/*
 * Copyright (c) 2004-2022 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.
 */
/*
 * nlookup() is the 'new' namei interface.  Rather then return directory and
 * leaf vnodes (in various lock states) the new interface instead deals in
 * namecache records.  Namecache records may represent both a positive or
 * a negative hit.  The namespace is locked via the namecache record instead
 * of via the vnode, and only the leaf namecache record (representing the
 * filename) needs to be locked.
 *
 * This greatly improves filesystem parallelism and is a huge simplification
 * of the API verses the old vnode locking / namei scheme.
 *
 * Filesystems must actively control the caching aspects of the namecache,
 * and since namecache pointers are used as handles they are non-optional
 * even for filesystems which do not generally wish to cache things.  It is
 * intended that a separate cache coherency API will be constructed to handle
 * these issues.
 */

#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/uio.h>
#include <sys/kernel.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/filedesc.h>
#include <sys/proc.h>
#include <sys/namei.h>
#include <sys/nlookup.h>
#include <sys/malloc.h>
#include <sys/stat.h>
#include <sys/objcache.h>
#include <sys/file.h>
#include <sys/kcollect.h>
#include <sys/sysctl.h>

#ifdef KTRACE
#include <sys/ktrace.h>
#endif

__read_mostly static int nlookup_max_retries = 4;
SYSCTL_INT(_debug, OID_AUTO, nlookup_max_retries, CTLFLAG_RW,
        &nlookup_max_retries, 0,
        "retries on generation mismatch");
__read_mostly static int nlookup_debug;
SYSCTL_INT(_debug, OID_AUTO, nlookup_debug, CTLFLAG_RW,
        &nlookup_debug, 0,
        "Force retry test");

static int naccess(struct nlookupdata *nd, struct nchandle *nch,
                        u_int *genp, int vmode,
                        struct ucred *cred, int *stickyp, int nchislocked);

/*
 * unmount operations flag NLC_IGNBADDIR in order to allow the
 * umount to successfully issue a nlookup() on the path in order
 * to extract the mount point.  Allow certain errors through.
 */
static __inline
int
keeperror(struct nlookupdata *nd, int error)
{
        if (error) {
                if ((nd->nl_flags & NLC_IGNBADDIR) == 0 ||
                   (error != EIO && error != EBADRPC && error != ESTALE)) {
                        return 1;
                }
        }
        return 0;
}

/*
 * Initialize a nlookup() structure, early error return for copyin faults
 * or a degenerate empty string (which is not allowed).
 *
 * The first process proc0's credentials are used if the calling thread
 * is not associated with a process context.
 *
 * MPSAFE
 */
int
nlookup_init(struct nlookupdata *nd, 
             const char *path, enum uio_seg seg, int flags)
{
    size_t pathlen;
    struct proc *p;
    thread_t td;
    int error;

    td = curthread;
    p = td->td_proc;

    /*
     * note: the pathlen set by copy*str() includes the terminating \0.
     */
    bzero(nd, sizeof(struct nlookupdata));
    nd->nl_path = objcache_get(namei_oc, M_WAITOK);
    nd->nl_flags |= NLC_HASBUF;
    if (seg == UIO_SYSSPACE) 
        error = copystr(path, nd->nl_path, MAXPATHLEN, &pathlen);
    else
        error = copyinstr(path, nd->nl_path, MAXPATHLEN, &pathlen);

