[unix-history] / sys / kern / vfs_cache.c

/*
 * Copyright (c) 1989 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University 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 REGENTS 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 REGENTS 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.
 *
 *	from: @(#)vfs_cache.c	7.8 (Berkeley) 2/28/91
 *	$Id: vfs_cache.c,v 1.2 1993/10/16 15:25:19 rgrimes Exp $
 */

#include "param.h"
#include "systm.h"
#include "time.h"
#include "mount.h"
#include "vnode.h"
#include "namei.h"
#include "errno.h"
#include "malloc.h"

/*
 * Name caching works as follows:
 *
 * Names found by directory scans are retained in a cache
 * for future reference.  It is managed LRU, so frequently
 * used names will hang around.  Cache is indexed by hash value
 * obtained from (vp, name) where vp refers to the directory
 * containing name.
 *
 * For simplicity (and economy of storage), names longer than
 * a maximum length of NCHNAMLEN are not cached; they occur
 * infrequently in any case, and are almost never of interest.
 *
 * Upon reaching the last segment of a path, if the reference
 * is for DELETE, or NOCACHE is set (rewrite), and the
 * name is located in the cache, it will be dropped.
 */

/*
 * Structures associated with name cacheing.
 */
union nchash {
	union	nchash *nch_head[2];
	struct	namecache *nch_chain[2];
} *nchashtbl;
#define	nch_forw	nch_chain[0]
#define	nch_back	nch_chain[1]

u_long	nchash;				/* size of hash table - 1 */
long	numcache;			/* number of cache entries allocated */
struct	namecache *nchhead, **nchtail;	/* LRU chain pointers */
struct	nchstats nchstats;		/* cache effectiveness statistics */

int doingcache = 1;			/* 1 => enable the cache */

/*
 * Look for a the name in the cache. We don't do this
 * if the segment name is long, simply so the cache can avoid
 * holding long names (which would either waste space, or
 * add greatly to the complexity).
 *
 * Lookup is called with ni_dvp pointing to the directory to search,
 * ni_ptr pointing to the name of the entry being sought, ni_namelen
 * tells the length of the name, and ni_hash contains a hash of
 * the name. If the lookup succeeds, the vnode is returned in ni_vp
 * and a status of -1 is returned. If the lookup determines that
 * the name does not exist (negative cacheing), a status of ENOENT
 * is returned. If the lookup fails, a status of zero is returned.
 */
int
cache_lookup(ndp)
	register struct nameidata *ndp;
{
	register struct vnode *dvp;
	register struct namecache *ncp;
	union nchash *nhp;

	if (!doingcache)
		return (0);
	if (ndp->ni_namelen > NCHNAMLEN) {
		nchstats.ncs_long++;
		ndp->ni_makeentry = 0;
		return (0);
	}
	dvp = ndp->ni_dvp;
	nhp = &nchashtbl[ndp->ni_hash & nchash];
	for (ncp = nhp->nch_forw; ncp != (struct namecache *)nhp;
	    ncp = ncp->nc_forw) {
		if (ncp->nc_dvp == dvp &&
		    ncp->nc_dvpid == dvp->v_id &&
		    ncp->nc_nlen == ndp->ni_namelen &&
		    !bcmp(ncp->nc_name, ndp->ni_ptr, (unsigned)ncp->nc_nlen))
			break;
	}
	if (ncp == (struct namecache *)nhp) {
		nchstats.ncs_miss++;
		return (0);
	}
	if (!ndp->ni_makeentry) {
		nchstats.ncs_badhits++;
	} else if (ncp->nc_vp == NULL) {
		if ((ndp->ni_nameiop & OPMASK) != CREATE) {
			nchstats.ncs_neghits++;
			/*
			 * Move this slot to end of LRU chain,
			 * if not already there.
			 */
			if (ncp->nc_nxt) {
				/* remove from LRU chain */
				*ncp->nc_prev = ncp->nc_nxt;
				ncp->nc_nxt->nc_prev = ncp->nc_prev;
				/* and replace at end of it */
				ncp->nc_nxt = NULL;
				ncp->nc_prev = nchtail;
				*nchtail = ncp;
				nchtail = &ncp->nc_nxt;
			}
			return (ENOENT);
		}
	} else if (ncp->nc_vpid != ncp->nc_vp->v_id) {
		nchstats.ncs_falsehits++;
	} else {
		nchstats.ncs_goodhits++;
		/*
		 * move this slot to end of LRU chain, if not already there
		 */
		if (ncp->nc_nxt) {
			/* remove from LRU chain */
			*ncp->nc_prev = ncp->nc_nxt;
			ncp->nc_nxt->nc_prev = ncp->nc_prev;
			/* and replace at end of it */
			ncp->nc_nxt = NULL;
			ncp->nc_prev = nchtail;
			*nchtail = ncp;
			nchtail = &ncp->nc_nxt;
		}
		ndp->ni_vp = ncp->nc_vp;
		return (-1);
	}

