xnu-1228.15.4.tar.gz

[apple/xnu.git] / bsd / vfs / vfs_cache.c

/*
 * Copyright (c) 2000-2007 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * 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
 */
/*
 * NOTICE: This file was modified by SPARTA, Inc. in 2005 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 */
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/time.h>
#include <sys/mount_internal.h>
#include <sys/vnode_internal.h>
#include <sys/namei.h>
#include <sys/errno.h>
#include <sys/malloc.h>
#include <sys/kauth.h>
#include <sys/user.h>
#include <sys/paths.h>

#if CONFIG_MACF
#include <security/mac_framework.h>
#endif

/*
 * 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.
 *
 * 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.
 */

LIST_HEAD(nchashhead, namecache) *nchashtbl;    /* Hash Table */
u_long  nchashmask;
u_long  nchash;                         /* size of hash table - 1 */
long    numcache;                       /* number of cache entries allocated */
int     desiredNodes;
int     desiredNegNodes;
int     ncs_negtotal;
TAILQ_HEAD(, namecache) nchead;         /* chain of all name cache entries */
TAILQ_HEAD(, namecache) neghead;        /* chain of only negative cache entries */


#if COLLECT_STATS

struct  nchstats nchstats;              /* cache effectiveness statistics */

#define NCHSTAT(v) {            \
        nchstats.v++;           \
}
#define NAME_CACHE_LOCK()               name_cache_lock()
#define NAME_CACHE_UNLOCK()             name_cache_unlock()
#define NAME_CACHE_LOCK_SHARED()        name_cache_lock()

#else

#define NCHSTAT(v)
#define NAME_CACHE_LOCK()               name_cache_lock()
#define NAME_CACHE_UNLOCK()             name_cache_unlock()
#define NAME_CACHE_LOCK_SHARED()        name_cache_lock_shared()

#endif


/* vars for name cache list lock */
lck_grp_t * namecache_lck_grp;
lck_grp_attr_t * namecache_lck_grp_attr;
lck_attr_t * namecache_lck_attr;
lck_rw_t * namecache_rw_lock;

static vnode_t cache_lookup_locked(vnode_t dvp, struct componentname *cnp);
static int  remove_name_locked(const char *);
static const char *add_name_locked(const char *, size_t, u_int, u_int);
static void init_string_table(void) __attribute__((section("__TEXT, initcode")));
static void cache_delete(struct namecache *, int);
static void cache_enter_locked(vnode_t dvp, vnode_t vp, struct componentname *cnp);

#ifdef DUMP_STRING_TABLE
/*
 * Internal dump function used for debugging
 */
void dump_string_table(void);
#endif  /* DUMP_STRING_TABLE */

static void init_crc32(void) __attribute__((section("__TEXT, initcode")));
static unsigned int crc32tab[256];


#define NCHHASH(dvp, hash_val) \
        (&nchashtbl[(dvp->v_id ^ (hash_val)) & nchashmask])



//
// This function builds the path to a filename in "buff".  The
// length of the buffer *INCLUDING* the trailing zero byte is
// returned in outlen.  NOTE: the length includes the trailing
// zero byte and thus the length is one greater than what strlen
// would return.  This is important and lots of code elsewhere
// in the kernel assumes this behavior.
// 
// This function can call vnop in file system if the parent vnode 
// does not exist or when called for hardlinks via volfs path.  
// If BUILDPATH_NO_FS_ENTER is set in flags, it only uses values present
// in the name cache and does not enter the file system.
//
int
build_path(vnode_t first_vp, char *buff, int buflen, int *outlen, int flags, vfs_context_t ctx)
{
        vnode_t vp;
        vnode_t proc_root_dir_vp;
        char *end;
        const char *str;
        int  len;
        int  ret = 0;
        int  fixhardlink;

        if (first_vp == NULLVP) {
                return (EINVAL);
        }
        /* Grab the process fd so we can evaluate fd_rdir. */
        if (vfs_context_proc(ctx)->p_fd) {
            proc_root_dir_vp = vfs_context_proc(ctx)->p_fd->fd_rdir;
        } else {
            proc_root_dir_vp = NULL;
        }
again:
        vp = first_vp;
        end = &buff[buflen-1];
        *end = '\0';

        /* Check if this is the root of a file system. */
        while (vp && vp->v_flag & VROOT) {
                if (vp->v_mount == NULL) {
                        return (EINVAL);
                }
                if ((vp->v_mount->mnt_flag & MNT_ROOTFS) || (vp == proc_root_dir_vp)) {
                        /*
                         * It's the root of the root file system, so it's
                         * just "/".
                         */
                        *--end = '/';
                        goto out;
                } else {
                        vp = vp->v_mount->mnt_vnodecovered;
                }
        }
        NAME_CACHE_LOCK_SHARED();

        while ((vp != NULLVP) && (vp->v_parent != vp)) {
                /*
                 * For hardlinks the v_name may be stale, so if its OK
                 * to enter a file system, ask the file system for the
                 * name and parent (below).
                 */
                fixhardlink = (vp->v_flag & VISHARDLINK) &&
                              (vp->v_mount->mnt_kern_flag & MNTK_PATH_FROM_ID) &&
                              !(flags & BUILDPATH_NO_FS_ENTER);
                if (!fixhardlink) {
                        str = vp->v_name;
                        if (str == NULL || *str == '\0') {
                                if (vp->v_parent != NULL) {
                                        ret = EINVAL;
                                } else {
                                        ret = ENOENT;
                                }
                                break;
                        }
                        len = strlen(str);
                        /*
                         * Check that there's enough space (including space for the '/')
                         */
                        if ((end - buff) < (len + 1)) {
                                ret = ENOSPC;
                                break;
                        }
                        /* Copy the name backwards. */
                        str += len;
        
                        for (; len > 0; len--) {
                               *--end = *--str;
                        }
                        /* Add a path separator. */
                        *--end = '/';
                }

                /*
                 * Walk up the parent chain.
                 */
                if (((vp->v_parent != NULLVP) && !fixhardlink) ||
                    (flags & BUILDPATH_NO_FS_ENTER)) {
                        vp = vp->v_parent;

                        // if the vnode we have in hand isn't a directory and it
                        // has a v_parent, then we started with the resource fork
                        // so skip up to avoid getting a duplicate copy of the
                        // file name in the path.
                        if (vp && !vnode_isdir(vp) && vp->v_parent) {
                            vp = vp->v_parent;
                        }
                } else /* No parent, go get it if supported. */ {
                        struct vnode_attr  va;
                        vnode_t  dvp;
                        int  vid;

                        /* Make sure file system supports obtaining a path from id. */
                        if (!(vp->v_mount->mnt_kern_flag & MNTK_PATH_FROM_ID)) {
                                ret = ENOENT;
                                break;
                        }
                        vid = vp->v_id;
                        NAME_CACHE_UNLOCK();

                        if (vnode_getwithvid(vp, vid) != 0) {
                                /* vnode was recycled, so start over. */
                                goto again;
                        }
                        
                        VATTR_INIT(&va);
                        VATTR_WANTED(&va, va_parentid);
                        if (fixhardlink) {
                                VATTR_WANTED(&va, va_name);
                                MALLOC_ZONE(va.va_name, caddr_t, MAXPATHLEN, M_NAMEI, M_WAITOK);
                        } else {
                                va.va_name = NULL;
                        }
                        /* Ask the file system for its parent id and for its name (optional). */
                        ret = vnode_getattr(vp, &va, ctx);

