Source to 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.
*
* @(#)vfs_cache.c 7.8 (Berkeley) 2/28/91
*/
#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.
*/
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
*/
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
*/
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
*/
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?
*/
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;
}
}