	/*
	 * Last component and we are renaming or deleting,
	 * the cache entry is invalid, or otherwise don't
	 * want cache entry to exist.
	 */
	/* remove from LRU chain */
	*ncp->nc_prev = ncp->nc_nxt;
	if (ncp->nc_nxt)
		ncp->nc_nxt->nc_prev = ncp->nc_prev;
	else
		nchtail = ncp->nc_prev;
	/* remove from hash chain */
	remque(ncp);
	/* insert at head of LRU list (first to grab) */
	ncp->nc_nxt = nchhead;
	ncp->nc_prev = &nchhead;
	nchhead->nc_prev = &ncp->nc_nxt;
	nchhead = ncp;
	/* and make a dummy hash chain */
	ncp->nc_forw = ncp;
	ncp->nc_back = ncp;
	return (0);
}

/*
 * Add an entry to the cache
 */
void
cache_enter(ndp)
	register struct nameidata *ndp;
{
	register struct namecache *ncp;
	union nchash *nhp;

	if (!doingcache)
		return;
	/*
	 * Free the cache slot at head of lru chain.
	 */
	if (numcache < desiredvnodes) {
		ncp = (struct namecache *)
			malloc((u_long)sizeof *ncp, M_CACHE, M_WAITOK);
		bzero((char *)ncp, sizeof *ncp);
		numcache++;
	} else if (ncp = nchhead) {
		/* remove from lru chain */
		*ncp->nc_prev = ncp->nc_nxt;
		if (ncp->nc_nxt)
			ncp->nc_nxt->nc_prev = ncp->nc_prev;
		else
			nchtail = ncp->nc_prev;
		/* remove from old hash chain */
		remque(ncp);
	} else
		return;
	/* grab the vnode we just found */
	ncp->nc_vp = ndp->ni_vp;
	if (ndp->ni_vp)
		ncp->nc_vpid = ndp->ni_vp->v_id;
	else
		ncp->nc_vpid = 0;
	/* fill in cache info */
	ncp->nc_dvp = ndp->ni_dvp;
	ncp->nc_dvpid = ndp->ni_dvp->v_id;
	ncp->nc_nlen = ndp->ni_namelen;
	bcopy(ndp->ni_ptr, ncp->nc_name, (unsigned)ncp->nc_nlen);
	/* link at end of lru chain */
	ncp->nc_nxt = NULL;
	ncp->nc_prev = nchtail;
	*nchtail = ncp;
	nchtail = &ncp->nc_nxt;
	/* and insert on hash chain */
	nhp = &nchashtbl[ndp->ni_hash & nchash];
	insque(ncp, nhp);
}

