usr/src/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.
 *
 *      @(#)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;
        }
}