    /*
     * Don't allow empty pathnames.
     * POSIX.1 requirement: "" is not a vaild file name.
     */
    if (error == 0 && pathlen <= 1)
        error = ENOENT;

    if (error == 0) {
        if (p && p->p_fd) {
            if (nd->nl_path[0] == '/') {
                    if ((flags & NLC_NLNCH_NOINIT) == 0) {
                            nd->nl_basench = &p->p_fd->fd_nrdir;
                            cache_copy(nd->nl_basench, &nd->nl_nch);
                    }
                    cache_copy(&p->p_fd->fd_nrdir, &nd->nl_rootnch);
                    if (p->p_fd->fd_njdir.ncp)
                        cache_copy(&p->p_fd->fd_njdir, &nd->nl_jailnch);
                    nd->nl_cred = td->td_ucred;
                    nd->nl_flags |= NLC_BORROWCRED;
            } else {
                    if ((flags & NLC_NLNCH_NOINIT) == 0) {
                            nd->nl_basench = &p->p_fd->fd_ncdir;
                            cache_copy(nd->nl_basench, &nd->nl_nch);
                    }
                    cache_copy(&p->p_fd->fd_nrdir, &nd->nl_rootnch);
                    if (p->p_fd->fd_njdir.ncp)
                        cache_copy(&p->p_fd->fd_njdir, &nd->nl_jailnch);
                    nd->nl_cred = td->td_ucred;
                    nd->nl_flags |= NLC_BORROWCRED;
            }
        } else {
            if ((flags & NLC_NLNCH_NOINIT) == 0) {
                    nd->nl_basench = &rootnch;
                    cache_copy(nd->nl_basench, &nd->nl_nch);
            }
            cache_copy(&rootnch, &nd->nl_rootnch);
            cache_copy(&rootnch, &nd->nl_jailnch);
            nd->nl_cred = proc0.p_ucred;
            nd->nl_flags |= NLC_BORROWCRED;
        }
        nd->nl_td = td;
        nd->nl_flags |= flags & ~NLC_NLNCH_NOINIT;
    } else {
        nlookup_done(nd);
    }
    return(error);
}


/*
 * nlookup_init() for "at" family of syscalls.
 *
 * Similar to nlookup_init() but if the path is relative and fd is not
 * AT_FDCWD, the path will be interpreted relative to the directory pointed
*  to by fd.  In this case, the file entry pointed to by fd is ref'ed and
*  returned in *fpp.
 *
 * If the call succeeds, nlookup_done_at() must be called to clean-up the nd
 * and release the ref to the file entry.
 */
int
nlookup_init_at(struct nlookupdata *nd, struct file **fpp, int fd, 
                const char *path, enum uio_seg seg, int flags)
{
        struct thread *td = curthread;
        struct file* fp;
        struct vnode *vp;
        int error;

        *fpp = NULL;

        /*
         * Resolve the path, we might have to copy it in from userland,
         * but don't initialize nl_basench, or nl_nch.
         */
        error = nlookup_init(nd, path, seg, flags | NLC_NLNCH_NOINIT);
        if (__predict_false(error))
                return (error);

        /*
         * Setup nl_basench (a pointer only not refd), and copy+ref
         * to initialize nl_nch.  Only applicable to relative paths.
         * For absolute paths, or if (fd) is degenerate, just use the
         * normal path.
         */
        if (nd->nl_path[0] == '/') {
                struct proc *p = curproc;
                nd->nl_basench = &p->p_fd->fd_nrdir;
        } else if (fd == AT_FDCWD) {
                struct proc *p = curproc;
                nd->nl_basench = &p->p_fd->fd_ncdir;
        } else {
                if ((error = holdvnode(td, fd, &fp)) != 0)
                        goto done;
                vp = (struct vnode*)fp->f_data;
                if (vp->v_type != VDIR || fp->f_nchandle.ncp == NULL) {
                        fdrop(fp);
                        fp = NULL;
                        error = ENOTDIR;
                        goto done;
                }
                nd->nl_basench = &fp->f_nchandle;
                *fpp = fp;
        }
        cache_copy(nd->nl_basench, &nd->nl_nch);
done:
        if (error)
                nlookup_done(nd);
        return (error);
}