/*
 * Name cache initialization, from vfs_init() when we are booting
 */
void
nchinit()
{
	register union nchash *nchp;
	long nchashsize;

	nchhead = 0;
	nchtail = &nchhead;
	nchashsize = roundup((desiredvnodes + 1) * sizeof *nchp / 2,
		NBPG * CLSIZE);
	nchashtbl = (union nchash *)malloc((u_long)nchashsize,
	    M_CACHE, M_WAITOK);
	for (nchash = 1; nchash <= nchashsize / sizeof *nchp; nchash <<= 1)
		/* void */;
	nchash = (nchash >> 1) - 1;
	for (nchp = &nchashtbl[nchash]; nchp >= nchashtbl; nchp--) {
		nchp->nch_head[0] = nchp;
		nchp->nch_head[1] = nchp;
	}
}

/*
 * Cache flush, a particular vnode; called when a vnode is renamed to
 * hide entries that would now be invalid
 */
void
cache_purge(vp)
	struct vnode *vp;
{
	union nchash *nhp;
	struct namecache *ncp;

	vp->v_id = ++nextvnodeid;
	if (nextvnodeid != 0)
		return;
	for (nhp = &nchashtbl[nchash]; nhp >= nchashtbl; nhp--) {
		for (ncp = nhp->nch_forw; ncp != (struct namecache *)nhp;
		    ncp = ncp->nc_forw) {
			ncp->nc_vpid = 0;
			ncp->nc_dvpid = 0;
		}
	}
	vp->v_id = ++nextvnodeid;
}

/*
 * Cache flush, a whole filesystem; called when filesys is umounted to
 * remove entries that would now be invalid
 *
 * The line "nxtcp = nchhead" near the end is to avoid potential problems
 * if the cache lru chain is modified while we are dumping the
 * inode.  This makes the algorithm O(n^2), but do you think I care?
 */
void
cache_purgevfs(mp)
	struct mount *mp;
{
	register struct namecache *ncp, *nxtcp;