                        if (fixhardlink) {
                                if ((ret == 0) && (VATTR_IS_SUPPORTED(&va, va_name))) {
                                        str = va.va_name;
                                } else if (vp->v_name) {
                                        str = vp->v_name;
                                        ret = 0;
                                } else {
                                        ret = ENOENT;
                                        goto bad_news;
                                }
                                len = strlen(str);

                                /* Check that there's enough space. */
                                if ((end - buff) < (len + 1)) {
                                        ret = ENOSPC;
                                } else {
                                        /* Copy the name backwards. */
                                        str += len;
                                        
                                        for (; len > 0; len--) {
                                                *--end = *--str;
                                        }
                                        /* Add a path separator. */
                                        *--end = '/';
                                }
                          bad_news:
                                FREE_ZONE(va.va_name, MAXPATHLEN, M_NAMEI);
                        }
                        if (ret || !VATTR_IS_SUPPORTED(&va, va_parentid)) {
                                vnode_put(vp);
                                ret = ENOENT;
                                goto out;
                        }
                        /* Ask the file system for the parent vnode. */
                        ret = VFS_VGET(vp->v_mount, (ino64_t)va.va_parentid, &dvp, ctx);
                        if (ret) {
                                vnode_put(vp);
                                goto out;
                        }
                        if (!fixhardlink && (vp->v_parent != dvp)) {
                                vnode_update_identity(vp, dvp, NULL, 0, 0, VNODE_UPDATE_PARENT);
                        }
                        vnode_put(vp);
                        vp = dvp;
                        /*
                         * We are no longer under the name cache lock here.
                         * So to avoid a race for vnode termination, take a
                         * reference on the vnode and drop that reference
                         * after reacquiring the name cache lock. We use the
                         * vnode_rele_ext call with the dont_reenter flag
                         * set to avoid re-entering the file system which
                         * could possibly re-enter the name cache.
                         */
                        if (vnode_ref(dvp) != 0) {
                                dvp = NULLVP;
                        }
                        vnode_put(vp);
                        NAME_CACHE_LOCK_SHARED();

                        if (dvp) {
                                vnode_rele_ext(dvp, 0, 1);
                        }

                        // if the vnode we have in hand isn't a directory and it
                        // has a v_parent, then we started with the resource fork
                        // so skip up to avoid getting a duplicate copy of the
                        // file name in the path.
                        if (vp && !vnode_isdir(vp) && vp->v_parent) {
                            vp = vp->v_parent;
                        }
                }
                /*
                 * When a mount point is crossed switch the vp.
                 * Continue until we find the root or we find
                 * a vnode that's not the root of a mounted
                 * file system.
                 */
                while (vp) {
                        if (vp == proc_root_dir_vp) {
                                NAME_CACHE_UNLOCK();
                                goto out;  /* encountered the root */
                        }
                        if (!(vp->v_flag & VROOT) || !vp->v_mount)
                                break;  /* not the root of a mounted FS */
                        vp = vp->v_mount->mnt_vnodecovered;
                }
        }
        NAME_CACHE_UNLOCK();
out:
        /* Slide the name down to the beginning of the buffer. */
        memmove(buff, end, &buff[buflen] - end);
    
        *outlen = &buff[buflen] - end;  /* length includes the trailing zero byte */
 
        return (ret);
}


/*
 * return NULLVP if vp's parent doesn't
 * exist, or we can't get a valid iocount
 * else return the parent of vp
 */
vnode_t
vnode_getparent(vnode_t vp)
{
        vnode_t pvp = NULLVP;
        int     pvid;

        NAME_CACHE_LOCK_SHARED();
        /*
         * v_parent is stable behind the name_cache lock
         * however, the only thing we can really guarantee
         * is that we've grabbed a valid iocount on the
         * parent of 'vp' at the time we took the name_cache lock...
         * once we drop the lock, vp could get re-parented
         */
        if ( (pvp = vp->v_parent) != NULLVP ) {
                pvid = pvp->v_id;

                NAME_CACHE_UNLOCK();

                if (vnode_getwithvid(pvp, pvid) != 0)
                        pvp = NULL;
        } else
                NAME_CACHE_UNLOCK();
        return (pvp);
}

const char *
vnode_getname(vnode_t vp)
{
        const char *name = NULL;

        NAME_CACHE_LOCK();
        
        if (vp->v_name)
                name = add_name_locked(vp->v_name, strlen(vp->v_name), 0, 0);
        NAME_CACHE_UNLOCK();

        return (name);
}

void
vnode_putname(const char *name)
{
        NAME_CACHE_LOCK();

        remove_name_locked(name);

        NAME_CACHE_UNLOCK();
}


/*
 * if VNODE_UPDATE_PARENT, and we can take
 * a reference on dvp, then update vp with
 * it's new parent... if vp already has a parent,
 * then drop the reference vp held on it
 *
 * if VNODE_UPDATE_NAME,
 * then drop string ref on v_name if it exists, and if name is non-NULL
 * then pick up a string reference on name and record it in v_name...
 * optionally pass in the length and hashval of name if known
 *
 * if VNODE_UPDATE_CACHE, flush the name cache entries associated with vp
 */
void
vnode_update_identity(vnode_t vp, vnode_t dvp, const char *name, int name_len, int name_hashval, int flags)
{
        struct  namecache *ncp;
        vnode_t old_parentvp = NULLVP;
#if NAMEDSTREAMS
        int isstream = (vp->v_flag & VISNAMEDSTREAM);
        int kusecountbumped = 0;
#endif

        if (flags & VNODE_UPDATE_PARENT) {
                if (dvp && vnode_ref(dvp) != 0) {
                        dvp = NULLVP;
                }
#if NAMEDSTREAMS
                /* Don't count a stream's parent ref during unmounts */
                if (isstream && dvp && (dvp != vp) && (dvp != vp->v_parent) && (dvp->v_type == VREG)) {
                        vnode_lock_spin(dvp);
                        ++dvp->v_kusecount;
                        kusecountbumped = 1;
                        vnode_unlock(dvp);
                }
#endif
        } else {
                dvp = NULLVP;
        }
        NAME_CACHE_LOCK();

        if ( (flags & VNODE_UPDATE_NAME) && (name != vp->v_name) ) {
                if (vp->v_name != NULL) {
                        remove_name_locked(vp->v_name);
                        vp->v_name = NULL;
                }
                if (name && *name) {
                        if (name_len == 0)
                                name_len = strlen(name);
                        vp->v_name = add_name_locked(name, name_len, name_hashval, 0);
                }
        }
        if (flags & VNODE_UPDATE_PARENT) {
                if (dvp != vp && dvp != vp->v_parent) {
                        old_parentvp = vp->v_parent;
                        vp->v_parent = dvp;
                        dvp = NULLVP;

