sunrpc/pmap_prot2.c

   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
  39
  40 /*
  41  * What is going on with linked lists? (!)
  42  * First recall the link list declaration from pmap_prot.h:
  43  *
  44  * struct pmaplist {
  45  *      struct pmap pml_map;
  46  *      struct pmaplist *pml_map;
  47  * };
  48  *
  49  * Compare that declaration with a corresponding xdr declaration that
  50  * is (a) pointer-less, and (b) recursive:
  51  *
  52  * typedef union switch (bool_t) {
  53  *
  54  *      case TRUE: struct {
  55  *              struct pmap;
  56  *              pmaplist_t foo;
  57  *      };
  58  *
  59  *      case FALSE: struct {};
  60  * } pmaplist_t;
  61  *
  62  * Notice that the xdr declaration has no nxt pointer while
  63  * the C declaration has no bool_t variable.  The bool_t can be
  64  * interpreted as ``more data follows me''; if FALSE then nothing
  65  * follows this bool_t; if TRUE then the bool_t is followed by
  66  * an actual struct pmap, and then (recursively) by the
  67  * xdr union, pamplist_t.
  68  *
  69  * This could be implemented via the xdr_union primitive, though this
  70  * would cause a one recursive call per element in the list.  Rather than do
  71  * that we can ``unwind'' the recursion
  72  * into a while loop and do the union arms in-place.
  73  *
  74  * The head of the list is what the C programmer wishes to past around
  75  * the net, yet is the data that the pointer points to which is interesting;
  76  * this sounds like a job for xdr_reference!
  77  */
  78 bool_t
  79 xdr_pmaplist (xdrs, rp)
  80      XDR *xdrs;
  81      struct pmaplist **rp;
  82 {
  83   /*
  84    * more_elements is pre-computed in case the direction is
  85    * XDR_ENCODE or XDR_FREE.  more_elements is overwritten by
  86    * xdr_bool when the direction is XDR_DECODE.
  87    */
  88   bool_t more_elements;
  89   int freeing = (xdrs->x_op == XDR_FREE);
  90   struct pmaplist *next = NULL;
  91
  92   while (TRUE)
  93     {
  94       more_elements = (bool_t) (*rp != NULL);
  95       if (!xdr_bool (xdrs, &more_elements))
  96         return FALSE;
  97       if (!more_elements)
  98         return TRUE;            /* we are done */
  99       /*
 100        * the unfortunate side effect of non-recursion is that in
 101        * the case of freeing we must remember the next object
 102        * before we free the current object ...
 103        */
 104       if (freeing)
 105         next = (*rp)->pml_next;
 106       if (!xdr_reference (xdrs, (caddr_t *) rp,
 107                           (u_int) sizeof (struct pmaplist),
 108                           (xdrproc_t) xdr_pmap))
 109           return FALSE;
 110       rp = freeing ? &next : &((*rp)->pml_next);
 111     }
 112 }
 113 libc_hidden_nolink (xdr_pmaplist, GLIBC_2_0)