[dragonfly.git] / sys / kern / vfs_cache.c

/*
 * Copyright (c) 2003,2004 The DragonFly Project.  All rights reserved.
 * 
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 * 
 * 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. Neither the name of The DragonFly Project 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 COPYRIGHT HOLDERS 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
 * COPYRIGHT HOLDERS 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.
 * 
 * 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.
 *
 *      @(#)vfs_cache.c 8.5 (Berkeley) 3/22/95
 * $FreeBSD: src/sys/kern/vfs_cache.c,v 1.42.2.6 2001/10/05 20:07:03 dillon Exp $
 * $DragonFly: src/sys/kern/vfs_cache.c,v 1.36 2004/10/07 10:03:02 dillon Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/mount.h>
#include <sys/vnode.h>
#include <sys/malloc.h>
#include <sys/sysproto.h>
#include <sys/proc.h>
#include <sys/namei.h>
#include <sys/nlookup.h>
#include <sys/filedesc.h>
#include <sys/fnv_hash.h>
#include <sys/globaldata.h>
#include <sys/kern_syscall.h>
#include <ddb/ddb.h>

/*
 * Random lookups in the cache are accomplished with a hash table using
 * a hash key of (nc_src_vp, name).
 *
 * Negative entries may exist and correspond to structures where nc_vp
 * is NULL.  In a negative entry, NCF_WHITEOUT will be set if the entry
 * corresponds to a whited-out directory entry (verses simply not finding the
 * entry at all).
 *
 * 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(hash)   (&nchashtbl[(hash) & nchash])
#define MINNEG          1024

MALLOC_DEFINE(M_VFSCACHE, "vfscache", "VFS name cache entries");

static LIST_HEAD(nchashhead, namecache) *nchashtbl;     /* Hash Table */
static struct namecache_list    ncneglist;              /* instead of vnode */

static u_long   nchash;                 /* size of hash table */
SYSCTL_ULONG(_debug, OID_AUTO, nchash, CTLFLAG_RD, &nchash, 0, "");

static u_long   ncnegfactor = 16;       /* ratio of negative entries */
SYSCTL_ULONG(_debug, OID_AUTO, ncnegfactor, CTLFLAG_RW, &ncnegfactor, 0, "");

static u_long   numneg;         /* number of cache entries allocated */
SYSCTL_ULONG(_debug, OID_AUTO, numneg, CTLFLAG_RD, &numneg, 0, "");

static u_long   numcache;               /* number of cache entries allocated */
SYSCTL_ULONG(_debug, OID_AUTO, numcache, CTLFLAG_RD, &numcache, 0, "");

static u_long   numunres;               /* number of unresolved entries */
SYSCTL_ULONG(_debug, OID_AUTO, numunres, CTLFLAG_RD, &numunres, 0, "");

SYSCTL_INT(_debug, OID_AUTO, vnsize, CTLFLAG_RD, 0, sizeof(struct vnode), "");
SYSCTL_INT(_debug, OID_AUTO, ncsize, CTLFLAG_RD, 0, sizeof(struct namecache), "");

static int cache_resolve_mp(struct namecache *ncp);
static void cache_rehash(struct namecache *ncp);

/*
 * The new name cache statistics
 */
SYSCTL_NODE(_vfs, OID_AUTO, cache, CTLFLAG_RW, 0, "Name cache statistics");
#define STATNODE(mode, name, var) \
        SYSCTL_ULONG(_vfs_cache, OID_AUTO, name, mode, var, 0, "");
STATNODE(CTLFLAG_RD, numneg, &numneg);
STATNODE(CTLFLAG_RD, numcache, &numcache);
static u_long numcalls; STATNODE(CTLFLAG_RD, numcalls, &numcalls);
static u_long dothits; STATNODE(CTLFLAG_RD, dothits, &dothits);
static u_long dotdothits; STATNODE(CTLFLAG_RD, dotdothits, &dotdothits);
static u_long numchecks; STATNODE(CTLFLAG_RD, numchecks, &numchecks);
static u_long nummiss; STATNODE(CTLFLAG_RD, nummiss, &nummiss);
static u_long nummisszap; STATNODE(CTLFLAG_RD, nummisszap, &nummisszap);
static u_long numposzaps; STATNODE(CTLFLAG_RD, numposzaps, &numposzaps);
static u_long numposhits; STATNODE(CTLFLAG_RD, numposhits, &numposhits);
static u_long numnegzaps; STATNODE(CTLFLAG_RD, numnegzaps, &numnegzaps);
static u_long numneghits; STATNODE(CTLFLAG_RD, numneghits, &numneghits);

struct nchstats nchstats[SMP_MAXCPU];
/*
 * Export VFS cache effectiveness statistics to user-land.
 *
 * The statistics are left for aggregation to user-land so
 * neat things can be achieved, like observing per-CPU cache
 * distribution.
 */
static int
sysctl_nchstats(SYSCTL_HANDLER_ARGS)
{
        struct globaldata *gd;
        int i, error;

        error = 0;
        for (i = 0; i < ncpus; ++i) {
                gd = globaldata_find(i);
                if ((error = SYSCTL_OUT(req, (void *)&(*gd->gd_nchstats),
                        sizeof(struct nchstats))))
                        break;
        }

        return (error);
}
SYSCTL_PROC(_vfs_cache, OID_AUTO, nchstats, CTLTYPE_OPAQUE|CTLFLAG_RD,
  0, 0, sysctl_nchstats, "S,nchstats", "VFS cache effectiveness statistics");

static void cache_zap(struct namecache *ncp);

/*
 * cache_hold() and cache_drop() prevent the premature deletion of a
 * namecache entry but do not prevent operations (such as zapping) on
 * that namecache entry.
 */
static __inline
struct namecache *
_cache_hold(struct namecache *ncp)
{
        ++ncp->nc_refs;
        return(ncp);
}

/*
 * When dropping an entry, if only one ref remains and the entry has not
 * been resolved, zap it.  Since the one reference is being dropped the
 * entry had better not be locked.
 */
static __inline
void
_cache_drop(struct namecache *ncp)
{
        KKASSERT(ncp->nc_refs > 0);
        if (ncp->nc_refs == 1 && 
            (ncp->nc_flag & NCF_UNRESOLVED) && 
            TAILQ_EMPTY(&ncp->nc_list)
        ) {
                KKASSERT(ncp->nc_exlocks == 0);
                cache_lock(ncp);
                cache_zap(ncp);
        } else {
                --ncp->nc_refs;
        }
}

/*
 * Link a new namecache entry to its parent.  Be careful to avoid races
 * if vhold() blocks in the future.
 *
 * If we are creating a child under an oldapi parent we must mark the
 * child as being an oldapi entry as well.
 */
static void
cache_link_parent(struct namecache *ncp, struct namecache *par)
{
        KKASSERT(ncp->nc_parent == NULL);
        ncp->nc_parent = par;
        if (TAILQ_EMPTY(&par->nc_list)) {
                TAILQ_INSERT_HEAD(&par->nc_list, ncp, nc_entry);
                /*
                 * Any vp associated with an ncp which has children must
                 * be held to prevent it from being recycled.
                 */
                if (par->nc_vp)
                        vhold(par->nc_vp);
        } else {
                TAILQ_INSERT_HEAD(&par->nc_list, ncp, nc_entry);
        }
}