                        if (old_parentvp)
                                flags |= VNODE_UPDATE_CACHE;
                }
        }
        if (flags & VNODE_UPDATE_CACHE) {
                while ( (ncp = LIST_FIRST(&vp->v_nclinks)) )
                        cache_delete(ncp, 1);
        }
        NAME_CACHE_UNLOCK();
        
        if (dvp != NULLVP) {
#if NAMEDSTREAMS
                /* Back-out the ref we took if we lost a race for vp->v_parent. */
                if (kusecountbumped) {
                        vnode_lock_spin(dvp);
                        if (dvp->v_kusecount > 0)
                                --dvp->v_kusecount;  
                        vnode_unlock(dvp);
                }
#endif
                vnode_rele(dvp);
        }
        if (old_parentvp) {
                struct  uthread *ut;

#if NAMEDSTREAMS
                if (isstream) {
                        vnode_lock_spin(old_parentvp);
                        if ((old_parentvp->v_type != VDIR) && (old_parentvp->v_kusecount > 0))
                                --old_parentvp->v_kusecount;
                        vnode_unlock(old_parentvp);
                }
#endif
                ut = get_bsdthread_info(current_thread());

                /*
                 * indicated to vnode_rele that it shouldn't do a
                 * vnode_reclaim at this time... instead it will
                 * chain the vnode to the uu_vreclaims list...
                 * we'll be responsible for calling vnode_reclaim
                 * on each of the vnodes in this list...
                 */
                ut->uu_defer_reclaims = 1;
                ut->uu_vreclaims = NULLVP;

                while ( (vp = old_parentvp) != NULLVP ) {
          
                        vnode_lock(vp);
                        vnode_rele_internal(vp, 0, 0, 1);

                        /*
                         * check to see if the vnode is now in the state
                         * that would have triggered a vnode_reclaim in vnode_rele
                         * if it is, we save it's parent pointer and then NULL
                         * out the v_parent field... we'll drop the reference
                         * that was held on the next iteration of this loop...
                         * this short circuits a potential deep recursion if we
                         * have a long chain of parents in this state... 
                         * we'll sit in this loop until we run into
                         * a parent in this chain that is not in this state
                         *
                         * make our check and the node_rele atomic
                         * with respect to the current vnode we're working on
                         * by holding the vnode lock
                         * if vnode_rele deferred the vnode_reclaim and has put
                         * this vnode on the list to be reaped by us, than
                         * it has left this vnode with an iocount == 1
                         */
                        if ( (vp->v_iocount == 1) && (vp->v_usecount == 0) &&
                             ((vp->v_lflag & (VL_MARKTERM | VL_TERMINATE | VL_DEAD)) == VL_MARKTERM)) {
                                /*
                                 * vnode_rele wanted to do a vnode_reclaim on this vnode
                                 * it should be sitting on the head of the uu_vreclaims chain
                                 * pull the parent pointer now so that when we do the
                                 * vnode_reclaim for each of the vnodes in the uu_vreclaims
                                 * list, we won't recurse back through here
                                 *
                                 * need to do a convert here in case vnode_rele_internal
                                 * returns with the lock held in the spin mode... it 
                                 * can drop and retake the lock under certain circumstances
                                 */
                                vnode_lock_convert(vp);

                                NAME_CACHE_LOCK();
                                old_parentvp = vp->v_parent;
                                vp->v_parent = NULLVP;
                                NAME_CACHE_UNLOCK();
                        } else {
                                /*
                                 * we're done... we ran into a vnode that isn't
                                 * being terminated
                                 */
                                old_parentvp = NULLVP;
                        }
                        vnode_unlock(vp);
                }
                ut->uu_defer_reclaims = 0;

                while ( (vp = ut->uu_vreclaims) != NULLVP) {
                        ut->uu_vreclaims = vp->v_defer_reclaimlist;
                        
                        /*
                         * vnode_put will drive the vnode_reclaim if
                         * we are still the only reference on this vnode
                         */
                        vnode_put(vp);
                }
        }
}


/*
 * Mark a vnode as having multiple hard links.  HFS makes use of this
 * because it keeps track of each link separately, and wants to know
 * which link was actually used.
 *
 * This will cause the name cache to force a VNOP_LOOKUP on the vnode
 * so that HFS can post-process the lookup.  Also, volfs will call
 * VNOP_GETATTR2 to determine the parent, instead of using v_parent.
 */
void vnode_setmultipath(vnode_t vp)
{
        vnode_lock_spin(vp);

        /*
         * In theory, we're changing the vnode's identity as far as the
         * name cache is concerned, so we ought to grab the name cache lock
         * here.  However, there is already a race, and grabbing the name
         * cache lock only makes the race window slightly smaller.
         *
         * The race happens because the vnode already exists in the name
         * cache, and could be found by one thread before another thread
         * can set the hard link flag.
         */

        vp->v_flag |= VISHARDLINK;

        vnode_unlock(vp);
}



/*
 * backwards compatibility
 */
void vnode_uncache_credentials(vnode_t vp)
{
        vnode_uncache_authorized_action(vp, KAUTH_INVALIDATE_CACHED_RIGHTS);
}


/*
 * use the exclusive form of NAME_CACHE_LOCK to protect the update of the
 * following fields in the vnode: v_cred_timestamp, v_cred, v_authorized_actions
 * we use this lock so that we can look at the v_cred and v_authorized_actions
 * atomically while behind the NAME_CACHE_LOCK in shared mode in 'cache_lookup_path',
 * which is the super-hot path... if we are updating the authorized actions for this
 * vnode, we are already in the super-slow and far less frequented path so its not
 * that bad that we take the lock exclusive for this case... of course we strive
 * to hold it for the minimum amount of time possible
 */

void vnode_uncache_authorized_action(vnode_t vp, kauth_action_t action)
{
        kauth_cred_t tcred = NOCRED;

        NAME_CACHE_LOCK();

        vp->v_authorized_actions &= ~action;

        if (action == KAUTH_INVALIDATE_CACHED_RIGHTS &&
            IS_VALID_CRED(vp->v_cred)) {
                /*
                 * Use a temp variable to avoid kauth_cred_unref() while NAME_CACHE_LOCK is held
                 */
                tcred = vp->v_cred;
                vp->v_cred = NOCRED;
        }
        NAME_CACHE_UNLOCK();

        if (tcred != NOCRED)
                kauth_cred_unref(&tcred);
}


boolean_t vnode_cache_is_authorized(vnode_t vp, vfs_context_t ctx, kauth_action_t action)
{
        kauth_cred_t    ucred;
        boolean_t       retval = FALSE;

        if ( (vp->v_mount->mnt_kern_flag & (MNTK_AUTH_OPAQUE | MNTK_AUTH_CACHE_TTL)) ) {
                /*
                 * a TTL is enabled on the rights cache... handle it here
                 * a TTL of 0 indicates that no rights should be cached
                 */
                if (vp->v_mount->mnt_authcache_ttl) {
                        if ( !(vp->v_mount->mnt_kern_flag & MNTK_AUTH_CACHE_TTL) ) {
                                /*
                                 * For filesystems marked only MNTK_AUTH_OPAQUE (generally network ones),
                                 * we will only allow a SEARCH right on a directory to be cached...
                                 * that cached right always has a default TTL associated with it
                                 */
                                if (action != KAUTH_VNODE_SEARCH || vp->v_type != VDIR)
                                        vp = NULLVP;
                        }
                        if (vp != NULLVP && vnode_cache_is_stale(vp) == TRUE) {
                                vnode_uncache_authorized_action(vp, vp->v_authorized_actions);
                                vp = NULLVP;
                        }
                } else
                        vp = NULLVP;
        }
        if (vp != NULLVP) {
                ucred = vfs_context_ucred(ctx);

