1  /*
       2   * pmap_prot2.c
       3   * Protocol for the local binder service, or pmap.
       4   *
       5   * Copyright (c) 2010, Oracle America, Inc.
       6   *
       7   * Redistribution and use in source and binary forms, with or without
       8   * modification, are permitted provided that the following conditions are
       9   * met:
      10   *
      11   *     * Redistributions of source code must retain the above copyright
      12   *       notice, this list of conditions and the following disclaimer.
      13   *     * Redistributions in binary form must reproduce the above
      14   *       copyright notice, this list of conditions and the following
      15   *       disclaimer in the documentation and/or other materials
      16   *       provided with the distribution.
      17   *     * Neither the name of the "Oracle America, Inc." nor the names of its
      18   *       contributors may be used to endorse or promote products derived
      19   *       from this software without specific prior written permission.
      20   *
      21   *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
      22   *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
      23   *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
      24   *   FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
      25   *   COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
      26   *   INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
      27   *   DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
      28   *   GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
      29   *   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
      30   *   WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
      31   *   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
      32   *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
      33   */
      34  
      35  #include <rpc/types.h>
      36  #include <rpc/xdr.h>
      37  #include <rpc/pmap_prot.h>
      38  #include <shlib-compat.h>
      39  
      40  
      41  /*
      42   * What is going on with linked lists? (!)
      43   * First recall the link list declaration from pmap_prot.h:
      44   *
      45   * struct pmaplist {
      46   *      struct pmap pml_map;
      47   *      struct pmaplist *pml_map;
      48   * };
      49   *
      50   * Compare that declaration with a corresponding xdr declaration that
      51   * is (a) pointer-less, and (b) recursive:
      52   *
      53   * typedef union switch (bool_t) {
      54   *
      55   *      case TRUE: struct {
      56   *              struct pmap;
      57   *              pmaplist_t foo;
      58   *      };
      59   *
      60   *      case FALSE: struct {};
      61   * } pmaplist_t;
      62   *
      63   * Notice that the xdr declaration has no nxt pointer while
      64   * the C declaration has no bool_t variable.  The bool_t can be
      65   * interpreted as ``more data follows me''; if FALSE then nothing
      66   * follows this bool_t; if TRUE then the bool_t is followed by
      67   * an actual struct pmap, and then (recursively) by the
      68   * xdr union, pamplist_t.
      69   *
      70   * This could be implemented via the xdr_union primitive, though this
      71   * would cause a one recursive call per element in the list.  Rather than do
      72   * that we can ``unwind'' the recursion
      73   * into a while loop and do the union arms in-place.
      74   *
      75   * The head of the list is what the C programmer wishes to past around
      76   * the net, yet is the data that the pointer points to which is interesting;
      77   * this sounds like a job for xdr_reference!
      78   */
      79  bool_t
      80  xdr_pmaplist (XDR *xdrs, struct pmaplist **rp)
      81  {
      82    /*
      83     * more_elements is pre-computed in case the direction is
      84     * XDR_ENCODE or XDR_FREE.  more_elements is overwritten by
      85     * xdr_bool when the direction is XDR_DECODE.
      86     */
      87    bool_t more_elements;
      88    int freeing = (xdrs->x_op == XDR_FREE);
      89    struct pmaplist *next = NULL;
      90  
      91    while (TRUE)
      92      {
      93        more_elements = (bool_t) (*rp != NULL);
      94        if (!xdr_bool (xdrs, &more_elements))
      95  	return FALSE;
      96        if (!more_elements)
      97  	return TRUE;		/* we are done */
      98        /*
      99         * the unfortunate side effect of non-recursion is that in
     100         * the case of freeing we must remember the next object
     101         * before we free the current object ...
     102         */
     103        if (freeing)
     104  	next = (*rp)->pml_next;
     105        if (!xdr_reference (xdrs, (caddr_t *) rp,
     106  			  (u_int) sizeof (struct pmaplist),
     107  			  (xdrproc_t) xdr_pmap))
     108  	  return FALSE;
     109        rp = freeing ? &next : &((*rp)->pml_next);
     110      }
     111  }
     112  libc_hidden_nolink_sunrpc (xdr_pmaplist, GLIBC_2_0)