8264 want support for promoting datasets in libzfs_core

*** 21,30 ****
--- 21,31 ----
  
  /*
   * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
   * Copyright (c) 2013 Steven Hartland. All rights reserved.
   * Copyright (c) 2014 Integros [integros.com]
+  * Copyright 2017 RackTop Systems.
   */
  
  /*
   * LibZFS_Core (lzc) is intended to replace most functionality in libzfs.
   * It has the following characteristics:
*** 201,210 ****
--- 202,232 ----
          error = lzc_ioctl(ZFS_IOC_CLONE, fsname, args, NULL);
          nvlist_free(args);
          return (error);
  }
  
+ int
+ lzc_promote(const char *fsname, char *snapnamebuf, int snapnamelen)
+ {
+         /*
+          * The promote ioctl is still legacy, so we need to construct our
+          * own zfs_cmd_t rather than using lzc_ioctl().
+          */
+         zfs_cmd_t zc = { 0 };
+ 
+         ASSERT3S(g_refcount, >, 0);
+         VERIFY3S(g_fd, !=, -1);
+ 
+         (void) strlcpy(zc.zc_name, fsname, sizeof (zc.zc_name));
+         if (ioctl(g_fd, ZFS_IOC_PROMOTE, &zc) != 0) {
+                 if (errno == EEXIST && snapnamebuf != NULL)
+                         (void) strlcpy(snapnamebuf, zc.zc_string, snapnamelen);
+                 return (errno);
+         }
+         return (0);
+ }
+ 
  /*
   * Creates snapshots.
   *
   * The keys in the snaps nvlist are the snapshots to be created.
   * They must all be in the same pool.
*** 328,338 ****
  boolean_t
  lzc_exists(const char *dataset)
  {
          /*
           * The objset_stats ioctl is still legacy, so we need to construct our
!          * own zfs_cmd_t rather than using zfsc_ioctl().
           */
          zfs_cmd_t zc = { 0 };
  
          ASSERT3S(g_refcount, >, 0);
          VERIFY3S(g_fd, !=, -1);
--- 350,360 ----
  boolean_t
  lzc_exists(const char *dataset)
  {
          /*
           * The objset_stats ioctl is still legacy, so we need to construct our
!          * own zfs_cmd_t rather than using lzc_ioctl().
           */
          zfs_cmd_t zc = { 0 };
  
          ASSERT3S(g_refcount, >, 0);
          VERIFY3S(g_fd, !=, -1);