/*
 * Remove the parent association from a namecache structure.  If this is
 * the last child of the parent the cache_drop(par) will attempt to
 * recursively zap the parent.
 */
static void
cache_unlink_parent(struct namecache *ncp)
{
        struct namecache *par;

        if ((par = ncp->nc_parent) != NULL) {
                ncp->nc_parent = NULL;
                par = cache_hold(par);
                TAILQ_REMOVE(&par->nc_list, ncp, nc_entry);
                if (par->nc_vp && TAILQ_EMPTY(&par->nc_list))
                        vdrop(par->nc_vp);
                cache_drop(par);
        }
}

/*
 * Allocate a new namecache structure.
 */
static struct namecache *
cache_alloc(int nlen)
{
        struct namecache *ncp;

        ncp = malloc(sizeof(*ncp), M_VFSCACHE, M_WAITOK|M_ZERO);
        if (nlen)
                ncp->nc_name = malloc(nlen, M_VFSCACHE, M_WAITOK);
        ncp->nc_nlen = nlen;
        ncp->nc_flag = NCF_UNRESOLVED;
        ncp->nc_error = ENOTCONN;       /* needs to be resolved */
        ncp->nc_refs = 1;
        TAILQ_INIT(&ncp->nc_list);
        cache_lock(ncp);
        return(ncp);
}

static void
cache_free(struct namecache *ncp)
{
        KKASSERT(ncp->nc_refs == 1 && ncp->nc_exlocks == 1);
        if (ncp->nc_name)
                free(ncp->nc_name, M_VFSCACHE);
        free(ncp, M_VFSCACHE);
}

/*
 * Ref and deref a namecache structure.
 */
struct namecache *
cache_hold(struct namecache *ncp)
{
        return(_cache_hold(ncp));
}

void
cache_drop(struct namecache *ncp)
{
        _cache_drop(ncp);
}

/*
 * Namespace locking.  The caller must already hold a reference to the
 * namecache structure in order to lock/unlock it.  This function prevents
 * the namespace from being created or destroyed by accessors other then
 * the lock holder.
 *
 * Note that holding a locked namecache structure prevents other threads
 * from making namespace changes (e.g. deleting or creating), prevents
 * vnode association state changes by other threads, and prevents the
 * namecache entry from being resolved or unresolved by other threads.
 *
 * The lock owner has full authority to associate/disassociate vnodes
 * and resolve/unresolve the locked ncp.
 *
 * In particular, if a vnode is associated with a locked cache entry
 * that vnode will *NOT* be recycled.  We accomplish this by vhold()ing the
 * vnode.  XXX we should find a more efficient way to prevent the vnode
 * from being recycled, but remember that any given vnode may have multiple
 * namecache associations (think hardlinks).
 */
void
cache_lock(struct namecache *ncp)
{
        thread_t td;
        int didwarn;

        KKASSERT(ncp->nc_refs != 0);
        didwarn = 0;
        td = curthread;

        for (;;) {
                if (ncp->nc_exlocks == 0) {
                        ncp->nc_exlocks = 1;
                        ncp->nc_locktd = td;
                        /* 
                         * The vp associated with a locked ncp must be held
                         * to prevent it from being recycled (which would
                         * cause the ncp to become unresolved).
                         *
                         * XXX loop on race for later MPSAFE work.
                         */
                        if (ncp->nc_vp)
                                vhold(ncp->nc_vp);
                        break;
                }
                if (ncp->nc_locktd == td) {
                        ++ncp->nc_exlocks;
                        break;
                }
                ncp->nc_flag |= NCF_LOCKREQ;
                if (tsleep(ncp, 0, "clock", hz) == EWOULDBLOCK) {
                        if (didwarn == 0) {
                                didwarn = 1;
                                printf("[diagnostic] cache_lock: blocked on %*.*s\n",
                                        ncp->nc_nlen, ncp->nc_nlen,
                                        ncp->nc_name);
                        }
                }
        }

        if (didwarn == 1) {
                printf("[diagnostic] cache_lock: unblocked %*.*s\n",
                        ncp->nc_nlen, ncp->nc_nlen, ncp->nc_name);
        }
}

void
cache_unlock(struct namecache *ncp)
{
        thread_t td = curthread;

        KKASSERT(ncp->nc_refs > 0);
        KKASSERT(ncp->nc_exlocks > 0);
        KKASSERT(ncp->nc_locktd == td);
        if (--ncp->nc_exlocks == 0) {
                if (ncp->nc_vp)
                        vdrop(ncp->nc_vp);
                ncp->nc_locktd = NULL;
                if (ncp->nc_flag & NCF_LOCKREQ) {
                        ncp->nc_flag &= ~NCF_LOCKREQ;
                        wakeup_one(ncp);
                }
        }
}

/*
 * ref-and-lock, unlock-and-deref functions.
 */
struct namecache *
cache_get(struct namecache *ncp)
{
        _cache_hold(ncp);
        cache_lock(ncp);
        return(ncp);
}

int
cache_get_nonblock(struct namecache *ncp)
{
        /* XXX MP */
        if (ncp->nc_exlocks == 0 || ncp->nc_locktd == curthread) {
                _cache_hold(ncp);
                cache_lock(ncp);
                return(0);
        }
        return(EWOULDBLOCK);
}

void
cache_put(struct namecache *ncp)
{
        cache_unlock(ncp);
        _cache_drop(ncp);
}

/*
 * Resolve an unresolved ncp by associating a vnode with it.  If the
 * vnode is NULL, a negative cache entry is created.
 *
 * The ncp should be locked on entry and will remain locked on return.
 */
void
cache_setvp(struct namecache *ncp, struct vnode *vp)
{
        KKASSERT(ncp->nc_flag & NCF_UNRESOLVED);
        ncp->nc_vp = vp;
        if (vp != NULL) {
                /*
                 * Any vp associated with an ncp which has children must
                 * be held.  Any vp associated with a locked ncp must be held.
                 */
                if (!TAILQ_EMPTY(&ncp->nc_list))
                        vhold(vp);
                TAILQ_INSERT_HEAD(&vp->v_namecache, ncp, nc_vnode);
                if (ncp->nc_exlocks)
                        vhold(vp);

                /*
                 * Set auxillary flags
                 */
                switch(vp->v_type) {
                case VDIR:
                        ncp->nc_flag |= NCF_ISDIR;
                        break;
                case VLNK:
                        ncp->nc_flag |= NCF_ISSYMLINK;
                        /* XXX cache the contents of the symlink */
                        break;
                default:
                        break;
                }
                ++numcache;
                ncp->nc_error = 0;
        } else {
                TAILQ_INSERT_TAIL(&ncneglist, ncp, nc_vnode);
                ++numneg;
                ncp->nc_error = ENOENT;
        }
        ncp->nc_flag &= ~NCF_UNRESOLVED;
}

/*
 * Disassociate the vnode or negative-cache association and mark a
 * namecache entry as unresolved again.  Note that the ncp is still
 * left in the hash table and still linked to its parent.
 *
 * The ncp should be locked and refd on entry and will remain locked and refd
 * on return.
 *
 * This routine is normally never called on a directory containing children.
 * However, NFS often does just that in its rename() code as a cop-out to
 * avoid complex namespace operations.  This disconnects a directory vnode
 * from its namecache and can cause the OLDAPI and NEWAPI to get out of
 * sync.
 */
void
cache_setunresolved(struct namecache *ncp)
{
        struct vnode *vp;

        if ((ncp->nc_flag & NCF_UNRESOLVED) == 0) {
                ncp->nc_flag |= NCF_UNRESOLVED;
                ncp->nc_flag &= ~(NCF_WHITEOUT|NCF_ISDIR|NCF_ISSYMLINK);
                ncp->nc_error = ENOTCONN;
                ++numunres;
                if ((vp = ncp->nc_vp) != NULL) {
                        --numcache;
                        ncp->nc_vp = NULL;      /* safety */
                        TAILQ_REMOVE(&vp->v_namecache, ncp, nc_vnode);

