OpenZFS 6052 - decouple lzc_create() from the implementation details

Authored by: Andriy Gapon <andriy.gapon@clusterhq.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov mail@gmelikov.ru

OpenZFS-issue: https://www.illumos.org/issues/6052
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/26455f9
Closes #5622

include/libzfs_core.h

@@ -38,8 +38,16 @@ extern "C" {
 int libzfs_core_init(void);
 void libzfs_core_fini(void);
 
+/*
+ * NB: this type should be kept binary compatible with dmu_objset_type_t.
+ */
+enum lzc_dataset_type {
+	LZC_DATSET_TYPE_ZFS = 2,
+	LZC_DATSET_TYPE_ZVOL
+};
+
 int lzc_snapshot(nvlist_t *, nvlist_t *, nvlist_t **);
-int lzc_create(const char *, dmu_objset_type_t, nvlist_t *);
+int lzc_create(const char *, enum lzc_dataset_type, nvlist_t *);
 int lzc_clone(const char *, const char *, nvlist_t *);
 int lzc_destroy_snaps(nvlist_t *, boolean_t, nvlist_t **);
 int lzc_bookmark(nvlist_t *, nvlist_t **);

include/sys/fs/zfs.h

@@ -54,6 +54,10 @@ typedef enum {
 	ZFS_TYPE_BOOKMARK	= (1 << 4)
 } zfs_type_t;
 
+/*
+ * NB: lzc_dataset_type should be updated whenever a new objset type is added,
+ * if it represents a real type of a dataset that can be created from userland.
+ */
 typedef enum dmu_objset_type {
 	DMU_OST_NONE,
 	DMU_OST_META,