/*
 * This works similarly to nlookup_init() but does not assume a process
 * context.  rootnch is always chosen for the root directory and the cred
 * and starting directory are supplied in arguments.
 */
int
nlookup_init_raw(struct nlookupdata *nd, 
             const char *path, enum uio_seg seg, int flags,
             struct ucred *cred, struct nchandle *ncstart)
{
    size_t pathlen;
    thread_t td;
    int error;

    td = curthread;

    bzero(nd, sizeof(struct nlookupdata));
    nd->nl_path = objcache_get(namei_oc, M_WAITOK);
    nd->nl_flags |= NLC_HASBUF;
    if (seg == UIO_SYSSPACE) 
        error = copystr(path, nd->nl_path, MAXPATHLEN, &pathlen);
    else
        error = copyinstr(path, nd->nl_path, MAXPATHLEN, &pathlen);

    /*
     * Don't allow empty pathnames.
     * POSIX.1 requirement: "" is not a vaild file name.
     */
    if (error == 0 && pathlen <= 1)
        error = ENOENT;

    if (error == 0) {
        cache_copy(ncstart, &nd->nl_nch);
        cache_copy(&rootnch, &nd->nl_rootnch);
        cache_copy(&rootnch, &nd->nl_jailnch);
        nd->nl_cred = crhold(cred);
        nd->nl_td = td;
        nd->nl_flags |= flags;
    } else {
        nlookup_done(nd);
    }
    return(error);
}

/*
 * This works similarly to nlookup_init_raw() but does not rely
 * on rootnch being initialized yet.
 */
int
nlookup_init_root(struct nlookupdata *nd, 
             const char *path, enum uio_seg seg, int flags,
             struct ucred *cred, struct nchandle *ncstart,
             struct nchandle *ncroot)
{
    size_t pathlen;
    thread_t td;
    int error;

    td = curthread;

    bzero(nd, sizeof(struct nlookupdata));
    nd->nl_path = objcache_get(namei_oc, M_WAITOK);
    nd->nl_flags |= NLC_HASBUF;
    if (seg == UIO_SYSSPACE) 
        error = copystr(path, nd->nl_path, MAXPATHLEN, &pathlen);
    else
        error = copyinstr(path, nd->nl_path, MAXPATHLEN, &pathlen);

    /*
     * Don't allow empty pathnames.
     * POSIX.1 requirement: "" is not a vaild file name.
     */
    if (error == 0 && pathlen <= 1)
        error = ENOENT;

    if (error == 0) {
        cache_copy(ncstart, &nd->nl_nch);
        cache_copy(ncroot, &nd->nl_rootnch);
        cache_copy(ncroot, &nd->nl_jailnch);
        nd->nl_cred = crhold(cred);
        nd->nl_td = td;
        nd->nl_flags |= flags;
    } else {
        nlookup_done(nd);
    }
    return(error);
}

#if 0
/*
 * Set a different credential; this credential will be used by future
 * operations performed on nd.nl_open_vp and nlookupdata structure.
 */
void
nlookup_set_cred(struct nlookupdata *nd, struct ucred *cred)
{
        KKASSERT(nd->nl_cred != NULL);

        if (nd->nl_cred != cred) {
                cred = crhold(cred);
                if ((nd->nl_flags & NLC_BORROWCRED) == 0)
                        crfree(nd->nl_cred);
                nd->nl_flags &= ~NLC_BORROWCRED;
                nd->nl_cred = cred;
        }
}
#endif