                        /*
                         * Any vp associated with an ncp with children is
                         * held by that ncp.  Any vp associated with a locked
                         * ncp is held by that ncp.  These conditions must be
                         * undone when the vp is cleared out from the ncp.
                         */
                        if (!TAILQ_EMPTY(&ncp->nc_list))
                                vdrop(vp);
                        if (ncp->nc_exlocks)
                                vdrop(vp);
                } else {
                        TAILQ_REMOVE(&ncneglist, ncp, nc_vnode);
                        --numneg;
                }

#if 0
                if (TAILQ_FIRST(&ncp->nc_list)) {
                        db_print_backtrace();
                        printf("[diagnostic] cache_setunresolved() called on directory with children: %p %*.*s\n", ncp, ncp->nc_nlen, ncp->nc_nlen, ncp->nc_name);
                }
#endif
        }
}

/*
 * Invalidate portions of a namecache entry.  The passed ncp should be
 * referenced and locked but we might not adhere to that rule during the
 * old api -> new api transition period.
 *
 * CINV_PARENT          - disconnect the ncp from its parent
 * CINV_SELF            - same as cache_setunresolved(ncp)
 * CINV_CHILDREN        - disconnect children of the ncp from the ncp
 */
void
cache_inval(struct namecache *ncp, int flags)
{
        struct namecache *kid;
        struct namecache *nextkid;

        if (flags & CINV_SELF)
                cache_setunresolved(ncp);
        if (flags & CINV_PARENT) {
                ncp->nc_flag |= NCF_REVALPARENT;
                cache_unlink_parent(ncp);
        }

        /*
         * TEMPORARY XX old-api / rename handling.  Any unresolved or
         * negative cache-hit children with a ref count of 0 must be
         * recursively destroyed or this disconnection from our parent,
         * or the childrens disconnection from us, may leave them dangling
         * forever.
         *
         * In the new API it won't be possible to unlink in the middle of
         * the topology and we will have a cache_rename() to physically
         * move a subtree from one place to another.
         */
        if (flags & (CINV_PARENT|CINV_CHILDREN)) {
                if ((kid = TAILQ_FIRST(&ncp->nc_list)) != NULL)
                        cache_hold(kid);
                while (kid) {
                        if ((nextkid = TAILQ_NEXT(kid, nc_entry)) != NULL)
                                cache_hold(nextkid);
                        if (kid->nc_refs == 0 &&
                            ((kid->nc_flag & NCF_UNRESOLVED) || 
                             kid->nc_vp == NULL)
                        ) {
                                cache_inval(kid, CINV_PARENT);
                        }
                        cache_drop(kid);
                        kid = nextkid;
                }
        }

        /*
         * TEMPORARY XXX old-api / rename handling.
         */
        if (flags & CINV_CHILDREN) {
                while ((kid = TAILQ_FIRST(&ncp->nc_list)) != NULL) {
                        kid->nc_flag |= NCF_REVALPARENT;
                        cache_hold(kid);
                        cache_unlink_parent(kid);
                        cache_drop(kid);
                }
        }
}

void
cache_inval_vp(struct vnode *vp, int flags)
{
        struct namecache *ncp;

        if (flags & CINV_SELF) {
                while ((ncp = TAILQ_FIRST(&vp->v_namecache)) != NULL) {
                        cache_hold(ncp);
                        KKASSERT((ncp->nc_flag & NCF_UNRESOLVED) == 0);
                        cache_inval(ncp, flags);
                        cache_drop(ncp);
                }
        } else {
                TAILQ_FOREACH(ncp, &vp->v_namecache, nc_vnode) {
                        cache_hold(ncp);
                        cache_inval(ncp, flags);
                        cache_drop(ncp);
                }
        }
}

/*
 * vget the vnode associated with the namecache entry.  Resolve the namecache
 * entry if necessary and deal with namecache/vp races.  The passed ncp must
 * be referenced and may be locked.  The ncp's ref/locking state is not 
 * effected by this call.
 *
 * lk_type may be LK_SHARED, LK_EXCLUSIVE.  A ref'd, possibly locked
 * (depending on the passed lk_type) will be returned in *vpp with an error
 * of 0, or NULL will be returned in *vpp with a non-0 error code.  The
 * most typical error is ENOENT, meaning that the ncp represents a negative
 * cache hit and there is no vnode to retrieve, but other errors can occur
 * too.
 *
 * The main race we have to deal with are namecache zaps.  The ncp itself
 * will not disappear since it is referenced, and it turns out that the
 * validity of the vp pointer can be checked simply by rechecking the
 * contents of ncp->nc_vp.
 */
int
cache_vget(struct namecache *ncp, struct ucred *cred,
           int lk_type, struct vnode **vpp)
{
        struct vnode *vp;
        int error;

again:
        vp = NULL;
        if (ncp->nc_flag & NCF_UNRESOLVED) {
                cache_lock(ncp);
                error = cache_resolve(ncp, cred);
                cache_unlock(ncp);
        } else {
                error = 0;
        }
        if (error == 0 && (vp = ncp->nc_vp) != NULL) {
                error = vget(vp, NULL, lk_type, curthread);
                if (error) {
                        if (vp != ncp->nc_vp)   /* handle cache_zap race */
                                goto again;
                        vp = NULL;
                } else if (vp != ncp->nc_vp) {  /* handle cache_zap race */
                        vput(vp);
                        goto again;
                }
        }
        if (error == 0 && vp == NULL)
                error = ENOENT;
        *vpp = vp;
        return(error);
}

int
cache_vref(struct namecache *ncp, struct ucred *cred, struct vnode **vpp)
{
        struct vnode *vp;
        int error;

again:
        vp = NULL;
        if (ncp->nc_flag & NCF_UNRESOLVED) {
                cache_lock(ncp);
                error = cache_resolve(ncp, cred);
                cache_unlock(ncp);
        } else {
                error = 0;
        }
        if (error == 0 && (vp = ncp->nc_vp) != NULL) {
                vref(vp);
                if (vp != ncp->nc_vp) {         /* handle cache_zap race */
                        vrele(vp);
                        goto again;
                }
        }
        if (error == 0 && vp == NULL)
                error = ENOENT;
        *vpp = vp;
        return(error);
}

/*
 * Zap a namecache entry.  The ncp is unconditionally set to an unresolved
 * state, which disassociates it from its vnode or ncneglist.
 *
 * Then, if there are no additional references to the ncp and no children,
 * the ncp is removed from the topology and destroyed.  This function will
 * also run through the nc_parent chain and destroy parent ncps if possible.
 * As a side benefit, it turns out the only conditions that allow running
 * up the chain are also the conditions to ensure no deadlock will occur.
 *
 * References and/or children may exist if the ncp is in the middle of the
 * topology, preventing the ncp from being destroyed.
 *
 * This function must be called with the ncp held and locked and will unlock
 * and drop it during zapping.
 */
static void
cache_zap(struct namecache *ncp)
{
        struct namecache *par;

        /*
         * Disassociate the vnode or negative cache ref and set NCF_UNRESOLVED.
         */
        cache_setunresolved(ncp);