	for (ncp = nchhead; ncp; ncp = nxtcp) {
		nxtcp = ncp->nc_nxt;
		if (ncp->nc_dvp == NULL || ncp->nc_dvp->v_mount != mp)
			continue;
		/* free the resources we had */
		ncp->nc_vp = NULL;
		ncp->nc_dvp = NULL;
		remque(ncp);		/* remove entry from its hash chain */
		ncp->nc_forw = ncp;	/* and make a dummy one */
		ncp->nc_back = ncp;
		/* delete this entry from LRU chain */
		*ncp->nc_prev = nxtcp;
		if (nxtcp)
			nxtcp->nc_prev = ncp->nc_prev;
		else
			nchtail = ncp->nc_prev;
		/* cause rescan of list, it may have altered */
		nxtcp = nchhead;
		/* put the now-free entry at head of LRU */
		ncp->nc_nxt = nxtcp;
		ncp->nc_prev = &nchhead;
		nxtcp->nc_prev = &ncp->nc_nxt;
		nchhead = ncp;
	}
}
Commit	Line	Data
15637ed4 RG	1	/*
	2	* Copyright (c) 1989 The Regents of the University of California.
	3	* All rights reserved.
	4	*
	5	* Redistribution and use in source and binary forms, with or without
	6	* modification, are permitted provided that the following conditions
	7	* are met:
	8	* 1. Redistributions of source code must retain the above copyright
	9	* notice, this list of conditions and the following disclaimer.
	10	* 2. Redistributions in binary form must reproduce the above copyright
	11	* notice, this list of conditions and the following disclaimer in the
	12	* documentation and/or other materials provided with the distribution.
	13	* 3. All advertising materials mentioning features or use of this software
	14	* must display the following acknowledgement:
	15	* This product includes software developed by the University of
	16	* California, Berkeley and its contributors.
	17	* 4. Neither the name of the University nor the names of its contributors
	18	* may be used to endorse or promote products derived from this software
	19	* without specific prior written permission.
	20	*
	21	* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	22	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	23	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	24	* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	25	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	26	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	27	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	28	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	29	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	30	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	31	* SUCH DAMAGE.
	32	*
600f7f07	33	* from: @(#)vfs_cache.c 7.8 (Berkeley) 2/28/91
4c45483e	34	* $Id: vfs_cache.c,v 1.2 1993/10/16 15:25:19 rgrimes Exp $
15637ed4 RG	35	*/
	36
	37	#include "param.h"
	38	#include "systm.h"
	39	#include "time.h"
	40	#include "mount.h"
	41	#include "vnode.h"
	42	#include "namei.h"
	43	#include "errno.h"
	44	#include "malloc.h"
	45
	46	/*
	47	* Name caching works as follows:
	48	*
	49	* Names found by directory scans are retained in a cache
	50	* for future reference. It is managed LRU, so frequently
	51	* used names will hang around. Cache is indexed by hash value
	52	* obtained from (vp, name) where vp refers to the directory
	53	* containing name.
	54	*
	55	* For simplicity (and economy of storage), names longer than
	56	* a maximum length of NCHNAMLEN are not cached; they occur
	57	* infrequently in any case, and are almost never of interest.
	58	*
	59	* Upon reaching the last segment of a path, if the reference
	60	* is for DELETE, or NOCACHE is set (rewrite), and the
	61	* name is located in the cache, it will be dropped.
	62	*/
	63
	64	/*
	65	* Structures associated with name cacheing.
	66	*/
	67	union nchash {
	68	union nchash *nch_head[2];
	69	struct namecache *nch_chain[2];
	70	} *nchashtbl;
	71	#define nch_forw nch_chain[0]
	72	#define nch_back nch_chain[1]
	73
	74	u_long nchash; /* size of hash table - 1 */