/*
 * Cleanup a nlookupdata structure after we are through with it.  This may
 * be called on any nlookupdata structure initialized with nlookup_init().
 * Calling nlookup_done() is mandatory in all cases except where nlookup_init()
 * returns an error, even if as a consumer you believe you have taken all
 * dynamic elements out of the nlookupdata structure.
 */
void
nlookup_done(struct nlookupdata *nd)
{
    if (nd->nl_nch.ncp) {
        if (nd->nl_flags & NLC_NCPISLOCKED)
            cache_unlock(&nd->nl_nch);
        cache_drop_and_cache(&nd->nl_nch, nd->nl_elmno);
    }
    nd->nl_flags &= ~NLC_NCPISLOCKED;
    if (nd->nl_rootnch.ncp)
        cache_drop_and_cache(&nd->nl_rootnch, 0);
    if (nd->nl_jailnch.ncp)
        cache_drop_and_cache(&nd->nl_jailnch, 0);
    if ((nd->nl_flags & NLC_HASBUF) && nd->nl_path) {
        objcache_put(namei_oc, nd->nl_path);
        nd->nl_path = NULL;
    }
    if (nd->nl_cred) {
        if ((nd->nl_flags & NLC_BORROWCRED) == 0)
            crfree(nd->nl_cred);
        nd->nl_cred = NULL;
        nd->nl_flags &= ~NLC_BORROWCRED;
    }
    if (nd->nl_open_vp) {
        if (nd->nl_flags & NLC_LOCKVP) {
                vn_unlock(nd->nl_open_vp);
                nd->nl_flags &= ~NLC_LOCKVP;
        }
        vn_close(nd->nl_open_vp, nd->nl_vp_fmode, NULL);
        nd->nl_open_vp = NULL;
    }
    if (nd->nl_dvp) {
        vrele(nd->nl_dvp);
        nd->nl_dvp = NULL;
    }
    nd->nl_flags = 0;   /* clear remaining flags (just clear everything) */
    nd->nl_basench = NULL;
}

/*
 * Works similarly to nlookup_done() when nd initialized with
 * nlookup_init_at().
 */
void
nlookup_done_at(struct nlookupdata *nd, struct file *fp)
{
        nlookup_done(nd);
        if (fp != NULL)
                fdrop(fp);
}

void
nlookup_zero(struct nlookupdata *nd)
{
        bzero(nd, sizeof(struct nlookupdata));
}

/*
 * Simple all-in-one nlookup.  Returns a locked namecache structure or NULL
 * if an error occured. 
 *
 * Note that the returned ncp is not checked for permissions, though VEXEC
 * is checked on the directory path leading up to the result.  The caller
 * must call naccess() to check the permissions of the returned leaf.
 */
struct nchandle
nlookup_simple(const char *str, enum uio_seg seg,
               int niflags, int *error)
{
    struct nlookupdata nd;
    struct nchandle nch;

    *error = nlookup_init(&nd, str, seg, niflags);
    if (*error == 0) {
            if ((*error = nlookup(&nd)) == 0) {
                    nch = nd.nl_nch;    /* keep hold ref from structure */
                    cache_zero(&nd.nl_nch); /* and NULL out */
            } else {
                    cache_zero(&nch);
            }
            nlookup_done(&nd);
    } else {
            cache_zero(&nch);
    }
    return(nch);
}

/*
 * Returns non-zero if the path element is the last element
 */
static
int
islastelement(const char *ptr)
{
        while (*ptr == '/')
                ++ptr;
        return (*ptr == 0);
}

/*
 * Returns non-zero if we need to lock the namecache element
 * exclusively.  Unless otherwise requested by NLC_SHAREDLOCK,
 * the last element of the namecache lookup will be locked
 * exclusively.
 *
 * O_CREAT or O_TRUNC need the last element to be locked exlcusively.
 * Intermediate elements are always locked shared.
 *
 * NOTE: Even if we return on-zero, an unresolved namecache record
 *       will always be locked exclusively.
 */
static __inline
int
wantsexcllock(struct nlookupdata *nd, int last_element)
{
        if ((nd->nl_flags & NLC_SHAREDLOCK) == 0)
                return(last_element);
        return 0;
}


