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>

*** 41,68 ****
  #include <sys/nvpair.h>
  #include "zfs_comutil.h"
  
  /*
   * Are there allocatable vdevs?
   */
  boolean_t
  zfs_allocatable_devs(nvlist_t *nv)
  {
!         uint64_t is_log;
          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;
                  (void) nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_IS_LOG,
                      &is_log);
!                 if (!is_log)
                          return (B_TRUE);
          }
          return (B_FALSE);
  }
  
--- 41,72 ----
  #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, 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 = is_special = 0;
                  (void) nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_IS_LOG,
                      &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);
  }