.c
+++ b/mars_buf.c
@@ -226,16 +226,30 @@ static int make_bio(struct buf_brick *brick, struct bio **_bio, void *data, loff
 	struct bio *bio = NULL;
 	struct block_device *bdev;
 
+	status = -EINVAL;
+	CHECK_PTR(brick, out);
 	if (unlikely(!brick->got_info)) {
 		struct request_queue *q;
 		status = get_info(brick);
 		if (status < 0)
 			goto out;
+		status = -EINVAL;
+		CHECK_PTR(brick->base_info.backing_file, out);
+		CHECK_PTR(brick->base_info.backing_file->f_mapping, out);
+		CHECK_PTR(brick->base_info.backing_file->f_mapping->host, out);
+		CHECK_PTR(brick->base_info.backing_file->f_mapping->host->i_sb, out);
 		bdev = brick->base_info.backing_file->f_mapping->host->i_sb->s_bdev;
+		if (!bdev && S_ISBLK(brick->base_info.backing_file->f_mapping->host->i_mode)) {
+			bdev = brick->base_info.backing_file->f_mapping->host->i_bdev;
+		}
+		CHECK_PTR(bdev, out);
+		brick->bdev = bdev;
 		q = bdev_get_queue(bdev);
+		CHECK_PTR(q, out);
 		brick->bvec_max = queue_max_hw_sectors(q) >> (PAGE_SHIFT - 9);
 	} else {
-		bdev = brick->base_info.backing_file->f_mapping->host->i_sb->s_bdev;
+		bdev = brick->bdev;
+		CHECK_PTR(bdev, out);
 	}
 
 	if (unlikely(ilen <= 0)) {
@@ -281,6 +295,8 @@ static int make_bio(struct buf_brick *brick, struct bio **_bio, void *data, loff
 			mylen = myrest;
 
 		page = virt_to_page(data);
+		if (!page)
+			goto out;
 
 		bio->bi_io_vec[i].bv_page = page;
 		bio->bi_io_vec[i].bv_len = mylen;
diff --git a/mars_buf.h b/mars_buf.h
index 1b5b65f4..4b6f6a03 100644
--- a/mars_buf.h
+++ b/mars_buf.h
@@ -46,6 +46,7 @@ struct buf_brick {
 	struct mars_info base_info;
 	int got_info;
 	int bvec_max;
+	struct block_device *bdev;
 
 	// statistics
 	unsigned long last_jiffies;
diff --git a/mars_test.c b/mars_test.c
index 35cef4ff..807c114f 100644
--- a/mars_test.c
+++ b/mars_test.c
@@ -189,6 +189,7 @@ void make_test_instance(void)
 	connect(last, trans_brick->outputs[0]);
 #else
 	(void)trans_brick;
+	(void)_trans_brick;
 	(void)tbuf_brick;
 	(void)_tbuf_brick;
 	(void)tdevice_brick;
@@ -233,7 +234,15 @@ void make_test_instance(void)
 	MARS_INF("------------- END INIT --------------\n");
 
 	_if_brick = (void*)if_brick;
-	_if_brick->ops->brick_switch(if_brick, true);
+	{
+		struct mars_info info = {};
+		int status = GENERIC_INPUT_CALL(_if_brick->inputs[0], mars_get_info, &info);
+		MARS_INF("INFO status=%d size=%lld transfer_order=%d transfer_size=%d %p\n", status, info.current_size, info.transfer_order, info.transfer_size, info.backing_file);
+	}
+
+	MARS_INF("------------- START GATE --------------\n");
+
+	_if_brick->ops->brick_switch(_if_brick, true);
 	//_if_brick->is_active = true;
 
 	msleep(2000);