src/pmap_prot2.c

/*
 * Copyright (c) 2009, Sun Microsystems, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * - Neither the name of Sun Microsystems, Inc. nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * pmap_prot2.c
 * Protocol for the local binder service, or pmap.
 *
 * Copyright (C) 1984, Sun Microsystems, Inc.
 */

#include <config.h>
#include <assert.h>

#include <rpc/types.h>
#include <rpc/xdr.h>
#include <rpc/pmap_prot.h>

/*
 * What is going on with linked lists? (!)
 * First recall the link list declaration from pmap_prot.h:
 *
 * struct pmaplist {
 * struct pmap pml_map;
 * struct pmaplist *pml_map;
 * };
 *
 * Compare that declaration with a corresponding xdr declaration that
 * is (a) pointer-less, and (b) recursive:
 *
 * typedef union switch (bool_t) {
 *
 * case true: struct {
 *  struct pmap;
 *   pmaplist_t foo;
 * };
 *
 * case false: struct {};
 * } pmaplist_t;
 *
 * Notice that the xdr declaration has no nxt pointer while
 * the C declaration has no bool_t variable.  The bool_t can be
 * interpreted as ``more data follows me''; if false then nothing
 * follows this bool_t; if true then the bool_t is followed by
 * an actual struct pmap, and then (recursively) by the
 * xdr union, pamplist_t.
 *
 * This could be implemented via the xdr_union primitive, though this
 * would cause a one recursive call per element in the list.  Rather than do
 * that we can ``unwind'' the recursion
 * into a while loop and do the union arms in-place.
 *
 * The head of the list is what the C programmer wishes to past around
 * the net, yet is the data that the pointer points to which is interesting;
 * this sounds like a job for xdr_reference!
 */
bool
xdr_pmaplist(XDR *xdrs, struct pmaplist **rp)
{
	/*
	 * more_elements is pre-computed in case the direction is
	 * XDR_ENCODE or XDR_FREE.  more_elements is overwritten by
	 * xdr_bool when the direction is XDR_DECODE.
	 */
	int freeing;
	struct pmaplist **next = NULL;	/* pacify gcc */
	bool_t more_elements = false;	/* yes, bool_t */

	assert(xdrs != NULL);
	assert(rp != NULL);

	freeing = (xdrs->x_op == XDR_FREE);

	for (;;) {
		more_elements = (bool_t) (*rp != NULL);
		if (!xdr_bool(xdrs, &more_elements))
			return (false);
		if (!more_elements)
			return (true);	/* we are done */
		/*
		 * the unfortunate side effect of non-recursion is that in
		 * the case of freeing we must remember the next object
		 * before we free the current object ...
		 */
		if (freeing)
			next = &((*rp)->pml_next);
		if (!xdr_reference
		    (xdrs, (caddr_t *) rp, (u_int) sizeof(struct pmaplist),
		     (xdrproc_t) xdr_pmap))
			return (false);
		rp = (freeing) ? next : &((*rp)->pml_next);
	}
}

/*
 * xdr_pmaplist_ptr() is specified to take a PMAPLIST *, but is identical in
 * functionality to xdr_pmaplist().
 */
bool
xdr_pmaplist_ptr(XDR *xdrs, struct pmaplist *rp)
{
	return xdr_pmaplist(xdrs, (struct pmaplist **)(void *)rp);
}