        /*
         * Try to scrap the entry and possibly tail-recurse on its parent.
         * We only scrap unref'd (other then our ref) unresolved entries,
         * we do not scrap 'live' entries.
         */
        while (ncp->nc_flag & NCF_UNRESOLVED) {
                /*
                 * Someone other then us has a ref, stop.
                 */
                if (ncp->nc_refs > 1)
                        goto done;

                /*
                 * We have children, stop.
                 */
                if (!TAILQ_EMPTY(&ncp->nc_list))
                        goto done;

                /*
                 * Remove ncp from the topology: hash table and parent linkage.
                 */
                if (ncp->nc_flag & NCF_HASHED) {
                        ncp->nc_flag &= ~NCF_HASHED;
                        LIST_REMOVE(ncp, nc_hash);
                }
                if ((par = ncp->nc_parent) != NULL) {
                        par = cache_hold(par);
                        TAILQ_REMOVE(&par->nc_list, ncp, nc_entry);
                        ncp->nc_parent = NULL;
                        if (par->nc_vp && TAILQ_EMPTY(&par->nc_list))
                                vdrop(par->nc_vp);
                }

                /*
                 * ncp should not have picked up any refs.  Physically
                 * destroy the ncp.
                 */
                KKASSERT(ncp->nc_refs == 1);
                --numunres;
                /* cache_unlock(ncp) not required */
                ncp->nc_refs = -1;      /* safety */
                if (ncp->nc_name)
                        free(ncp->nc_name, M_VFSCACHE);
                free(ncp, M_VFSCACHE);

                /*
                 * Loop on the parent (it may be NULL).  Only bother looping
                 * if the parent has a single ref (ours), which also means
                 * we can lock it trivially.
                 */
                ncp = par;
                if (ncp == NULL)
                        return;
                if (ncp->nc_refs != 1) {
                        cache_drop(ncp);
                        return;
                }
                KKASSERT(par->nc_exlocks == 0);
                cache_lock(ncp);
        }
done:
        cache_unlock(ncp);
        --ncp->nc_refs;
}

/*
 * NEW NAMECACHE LOOKUP API
 *
 * Lookup an entry in the cache.  A locked, referenced, non-NULL 
 * entry is *always* returned, even if the supplied component is illegal.
 * The returned namecache entry should be returned to the system with
 * cache_put() or cache_unlock() + cache_drop().
 *
 * namecache locks are recursive but care must be taken to avoid lock order
 * reversals.
 *
 * Nobody else will be able to manipulate the associated namespace (e.g.
 * create, delete, rename, rename-target) until the caller unlocks the
 * entry.
 *
 * The returned entry will be in one of three states:  positive hit (non-null
 * vnode), negative hit (null vnode), or unresolved (NCF_UNRESOLVED is set).
 * Unresolved entries must be resolved through the filesystem to associate the
 * vnode and/or determine whether a positive or negative hit has occured.
 *
 * It is not necessary to lock a directory in order to lock namespace under
 * that directory.  In fact, it is explicitly not allowed to do that.  A
 * directory is typically only locked when being created, renamed, or
 * destroyed.
 *
 * The directory (par) may be unresolved, in which case any returned child
 * will likely also be marked unresolved.  Likely but not guarenteed.  Since
 * the filesystem VOP_NEWLOOKUP() requires a resolved directory vnode the
 * caller is responsible for resolving the namecache chain top-down.  This API 
 * specifically allows whole chains to be created in an unresolved state.
 */
struct namecache *
cache_nlookup(struct namecache *par, struct nlcomponent *nlc)
{
        struct namecache *ncp;
        struct namecache *new_ncp;
        struct nchashhead *nchpp;
        u_int32_t hash;
        globaldata_t gd;

        numcalls++;
        gd = mycpu;

        /*
         * Try to locate an existing entry
         */
        hash = fnv_32_buf(nlc->nlc_nameptr, nlc->nlc_namelen, FNV1_32_INIT);
        hash = fnv_32_buf(&par, sizeof(par), hash);
        new_ncp = NULL;
restart:
        LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
                numchecks++;

                /*
                 * Zap entries that have timed out.
                 */
                if (ncp->nc_timeout && 
                    (int)(ncp->nc_timeout - ticks) < 0 &&
                    (ncp->nc_flag & NCF_UNRESOLVED) == 0 &&
                    ncp->nc_exlocks == 0
                ) {
                        cache_zap(cache_get(ncp));
                        goto restart;
                }

                /*
                 * Break out if we find a matching entry.  Note that
                 * UNRESOLVED entries may match.
                 */
                if (ncp->nc_parent == par &&
                    ncp->nc_nlen == nlc->nlc_namelen &&
                    bcmp(ncp->nc_name, nlc->nlc_nameptr, ncp->nc_nlen) == 0
                ) {
                        if (cache_get_nonblock(ncp) == 0) {
                                if (new_ncp)
                                        cache_free(new_ncp);
                                goto found;
                        }
                        cache_get(ncp);
                        cache_put(ncp);
                        goto restart;
                }
        }

        /*
         * We failed to locate an entry, create a new entry and add it to
         * the cache.  We have to relookup after possibly blocking in
         * malloc.
         */
        if (new_ncp == NULL) {
                new_ncp = cache_alloc(nlc->nlc_namelen);
                goto restart;
        }

        ncp = new_ncp;

        /*
         * Initialize as a new UNRESOLVED entry, lock (non-blocking),
         * and link to the parent.
         */
        bcopy(nlc->nlc_nameptr, ncp->nc_name, nlc->nlc_namelen);
        nchpp = NCHHASH(hash);
        LIST_INSERT_HEAD(nchpp, ncp, nc_hash);
        ncp->nc_flag |= NCF_HASHED;
        cache_link_parent(ncp, par);
found:
        return(ncp);
}

/*
 * Resolve an unresolved namecache entry, generally by looking it up.
 * The passed ncp must be locked and refd. 
 *
 * Theoretically since a vnode cannot be recycled while held, and since
 * the nc_parent chain holds its vnode as long as children exist, the
 * direct parent of the cache entry we are trying to resolve should
 * have a valid vnode.  If not then generate an error that we can 
 * determine is related to a resolver bug.
 */
int
cache_resolve(struct namecache *ncp, struct ucred *cred)
{
        struct namecache *par;
        struct namecache *scan;
        int error;

restart:
        /*
         * If the ncp is already resolved we have nothing to do.
         */
        if ((ncp->nc_flag & NCF_UNRESOLVED) == 0)
                return (ncp->nc_error);

        /*
         * Mount points need special handling because the parent does not
         * belong to the same filesystem as the ncp.
         */
        if (ncp->nc_flag & NCF_MOUNTPT)
                return (cache_resolve_mp(ncp));

        /*
         * We expect an unbroken chain of ncps to at least the mount point,
         * and even all the way to root (but this code doesn't have to go
         * past the mount point).
         */
        if (ncp->nc_parent == NULL) {
                printf("EXDEV case 1 %p %*.*s\n", ncp,
                        ncp->nc_nlen, ncp->nc_nlen, ncp->nc_name);
                ncp->nc_error = EXDEV;
                return(ncp->nc_error);
        }

