NEX-4649 zpool create <name> special <disk> command hangs
Reviewed by: Alex Aizman <alex.aizman@nexenta.com>
Reviewed by: Roman Strashkin <roman.strashkin@gmail.com>

@@ -41,28 +41,32 @@
 #include <sys/nvpair.h>
 #include "zfs_comutil.h"
 
 /*
  * Are there allocatable vdevs?
+ * Any pool must have at least one normal (metaslab) class vdev, which means:
+ * at least one that is simultaneously non-slog and non-special
  */
 boolean_t
 zfs_allocatable_devs(nvlist_t *nv)
 {
-        uint64_t is_log;
+        uint64_t is_log, is_special;
         uint_t c;
         nvlist_t **child;
         uint_t children;
 
         if (nvlist_lookup_nvlist_array(nv, ZPOOL_CONFIG_CHILDREN,
             &child, &children) != 0) {
                 return (B_FALSE);
         }
         for (c = 0; c < children; c++) {
-                is_log = 0;
+                is_log = is_special = 0;
                 (void) nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_IS_LOG,
                     &is_log);
-                if (!is_log)
+                (void) nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_IS_SPECIAL,
+                    &is_special);
+                if (!is_log && !is_special)
                         return (B_TRUE);
         }
         return (B_FALSE);
 }