                NAME_CACHE_LOCK_SHARED();

                if (vp->v_cred == ucred && (vp->v_authorized_actions & action) == action)
                        retval = TRUE;
                
                NAME_CACHE_UNLOCK();
        }
        return retval;
}


void vnode_cache_authorized_action(vnode_t vp, vfs_context_t ctx, kauth_action_t action)
{
        kauth_cred_t tcred = NOCRED;
        kauth_cred_t ucred;
        struct timeval tv;
        boolean_t ttl_active = FALSE;

        ucred = vfs_context_ucred(ctx);

        if (!IS_VALID_CRED(ucred) || action == 0)
                return;

        if ( (vp->v_mount->mnt_kern_flag & (MNTK_AUTH_OPAQUE | MNTK_AUTH_CACHE_TTL)) ) {
                /*
                 * a TTL is enabled on the rights cache... handle it here
                 * a TTL of 0 indicates that no rights should be cached
                 */
                if (vp->v_mount->mnt_authcache_ttl == 0) 
                        return;

                if ( !(vp->v_mount->mnt_kern_flag & MNTK_AUTH_CACHE_TTL) ) {
                        /*
                         * only cache SEARCH action for filesystems marked
                         * MNTK_AUTH_OPAQUE on VDIRs...
                         * the lookup_path code will time these out
                         */
                        if ( (action & ~KAUTH_VNODE_SEARCH) || vp->v_type != VDIR )
                                return;
                }
                ttl_active = TRUE;

                microuptime(&tv);
        }
        NAME_CACHE_LOCK();

        if (vp->v_cred != ucred) {
                kauth_cred_ref(ucred);
                /*
                 * Use a temp variable to avoid kauth_cred_unref() while NAME_CACHE_LOCK is held
                 */
                tcred = vp->v_cred;
                vp->v_cred = ucred;
                vp->v_authorized_actions = 0;
        }
        if (ttl_active == TRUE && vp->v_authorized_actions == 0) {
                /*
                 * only reset the timestamnp on the
                 * first authorization cached after the previous
                 * timer has expired or we're switching creds...
                 * 'vnode_cache_is_authorized' will clear the 
                 * authorized actions if the TTL is active and
                 * it has expired
                 */
                vp->v_cred_timestamp = tv.tv_sec;
        }
        vp->v_authorized_actions |= action;

        NAME_CACHE_UNLOCK();

        if (IS_VALID_CRED(tcred))
                kauth_cred_unref(&tcred);
}


boolean_t vnode_cache_is_stale(vnode_t vp)
{
        struct timeval  tv;
        boolean_t       retval;

        microuptime(&tv);

        if ((tv.tv_sec - vp->v_cred_timestamp) > vp->v_mount->mnt_authcache_ttl)
                retval = TRUE;
        else
                retval = FALSE;

        return retval;
}



/*
 * Returns:     0                       Success
 *              ERECYCLE                vnode was recycled from underneath us.  Force lookup to be re-driven from namei.
 *                                              This errno value should not be seen by anyone outside of the kernel.
 */
int 
cache_lookup_path(struct nameidata *ndp, struct componentname *cnp, vnode_t dp, 
                vfs_context_t ctx, int *trailing_slash, int *dp_authorized, vnode_t last_dp)
{
        char            *cp;            /* pointer into pathname argument */
        int             vid;
        int             vvid = 0;       /* protected by vp != NULLVP */
        vnode_t         vp = NULLVP;
        vnode_t         tdp = NULLVP;
        kauth_cred_t    ucred;
        boolean_t       ttl_enabled = FALSE;
        struct timeval  tv;
    mount_t             mp;
        unsigned int    hash;
        int             error = 0;

        ucred = vfs_context_ucred(ctx);
        *trailing_slash = 0;

        NAME_CACHE_LOCK_SHARED();

        if ( dp->v_mount && (dp->v_mount->mnt_kern_flag & (MNTK_AUTH_OPAQUE | MNTK_AUTH_CACHE_TTL)) ) {
                ttl_enabled = TRUE;
                microuptime(&tv);
        }
        for (;;) {
                /*
                 * Search a directory.
                 *
                 * The cn_hash value is for use by cache_lookup
                 * The last component of the filename is left accessible via
                 * cnp->cn_nameptr for callers that need the name.
                 */
                hash = 0;
                cp = cnp->cn_nameptr;

                while (*cp && (*cp != '/')) {
                        hash ^= crc32tab[((hash >> 24) ^ (unsigned char)*cp++)];
                }
                /*
                 * the crc generator can legitimately generate
                 * a 0... however, 0 for us means that we
                 * haven't computed a hash, so use 1 instead
                 */
                if (hash == 0)
                        hash = 1;
                cnp->cn_hash = hash;
                cnp->cn_namelen = cp - cnp->cn_nameptr;

                ndp->ni_pathlen -= cnp->cn_namelen;
                ndp->ni_next = cp;

                /*
                 * Replace multiple slashes by a single slash and trailing slashes
                 * by a null.  This must be done before VNOP_LOOKUP() because some
                 * fs's don't know about trailing slashes.  Remember if there were
                 * trailing slashes to handle symlinks, existing non-directories
                 * and non-existing files that won't be directories specially later.
                 */
                while (*cp == '/' && (cp[1] == '/' || cp[1] == '\0')) {
                        cp++;
                        ndp->ni_pathlen--;

                        if (*cp == '\0') {
                                *trailing_slash = 1;
                                *ndp->ni_next = '\0';
                        }
                }
                ndp->ni_next = cp;

                cnp->cn_flags &= ~(MAKEENTRY | ISLASTCN | ISDOTDOT);

                if (*cp == '\0')
                        cnp->cn_flags |= ISLASTCN;

                if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.' && cnp->cn_nameptr[0] == '.')
                        cnp->cn_flags |= ISDOTDOT;

                *dp_authorized = 0;
#if NAMEDRSRCFORK
                /*
                 * Process a request for a file's resource fork.
                 *
                 * Consume the _PATH_RSRCFORKSPEC suffix and tag the path.
                 */
                if ((ndp->ni_pathlen == sizeof(_PATH_RSRCFORKSPEC)) &&
                    (cp[1] == '.' && cp[2] == '.') &&
                    bcmp(cp, _PATH_RSRCFORKSPEC, sizeof(_PATH_RSRCFORKSPEC)) == 0) {
                        /* Skip volfs file systems that don't support native streams. */
                        if ((dp->v_mount != NULL) &&
                            (dp->v_mount->mnt_flag & MNT_DOVOLFS) &&
                            (dp->v_mount->mnt_kern_flag & MNTK_NAMED_STREAMS) == 0) {
                                goto skiprsrcfork;
                        }
                        cnp->cn_flags |= CN_WANTSRSRCFORK;
                        cnp->cn_flags |= ISLASTCN;
                        ndp->ni_next[0] = '\0';
                        ndp->ni_pathlen = 1;
                }
skiprsrcfork:
#endif