        /*
         * The vp's of the parent directories in the chain are held via vhold()
         * due to the existance of the child, and should not disappear. 
         * However, there are cases where they can disappear:
         *
         *      - due to filesystem I/O errors.
         *      - due to NFS being stupid about tracking the namespace and
         *        destroys the namespace for entire directories quite often.
         *      - due to forced unmounts.
         *
         * When this occurs we have to track the chain backwards and resolve
         * it, looping until the resolver catches up to the current node.  We
         * could recurse here but we might run ourselves out of kernel stack
         * so we do it in a more painful manner.  This situation really should
         * not occur all that often, or if it does not have to go back too
         * many nodes to resolve the ncp.
         */
        while (ncp->nc_parent->nc_vp == NULL) {
                par = ncp->nc_parent;
                while (par->nc_parent && par->nc_parent->nc_vp == NULL)
                        par = par->nc_parent;
                if (par->nc_parent == NULL) {
                        printf("EXDEV case 2 %*.*s\n",
                                par->nc_nlen, par->nc_nlen, par->nc_name);
                        return (EXDEV);
                }
                printf("[diagnostic] cache_resolve: had to recurse on %*.*s\n",
                        par->nc_nlen, par->nc_nlen, par->nc_name);
                /*
                 * The parent is not set in stone, ref and lock it to prevent
                 * it from disappearing.  Also note that due to renames it
                 * is possible for our ncp to move and for par to no longer
                 * be one of its parents.  We resolve it anyway, the loop 
                 * will handle any moves.
                 */
                cache_get(par);
                if (par->nc_flag & NCF_MOUNTPT) {
                        cache_resolve_mp(par);
                } else if (par->nc_parent->nc_vp == NULL) {
                        printf("[diagnostic] cache_resolve: raced on %*.*s\n", par->nc_nlen, par->nc_nlen, par->nc_name);
                        cache_put(par);
                        continue;
                } else {
                        par->nc_error = 
                            vop_resolve(par->nc_parent->nc_vp->v_ops, par, cred);
                }
                if ((error = par->nc_error) != 0) {
                        if (par->nc_error != EAGAIN) {
                                printf("EXDEV case 3 %*.*s error %d\n",
                                    par->nc_nlen, par->nc_nlen, par->nc_name,
                                    par->nc_error);
                                cache_put(par);
                                return(error);
                        }
                        printf("[diagnostic] cache_resolve: EAGAIN par %p %*.*s\n",
                                par, par->nc_nlen, par->nc_nlen, par->nc_name);
                }
                cache_put(par);
                /* loop */
        }

        /*
         * Call vop_resolve() to get the vp, then scan for any disconnected
         * ncp's and reattach them.  If this occurs the original ncp is marked
         * EAGAIN to force a relookup.
         */
        KKASSERT((ncp->nc_flag & NCF_MOUNTPT) == 0);
        ncp->nc_error = vop_resolve(ncp->nc_parent->nc_vp->v_ops, ncp, cred);
        if (ncp->nc_error == EAGAIN) {
                printf("[diagnostic] cache_resolve: EAGAIN ncp %p %*.*s\n",
                        ncp, ncp->nc_nlen, ncp->nc_nlen, ncp->nc_name);
                goto restart;
        }
        if (ncp->nc_error == 0) {
                TAILQ_FOREACH(scan, &ncp->nc_vp->v_namecache, nc_vnode) {
                        if (scan != ncp && (scan->nc_flag & NCF_REVALPARENT)) {
                                cache_hold(scan);
                                cache_link_parent(scan, ncp->nc_parent);
                                cache_unlink_parent(ncp);
                                scan->nc_flag &= ~NCF_REVALPARENT;
                                ncp->nc_error = EAGAIN;
                                if (scan->nc_flag & NCF_HASHED)
                                        cache_rehash(scan);
                                printf("[diagnostic] cache_resolve: relinked %*.*s\n", scan->nc_nlen, scan->nc_nlen, scan->nc_name);
                                cache_drop(scan);
                                break;
                        }
                }
        }
        return(ncp->nc_error);
}

/*
 * Resolve the ncp associated with a mount point.  Such ncp's almost always
 * remain resolved and this routine is rarely called.  NFS MPs tends to force
 * re-resolution more often due to its mac-truck-smash-the-namecache
 * method of tracking namespace changes.
 *
 * The passed ncp must be locked.
 */
static int
cache_resolve_mp(struct namecache *ncp)
{
        struct vnode *vp;
        struct mount *mp = ncp->nc_mount;

        KKASSERT(mp != NULL);
        if (ncp->nc_flag & NCF_UNRESOLVED) {
                while (vfs_busy(mp, 0, NULL, curthread))
                        ;
                ncp->nc_error = VFS_ROOT(mp, &vp);
                if (ncp->nc_error == 0) {
                        cache_setvp(ncp, vp);
                        vput(vp);
                } else {
                        printf("[diagnostic] cache_resolve_mp: failed to resolve mount %p\n", mp);
                        cache_setvp(ncp, NULL);
                }
                vfs_unbusy(mp, curthread);
        }
        return(ncp->nc_error);
}

/*
 * Lookup an entry in the cache.
 *
 * XXX OLD API ROUTINE!  WHEN ALL VFSs HAVE BEEN CLEANED UP THIS PROCEDURE
 * WILL BE REMOVED.  NOTE: even though this is an old api function it had
 * to be modified to vref() the returned vnode (whereas in 4.x an unreferenced
 * vnode was returned).  This is necessary because our namecache structure
 * manipulation can cause the vnode to be recycled if it isn't refd.
 *
 * 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, a REFd but unlocked 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.
 *
 * Matching UNRESOLVED entries are resolved.
 *
 * HACKS: we create dummy nodes for parents
 */
int
cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
{
        struct namecache *ncp;
        struct namecache *par;
        struct namecache *bpar;
        u_int32_t hash;
        globaldata_t gd = mycpu;

        numcalls++;
        *vpp = NULL;

        /*
         * Obtain the namecache entry associated with dvp.  If there is no
         * entry then assume a miss.
         */
        if ((par = TAILQ_FIRST(&dvp->v_namecache)) == NULL) {
                if ((cnp->cn_flags & CNP_MAKEENTRY) == 0) {
                        nummisszap++;
                } else {
                        nummiss++;
                }
                gd->gd_nchstats->ncs_miss++;
                return (0);
        }

        /*
         * Deal with "." and "..".   Note that if the namecache is disjoint,
         * we won't find a vnode for ".." and we return a miss.
         */
        if (cnp->cn_nameptr[0] == '.') {
                if (cnp->cn_namelen == 1) {
                        *vpp = dvp;
                        vref(*vpp);
                        dothits++;
                        numposhits++;   /* include in total statistics */
                        return (-1);
                }
                if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
                        if ((cnp->cn_flags & CNP_MAKEENTRY) == 0) {
                                dotdothits++;
                                numposhits++;
                                return (0);
                        }
                        if (par->nc_parent == NULL ||
                            par->nc_parent->nc_vp == NULL) {
                                nummiss++;
                                gd->gd_nchstats->ncs_miss++;
                                return (0);
                        }
                        *vpp = par->nc_parent->nc_vp;
                        vref(*vpp);
                        dotdothits++;
                        numposhits++;   /* include in total statistics */
                        return (-1);
                }
        }

        /*
         * Try to locate an existing entry
         */
        cache_hold(par);
        hash = fnv_32_buf(cnp->cn_nameptr, cnp->cn_namelen, FNV1_32_INIT);
        bpar = par;
        hash = fnv_32_buf(&bpar, sizeof(bpar), hash);
restart:
        LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
                numchecks++;

                /*
                 * Zap entries that have timed out.  Don't do anything if
                 * the entry is in an unresolved state or is held locked.
                 */
                if (ncp->nc_timeout && 
                    (int)(ncp->nc_timeout - ticks) < 0 &&
                    (ncp->nc_flag & NCF_UNRESOLVED) == 0 &&
                    ncp->nc_exlocks == 0
                ) {
                        cache_zap(cache_get(ncp));
                        goto restart;
                }

