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         register XDR *xdrs;
  87         register 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         register int freeing = (xdrs->x_op == XDR_FREE);
  96         register struct pmaplist **next;
  97
  98         while (TRUE) {
  99                 more_elements = (bool_t)(*rp != NULL);
 100                 if (! xdr_bool(xdrs, &more_elements))
 101                         return (FALSE);
 102                 if (! more_elements)
 103                         return (TRUE);  /* we are done */
 104                 /*
 105                  * the unfortunate side effect of non-recursion is that in
 106                  * the case of freeing we must remember the next object
 107                  * before we free the current object ...
 108                  */
 109                 if (freeing)
 110                         next = &((*rp)->pml_next);
 111                 if (! xdr_reference(xdrs, (caddr_t *)rp,
 112                     (u_int)sizeof(struct pmaplist), xdr_pmap))
 113                         return (FALSE);
 114                 rp = (freeing) ? next : &((*rp)->pml_next);
 115         }
 116 }