#if CONFIG_MACF

                /* 
                 * Name cache provides authorization caching (see below)
                 * that will short circuit MAC checks in lookup().
                 * We must perform MAC check here.  On denial
                 * dp_authorized will remain 0 and second check will
                 * be perfomed in lookup().
                 */
                if (!(cnp->cn_flags & DONOTAUTH)) {
                        error = mac_vnode_check_lookup(ctx, dp, cnp);
                        if (error) {
                                name_cache_unlock();
                                goto errorout;
                        }
                }
#endif /* MAC */
                if (ttl_enabled && ((tv.tv_sec - dp->v_cred_timestamp) > dp->v_mount->mnt_authcache_ttl))
                        break;

                /*
                 * NAME_CACHE_LOCK holds these fields stable
                 */
                if ((dp->v_cred != ucred || !(dp->v_authorized_actions & KAUTH_VNODE_SEARCH)) &&
                    !(dp->v_authorized_actions & KAUTH_VNODE_SEARCHBYANYONE))
                        break;

                /*
                 * indicate that we're allowed to traverse this directory...
                 * even if we fail the cache lookup or decide to bail for
                 * some other reason, this information is valid and is used
                 * to avoid doing a vnode_authorize before the call to VNOP_LOOKUP
                 */
                *dp_authorized = 1;

                if ( (cnp->cn_flags & (ISLASTCN | ISDOTDOT)) ) {
                        if (cnp->cn_nameiop != LOOKUP)
                                break;
                        if (cnp->cn_flags & (LOCKPARENT | NOCACHE))
                                break;
                        if (cnp->cn_flags & ISDOTDOT) {
                                /*
                                 * Force directory hardlinks to go to
                                 * file system for ".." requests.
                                 */
                                if (dp && (dp->v_flag & VISHARDLINK)) {
                                        break;
                                }
                                /*
                                 * Quit here only if we can't use
                                 * the parent directory pointer or
                                 * don't have one.  Otherwise, we'll
                                 * use it below.
                                 */
                                if ((dp->v_flag & VROOT)  ||
                                    dp == ndp->ni_rootdir ||
                                    dp->v_parent == NULLVP)
                                        break;
                        }
                }

                /*
                 * "." and ".." aren't supposed to be cached, so check
                 * for them before checking the cache.
                 */
                if (cnp->cn_namelen == 1 && cnp->cn_nameptr[0] == '.')
                        vp = dp;
                else if ((cnp->cn_flags & ISDOTDOT) && dp->v_parent)
                        vp = dp->v_parent;
                else {
                        if ( (vp = cache_lookup_locked(dp, cnp)) == NULLVP)
                                break;
                }

                if ( (cnp->cn_flags & ISLASTCN) )
                        break;

                if (vp->v_type != VDIR) {
                        if (vp->v_type != VLNK)
                                vp = NULL;
                        break;
                }
                if ( (mp = vp->v_mountedhere) && ((cnp->cn_flags & NOCROSSMOUNT) == 0)) {

                        if (mp->mnt_realrootvp == NULLVP || mp->mnt_generation != mount_generation ||
                                mp->mnt_realrootvp_vid != mp->mnt_realrootvp->v_id)
                                break;
                        vp = mp->mnt_realrootvp;
                }
                dp = vp;
                vp = NULLVP;

                cnp->cn_nameptr = ndp->ni_next + 1;
                ndp->ni_pathlen--;
                while (*cnp->cn_nameptr == '/') {
                        cnp->cn_nameptr++;
                        ndp->ni_pathlen--;
                }
        }
        if (vp != NULLVP)
                vvid = vp->v_id;
        vid = dp->v_id;
        
        NAME_CACHE_UNLOCK();

        if ((vp != NULLVP) && (vp->v_type != VLNK) &&
            ((cnp->cn_flags & (ISLASTCN | LOCKPARENT | WANTPARENT | SAVESTART)) == ISLASTCN)) {
                /*
                 * if we've got a child and it's the last component, and 
                 * the lookup doesn't need to return the parent then we
                 * can skip grabbing an iocount on the parent, since all
                 * we're going to do with it is a vnode_put just before
                 * we return from 'lookup'.  If it's a symbolic link,
                 * we need the parent in case the link happens to be
                 * a relative pathname.
                 */
                tdp = dp;
                dp = NULLVP;
        } else {
need_dp:
                /*
                 * return the last directory we looked at
                 * with an io reference held. If it was the one passed
                 * in as a result of the last iteration of VNOP_LOOKUP,
                 * it should already hold an io ref. No need to increase ref.
                 */
                if (last_dp != dp){
                        
                        if (dp == ndp->ni_usedvp) {
                                /*
                                 * if this vnode matches the one passed in via USEDVP
                                 * than this context already holds an io_count... just
                                 * use vnode_get to get an extra ref for lookup to play
                                 * with... can't use the getwithvid variant here because
                                 * it will block behind a vnode_drain which would result
                                 * in a deadlock (since we already own an io_count that the
                                 * vnode_drain is waiting on)... vnode_get grabs the io_count
                                 * immediately w/o waiting... it always succeeds
                                 */
                                vnode_get(dp);
                        } else if ( (vnode_getwithvid(dp, vid)) ) {
                                /*
                                 * failure indicates the vnode
                                 * changed identity or is being
                                 * TERMINATED... in either case
                                 * punt this lookup.
                                 * 
                                 * don't necessarily return ENOENT, though, because
                                 * we really want to go back to disk and make sure it's
                                 * there or not if someone else is changing this
                                 * vnode.
                                 */
                                error = ERECYCLE;
                                goto errorout;
                        }
                }
        }
        if (vp != NULLVP) {
                if ( (vnode_getwithvid(vp, vvid)) ) {
                        vp = NULLVP;

                        /*
                         * can't get reference on the vp we'd like
                         * to return... if we didn't grab a reference
                         * on the directory (due to fast path bypass),
                         * then we need to do it now... we can't return
                         * with both ni_dvp and ni_vp NULL, and no 
                         * error condition
                         */
                        if (dp == NULLVP) {
                                dp = tdp;
                                goto need_dp;
                        }
                }
        }
        ndp->ni_dvp = dp;
        ndp->ni_vp  = vp;

errorout:
        /* 
         * If we came into cache_lookup_path after an iteration of the lookup loop that
         * resulted in a call to VNOP_LOOKUP, then VNOP_LOOKUP returned a vnode with a io ref
         * on it.  It is now the job of cache_lookup_path to drop the ref on this vnode 
         * when it is no longer needed.  If we get to this point, and last_dp is not NULL
         * and it is ALSO not the dvp we want to return to caller of this function, it MUST be
         * the case that we got to a subsequent path component and this previous vnode is 
         * no longer needed.  We can then drop the io ref on it.
         */
        if ((last_dp != NULLVP) && (last_dp != ndp->ni_dvp)){
                vnode_put(last_dp);
        }
        