/*
 * Do a generic nlookup.  Note that the passed nd is not nlookup_done()'d
 * on return, even if an error occurs.  If no error occurs or NLC_CREATE
 * is flagged and ENOENT is returned, then the returned nl_nch is always
 * referenced and locked exclusively.
 *
 * WARNING: For any general error other than ENOENT w/NLC_CREATE, the
 *          the resulting nl_nch may or may not be locked and if locked
 *          might be locked either shared or exclusive.
 *
 * Intermediate directory elements, including the current directory, require
 * execute (search) permission.  nlookup does not examine the access 
 * permissions on the returned element.
 *
 * If NLC_CREATE is set the last directory must allow node creation,
 * and an error code of 0 will be returned for a non-existant
 * target (not ENOENT).
 *
 * If NLC_RENAME_DST is set the last directory mut allow node deletion,
 * plus the sticky check is made, and an error code of 0 will be returned
 * for a non-existant target (not ENOENT).
 *
 * If NLC_DELETE is set the last directory mut allow node deletion,
 * plus the sticky check is made.
 *
 * If NLC_REFDVP is set nd->nl_dvp will be set to the directory vnode
 * of the returned entry.  The vnode will be referenced but not locked.
 *
 * IF THE PATH REPRESENTS A MOUNT POINT CROSSING THEN NLC_REFDVP WILL SET
 * NL_DVP TO NULL AND RETURN NO ERROR (ERROR == 0), allowing the operation
 * to return up the stack.  The nch will only be referenced and not locked.
 * High level code must check this case and do the right thing since,
 * typically, it means things like 'mkdir' should fail with EEXIST.  For
 * example 'mkdir /var/cache' where /var/cache is a null-mount from
 * /build/var.cache, needs to return EEXIST rather than a mount-crossing
 * failure.
 *
 * NOTE: As an optimization we attempt to obtain a shared namecache lock
 *       on any intermediate elements.  On success, the returned element
 *       is ALWAYS locked exclusively.
 *
 * NOTE: If for any reason the nc_generation number of the ncp's being
 *       evaluated changes, the lookup is retried.
 */
int
nlookup(struct nlookupdata *nd)
{
    globaldata_t gd = mycpu;
    struct nlcomponent nlc;
    struct nchandle nch;
    struct nchandle nctmp;
    struct mount *mp;
    int wasdotordotdot;
    char *path_reset;
    char *ptr;
    char *nptr;
    int error;
    int len;
    int dflags;
    int hit = 1;
    int saveflag = nd->nl_flags;
    int max_retries = nlookup_max_retries;
    u_int nl_gen;
    u_int nch_gen;
    int gen_changed;
    boolean_t doretry = FALSE;
    boolean_t inretry = FALSE;

    path_reset = NULL;

nlookup_start:

#ifdef KTRACE
    if (KTRPOINT(nd->nl_td, KTR_NAMEI))
        ktrnamei(nd->nl_td->td_lwp, nd->nl_path);
#endif
    bzero(&nlc, sizeof(nlc));

    /*
     * Setup for the loop.  The current working namecache element is
     * always at least referenced.  We lock it as required, but always
     * return a locked, resolved namecache entry.
     */
    nd->nl_loopcnt = 0;
    nd->nl_dir_error = 0;
    if (nd->nl_dvp) {
        vrele(nd->nl_dvp);
        nd->nl_dvp = NULL;
    }
    ptr = nd->nl_path;

    nl_gen = nd->nl_nch.ncp ? nd->nl_nch.ncp->nc_generation : 0;
    nl_gen &= ~3;
    gen_changed = 0;

    /*
     * Loop on the path components.  At the top of the loop nd->nl_nch
     * is ref'd and unlocked and represents our current position.
     */
    for (;;) {
        int last_element;

        ++nd->nl_elmno;
        KKASSERT((nd->nl_flags & NLC_NCPISLOCKED) == 0);

        /*
         * Check if the root directory should replace the current
         * directory.  This is done at the start of a translation
         * or after a symbolic link has been found.  In other cases
         * ptr will never be pointing at a '/'.
         */
        if (*ptr == '/') {
            do {
                ++ptr;
            } while (*ptr == '/');

            /*
             * We might already be at the root as a pre-optimization
             */
            if (nd->nl_nch.mount != nd->nl_rootnch.mount ||
                nd->nl_nch.ncp != nd->nl_rootnch.ncp) {
                cache_drop_and_cache(&nd->nl_nch, 0);
                cache_copy(&nd->nl_rootnch, &nd->nl_nch);
                nl_gen = nd->nl_nch.ncp->nc_generation & ~3;
            }