                /*
                 * Break out if we find a matching entry.
                 */
                if (ncp->nc_parent == par &&
                    ncp->nc_nlen == cnp->cn_namelen &&
                    bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen) == 0
                ) {
                        if (cache_get_nonblock(ncp) == 0)
                                break;
                        cache_get(ncp);
                        cache_put(ncp);
                        goto restart;
                }
        }
        cache_drop(par);

        /*
         * We found an entry but it is unresolved, act the same as if we
         * failed to locate the entry.  cache_enter() will do the right
         * thing.
         */
        if (ncp && (ncp->nc_flag & NCF_UNRESOLVED)) {
                cache_put(ncp);
                ncp = NULL;
        }

        /*
         * If we failed to locate an entry, return 0 (indicates failure).
         */
        if (ncp == NULL) {
                if ((cnp->cn_flags & CNP_MAKEENTRY) == 0) {
                        nummisszap++;
                } else {
                        nummiss++;
                }
                gd->gd_nchstats->ncs_miss++;
                return (0);
        }

        /*
         * If we found an entry, but we don't want to have one, we just
         * return.  The old API tried to zap the entry in the vfs_lookup()
         * phase but this is too early to know whether the operation
         * will have succeeded or not.  The new API zaps it after the
         * operation has succeeded, not here.
         *
         * At the same time, the old api's rename() function uses the
         * old api lookup to clear out any negative cache hit on the
         * target name.  We still have to do that.
         */
        if ((cnp->cn_flags & CNP_MAKEENTRY) == 0) {
                if (cnp->cn_nameiop == NAMEI_RENAME && ncp->nc_vp == NULL)
                        cache_zap(ncp);
                else
                        cache_put(ncp);
                return (0);
        }

        /*
         * If the vnode is not NULL then return the positive match.
         */
        if (ncp->nc_vp) {
                numposhits++;
                gd->gd_nchstats->ncs_goodhits++;
                *vpp = ncp->nc_vp;
                vref(*vpp);
                cache_put(ncp);
                return (-1);
        }

        /*
         * If the vnode is NULL we found a negative match.  If we want to
         * create it, purge the negative match and return failure (as if
         * we hadn't found a match in the first place).
         */
        if (cnp->cn_nameiop == NAMEI_CREATE) {
                numnegzaps++;
                gd->gd_nchstats->ncs_badhits++;
                cache_zap(ncp);
                return (0);
        }

        numneghits++;

        /*
         * We found a "negative" match, ENOENT notifies client of this match.
         * The nc_flag field records whether this is a whiteout.  Since there
         * is no vnode we can use the vnode tailq link field with ncneglist.
         */
        TAILQ_REMOVE(&ncneglist, ncp, nc_vnode);
        TAILQ_INSERT_TAIL(&ncneglist, ncp, nc_vnode);
        gd->gd_nchstats->ncs_neghits++;
        if (ncp->nc_flag & NCF_WHITEOUT)
                cnp->cn_flags |= CNP_ISWHITEOUT;
        cache_put(ncp);
        return (ENOENT);
}

/*
 * Add an entry to the cache.  (OLD API)
 *
 * XXX OLD API ROUTINE!  WHEN ALL VFSs HAVE BEEN CLEANED UP THIS PROCEDURE
 * WILL BE REMOVED.
 *
 * Generally speaking this is 'optional'.  It's ok to do nothing at all.
 * The only reason I don't just return is to try to set nc_timeout if
 * requested.
 */
void
cache_enter(struct vnode *dvp, struct vnode *vp, struct componentname *cnp)
{
        struct namecache *par;
        struct namecache *ncp;
        struct namecache *new_ncp;
        struct namecache *bpar;
        struct nchashhead *nchpp;
        u_int32_t hash;

        /*
         * If the directory has no namecache entry we bail.  This will result
         * in a lot of misses but frankly we don't have much of a choice if
         * we want to be compatible with the new api's storage scheme.
         */
        if ((ncp = TAILQ_FIRST(&dvp->v_namecache)) == NULL)
                return;
        cache_hold(ncp);

        /*
         * This may be a bit confusing.  "." and ".." are 'virtual' entries.
         * We do not actually create a namecache entry representing either.
         * However, the ".." case is used to linkup a potentially disjoint
         * directory with its parent, to disconnect a directory from its
         * parent, or to change an existing linkage that may no longer be
         * correct (as might occur when a subdirectory is renamed).
         */

        if (cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.') {
                cache_drop(ncp);
                return;
        }
        if (cnp->cn_namelen == 2 && cnp->cn_nameptr[0] == '.' &&
            cnp->cn_nameptr[1] == '.'
        ) {
                cache_drop(ncp);
                return;
        }

        /*
         * Ok, no special cases, ncp is actually the parent directory so
         * assign it to par.  Note that it is held.
         */
        par = ncp;

        /*
         * Try to find a match in the hash table, allocate a new entry if
         * we can't.  We have to retry the loop after any potential blocking
         * situation.
         */
        bpar = par;
        hash = fnv_32_buf(cnp->cn_nameptr, cnp->cn_namelen, FNV1_32_INIT);
        hash = fnv_32_buf(&bpar, sizeof(bpar), hash);

        new_ncp = NULL;
againagain:
        LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
                numchecks++;

                /*
                 * Break out if we find a matching entry.  Because cache_enter
                 * is called with one or more vnodes potentially locked, we
                 * cannot block trying to get the ncp lock (or we might 
                 * deadlock).
                 */
                if (ncp->nc_parent == par &&
                    ncp->nc_nlen == cnp->cn_namelen &&
                    bcmp(ncp->nc_name, cnp->cn_nameptr, ncp->nc_nlen) == 0
                ) {
                        if (cache_get_nonblock(ncp) != 0) {
                                printf("[diagnostic] cache_enter: avoided race on %p %*.*s\n", ncp, ncp->nc_nlen, ncp->nc_nlen, ncp->nc_name);
                                cache_drop(par);
                                return;
                        }
                        break;
                }
        }
        if (ncp == NULL) {
                if (new_ncp == NULL) {
                        new_ncp = cache_alloc(cnp->cn_namelen);
                        goto againagain;
                }
                ncp = new_ncp;
                bcopy(cnp->cn_nameptr, ncp->nc_name, cnp->cn_namelen);
                nchpp = NCHHASH(hash);
                LIST_INSERT_HEAD(nchpp, ncp, nc_hash);
                ncp->nc_flag |= NCF_HASHED;
                cache_link_parent(ncp, par);
        } else if (new_ncp) {
                cache_free(new_ncp);
        }
        cache_drop(par);

        /*
         * Avoid side effects if we are simply re-entering the same
         * information.
         */
        if ((ncp->nc_flag & NCF_UNRESOLVED) == 0 && ncp->nc_vp == vp) {
                ncp->nc_error = vp ? 0 : ENOENT;
        } else {
                cache_setunresolved(ncp);
                cache_setvp(ncp, vp);
        }

        /*
         * Set a timeout
         */
        if (cnp->cn_flags & CNP_CACHETIMEOUT) {
                if ((ncp->nc_timeout = ticks + cnp->cn_timeout) == 0)
                        ncp->nc_timeout = 1;
        }