	75	long numcache; /* number of cache entries allocated */
	76	struct namecache nchhead, nchtail; / LRU chain pointers */
	77	struct nchstats nchstats; /* cache effectiveness statistics */
	78
	79	int doingcache = 1; /* 1 => enable the cache */
	80
	81	/*
	82	* Look for a the name in the cache. We don't do this
	83	* if the segment name is long, simply so the cache can avoid
	84	* holding long names (which would either waste space, or
	85	* add greatly to the complexity).
	86	*
	87	* Lookup is called with ni_dvp pointing to the directory to search,
	88	* ni_ptr pointing to the name of the entry being sought, ni_namelen
	89	* tells the length of the name, and ni_hash contains a hash of
	90	* the name. If the lookup succeeds, the vnode is returned in ni_vp
	91	* and a status of -1 is returned. If the lookup determines that
	92	* the name does not exist (negative cacheing), a status of ENOENT
	93	* is returned. If the lookup fails, a status of zero is returned.
	94	*/
4c45483e	95	int
15637ed4 RG	96	cache_lookup(ndp)
	97	register struct nameidata *ndp;
	98	{
	99	register struct vnode *dvp;
	100	register struct namecache *ncp;
	101	union nchash *nhp;
	102
	103	if (!doingcache)
	104	return (0);
	105	if (ndp->ni_namelen > NCHNAMLEN) {
	106	nchstats.ncs_long++;
	107	ndp->ni_makeentry = 0;
	108	return (0);
	109	}
	110	dvp = ndp->ni_dvp;
	111	nhp = &nchashtbl[ndp->ni_hash & nchash];
	112	for (ncp = nhp->nch_forw; ncp != (struct namecache *)nhp;
	113	ncp = ncp->nc_forw) {
	114	if (ncp->nc_dvp == dvp &&
	115	ncp->nc_dvpid == dvp->v_id &&
	116	ncp->nc_nlen == ndp->ni_namelen &&
	117	!bcmp(ncp->nc_name, ndp->ni_ptr, (unsigned)ncp->nc_nlen))
	118	break;
	119	}
	120	if (ncp == (struct namecache *)nhp) {
	121	nchstats.ncs_miss++;
	122	return (0);
	123	}
	124	if (!ndp->ni_makeentry) {
	125	nchstats.ncs_badhits++;
	126	} else if (ncp->nc_vp == NULL) {
	127	if ((ndp->ni_nameiop & OPMASK) != CREATE) {
	128	nchstats.ncs_neghits++;
	129	/*
	130	* Move this slot to end of LRU chain,
	131	* if not already there.
	132	*/
	133	if (ncp->nc_nxt) {
	134	/* remove from LRU chain */
	135	*ncp->nc_prev = ncp->nc_nxt;
	136	ncp->nc_nxt->nc_prev = ncp->nc_prev;
	137	/* and replace at end of it */
	138	ncp->nc_nxt = NULL;
	139	ncp->nc_prev = nchtail;
	140	*nchtail = ncp;
	141	nchtail = &ncp->nc_nxt;
	142	}
	143	return (ENOENT);
	144	}
	145	} else if (ncp->nc_vpid != ncp->nc_vp->v_id) {
	146	nchstats.ncs_falsehits++;
	147	} else {
	148	nchstats.ncs_goodhits++;
	149	/*
	150	* move this slot to end of LRU chain, if not already there
	151	*/
	152	if (ncp->nc_nxt) {
	153	/* remove from LRU chain */
	154	*ncp->nc_prev = ncp->nc_nxt;
	155	ncp->nc_nxt->nc_prev = ncp->nc_prev;
	156	/* and replace at end of it */
	157	ncp->nc_nxt = NULL;
	158	ncp->nc_prev = nchtail;
	159	*nchtail = ncp;
160	nchtail = &ncp->nc_nxt;
161	}
162	ndp->ni_vp = ncp->nc_vp;
163	return (-1);
164	}
165
166	/*
167	* Last component and we are renaming or deleting,
168	* the cache entry is invalid, or otherwise don't
169	* want cache entry to exist.
170	*/
171	/* remove from LRU chain */
172	*ncp->nc_prev = ncp->nc_nxt;
173	if (ncp->nc_nxt)
174	ncp->nc_nxt->nc_prev = ncp->nc_prev;
175	else
176	nchtail = ncp->nc_prev;
177	/* remove from hash chain */
178	remque(ncp);
179	/* insert at head of LRU list (first to grab) */
180	ncp->nc_nxt = nchhead;
181	ncp->nc_prev = &nchhead;
182	nchhead->nc_prev = &ncp->nc_nxt;
183	nchhead = ncp;
184	/* and make a dummy hash chain */
185	ncp->nc_forw = ncp;
186	ncp->nc_back = ncp;
187	return (0);
188	}
189
190	/*
191	* Add an entry to the cache
192	*/
4c45483e	193	void
15637ed4 RG	194	cache_enter(ndp)
	195	register struct nameidata *ndp;
	196	{
	197	register struct namecache *ncp;
	198	union nchash *nhp;
