text: /*
   * Copyright (c) 1989, 1993, 1995
   *	The Regents of the University of California.  All rights reserved.
   *
   * This code is derived from software contributed to Berkeley by
   * Poul-Henning Kamp of the FreeBSD Project.
   *
   * 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,v 1.11 1995/03/12 02:01:20 phk Exp $
   *
   *	@(#)vfs_cache.c	8.5 (Berkeley) 3/22/95
   */
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/time.h>
  #include <sys/mount.h>
  #include <sys/vnode.h>
  #include <sys/namei.h>
  #include <sys/errno.h>
  #include <sys/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.
   *
   * If it is a "negative" entry, (i.e. for a name that is known NOT to
   * exist) the vnode pointer will be NULL.
   *
   * 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.
   */
  #define NCHHASH(dvp, cnp) \
  	(&nchashtbl[((dvp)->v_id + (cnp)->cn_hash) & nchash])
  LIST_HEAD(nchashhead, namecache) *nchashtbl;	/* Hash Table */
  u_long	nchash;				/* size of hash table - 1 */
  long	numcache;			/* number of cache entries allocated */
  TAILQ_HEAD(, namecache) nclruhead;	/* LRU chain */
  struct	nchstats nchstats;		/* cache effectiveness statistics */
  
  int doingcache = 1;			/* 1 => enable the cache */
  
  /*
   * Delete an entry from its hash list and move it to the front
   * of the LRU list for immediate reuse.
   */
  #define PURGE(ncp)  {						\
  	LIST_REMOVE(ncp, nc_hash);				\
  	ncp->nc_hash.le_prev = 0;				\
  	TAILQ_REMOVE(&nclruhead, ncp, nc_lru);			\
  	TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru);		\
  }
  
  /*
   * Move an entry that has been used to the tail of the LRU list
   * so that it will be preserved for future use.
   */
  #define TOUCH(ncp)  {						\
  	if (ncp->nc_lru.tqe_next != 0) {			\
  		TAILQ_REMOVE(&nclruhead, ncp, nc_lru);		\
  		TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);	\
  	}							\
  }
  
  /*
   * Lookup an entry 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 dvp pointing to the directory to search,
   * cnp pointing to the name of the entry being sought. If the lookup
   * succeeds, the vnode is returned in *vpp, 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(dvp, vpp, cnp)
  	struct vnode *dvp;
  	struct vnode **vpp;
  	struct componentname *cnp;
  {
  	register struct namecache *ncp, *nnp;
  	register struct nchashhead *ncpp;
  
  	if (!doingcache) {
  		cnp->cn_flags &= ~MAKEENTRY;
  		return (0);
  	}
  	if (cnp->cn_namelen > NCHNAMLEN) {
  		nchstats.ncs_long++;
  		cnp->cn_flags &= ~MAKEENTRY;
  		return (0);
  	}
  
  	ncpp = NCHHASH(dvp, cnp);
  	for (ncp = ncpp->lh_first; ncp != 0; ncp = nnp) {
  		nnp = ncp->nc_hash.le_next;
  		/* If one of the vp's went stale, don't bother anymore. */
  		if ((ncp->nc_dvpid != ncp->nc_dvp->v_id) ||
  		    (ncp->nc_vp && ncp->nc_vpid != ncp->nc_vp->v_id)) {
  			nchstats.ncs_falsehits++;
  			PURGE(ncp);
  			continue;
  		}
  		/* Now that we know the vp's to be valid, is it ours ? */
  		if (ncp->nc_dvp == dvp &&
  		    ncp->nc_nlen == cnp->cn_namelen &&
  		    !bcmp(ncp->nc_name, cnp->cn_nameptr, (u_int)ncp->nc_nlen))
  			break;
  	}
  
  	/* We failed to find an entry */
  	if (ncp == 0) {
  		nchstats.ncs_miss++;
  		return (0);
  	}
  
  	/* We don't want to have an entry, so dump it */
  	if ((cnp->cn_flags & MAKEENTRY) == 0) {
  		nchstats.ncs_badhits++;
  		PURGE(ncp);
  		return (0);
  	} 
  
  	/* We found a "positive" match, return the vnode */
          if (ncp->nc_vp) {
  		nchstats.ncs_goodhits++;
  		TOUCH(ncp);
  		*vpp = ncp->nc_vp;
  		return (-1);
  	}
  
  	/* We found a negative match, and want to create it, so purge */
  	if (cnp->cn_nameiop == CREATE) {
  		nchstats.ncs_badhits++;
  		PURGE(ncp);
  		return (0);
  	}
  