            /*
             * Fast-track termination.  There is no parent directory of
             * the root in the same mount from the point of view of
             * the caller so return EACCES if NLC_REFDVP is specified,
             * and EEXIST if NLC_CREATE is also specified.
             * e.g. 'rmdir /' or 'mkdir /' are not allowed.
             */
            if (*ptr == 0) {
                if (nd->nl_flags & NLC_REFDVP)
                        error = (nd->nl_flags & NLC_CREATE) ? EEXIST : EACCES;
                else
                        error = 0;
                nd->nl_flags |= NLC_NCPISLOCKED;
                cache_lock_maybe_shared(&nd->nl_nch,
                                        wantsexcllock(nd, islastelement(ptr)));
                break;
            }
            continue;
        }

        /*
         * Pre-calculate next path component so we can check whether the
         * current component directory is the last directory in the path
         * or not.
         */
        for (nptr = ptr; *nptr && *nptr != '/'; ++nptr)
                ;

        /*
         * nd->nl_nch is referenced and not locked here.
         *
         * Check directory search permissions.  This will load dflags to
         * obtain directory-special permissions to be checked along with the
         * last component.
         *
         * We only need to pass-in &dflags for the second-to-last component.
         * Optimize by passing-in NULL for any prior components, which may
         * allow the code to bypass the naccess() call.
         *
         * naccess() is optimized to avoid having to lock the nch or get
         * the related vnode if cached perms are sufficient.
         */
        dflags = 0;
        if (*nptr == '/' || (saveflag & NLC_MODIFYING_MASK) == 0) {
            error = naccess(nd, &nd->nl_nch, &nl_gen, NLC_EXEC,
                            nd->nl_cred, NULL, 0);
        } else {
            error = naccess(nd, &nd->nl_nch, &nl_gen, NLC_EXEC,
                            nd->nl_cred, &dflags, 0);
        }
        if (error) {
            if (keeperror(nd, error))
                break;
            error = 0;
        }

        /*
         * Extract the next (or last) path component.  Path components are
         * limited to 255 characters.
         */
        nlc.nlc_nameptr = ptr;
        nlc.nlc_namelen = nptr - ptr;
        ptr = nptr;
        if (nlc.nlc_namelen >= 256) {
            error = ENAMETOOLONG;
            break;
        }
        last_element = islastelement(nptr);

        /*
         * Lookup the path component in the cache, creating an unresolved
         * entry if necessary.  We have to handle "." and ".." as special
         * cases.
         *
         * When handling ".." we have to detect a traversal back through a
         * mount point.   If we are at the root, ".." just returns the root.
         *
         * When handling "." or ".." we also have to recalculate dflags
         * since our dflags will be for some sub-directory instead of the
         * parent dir.
         *
         * This subsection returns a referenced and possibly locked 'nch'.
         * The locking status is based on the last_element flag.
         *
         * The namecache topology is not allowed to be disconnected, so 
         * encountering a NULL parent will generate EINVAL.  This typically
         * occurs when a directory is removed out from under a process.
         *
         * WARNING! The unlocking of nd->nl_nch is sensitive code.
         */
        KKASSERT((nd->nl_flags & NLC_NCPISLOCKED) == 0);