	199
	200	if (!doingcache)
	201	return;
	202	/*
	203	* Free the cache slot at head of lru chain.
	204	*/
	205	if (numcache < desiredvnodes) {
	206	ncp = (struct namecache *)
	207	malloc((u_long)sizeof *ncp, M_CACHE, M_WAITOK);
	208	bzero((char )ncp, sizeof ncp);
	209	numcache++;
	210	} else if (ncp = nchhead) {
	211	/* remove from lru chain */
	212	*ncp->nc_prev = ncp->nc_nxt;
	213	if (ncp->nc_nxt)
	214	ncp->nc_nxt->nc_prev = ncp->nc_prev;
	215	else
	216	nchtail = ncp->nc_prev;
	217	/* remove from old hash chain */
	218	remque(ncp);
	219	} else
	220	return;
	221	/* grab the vnode we just found */
	222	ncp->nc_vp = ndp->ni_vp;
	223	if (ndp->ni_vp)
	224	ncp->nc_vpid = ndp->ni_vp->v_id;
	225	else
	226	ncp->nc_vpid = 0;
	227	/* fill in cache info */
	228	ncp->nc_dvp = ndp->ni_dvp;
	229	ncp->nc_dvpid = ndp->ni_dvp->v_id;
	230	ncp->nc_nlen = ndp->ni_namelen;
	231	bcopy(ndp->ni_ptr, ncp->nc_name, (unsigned)ncp->nc_nlen);
	232	/* link at end of lru chain */
	233	ncp->nc_nxt = NULL;
	234	ncp->nc_prev = nchtail;
	235	*nchtail = ncp;
	236	nchtail = &ncp->nc_nxt;
	237	/* and insert on hash chain */
	238	nhp = &nchashtbl[ndp->ni_hash & nchash];
	239	insque(ncp, nhp);
	240	}
	241
	242	/*
	243	* Name cache initialization, from vfs_init() when we are booting
	244	*/
4c45483e	245	void
15637ed4 RG	246	nchinit()
	247	{
	248	register union nchash *nchp;
	249	long nchashsize;
	250
	251	nchhead = 0;
	252	nchtail = &nchhead;
	253	nchashsize = roundup((desiredvnodes + 1) * sizeof *nchp / 2,
	254	NBPG * CLSIZE);
	255	nchashtbl = (union nchash *)malloc((u_long)nchashsize,
	256	M_CACHE, M_WAITOK);
	257	for (nchash = 1; nchash <= nchashsize / sizeof *nchp; nchash <<= 1)
	258	/* void */;
	259	nchash = (nchash >> 1) - 1;
	260	for (nchp = &nchashtbl[nchash]; nchp >= nchashtbl; nchp--) {
	261	nchp->nch_head[0] = nchp;
	262	nchp->nch_head[1] = nchp;
	263	}
	264	}
	265
	266	/*
	267	* Cache flush, a particular vnode; called when a vnode is renamed to
	268	* hide entries that would now be invalid
	269	*/
4c45483e	270	void
15637ed4 RG	271	cache_purge(vp)
	272	struct vnode *vp;
	273	{
	274	union nchash *nhp;
	275	struct namecache *ncp;
	276
	277	vp->v_id = ++nextvnodeid;
	278	if (nextvnodeid != 0)
	279	return;
	280	for (nhp = &nchashtbl[nchash]; nhp >= nchashtbl; nhp--) {
	281	for (ncp = nhp->nch_forw; ncp != (struct namecache *)nhp;
	282	ncp = ncp->nc_forw) {
	283	ncp->nc_vpid = 0;
	284	ncp->nc_dvpid = 0;
	285	}
	286	}
	287	vp->v_id = ++nextvnodeid;
	288	}
	289
	290	/*
	291	* Cache flush, a whole filesystem; called when filesys is umounted to
	292	* remove entries that would now be invalid
	293	*
	294	* The line "nxtcp = nchhead" near the end is to avoid potential problems
	295	* if the cache lru chain is modified while we are dumping the
	296	* inode. This makes the algorithm O(n^2), but do you think I care?
	297	*/
4c45483e	298	void
15637ed4 RG	299	cache_purgevfs(mp)
	300	struct mount *mp;
	301	{
	302	register struct namecache ncp, nxtcp;
	303
	304	for (ncp = nchhead; ncp; ncp = nxtcp) {
	305	nxtcp = ncp->nc_nxt;
	306	if (ncp->nc_dvp == NULL \|\| ncp->nc_dvp->v_mount != mp)
	307	continue;
	308	/* free the resources we had */
	309	ncp->nc_vp = NULL;
	310	ncp->nc_dvp = NULL;
	311	remque(ncp); /* remove entry from its hash chain */
	312	ncp->nc_forw = ncp; /* and make a dummy one */
	313	ncp->nc_back = ncp;
	314	/* delete this entry from LRU chain */
	315	*ncp->nc_prev = nxtcp;
	316	if (nxtcp)
	317	nxtcp->nc_prev = ncp->nc_prev;
	318	else
	319	nchtail = ncp->nc_prev;
	320	/* cause rescan of list, it may have altered */
	321	nxtcp = nchhead;
	322	/* put the now-free entry at head of LRU */
	323	ncp->nc_nxt = nxtcp;
	324	ncp->nc_prev = &nchhead;
	325	nxtcp->nc_prev = &ncp->nc_nxt;
	326	nchhead = ncp;
	327	}
	328	}