  	/*
  	 * We found a "negative" match, ENOENT notifies client of this match.
  	 * The nc_vpid field records whether this is a whiteout.
  	 */
  	nchstats.ncs_neghits++;
  	TOUCH(ncp);
  	cnp->cn_flags |= ncp->nc_vpid;
  	return (ENOENT);
  }
  
  /*
   * Add an entry to the cache.
   */
  void
  cache_enter(dvp, vp, cnp)
  	struct vnode *dvp;
  	struct vnode *vp;
  	struct componentname *cnp;
  {
  	register struct namecache *ncp;
  	register struct nchashhead *ncpp;
  
  	if (!doingcache)
  		return;
  
  #ifdef DIAGNOSTIC
  	if (cnp->cn_namelen > NCHNAMLEN)
  		panic("cache_enter: name too long");
  #endif
  
  	/*
  	 * We allocate a new entry if we are less than the maximum
  	 * allowed and the one at the front of the LRU list is in use.
  	 * Otherwise we use the one at the front of the LRU list.
  	 */
  	if (numcache < desiredvnodes &&
  	    ((ncp = nclruhead.tqh_first) == NULL ||
  	    ncp->nc_hash.le_prev != 0)) {
  		/* Add one more entry */
  		ncp = (struct namecache *)
  			malloc((u_long)sizeof *ncp, M_CACHE, M_WAITOK);
  		bzero((char *)ncp, sizeof *ncp);
  		numcache++;
  	} else if (ncp = nclruhead.tqh_first) {
  		/* reuse an old entry */
  		TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
  		if (ncp->nc_hash.le_prev != 0) {
  			LIST_REMOVE(ncp, nc_hash);
  			ncp->nc_hash.le_prev = 0;
  		}
  	} else {
  		/* give up */
  		return;
  	}
  
  	/*
  	 * Fill in cache info, if vp is NULL this is a "negative" cache entry.
  	 * For negative entries, we have to record whether it is a whiteout.
  	 * the whiteout flag is stored in the nc_vpid field which is
  	 * otherwise unused.
  	 */
  	ncp->nc_vp = vp;
  	if (vp)
  		ncp->nc_vpid = vp->v_id;
  	else
  		ncp->nc_vpid = cnp->cn_flags & ISWHITEOUT;
  	ncp->nc_dvp = dvp;
  	ncp->nc_dvpid = dvp->v_id;
  	ncp->nc_nlen = cnp->cn_namelen;
  	bcopy(cnp->cn_nameptr, ncp->nc_name, (unsigned)ncp->nc_nlen);
  	TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
  	ncpp = NCHHASH(dvp, cnp);
  	LIST_INSERT_HEAD(ncpp, ncp, nc_hash);
  }
  
  /*
   * Name cache initialization, from vfs_init() when we are booting
   */
  void
  nchinit()
  {
  
  	TAILQ_INIT(&nclruhead);
  	nchashtbl = hashinit(desiredvnodes, M_CACHE, &nchash);
  }
  
  /*
   * Invalidate a all entries to particular vnode.
   * 
   * We actually just increment the v_id, that will do it. The entries will
   * be purged by lookup as they get found. If the v_id wraps around, we
   * need to ditch the entire cache, to avoid confusion. No valid vnode will
   * ever have (v_id == 0).
   */
  void
  cache_purge(vp)
  	struct vnode *vp;
  {
  	struct namecache *ncp;
  	struct nchashhead *ncpp;
  
  	vp->v_id = ++nextvnodeid;
  	if (nextvnodeid != 0)
  		return;
  	for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
  		while (ncp = ncpp->lh_first)
  			PURGE(ncp);
  	}
  	vp->v_id = ++nextvnodeid;
  }
  
  /*
   * Flush all entries referencing a particular filesystem.
   *
   * Since we need to check it anyway, we will flush all the invalid
   * entriess at the same time.
   */
  void
  cache_purgevfs(mp)
  	struct mount *mp;
  {
  	struct nchashhead *ncpp;
  	struct namecache *ncp, *nnp;
  
  	/* Scan hash tables for applicable entries */
  	for (ncpp = &nchashtbl[nchash]; ncpp >= nchashtbl; ncpp--) {
  		for (ncp = ncpp->lh_first; ncp != 0; ncp = nnp) {
  			nnp = ncp->nc_hash.le_next;
  			if (ncp->nc_dvpid != ncp->nc_dvp->v_id ||
  			    (ncp->nc_vp && ncp->nc_vpid != ncp->nc_vp->v_id) ||
  			    ncp->nc_dvp->v_mount == mp) {
  				PURGE(ncp);
  			}
  		}
  	}
  }
  