1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
326 lines
9.0 KiB
C
326 lines
9.0 KiB
C
/*
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* Copyright (c) 1989, 1993
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* The Regents of the University of California. All rights reserved.
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* Copyright (c) 1995
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* Poul-Henning Kamp. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)vfs_cache.c 8.3 (Berkeley) 8/22/94
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* $FreeBSD$
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*/
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/kernel.h>
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#include <sys/sysctl.h>
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#include <sys/time.h>
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#include <sys/mount.h>
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#include <sys/vnode.h>
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#include <sys/namei.h>
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#include <sys/errno.h>
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#include <sys/malloc.h>
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#define MAXVNODEUSE 32
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/*
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* Name caching works as follows:
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*
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* Names found by directory scans are retained in a cache
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* for future reference. It is managed LRU, so frequently
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* used names will hang around. Cache is indexed by hash value
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* obtained from (vp, name) where vp refers to the directory
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* containing name.
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*
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* If it is a "negative" entry, (that we know a name to >not< exist)
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* we point out entry at our own "nchENOENT", to avoid too much special
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* casing in the inner loops of lookup.
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*
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* For simplicity (and economy of storage), names longer than
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* a maximum length of NCHNAMLEN are not cached; they occur
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* infrequently in any case, and are almost never of interest.
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*
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* Upon reaching the last segment of a path, if the reference
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* is for DELETE, or NOCACHE is set (rewrite), and the
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* name is located in the cache, it will be dropped.
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*/
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/*
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* Structures associated with name cacheing.
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*/
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static LIST_HEAD(nchashhead, namecache) *nchashtbl; /* Hash Table */
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static TAILQ_HEAD(, namecache) nclruhead; /* LRU chain */
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static u_long nchash; /* size of hash table */
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struct nchstats nchstats; /* cache effectiveness statistics */
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static struct vnode nchENOENT; /* our own "novnode" */
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static int doingcache = 1; /* 1 => enable the cache */
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SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, "");
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static u_long numcache;
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u_long numvnodes;
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#ifdef NCH_STATISTICS
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u_long nchnbr;
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#define NCHNBR(ncp) (ncp)->nc_nbr = ++nchnbr;
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#define NCHHIT(ncp) (ncp)->nc_hits++
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#else
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#define NCHNBR(ncp)
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#define NCHHIT(ncp)
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#endif
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#define PURGE(ncp) { \
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LIST_REMOVE(ncp, nc_hash); \
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ncp->nc_hash.le_prev = 0; \
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TAILQ_REMOVE(&nclruhead, ncp, nc_lru); \
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TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru); }
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#define TOUCH(ncp) { \
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if (ncp->nc_lru.tqe_next == 0) { } else { \
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TAILQ_REMOVE(&nclruhead, ncp, nc_lru); \
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TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru); \
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NCHNBR(ncp); } }
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/*
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* Lookup an entry in the cache
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*
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* We don't do this if the segment name is long, simply so the cache
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* can avoid holding long names (which would either waste space, or
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* add greatly to the complexity).
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*
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* Lookup is called with dvp pointing to the directory to search,
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* cnp pointing to the name of the entry being sought.
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* If the lookup succeeds, the vnode is returned in *vpp, and a status
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* of -1 is returned.
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* If the lookup determines that the name does not exist (negative cacheing),
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* a status of ENOENT is returned.
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* If the lookup fails, a status of zero is returned.
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*/
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int
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cache_lookup(dvp, vpp, cnp)
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struct vnode *dvp;
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struct vnode **vpp;
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struct componentname *cnp;
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{
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register struct namecache *ncp,*nnp;
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register struct nchashhead *ncpp;
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if (!doingcache) {
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cnp->cn_flags &= ~MAKEENTRY;
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return (0);
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}
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if (cnp->cn_namelen > NCHNAMLEN) {
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nchstats.ncs_long++;
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cnp->cn_flags &= ~MAKEENTRY;
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return (0);
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}
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ncpp = &nchashtbl[(dvp->v_id + cnp->cn_hash) % nchash];
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for (ncp = ncpp->lh_first; ncp != 0; ncp = nnp) {
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nnp = ncp->nc_hash.le_next;
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/* If one of the vp's went stale, don't bother anymore. */
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if ((ncp->nc_dvpid != ncp->nc_dvp->v_id) ||
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(ncp->nc_vpid != ncp->nc_vp->v_id)) {
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nchstats.ncs_falsehits++;
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PURGE(ncp);
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continue;
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}
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/* Now that we know the vp's to be valid, is it ours ? */
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if (ncp->nc_dvp == dvp &&
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ncp->nc_nlen == cnp->cn_namelen &&
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!bcmp(ncp->nc_name, cnp->cn_nameptr, (u_int)ncp->nc_nlen))
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goto found; /* Fanatism considered bad. */
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}
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nchstats.ncs_miss++;
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return (0);
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found:
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NCHHIT(ncp);
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/* We don't want to have an entry, so dump it */
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if ((cnp->cn_flags & MAKEENTRY) == 0) {
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nchstats.ncs_badhits++;
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PURGE(ncp);
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return (0);
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}
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/* We found a "positive" match, return the vnode */
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if (ncp->nc_vp != &nchENOENT) {
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nchstats.ncs_goodhits++;
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TOUCH(ncp);
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*vpp = ncp->nc_vp;
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if ((*vpp)->v_usage < MAXVNODEUSE)
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(*vpp)->v_usage++;
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return (-1);
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}
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/* We found a negative match, and want to create it, so purge */
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if (cnp->cn_nameiop == CREATE) {
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nchstats.ncs_badhits++;
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PURGE(ncp);
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return (0);
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}
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/* The name does not exists */
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nchstats.ncs_neghits++;
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TOUCH(ncp);
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return (ENOENT);
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}
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/*
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* Add an entry to the cache.