        if (nlc.nlc_namelen == 1 && nlc.nlc_nameptr[0] == '.') {
            if (last_element) {
                cache_get_maybe_shared(&nd->nl_nch, &nch,
                                       wantsexcllock(nd, 1));
            } else {
                cache_copy(&nd->nl_nch, &nch);
            }
            nch_gen = nch.ncp->nc_generation & ~3;
            wasdotordotdot = 1;
        } else if (nlc.nlc_namelen == 2 && 
                   nlc.nlc_nameptr[0] == '.' && nlc.nlc_nameptr[1] == '.') {
            if (nd->nl_nch.mount == nd->nl_rootnch.mount &&
                nd->nl_nch.ncp == nd->nl_rootnch.ncp
            ) {
                /*
                 * ".." at the root returns the root
                 */
                if (last_element) {
                    cache_get_maybe_shared(&nd->nl_nch, &nch,
                                           wantsexcllock(nd, 1));
                } else {
                    cache_copy(&nd->nl_nch, &nch);
                }
            } else {
                /*
                 * Locate the parent ncp.  If we are at the root of a
                 * filesystem mount we have to skip to the mounted-on
                 * point in the underlying filesystem.
                 *
                 * Expect the parent to always be good since the
                 * mountpoint doesn't go away.  XXX hack.  cache_get()
                 * requires the ncp to already have a ref as a safety.
                 *
                 * However, a process which has been broken out of a chroot
                 * will wind up with a NULL parent if it tries to '..' above
                 * the real root, deal with the case.  Note that this does
                 * not protect us from a jail breakout, it just stops a panic
                 * if the jail-broken process tries to '..' past the real
                 * root.
                 */
                nctmp = nd->nl_nch;
                while (nctmp.ncp == nctmp.mount->mnt_ncmountpt.ncp) {
                        nctmp = nctmp.mount->mnt_ncmounton;
                        if (nctmp.ncp == NULL)
                                break;
                }
                if (nctmp.ncp == NULL) {
                        if (curthread->td_proc) {
                                kprintf("vfs_nlookup: '..' traverse broke "
                                        "jail: pid %d (%s)\n",
                                        curthread->td_proc->p_pid,
                                        curthread->td_comm);
                        }
                        nctmp = nd->nl_rootnch;
                } else {
                        nctmp.ncp = nctmp.ncp->nc_parent;
                }
                if (last_element) {
                    cache_get_maybe_shared(&nctmp, &nch,
                                           wantsexcllock(nd, 1));
                } else {
                    cache_copy(&nctmp, &nch);
                }
            }
            nch_gen = nch.ncp->nc_generation & ~3;
            wasdotordotdot = 2;
        } else {
            /*
             * Quickly lookup the component.  If we can't find it, then
             * slowly lookup and resolve the component.
             */
            if (last_element) {
                    error = cache_nlookup_maybe_shared(&nd->nl_nch, &nlc,
                                                       wantsexcllock(nd, 1),
                                                       &nch);
            } else {
                    nch = cache_nlookup_nonlocked(&nd->nl_nch, &nlc);
                    if (nch.ncp == NULL)
                        error = EWOULDBLOCK;
            }

            /*
             * At this point the only possible error is EWOULDBLOCK.
             *
             * If no error nch is set and referenced, and then also locked
             * according to last_element.  For EWOULDBLOCK nch is not set.
             * For any other error nch is set and referenced, but not locked.
             *
             * On EWOULDBLOCK the ncp may be unresolved (if not locked it can
             * become unresolved at any time, but we don't care at this time).
             */
            if (error == EWOULDBLOCK) {
                nch = cache_nlookup(&nd->nl_nch, &nlc);
                if (nch.ncp->nc_flag & NCF_UNRESOLVED)
                    hit = 0;
                for (;;) {
                    error = cache_resolve(&nch, &nch_gen, nd->nl_cred);
                    if (error != EAGAIN &&
                        (nch.ncp->nc_flag & NCF_DESTROYED) == 0) {
                            if (error == ESTALE) {
                                if (!inretry)
                                    error = ENOENT;
                                doretry = TRUE;
                            }
                            if (last_element == 0)
                                    cache_unlock(&nch);
                            break;
                    }
                    kprintf("[diagnostic] nlookup: relookup %*.*s\n",
                            nch.ncp->nc_nlen, nch.ncp->nc_nlen,
                            nch.ncp->nc_name);
                    cache_put(&nch);
                    nch = cache_nlookup(&nd->nl_nch, &nlc);
                }
            }
            nch_gen = nch.ncp->nc_generation & ~3;
            wasdotordotdot = 0;
        }