        //initialized to 0, should be the same if no error cases occurred.
        return error;
}


static vnode_t
cache_lookup_locked(vnode_t dvp, struct componentname *cnp)
{
        struct namecache *ncp;
        struct nchashhead *ncpp;
        long namelen = cnp->cn_namelen;
        char *nameptr = cnp->cn_nameptr;
        unsigned int hashval = (cnp->cn_hash & NCHASHMASK);
        vnode_t vp;
        
        ncpp = NCHHASH(dvp, cnp->cn_hash);
        LIST_FOREACH(ncp, ncpp, nc_hash) {
                if ((ncp->nc_dvp == dvp) && (ncp->nc_hashval == hashval)) {
                        if (memcmp(ncp->nc_name, nameptr, namelen) == 0 && ncp->nc_name[namelen] == 0)
                                break;
                }
        }
        if (ncp == 0) {
                /*
                 * We failed to find an entry
                 */
                NCHSTAT(ncs_miss);
                return (NULL);
        }
        NCHSTAT(ncs_goodhits);

        vp = ncp->nc_vp;
        if (vp && (vp->v_flag & VISHARDLINK)) {
                        /*
                         * The file system wants a VNOP_LOOKUP on this vnode
                         */
                        vp = NULL;
        }
        
        return (vp);
}


//
// Have to take a len argument because we may only need to
// hash part of a componentname.
//
static unsigned int
hash_string(const char *cp, int len)
{
    unsigned hash = 0;

    if (len) {
            while (len--) {
                    hash ^= crc32tab[((hash >> 24) ^ (unsigned char)*cp++)];
            }
    } else {
            while (*cp != '\0') {
                    hash ^= crc32tab[((hash >> 24) ^ (unsigned char)*cp++)];
            }
    }
    /*
     * the crc generator can legitimately generate
     * a 0... however, 0 for us means that we
     * haven't computed a hash, so use 1 instead
     */
    if (hash == 0)
            hash = 1;
    return hash;
}


/*
 * 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(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
{
        struct namecache *ncp;
        struct nchashhead *ncpp;
        long namelen = cnp->cn_namelen;
        char *nameptr = cnp->cn_nameptr;
        unsigned int hashval = (cnp->cn_hash & NCHASHMASK);
        boolean_t       have_exclusive = FALSE;
        uint32_t vid;
        vnode_t  vp;

        NAME_CACHE_LOCK_SHARED();

        ncpp = NCHHASH(dvp, cnp->cn_hash);
relook:
        LIST_FOREACH(ncp, ncpp, nc_hash) {
                if ((ncp->nc_dvp == dvp) && (ncp->nc_hashval == hashval)) {
                        if (memcmp(ncp->nc_name, nameptr, namelen) == 0 && ncp->nc_name[namelen] == 0)
                                break;
                }
        }
        /* We failed to find an entry */
        if (ncp == 0) {
                NCHSTAT(ncs_miss);
                NAME_CACHE_UNLOCK();
                return (0);
        }

        /* We don't want to have an entry, so dump it */
        if ((cnp->cn_flags & MAKEENTRY) == 0) {
                if (have_exclusive == TRUE) {
                        NCHSTAT(ncs_badhits);
                        cache_delete(ncp, 1);
                        NAME_CACHE_UNLOCK();
                        return (0);
                }
                NAME_CACHE_UNLOCK();
                NAME_CACHE_LOCK();
                have_exclusive = TRUE;
                goto relook;
        } 
        vp = ncp->nc_vp;

        /* We found a "positive" match, return the vnode */
        if (vp) {
                NCHSTAT(ncs_goodhits);

                vid = vp->v_id;
                NAME_CACHE_UNLOCK();

                if (vnode_getwithvid(vp, vid)) {
#if COLLECT_STATS
                        NAME_CACHE_LOCK();
                        NCHSTAT(ncs_badvid);
                        NAME_CACHE_UNLOCK();
#endif
                        return (0);
                }
                *vpp = vp;
                return (-1);
        }

        /* We found a negative match, and want to create it, so purge */
        if (cnp->cn_nameiop == CREATE || cnp->cn_nameiop == RENAME) {
                if (have_exclusive == TRUE) {
                        NCHSTAT(ncs_badhits);
                        cache_delete(ncp, 1);
                        NAME_CACHE_UNLOCK();
                        return (0);
                }
                NAME_CACHE_UNLOCK();
                NAME_CACHE_LOCK();
                have_exclusive = TRUE;
                goto relook;
        }

        /*
         * We found a "negative" match, ENOENT notifies client of this match.
         * The nc_whiteout field records whether this is a whiteout.
         */
        NCHSTAT(ncs_neghits);

        if (ncp->nc_whiteout)
                cnp->cn_flags |= ISWHITEOUT;
        NAME_CACHE_UNLOCK();
        return (ENOENT);
}


/*
 * Add an entry to the cache...
 * but first check to see if the directory
 * that this entry is to be associated with has
 * had any cache_purges applied since we took
 * our identity snapshot... this check needs to
 * be done behind the name cache lock
 */
void
cache_enter_with_gen(struct vnode *dvp, struct vnode *vp, struct componentname *cnp, int gen)
{

        if (cnp->cn_hash == 0)
                cnp->cn_hash = hash_string(cnp->cn_nameptr, cnp->cn_namelen);

        NAME_CACHE_LOCK();

        if (dvp->v_nc_generation == gen)
                cache_enter_locked(dvp, vp, cnp);

        NAME_CACHE_UNLOCK();
}


/*
 * Add an entry to the cache.
 */
void
cache_enter(struct vnode *dvp, struct vnode *vp, struct componentname *cnp)
{
        if (cnp->cn_hash == 0)
                cnp->cn_hash = hash_string(cnp->cn_nameptr, cnp->cn_namelen);

        NAME_CACHE_LOCK();

        cache_enter_locked(dvp, vp, cnp);

        NAME_CACHE_UNLOCK();
}


static void
cache_enter_locked(struct vnode *dvp, struct vnode *vp, struct componentname *cnp)
{
        struct namecache *ncp, *negp;
        struct nchashhead *ncpp;

        /*
         * if the entry is for -ve caching vp is null
         */
        if ((vp != NULLVP) && (LIST_FIRST(&vp->v_nclinks))) {
                /*
                 * someone beat us to the punch..
                 * this vnode is already in the cache
                 */
                return;
        }
        /*
         * We allocate a new entry if we are less than the maximum
         * allowed and the one at the front of the list is in use.
         * Otherwise we use the one at the front of the list.
         */
        if (numcache < desiredNodes &&
            ((ncp = nchead.tqh_first) == NULL ||
              ncp->nc_hash.le_prev != 0)) {
                /*
                 * Allocate one more entry
                 */
                ncp = (struct namecache *)_MALLOC_ZONE((u_long)sizeof *ncp, M_CACHE, M_WAITOK);
                numcache++;
        } else {
                /*
                 * reuse an old entry
                 */
                ncp = TAILQ_FIRST(&nchead);
                TAILQ_REMOVE(&nchead, ncp, nc_entry);

                if (ncp->nc_hash.le_prev != 0) {
                       /*
                        * still in use... we need to
                        * delete it before re-using it
                        */
                        NCHSTAT(ncs_stolen);
                        cache_delete(ncp, 0);
                }
        }
        NCHSTAT(ncs_enters);

        /*
         * Fill in cache info, if vp is NULL this is a "negative" cache entry.
         */
        ncp->nc_vp = vp;
        ncp->nc_dvp = dvp;
        ncp->nc_hashval = cnp->cn_hash;
        ncp->nc_whiteout = FALSE;
        ncp->nc_name = add_name_locked(cnp->cn_nameptr, cnp->cn_namelen, cnp->cn_hash, 0);