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*/
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void
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cache_enter(dvp, vp, cnp)
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struct vnode *dvp;
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struct vnode *vp;
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struct componentname *cnp;
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{
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register struct namecache *ncp;
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register struct nchashhead *ncpp;
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if (!doingcache)
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return;
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if (cnp->cn_namelen > NCHNAMLEN) {
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printf("cache_enter: name too long");
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return;
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}
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if (numcache < numvnodes) {
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/* Add one more entry */
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ncp = (struct namecache *)
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malloc((u_long)sizeof *ncp, M_CACHE, M_WAITOK);
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bzero((char *)ncp, sizeof *ncp);
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numcache++;
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} else if (ncp = nclruhead.tqh_first) {
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/* reuse an old entry */
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TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
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if (ncp->nc_hash.le_prev != 0) {
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LIST_REMOVE(ncp, nc_hash);
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ncp->nc_hash.le_prev = 0;
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}
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} else {
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/* give up */
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return;
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}
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/* If vp is NULL this is a "negative" cache entry */
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if (!vp)
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vp = &nchENOENT;
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/* fill in cache info */
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ncp->nc_vp = vp;
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if (vp->v_usage < MAXVNODEUSE)
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++vp->v_usage;
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ncp->nc_vpid = vp->v_id;
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ncp->nc_dvp = dvp;
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ncp->nc_dvpid = dvp->v_id;
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ncp->nc_nlen = cnp->cn_namelen;
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bcopy(cnp->cn_nameptr, ncp->nc_name, (unsigned)ncp->nc_nlen);
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TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
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ncpp = &nchashtbl[(dvp->v_id + cnp->cn_hash) % nchash];
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LIST_INSERT_HEAD(ncpp, ncp, nc_hash);
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}
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/*
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* Name cache initialization, from vfs_init() when we are booting
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*/
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void
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nchinit()
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{
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TAILQ_INIT(&nclruhead);
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nchashtbl = phashinit(desiredvnodes, M_CACHE, &nchash);
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cache_purge(&nchENOENT); /* Initialize v_id */
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}
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/*
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* Invalidate all entries to a particular vnode.
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*
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* We actually just increment the v_id, that will do it. The stale entries
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* will be purged by lookup as they get found.
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* If the v_id wraps around, we need to ditch the entire cache, to avoid
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* confusion.
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* No valid vnode will ever have (v_id == 0).
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*/
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void
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cache_purge(vp)
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struct vnode *vp;
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{
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struct nchashhead *ncpp;
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static u_long nextvnodeid;
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vp->v_id = ++nextvnodeid;
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if (nextvnodeid != 0)
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return;
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for (ncpp = &nchashtbl[nchash - 1]; ncpp >= nchashtbl; ncpp--) {
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while(ncpp->lh_first)
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PURGE(ncpp->lh_first);
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}
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nchENOENT.v_id = ++nextvnodeid;
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vp->v_id = ++nextvnodeid;
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}
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/*
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* Flush all entries referencing a particular filesystem.
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*
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* Since we need to check it anyway, we will flush all the invalid
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* entries at the same time.
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*
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* If we purge anything, we scan the hash-bucket again. There is only
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* a handful of entries, so it cheap and simple.
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*/
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void
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cache_purgevfs(mp)
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struct mount *mp;
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{
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struct nchashhead *ncpp;
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struct namecache *ncp;
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/* Scan hash tables for applicable entries */
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for (ncpp = &nchashtbl[nchash - 1]; ncpp >= nchashtbl; ncpp--) {
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ncp = ncpp->lh_first;
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while(ncp) {
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if (ncp->nc_dvpid != ncp->nc_dvp->v_id ||
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ncp->nc_vpid != ncp->nc_vp->v_id ||
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ncp->nc_dvp->v_mount == mp) {
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PURGE(ncp);
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ncp = ncpp->lh_first;
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} else {
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ncp = ncp->nc_hash.le_next;
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}
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}
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}
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}
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