4220 beadm mount of old BE with zones fails "Read only filesystem"
4235 beadm(1M) mount options undocumented in man page

*** 380,408 ****
           * mount all supported non-global zones.
           */
          if (getzoneid() == GLOBAL_ZONEID &&
              !(flags & BE_MOUNT_FLAG_NO_ZONES) &&
              be_get_uuid(bt.obe_root_ds, &uu) == BE_SUCCESS) {
!                 if ((ret = be_mount_zones(zhp, &md)) != BE_SUCCESS) {
!                         (void) _be_unmount(bt.obe_name, 0);
!                         if (gen_tmp_altroot)
!                                 free(tmp_altroot);
!                         ZFS_CLOSE(zhp);
!                         return (ret);
                  }
          }
  
          ZFS_CLOSE(zhp);
  
          /*
           * If a NULL altroot was passed in, pass the generated altroot
           * back to the caller in altroot.
           */
!         if (gen_tmp_altroot)
                  *altroot = tmp_altroot;
  
!         return (BE_SUCCESS);
  }
  
  /*
   * Function:    _be_unmount
   * Description: Unmount a BE.
--- 380,408 ----
           * mount all supported non-global zones.
           */
          if (getzoneid() == GLOBAL_ZONEID &&
              !(flags & BE_MOUNT_FLAG_NO_ZONES) &&
              be_get_uuid(bt.obe_root_ds, &uu) == BE_SUCCESS) {
!                 if (be_mount_zones(zhp, &md) != BE_SUCCESS) {
!                         ret = BE_ERR_NO_MOUNTED_ZONE;
                  }
          }
  
          ZFS_CLOSE(zhp);
  
          /*
           * If a NULL altroot was passed in, pass the generated altroot
           * back to the caller in altroot.
           */
!         if (gen_tmp_altroot) {
!                 if (ret == BE_SUCCESS || ret == BE_ERR_NO_MOUNTED_ZONE)
                          *altroot = tmp_altroot;
+                 else
+                         free(tmp_altroot);
+         }
  
!         return (ret);
  }
  
  /*
   * Function:    _be_unmount
   * Description: Unmount a BE.
*** 1710,1723 ****
  }
  
  /*
   * Function:    loopback_mount_zonepath
   * Description: This function loopback mounts a zonepath into the altroot
!  *              area of the BE being mounted.  Since these are shared file
!  *              systems, they are expected to be already mounted for the
!  *              current BE, and this function just loopback mounts them into
!  *              the BE mountpoint.
   * Parameters:
   *              zonepath - pointer to zone path in the current BE
   *              md - be_mount_data_t pointer
   * Returns:
   *              BE_SUCCESS - Success
--- 1710,1720 ----
  }
  
  /*
   * Function:    loopback_mount_zonepath
   * Description: This function loopback mounts a zonepath into the altroot
!  *              area of the BE being mounted.
   * Parameters:
   *              zonepath - pointer to zone path in the current BE
   *              md - be_mount_data_t pointer
   * Returns:
   *              BE_SUCCESS - Success