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

@@ -380,29 +380,29 @@
          * 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);
+                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 (gen_tmp_altroot) {
+                if (ret == BE_SUCCESS || ret == BE_ERR_NO_MOUNTED_ZONE)
                 *altroot = tmp_altroot;
+                else
+                        free(tmp_altroot);
+        }
 
-        return (BE_SUCCESS);
+        return (ret);
 }
 
 /*
  * Function:    _be_unmount
  * Description: Unmount a BE.

@@ -1710,14 +1710,11 @@
 }
 
 /*
  * 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.
+ *              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