db_lookup.c

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· C语言 代码 · 共 194 行

#ifndef lint
static	char	*sccsid = "@(#)db_lookup.c	4.1	(ULTRIX)	7/2/90";
#endif lint

/************************************************************************
 *									*
 *			Copyright (c) 1984-1988 by			*
 *		Digital Equipment Corporation, Maynard, MA		*
 *			All rights reserved.				*
 *									*
 *   This software is furnished under a license and may be used and	*
 *   copied  only  in accordance with the terms of such license and	*
 *   with the  inclusion  of  the  above  copyright  notice.   This	*
 *   software  or  any  other copies thereof may not be provided or	*
 *   otherwise made available to any other person.  No title to and	*
 *   ownership of the software is hereby transferred.			*
 *									*
 *   This software is  derived  from  software  received  from  the	*
 *   University    of   California,   Berkeley,   and   from   Bell	*
 *   Laboratories.  Use, duplication, or disclosure is  subject  to	*
 *   restrictions  under  license  agreements  with  University  of	*
 *   California and with AT&T.						*
 *									*
 *   The information in this software is subject to change  without	*
 *   notice  and should not be construed as a commitment by Digital	*
 *   Equipment Corporation.						*
 *									*
 *   Digital assumes no responsibility for the use  or  reliability	*
 *   of its software on equipment which is not supplied by Digital.	*
 *									*
 ************************************************************************/
/*
 * Copyright (c) 1986 Regents of the University of California
 *	All Rights Reserved
 */

/*
 * Modification History:
 *
 * 18-Jan-88	logcher
 *	Added BIND 4.7.3.
 *
 */

/*
 * Table lookup routines.
 */

#include <sys/types.h>
#include <stdio.h>
#include <arpa/nameser.h>
#include "db.h"

struct hashbuf *hashtab;	/* root hash table */
struct hashbuf *fcachetab;	/* hash table of cache read from file */

#ifdef DEBUG
extern int debug;
extern FILE *ddt;
#endif

/* 
 * Lookup 'name' and return a pointer to the namebuf;
 * NULL otherwise. If 'insert', insert name into tables.
 * Wildcard lookups are handled.
 */
struct namebuf *
nlookup(name, htpp, fname, insert)
	char *name;
	struct hashbuf **htpp;
	char **fname;
	int insert;
{
	register struct namebuf *np;
	register char *cp;
	register int c;
	register unsigned hval;
	register struct hashbuf *htp;
	struct namebuf *parent = NULL;

	htp = *htpp;
	hval = 0;
	*fname = "???";
	for (cp = name; c = *cp++; ) {
		if (c == '.') {
			parent = np = nlookup(cp, htpp, fname, insert);
			if (np == NULL)
				return (NULL);
			if (*fname != cp)
				return (np);
			if ((htp = np->n_hash) == NULL) {
				if (!insert) {
					if (np->n_dname[0] == '*' && 
					    np->n_dname[1] == '\0')
						*fname = name;
					return (np);
				}
				htp = savehash((struct hashbuf *)NULL);
				np->n_hash = htp;
			}
			*htpp = htp;
			break;
		}
		hval <<= HASHSHIFT;
		hval += c & HASHMASK;
	}
	c = *--cp;
	*cp = '\0';
	/*
	 * Lookup this label in current hash table.
	 */
	for (np = htp->h_tab[hval % htp->h_size]; np != NULL; np = np->n_next) {

#ifdef ALLOW_UPDATES
		/* Note: at this point, if np->n_data is NULL, we could be in
		   one of two situations: Either we have come across a name
		   for which all the RRs have been (dynamically) deleted, or
		   else we have come across a name which has no RRs
		   associated with it because it is just a place holder
		   (e.g., EDU).  In the former case, we would like to delete
		   the namebuf, since it is no longer of use, but in the
		   latter case we need to hold on to it, so future lookups
		   that depend on it don't fail.  The only way I can see of
		   doing this is to always leave the namebufs around
		   (although then the memory usage continues to grow whenever
		   names are added, and can never shrink back down completely
		   when all their associated RRs are deleted). */
#endif ALLOW_UPDATES

		if (np->n_hashval == hval &&
		    strcasecmp(name, np->n_dname) == 0) {
			*cp = c;
			*fname = name;
			return (np);
		}
	}
	if (!insert) {
		/*
		 * look for wildcard in this hash table
		 */
		hval = ('*' & HASHMASK)  % htp->h_size;
		for (np = htp->h_tab[hval]; np != NULL; np = np->n_next) {
			if (np->n_dname[0] == '*'  && np->n_dname[1] == '\0') {
				*cp = c;
				*fname = name;
				return (np);
			}
		}
		*cp = c;
		return (parent);
	}
	np = savename(name);
	np->n_parent = parent;
	np->n_hashval = hval;
	hval %= htp->h_size;
	np->n_next = htp->h_tab[hval];
	htp->h_tab[hval] = np;
	/* increase hash table size */
	if (++htp->h_cnt > htp->h_size * 2) {
		*htpp = savehash(htp);
		if (parent == NULL) {
			if (htp == hashtab)
			    hashtab = *htpp;
			else
			    fcachetab = *htpp;
		}
		else
			parent->n_hash = *htpp;
		htp = *htpp;
	}
	*cp = c;
	*fname = name;
	return (np);
}

/*
 * Does the data record match the class and type?
 */
match(dp, class, type)
	register struct databuf *dp;
	register int class, type;
{
#ifdef DEBUG
	if (debug >= 5)
		fprintf(ddt,"match(0x%x, %d, %d) %d, %d\n", dp, class, type,
			dp->d_class, dp->d_type);
#endif
	if (dp->d_class != class && class != C_ANY)
		return (0);
	if (dp->d_type != type && type != T_ANY)
		return (0);
	return (1);
}