sunrpc/pmap_prot2.c

   1 /* @(#)pmap_prot2.c     2.1 88/07/29 4.0 RPCSRC */
   2 /*
   3  * Sun RPC is a product of Sun Microsystems, Inc. and is provided for
   4  * unrestricted use provided that this legend is included on all tape
   5  * media and as a part of the software program in whole or part.  Users
   6  * may copy or modify Sun RPC without charge, but are not authorized
   7  * to license or distribute it to anyone else except as part of a product or
   8  * program developed by the user.
   9  *
  10  * SUN RPC IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING THE
  11  * WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR
  12  * PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE.
  13  *
  14  * Sun RPC is provided with no support and without any obligation on the
  15  * part of Sun Microsystems, Inc. to assist in its use, correction,
  16  * modification or enhancement.
  17  *
  18  * SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE
  19  * INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY SUN RPC
  20  * OR ANY PART THEREOF.
  21  *
  22  * In no event will Sun Microsystems, Inc. be liable for any lost revenue
  23  * or profits or other special, indirect and consequential damages, even if
  24  * Sun has been advised of the possibility of such damages.
  25  *
  26  * Sun Microsystems, Inc.
  27  * 2550 Garcia Avenue
  28  * Mountain View, California  94043
  29  */
  30 #if !defined(lint) && defined(SCCSIDS)
  31 static char sccsid[] = "@(#)pmap_prot2.c 1.3 87/08/11 Copyr 1984 Sun Micro";
  32 #endif
  33
  34 /*
  35  * pmap_prot2.c
  36  * Protocol for the local binder service, or pmap.
  37  *
  38  * Copyright (C) 1984, Sun Microsystems, Inc.
  39  */
  40
  41 #include <rpc/types.h>
  42 #include <rpc/xdr.h>
  43 #include <rpc/pmap_prot.h>
  44
  45
  46 /*
  47  * What is going on with linked lists? (!)
  48  * First recall the link list declaration from pmap_prot.h:
  49  *
  50  * struct pmaplist {
  51  *      struct pmap pml_map;
  52  *      struct pmaplist *pml_map;
  53  * };
  54  *
  55  * Compare that declaration with a corresponding xdr declaration that
  56  * is (a) pointer-less, and (b) recursive:
  57  *
  58  * typedef union switch (bool_t) {
  59  *
  60  *      case TRUE: struct {
  61  *              struct pmap;
  62  *              pmaplist_t foo;
  63  *      };
  64  *
  65  *      case FALSE: struct {};
  66  * } pmaplist_t;
  67  *
  68  * Notice that the xdr declaration has no nxt pointer while
  69  * the C declaration has no bool_t variable.  The bool_t can be
  70  * interpreted as ``more data follows me''; if FALSE then nothing
  71  * follows this bool_t; if TRUE then the bool_t is followed by
  72  * an actual struct pmap, and then (recursively) by the
  73  * xdr union, pamplist_t.
  74  *
  75  * This could be implemented via the xdr_union primitive, though this
  76  * would cause a one recursive call per element in the list.  Rather than do
  77  * that we can ``unwind'' the recursion
  78  * into a while loop and do the union arms in-place.
  79  *
  80  * The head of the list is what the C programmer wishes to past around
  81  * the net, yet is the data that the pointer points to which is interesting;
  82  * this sounds like a job for xdr_reference!
  83  */
  84 bool_t
  85 xdr_pmaplist (xdrs, rp)
  86      XDR *xdrs;
  87      struct pmaplist **rp;
  88 {
  89   /*
  90    * more_elements is pre-computed in case the direction is
  91    * XDR_ENCODE or XDR_FREE.  more_elements is overwritten by
  92    * xdr_bool when the direction is XDR_DECODE.
  93    */
  94   bool_t more_elements;
  95   int freeing = (xdrs->x_op == XDR_FREE);
  96   struct pmaplist **next = NULL;
  97
  98   while (TRUE)
  99     {
 100       more_elements = (bool_t) (*rp != NULL);
 101       if (!xdr_bool (xdrs, &more_elements))
 102         return FALSE;
 103       if (!more_elements)
 104         return TRUE;            /* we are done */
 105       /*
 106        * the unfortunate side effect of non-recursion is that in
 107        * the case of freeing we must remember the next object
 108        * before we free the current object ...
 109        */
 110       if (freeing)
 111         next = &((*rp)->pml_next);
 112       if (!xdr_reference (xdrs, (caddr_t *) rp,
 113                           (u_int) sizeof (struct pmaplist),
 114                           (xdrproc_t) xdr_pmap))
 115           return FALSE;
 116       rp = freeing ? next : &((*rp)->pml_next);
 117     }
 118 }