        /*
         * make us the newest entry in the cache
         * i.e. we'll be the last to be stolen
         */
        TAILQ_INSERT_TAIL(&nchead, ncp, nc_entry);

        ncpp = NCHHASH(dvp, cnp->cn_hash);
#if DIAGNOSTIC
        {
                struct namecache *p;

                for (p = ncpp->lh_first; p != 0; p = p->nc_hash.le_next)
                        if (p == ncp)
                                panic("cache_enter: duplicate");
        }
#endif
        /*
         * make us available to be found via lookup
         */
        LIST_INSERT_HEAD(ncpp, ncp, nc_hash);

        if (vp) {
               /*
                * add to the list of name cache entries
                * that point at vp
                */
                LIST_INSERT_HEAD(&vp->v_nclinks, ncp, nc_un.nc_link);
        } else {
                /*
                 * this is a negative cache entry (vp == NULL)
                 * stick it on the negative cache list
                 * and record the whiteout state
                 */
                TAILQ_INSERT_TAIL(&neghead, ncp, nc_un.nc_negentry);
          
                if (cnp->cn_flags & ISWHITEOUT)
                        ncp->nc_whiteout = TRUE;
                ncs_negtotal++;

                if (ncs_negtotal > desiredNegNodes) {
                       /*
                        * if we've reached our desired limit
                        * of negative cache entries, delete
                        * the oldest
                        */
                        negp = TAILQ_FIRST(&neghead);
                        TAILQ_REMOVE(&neghead, negp, nc_un.nc_negentry);

                        cache_delete(negp, 1);
                }
        }
        /*
         * add us to the list of name cache entries that
         * are children of dvp
         */
        LIST_INSERT_HEAD(&dvp->v_ncchildren, ncp, nc_child);
}


/*
 * Initialize CRC-32 remainder table.
 */
static void init_crc32(void)
{
        /*
         * the CRC-32 generator polynomial is:
         *   x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + x^10
         *        + x^8  + x^7  + x^5  + x^4  + x^2  + x + 1
         */
        unsigned int crc32_polynomial = 0x04c11db7;
        unsigned int i,j;

        /*
         * pre-calculate the CRC-32 remainder for each possible octet encoding
         */
        for (i = 0;  i < 256;  i++) {
                unsigned int crc_rem = i << 24;

                for (j = 0;  j < 8;  j++) {
                        if (crc_rem & 0x80000000)
                                crc_rem = (crc_rem << 1) ^ crc32_polynomial;
                        else
                                crc_rem = (crc_rem << 1);
                }
                crc32tab[i] = crc_rem;
        }
}


/*
 * Name cache initialization, from vfs_init() when we are booting
 */
void
nchinit(void)
{
        desiredNegNodes = (desiredvnodes / 10);
        desiredNodes = desiredvnodes + desiredNegNodes;

        TAILQ_INIT(&nchead);
        TAILQ_INIT(&neghead);

        init_crc32();

        nchashtbl = hashinit(MAX(CONFIG_NC_HASH, (2 *desiredNodes)), M_CACHE, &nchash);
        nchashmask = nchash;
        nchash++;

        init_string_table();
        
        /* Allocate mount list lock group attribute and group */
        namecache_lck_grp_attr= lck_grp_attr_alloc_init();

        namecache_lck_grp = lck_grp_alloc_init("Name Cache",  namecache_lck_grp_attr);
        
        /* Allocate mount list lock attribute */
        namecache_lck_attr = lck_attr_alloc_init();

        /* Allocate mount list lock */
        namecache_rw_lock = lck_rw_alloc_init(namecache_lck_grp, namecache_lck_attr);


}

void
name_cache_lock_shared(void)
{
        lck_rw_lock_shared(namecache_rw_lock);
}

void
name_cache_lock(void)
{
        lck_rw_lock_exclusive(namecache_rw_lock);
}

void
name_cache_unlock(void)
{
        lck_rw_done(namecache_rw_lock);
}


int
resize_namecache(u_int newsize)
{
    struct nchashhead   *new_table;
    struct nchashhead   *old_table;
    struct nchashhead   *old_head, *head;
    struct namecache    *entry, *next;
    uint32_t            i, hashval;
    int                 dNodes, dNegNodes;
    u_long              new_size, old_size;

    dNegNodes = (newsize / 10);
    dNodes = newsize + dNegNodes;

    // we don't support shrinking yet
    if (dNodes < desiredNodes) {
        return 0;
    }
    new_table = hashinit(2 * dNodes, M_CACHE, &nchashmask);
    new_size  = nchashmask + 1;

    if (new_table == NULL) {
        return ENOMEM;
    }

    NAME_CACHE_LOCK();
    // do the switch!
    old_table = nchashtbl;
    nchashtbl = new_table;
    old_size  = nchash;
    nchash    = new_size;

    // walk the old table and insert all the entries into
    // the new table
    //
    for(i=0; i < old_size; i++) {
        old_head = &old_table[i];
        for (entry=old_head->lh_first; entry != NULL; entry=next) {
            //
            // XXXdbg - Beware: this assumes that hash_string() does
            //                  the same thing as what happens in
            //                  lookup() over in vfs_lookup.c
            hashval = hash_string(entry->nc_name, 0);
            entry->nc_hashval = hashval;
            head = NCHHASH(entry->nc_dvp, hashval);
            
            next = entry->nc_hash.le_next;
            LIST_INSERT_HEAD(head, entry, nc_hash);
        }
    }
    desiredNodes = dNodes;
    desiredNegNodes = dNegNodes;
    
    NAME_CACHE_UNLOCK();
    FREE(old_table, M_CACHE);

    return 0;
}

static void
cache_delete(struct namecache *ncp, int age_entry)
{
        NCHSTAT(ncs_deletes);

        if (ncp->nc_vp) {
                LIST_REMOVE(ncp, nc_un.nc_link);
        } else {
                TAILQ_REMOVE(&neghead, ncp, nc_un.nc_negentry);
                ncs_negtotal--;
        }
        LIST_REMOVE(ncp, nc_child);

        LIST_REMOVE(ncp, nc_hash);
        /*
         * this field is used to indicate
         * that the entry is in use and
         * must be deleted before it can 
         * be reused...
         */
        ncp->nc_hash.le_prev = NULL;

        if (age_entry) {
                /*
                 * make it the next one available
                 * for cache_enter's use
                 */
                TAILQ_REMOVE(&nchead, ncp, nc_entry);
                TAILQ_INSERT_HEAD(&nchead, ncp, nc_entry);
        }
        remove_name_locked(ncp->nc_name);
        ncp->nc_name = NULL;
}


/*
 * purge the entry associated with the 
 * specified vnode from the name cache
 */
void
cache_purge(vnode_t vp)
{
        struct namecache *ncp;
        kauth_cred_t tcred = NULL;

        if ((LIST_FIRST(&vp->v_nclinks) == NULL) && (LIST_FIRST(&vp->v_ncchildren) == NULL) && (vp->v_cred == NOCRED))
                return;

        NAME_CACHE_LOCK();

        if (vp->v_parent)
                vp->v_parent->v_nc_generation++;

        while ( (ncp = LIST_FIRST(&vp->v_nclinks)) )
                cache_delete(ncp, 1);

        while ( (ncp = LIST_FIRST(&vp->v_ncchildren)) )
                cache_delete(ncp, 1);

