Index: sys/boot/ofw/libofw/ofw_disk.c
===================================================================
--- sys/boot/ofw/libofw/ofw_disk.c
+++ sys/boot/ofw/libofw/ofw_disk.c
@@ -154,11 +154,26 @@
 }
 
 static int
-ofwd_ioctl(struct open_file *f __unused, u_long cmd __unused,
-    void *data __unused)
+ofwd_ioctl(struct open_file *f, u_long cmd, void *data)
 {
+	struct ofw_devdesc *dev = f->f_devdata;
+	int block_size;
+	unsigned int n;
 
-	return (EINVAL);
+	switch (cmd) {
+	case DIOCGSECTORSIZE:
+		block_size = OF_block_size(dev->d_handle);
+		*(u_int *)data = block_size;
+		break;
+	case DIOCGMEDIASIZE:
+		block_size = OF_block_size(dev->d_handle);
+		n = OF_blocks(dev->d_handle);
+		*(uint64_t *)data = (uint64_t)(n * block_size);
+		break;
+	default:
+		return (ENOTTY);
+	}
+	return (0);
 }
 
 static int
Index: sys/boot/ofw/libofw/openfirm.h
===================================================================
--- sys/boot/ofw/libofw/openfirm.h
+++ sys/boot/ofw/libofw/openfirm.h
@@ -105,6 +105,8 @@
 int		OF_read(ihandle_t, void *, int);
 int		OF_write(ihandle_t, void *, int);
 int		OF_seek(ihandle_t, u_quad_t);
+unsigned int	OF_blocks(ihandle_t);
+int		OF_block_size(ihandle_t);
 
 /* Memory functions */
 void 		*OF_claim(void *, u_int, u_int);
Index: sys/boot/ofw/libofw/openfirm.c
===================================================================
--- sys/boot/ofw/libofw/openfirm.c
+++ sys/boot/ofw/libofw/openfirm.c
@@ -622,6 +622,53 @@
 	return (args.status);
 }
 
+/* Blocks. */
+unsigned int
+OF_blocks(ihandle_t instance)
+{
+	static struct {
+		cell_t name;
+		cell_t nargs;
+		cell_t nreturns;
+		cell_t instance;
+		cell_t result;
+		cell_t blocks;
+	} args = {
+		(cell_t)"#blocks",
+		2,
+		1,
+	};
+
+	args.instance = instance;
+	if (openfirmware(&args) == -1)
+		return ((unsigned int)-1);
+	return (args.blocks);
+}
+
+/* Block size. */
+int
+OF_block_size(ihandle_t instance)
+{
+	static struct {
+		cell_t name;
+		cell_t nargs;
+		cell_t nreturns;
+		cell_t instance;
+		cell_t result;
+		cell_t size;
+	} args = {
+		(cell_t)"block-size",
+		2,
+		1,
+	};
+
+	args.instance = instance;
+	if (openfirmware(&args) == -1)
+		return (512);
+	return (args.size);
+}
+
+/* 
 /*
  * Memory functions
  */
Index: sys/boot/sparc64/loader/main.c
===================================================================
--- sys/boot/sparc64/loader/main.c
+++ sys/boot/sparc64/loader/main.c
@@ -735,6 +735,16 @@
 }
 
 #ifdef LOADER_ZFS_SUPPORT
+uint64_t
+ldi_get_size(void *priv)
+{
+	int fd = (uintptr_t) priv;
+	uint64_t size;
+
+	ioctl(fd, DIOCGMEDIASIZE, &size);
+	return (size);
+}
+
 static void
 sparc64_zfs_probe(void)
 {