        /*
         * If the target vnode is NULL if this is to be a negative cache
         * entry.
         */
        if (vp == NULL) {
                ncp->nc_flag &= ~NCF_WHITEOUT;
                if (cnp->cn_flags & CNP_ISWHITEOUT)
                        ncp->nc_flag |= NCF_WHITEOUT;
        }
        cache_put(ncp);

        /*
         * Don't cache too many negative hits
         */
        if (numneg > MINNEG && numneg * ncnegfactor > numcache) {
                ncp = TAILQ_FIRST(&ncneglist);
                KKASSERT(ncp != NULL);
                if (cache_get_nonblock(ncp) == 0)
                        cache_zap(ncp);
        }
}

static void
cache_rehash(struct namecache *ncp)
{
        struct nchashhead *nchpp;
        u_int32_t hash;

        if (ncp->nc_flag & NCF_HASHED) {
                ncp->nc_flag &= ~NCF_HASHED;
                LIST_REMOVE(ncp, nc_hash);
        }
        hash = fnv_32_buf(ncp->nc_name, ncp->nc_nlen, FNV1_32_INIT);
        hash = fnv_32_buf(&ncp->nc_parent, sizeof(ncp->nc_parent), hash);
        nchpp = NCHHASH(hash);
        LIST_INSERT_HEAD(nchpp, ncp, nc_hash);
        ncp->nc_flag |= NCF_HASHED;
}


/*
 * Name cache initialization, from vfsinit() when we are booting
 */
void
nchinit(void)
{
        int i;
        globaldata_t gd;

        /* initialise per-cpu namecache effectiveness statistics. */
        for (i = 0; i < ncpus; ++i) {
                gd = globaldata_find(i);
                gd->gd_nchstats = &nchstats[i];
        }
        
        TAILQ_INIT(&ncneglist);
        nchashtbl = hashinit(desiredvnodes*2, M_VFSCACHE, &nchash);
}

/*
 * Called from start_init() to bootstrap the root filesystem.  Returns
 * a referenced, unlocked namecache record.
 */
struct namecache *
cache_allocroot(struct vnode *vp)
{
        struct namecache *ncp = cache_alloc(0);

        ncp->nc_flag |= NCF_MOUNTPT | NCF_ROOT;
        cache_setvp(ncp, vp);
        return(ncp);
}

/*
 * vfs_cache_setroot()
 *
 *      Create an association between the root of our namecache and
 *      the root vnode.  This routine may be called several times during
 *      booting.
 *
 *      If the caller intends to save the returned namecache pointer somewhere
 *      it must cache_hold() it.
 */
void
vfs_cache_setroot(struct vnode *nvp, struct namecache *ncp)
{
        struct vnode *ovp;
        struct namecache *oncp;

        ovp = rootvnode;
        oncp = rootncp;
        rootvnode = nvp;
        rootncp = ncp;

        if (ovp)
                vrele(ovp);
        if (oncp)
                cache_drop(oncp);
}

/*
 * Invalidate all namecache entries to a particular vnode as well as 
 * any direct children of that vnode in the namecache.  This is a 
 * 'catch all' purge used by filesystems that do not know any better.
 *
 * A new vnode v_id is generated.  Note that no vnode will ever have a
 * v_id of 0.
 *
 * Note that the linkage between the vnode and its namecache entries will
 * be removed, but the namecache entries themselves might stay put due to
 * active references from elsewhere in the system or due to the existance of
 * the children.   The namecache topology is left intact even if we do not
 * know what the vnode association is.  Such entries will be marked
 * NCF_UNRESOLVED.
 *
 * XXX: Only time and the size of v_id prevents this from failing:
 * XXX: In theory we should hunt down all (struct vnode*, v_id)
 * XXX: soft references and nuke them, at least on the global
 * XXX: v_id wraparound.  The period of resistance can be extended
 * XXX: by incrementing each vnodes v_id individually instead of
 * XXX: using the global v_id.
 */
void
cache_purge(struct vnode *vp)
{
        static u_long nextid;

        cache_inval_vp(vp, CINV_PARENT | CINV_SELF | CINV_CHILDREN);

        /*
         * Calculate a new unique id for ".." handling
         */
        do {
                nextid++;
        } while (nextid == vp->v_id || nextid == 0);
        vp->v_id = nextid;
}

/*
 * Flush all entries referencing a particular filesystem.
 *
 * Since we need to check it anyway, we will flush all the invalid
 * entries at the same time.
 */
void
cache_purgevfs(struct mount *mp)
{
        struct nchashhead *nchpp;
        struct namecache *ncp, *nnp;

        /*
         * Scan hash tables for applicable entries.
         */
        for (nchpp = &nchashtbl[nchash]; nchpp >= nchashtbl; nchpp--) {
                ncp = LIST_FIRST(nchpp);
                if (ncp)
                        cache_hold(ncp);
                while (ncp) {
                        nnp = LIST_NEXT(ncp, nc_hash);
                        if (nnp)
                                cache_hold(nnp);
                        if (ncp->nc_vp && ncp->nc_vp->v_mount == mp) {
                                cache_lock(ncp);
                                cache_zap(ncp);
                        } else {
                                cache_drop(ncp);
                        }
                        ncp = nnp;
                }
        }
}

/*
 * cache_leaf_test()
 *
 *      Test whether the vnode is at a leaf in the nameicache tree.
 *
 *      Returns 0 if it is a leaf, -1 if it isn't.
 */
int
cache_leaf_test(struct vnode *vp)
{
        struct namecache *scan;
        struct namecache *ncp;

        TAILQ_FOREACH(scan, &vp->v_namecache, nc_vnode) {
                TAILQ_FOREACH(ncp, &scan->nc_list, nc_entry) {
                        /* YYY && ncp->nc_vp->v_type == VDIR ? */
                        if (ncp->nc_vp != NULL)
                                return(-1);
                }
        }
        return(0);
}

/*
 * Perform canonical checks and cache lookup and pass on to filesystem
 * through the vop_cachedlookup only if needed.
 *
 * vop_lookup_args {
 *      struct vnode a_dvp;
 *      struct vnode **a_vpp;
 *      struct componentname *a_cnp;
 * }
 */
int
vfs_cache_lookup(struct vop_lookup_args *ap)
{
        struct vnode *dvp, *vp;
        int lockparent;
        int error;
        struct vnode **vpp = ap->a_vpp;
        struct componentname *cnp = ap->a_cnp;
        struct ucred *cred = cnp->cn_cred;
        int flags = cnp->cn_flags;
        struct thread *td = cnp->cn_td;
        u_long vpid;    /* capability number of vnode */