        /*
         * Use a temp variable to avoid kauth_cred_unref() while NAME_CACHE_LOCK is held
         */
        tcred = vp->v_cred;
        vp->v_cred = NOCRED;
        vp->v_authorized_actions = 0;

        NAME_CACHE_UNLOCK();

        if (IS_VALID_CRED(tcred))
                kauth_cred_unref(&tcred);
}

/*
 * Purge all negative cache entries that are children of the
 * given vnode.  A case-insensitive file system (or any file
 * system that has multiple equivalent names for the same
 * directory entry) can use this when creating or renaming
 * to remove negative entries that may no longer apply.
 */
void
cache_purge_negatives(vnode_t vp)
{
        struct namecache *ncp;

        NAME_CACHE_LOCK();

        LIST_FOREACH(ncp, &vp->v_ncchildren, nc_child)
                if (ncp->nc_vp == NULL)
                        cache_delete(ncp , 1);

        NAME_CACHE_UNLOCK();
}

/*
 * 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 *ncpp;
        struct namecache *ncp;

        NAME_CACHE_LOCK();
        /* Scan hash tables for applicable entries */
        for (ncpp = &nchashtbl[nchash - 1]; ncpp >= nchashtbl; ncpp--) {
restart:          
                for (ncp = ncpp->lh_first; ncp != 0; ncp = ncp->nc_hash.le_next) {
                        if (ncp->nc_dvp->v_mount == mp) {
                                cache_delete(ncp, 0);
                                goto restart;
                        }
                }
        }
        NAME_CACHE_UNLOCK();
}



//
// String ref routines
//
static LIST_HEAD(stringhead, string_t) *string_ref_table;
static u_long   string_table_mask;
static uint32_t max_chain_len=0;
static struct stringhead *long_chain_head=NULL;
static uint32_t filled_buckets=0;
static uint32_t num_dups=0;
static uint32_t nstrings=0;

typedef struct string_t {
    LIST_ENTRY(string_t)  hash_chain;
    const char *str;
    uint32_t              refcount;
} string_t;



static int
resize_string_ref_table(void)
{
    struct stringhead *new_table;
    struct stringhead *old_table;
    struct stringhead *old_head, *head;
    string_t          *entry, *next;
    uint32_t           i, hashval;
    u_long             new_mask, old_mask;

    new_table = hashinit((string_table_mask + 1) * 2, M_CACHE, &new_mask);
    if (new_table == NULL) {
        return ENOMEM;
    }

    // do the switch!
    old_table         = string_ref_table;
    string_ref_table  = new_table;
    old_mask          = string_table_mask;
    string_table_mask = new_mask;

    printf("resize: max chain len %d, new table size %lu\n",
           max_chain_len, new_mask + 1);
    max_chain_len   = 0;
    long_chain_head = NULL;
    filled_buckets  = 0;

    // walk the old table and insert all the entries into
    // the new table
    //
    for(i=0; i <= old_mask; i++) {
        old_head = &old_table[i];
        for (entry=old_head->lh_first; entry != NULL; entry=next) {
            hashval = hash_string((const char *)entry->str, 0);
            head = &string_ref_table[hashval & string_table_mask];
            if (head->lh_first == NULL) {
                filled_buckets++;
            }

            next = entry->hash_chain.le_next;
            LIST_INSERT_HEAD(head, entry, hash_chain);
        }
    }
    
    FREE(old_table, M_CACHE);

    return 0;
}


static void
init_string_table(void)
{
        string_ref_table = hashinit(CONFIG_VFS_NAMES, M_CACHE, &string_table_mask);
}


const char *
vfs_addname(const char *name, size_t len, u_int hashval, u_int flags)
{
        const char * ptr;

        NAME_CACHE_LOCK();
        ptr = add_name_locked(name, len, hashval, flags);
        NAME_CACHE_UNLOCK();

        return(ptr);
}

static const char *
add_name_locked(const char *name, size_t len, u_int hashval, __unused u_int flags)
{
    struct stringhead *head;
    string_t          *entry;
    uint32_t          chain_len = 0;
    char              *ptr;
    
    //
    // If the table gets more than 3/4 full, resize it
    //
    if (4*filled_buckets >= ((string_table_mask + 1) * 3)) {
                if (resize_string_ref_table() != 0) {
                        printf("failed to resize the hash table.\n");
                }
    }
    if (hashval == 0) {
        hashval = hash_string(name, 0);
    }

    //
    // if the length already accounts for the null-byte, then
    // subtract one so later on we don't index past the end
    // of the string.
    //
    if (len > 0 && name[len-1] == '\0') {
        len--;
    }

    head = &string_ref_table[hashval & string_table_mask];
    for (entry=head->lh_first; entry != NULL; chain_len++, entry=entry->hash_chain.le_next) {
        if (memcmp(entry->str, name, len) == 0 && entry->str[len] == '\0') {
            entry->refcount++;
            num_dups++;
            break;
        }
    }

    if (entry == NULL) {
        // it wasn't already there so add it.
        MALLOC(entry, string_t *, sizeof(string_t) + len + 1, M_TEMP, M_WAITOK);

        // have to get "head" again because we could have blocked
        // in malloc and thus head could have changed.
        //
        head = &string_ref_table[hashval & string_table_mask];
        if (head->lh_first == NULL) {
            filled_buckets++;
        }

        ptr = (char *)((char *)entry + sizeof(string_t));
        strncpy(ptr, name, len);
        ptr[len] = '\0';
        entry->str = ptr;
        entry->refcount = 1;
        LIST_INSERT_HEAD(head, entry, hash_chain);

        if (chain_len > max_chain_len) {
            max_chain_len   = chain_len;
            long_chain_head = head;
        }

        nstrings++;
    }
    
    return (const char *)entry->str;
}

int
vfs_removename(const char *nameref)
{
        int i;

        NAME_CACHE_LOCK();
        i = remove_name_locked(nameref);
        NAME_CACHE_UNLOCK();

        return(i);
        
}


static int
remove_name_locked(const char *nameref)
{
    struct stringhead *head;
    string_t          *entry;
    uint32_t           hashval;
    const char        *ptr;

    hashval = hash_string(nameref, 0);
    head = &string_ref_table[hashval & string_table_mask];
    for (entry=head->lh_first; entry != NULL; entry=entry->hash_chain.le_next) {
        if (entry->str == nameref) {
            entry->refcount--;
            if (entry->refcount == 0) {
                LIST_REMOVE(entry, hash_chain);
                if (head->lh_first == NULL) {
                    filled_buckets--;
                }
                ptr = entry->str;
                entry->str = NULL;
                nstrings--;

                FREE(entry, M_TEMP);
            } else {
                num_dups--;
            }

            return 0;
        }
    }

    return ENOENT;
}


#ifdef DUMP_STRING_TABLE
void
dump_string_table(void)
{
    struct stringhead *head;
    string_t          *entry;
    u_long            i;
    
    NAME_CACHE_LOCK_SHARED();

    for (i = 0; i <= string_table_mask; i++) {
        head = &string_ref_table[i];
        for (entry=head->lh_first; entry != NULL; entry=entry->hash_chain.le_next) {
            printf("%6d - %s\n", entry->refcount, entry->str);
        }
    }
    NAME_CACHE_UNLOCK();
}
#endif  /* DUMP_STRING_TABLE */