--- a/usr/src/common/zfs/zfs_comutil.c	Tue Mar 16 06:44:44 2010 -0700
+++ b/usr/src/common/zfs/zfs_comutil.c	Tue Mar 16 09:43:38 2010 -0600
@@ -39,6 +39,7 @@
 #include <sys/fs/zfs.h>
 #include <sys/int_limits.h>
 #include <sys/nvpair.h>
+#include "zfs_comutil.h"
 
 /*
  * Are there allocatable vdevs?
@@ -103,3 +104,56 @@
 	if (zrpp->zrp_request == 0)
 		zrpp->zrp_request = ZPOOL_NO_REWIND;
 }
+
+typedef struct zfs_version_spa_map {
+	int	version_zpl;
+	int	version_spa;
+} zfs_version_spa_map_t;
+
+/*
+ * Keep this table in monotonically increasing version number order.
+ */
+static zfs_version_spa_map_t zfs_version_table[] = {
+	{ZPL_VERSION_INITIAL, SPA_VERSION_INITIAL},
+	{ZPL_VERSION_DIRENT_TYPE, SPA_VERSION_INITIAL},
+	{ZPL_VERSION_FUID, SPA_VERSION_FUID},
+	{ZPL_VERSION_USERSPACE, SPA_VERSION_USERSPACE},
+	{ZPL_VERSION_SA, SPA_VERSION_SA},
+	{0, 0}
+};
+
+/*
+ * Return the max zpl version for a corresponding spa version
+ * -1 is returned if no mapping exists.
+ */
+int
+zfs_zpl_version_map(int spa_version)
+{
+	int i;
+	int version = -1;
+
+	for (i = 0; zfs_version_table[i].version_spa; i++) {
+		if (spa_version >= zfs_version_table[i].version_spa)
+			version = zfs_version_table[i].version_zpl;
+	}
+
+	return (version);
+}
+
+/*
+ * Return the min spa version for a corresponding spa version
+ * -1 is returned if no mapping exists.
+ */
+int
+zfs_spa_version_map(int zpl_version)
+{
+	int i;
+	int version = -1;
+
+	for (i = 0; zfs_version_table[i].version_zpl; i++) {
+		if (zfs_version_table[i].version_zpl >= zpl_version)
+			return (zfs_version_table[i].version_spa);
+	}
+
+	return (version);
+}