        *vpp = NULL;
        dvp = ap->a_dvp;
        lockparent = flags & CNP_LOCKPARENT;

        if (dvp->v_type != VDIR)
                return (ENOTDIR);

        if ((flags & CNP_ISLASTCN) && (dvp->v_mount->mnt_flag & MNT_RDONLY) &&
            (cnp->cn_nameiop == NAMEI_DELETE || cnp->cn_nameiop == NAMEI_RENAME)) {
                return (EROFS);
        }

        error = VOP_ACCESS(dvp, VEXEC, cred, td);

        if (error)
                return (error);

        error = cache_lookup(dvp, vpp, cnp);

        if (!error) 
                return (VOP_CACHEDLOOKUP(dvp, vpp, cnp));

        if (error == ENOENT)
                return (error);

        vp = *vpp;
        vpid = vp->v_id;
        cnp->cn_flags &= ~CNP_PDIRUNLOCK;
        if (dvp == vp) {   /* lookup on "." */
                vref(vp);
                error = 0;
        } else if (flags & CNP_ISDOTDOT) {
                VOP_UNLOCK(dvp, NULL, 0, td);
                cnp->cn_flags |= CNP_PDIRUNLOCK;
                error = vget(vp, NULL, LK_EXCLUSIVE, td);
                if (!error && lockparent && (flags & CNP_ISLASTCN)) {
                        if ((error = vn_lock(dvp, NULL, LK_EXCLUSIVE, td)) == 0)
                                cnp->cn_flags &= ~CNP_PDIRUNLOCK;
                }
        } else {
                error = vget(vp, NULL, LK_EXCLUSIVE, td);
                if (!lockparent || error || !(flags & CNP_ISLASTCN)) {
                        VOP_UNLOCK(dvp, NULL, 0, td);
                        cnp->cn_flags |= CNP_PDIRUNLOCK;
                }
        }
        /*
         * Check that the capability number did not change
         * while we were waiting for the lock.
         */
        if (!error) {
                if (vpid == vp->v_id)
                        return (0);
                vput(vp);
                if (lockparent && dvp != vp && (flags & CNP_ISLASTCN)) {
                        VOP_UNLOCK(dvp, NULL, 0, td);
                        cnp->cn_flags |= CNP_PDIRUNLOCK;
                }
        }
        if (cnp->cn_flags & CNP_PDIRUNLOCK) {
                error = vn_lock(dvp, NULL, LK_EXCLUSIVE, td);
                if (error)
                        return (error);
                cnp->cn_flags &= ~CNP_PDIRUNLOCK;
        }
        return (VOP_CACHEDLOOKUP(dvp, vpp, cnp));
}

static int disablecwd;
SYSCTL_INT(_debug, OID_AUTO, disablecwd, CTLFLAG_RW, &disablecwd, 0, "");

static u_long numcwdcalls; STATNODE(CTLFLAG_RD, numcwdcalls, &numcwdcalls);
static u_long numcwdfail1; STATNODE(CTLFLAG_RD, numcwdfail1, &numcwdfail1);
static u_long numcwdfail2; STATNODE(CTLFLAG_RD, numcwdfail2, &numcwdfail2);
static u_long numcwdfail3; STATNODE(CTLFLAG_RD, numcwdfail3, &numcwdfail3);
static u_long numcwdfail4; STATNODE(CTLFLAG_RD, numcwdfail4, &numcwdfail4);
static u_long numcwdfound; STATNODE(CTLFLAG_RD, numcwdfound, &numcwdfound);

int
__getcwd(struct __getcwd_args *uap)
{
        int buflen;
        int error;
        char *buf;
        char *bp;

        if (disablecwd)
                return (ENODEV);

        buflen = uap->buflen;
        if (buflen < 2)
                return (EINVAL);
        if (buflen > MAXPATHLEN)
                buflen = MAXPATHLEN;

        buf = malloc(buflen, M_TEMP, M_WAITOK);
        bp = kern_getcwd(buf, buflen, &error);
        if (error == 0)
                error = copyout(bp, uap->buf, strlen(bp) + 1);
        free(buf, M_TEMP);
        return (error);
}

char *
kern_getcwd(char *buf, size_t buflen, int *error)
{
        struct proc *p = curproc;
        char *bp;
        int i, slash_prefixed;
        struct filedesc *fdp;
        struct namecache *ncp;

        numcwdcalls++;
        bp = buf;
        bp += buflen - 1;
        *bp = '\0';
        fdp = p->p_fd;
        slash_prefixed = 0;

        ncp = fdp->fd_ncdir;
        while (ncp && ncp != fdp->fd_nrdir && (ncp->nc_flag & NCF_ROOT) == 0) {
                if (ncp->nc_flag & NCF_MOUNTPT) {
                        if (ncp->nc_mount == NULL) {
                                *error = EBADF;         /* forced unmount? */
                                return(NULL);
                        }
                        ncp = ncp->nc_parent;
                        continue;
                }
                for (i = ncp->nc_nlen - 1; i >= 0; i--) {
                        if (bp == buf) {
                                numcwdfail4++;
                                *error = ENOMEM;
                                return(NULL);
                        }
                        *--bp = ncp->nc_name[i];
                }
                if (bp == buf) {
                        numcwdfail4++;
                        *error = ENOMEM;
                        return(NULL);
                }
                *--bp = '/';
                slash_prefixed = 1;
                ncp = ncp->nc_parent;
        }
        if (ncp == NULL) {
                numcwdfail2++;
                *error = ENOENT;
                return(NULL);
        }
        if (!slash_prefixed) {
                if (bp == buf) {
                        numcwdfail4++;
                        *error = ENOMEM;
                        return(NULL);
                }
                *--bp = '/';
        }
        numcwdfound++;
        *error = 0;
        return (bp);
}

/*
 * Thus begins the fullpath magic.
 */

#undef STATNODE
#define STATNODE(name)                                                  \
        static u_int name;                                              \
        SYSCTL_UINT(_vfs_cache, OID_AUTO, name, CTLFLAG_RD, &name, 0, "")

static int disablefullpath;
SYSCTL_INT(_debug, OID_AUTO, disablefullpath, CTLFLAG_RW,
    &disablefullpath, 0, "");

STATNODE(numfullpathcalls);
STATNODE(numfullpathfail1);
STATNODE(numfullpathfail2);
STATNODE(numfullpathfail3);
STATNODE(numfullpathfail4);
STATNODE(numfullpathfound);

int
vn_fullpath(struct proc *p, struct vnode *vn, char **retbuf, char **freebuf) 
{
        char *bp, *buf;
        int i, slash_prefixed;
        struct filedesc *fdp;
        struct namecache *ncp;

        numfullpathcalls++;
        if (disablefullpath)
                return (ENODEV);

        if (p == NULL)
                return (EINVAL);

        /* vn is NULL, client wants us to use p->p_textvp */
        if (vn == NULL) {
                if ((vn = p->p_textvp) == NULL)
                        return (EINVAL);
        }
        ncp = TAILQ_FIRST(&vn->v_namecache);
        if (ncp == NULL)
                return (EINVAL);

        buf = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
        bp = buf + MAXPATHLEN - 1;
        *bp = '\0';
        fdp = p->p_fd;
        slash_prefixed = 0;
        while (ncp && ncp != fdp->fd_nrdir && (ncp->nc_flag & NCF_ROOT) == 0) {
                if (ncp->nc_flag & NCF_MOUNTPT) {
                        if (ncp->nc_mount == NULL) {
                                free(buf, M_TEMP);
                                return(EBADF);
                        }
                        ncp = ncp->nc_parent;
                        continue;
                }
                for (i = ncp->nc_nlen - 1; i >= 0; i--) {
                        if (bp == buf) {
                                numfullpathfail4++;
                                free(buf, M_TEMP);
                                return (ENOMEM);
                        }
                        *--bp = ncp->nc_name[i];
                }
                if (bp == buf) {
                        numfullpathfail4++;
                        free(buf, M_TEMP);
                        return (ENOMEM);
                }
                *--bp = '/';
                slash_prefixed = 1;
                ncp = ncp->nc_parent;
        }
        if (ncp == NULL) {
                numfullpathfail2++;
                free(buf, M_TEMP);
                return (ENOENT);
        }
        if (!slash_prefixed) {
                if (bp == buf) {
                        numfullpathfail4++;
                        free(buf, M_TEMP);
                        return (ENOMEM);
                }
                *--bp = '/';
        }
        numfullpathfound++;
        *retbuf = bp; 
        *freebuf = buf;
        return (0);
}