        /*
         * If the component is "." or ".." our dflags no longer represents
         * the parent directory and we have to explicitly look it up.
         *
         * Expect the parent to be good since nch is locked.
         *
         * nch will continue to be valid even if an error occurs after this
         * point.
         */
        if (wasdotordotdot && error == 0) {
            struct nchandle par;

            dflags = 0;
            if (last_element == 0)
                cache_lock_maybe_shared(&nch, wantsexcllock(nd, 0));

            if ((par.ncp = nch.ncp->nc_parent) != NULL) {
                u_int dummy_gen = 0;

                par.mount = nch.mount;
                cache_hold(&par);
                error = naccess(nd, &par, &dummy_gen, 0, nd->nl_cred, &dflags, 0);
                cache_drop_and_cache(&par, nd->nl_elmno - 1);
                if (error) {
                    if (!keeperror(nd, error))
                        error = 0;
                    if (error == EINVAL) {
                        kprintf("nlookup (%s): trailing . or .. retry on %s\n",
                                curthread->td_comm, nd->nl_path);
                        doretry = TRUE;
                    }
                }
            }

            if (last_element == 0)
                cache_unlock(&nch);
        }

        /*
         * [end of subsection]
         *
         * nch is referenced and locked according to (last_element).
         * nd->nl_nch is unlocked and referenced.
         * nl_gen and nch_gen are both set.
         */
        KKASSERT((nd->nl_flags & NLC_NCPISLOCKED) == 0);

        /*
         * Resolve the namespace if necessary.  The ncp returned by
         * cache_nlookup() is referenced, and also locked according
         * to last_element.
         *
         * XXX neither '.' nor '..' should return EAGAIN since they were
         * previously resolved and thus cannot be newly created ncp's.
         */
        if (nch.ncp->nc_flag & NCF_UNRESOLVED) {
            if (last_element == 0)
                cache_lock(&nch);
            hit = 0;
            error = cache_resolve(&nch, &nch_gen, nd->nl_cred);
            if (error == ESTALE) {
                if (!inretry)
                    error = ENOENT;
                doretry = TRUE;
            }
            if (last_element == 0)
                cache_unlock(&nch);
            KKASSERT(error != EAGAIN);
        } else {
            error = nch.ncp->nc_error;
        }

        /*
         * Early completion.  ENOENT is not an error if this is the last
         * component and NLC_CREATE or NLC_RENAME (rename target) was
         * requested.  Note that ncp->nc_error is left as ENOENT in that
         * case, which we check later on.
         *
         * Also handle invalid '.' or '..' components terminating a path
         * for a create/rename/delete.  The standard requires this and pax
         * pretty stupidly depends on it.
         */
        if (last_element) {
            if (error == ENOENT &&
                (nd->nl_flags & (NLC_CREATE | NLC_RENAME_DST)))
            {
                if (nd->nl_flags & NLC_NFS_RDONLY) {
                        error = EROFS;
                } else {
                        error = naccess(nd, &nch, &nch_gen,
                                        nd->nl_flags | dflags,
                                        nd->nl_cred, NULL, last_element);
                }
            }
            if (error == 0 && wasdotordotdot &&
                (nd->nl_flags & (NLC_CREATE | NLC_DELETE |
                                 NLC_RENAME_SRC | NLC_RENAME_DST)))
            {
                /*
                 * POSIX junk
                 */
                if (nd->nl_flags & NLC_CREATE)
                        error = EEXIST;
                else if (nd->nl_flags & NLC_DELETE)
                        error = (wasdotordotdot == 1) ? EINVAL : ENOTEMPTY;
                else
                        error = EINVAL;
            }
        }

        /*
         * Early completion on error.
         */
        if (error) {
            if (last_element)
                    cache_unlock(&nch);
            cache_drop_and_cache(&nch, nd->nl_elmno);
            break;
        }

        /*
         * If the element is a symlink and it is either not the last
         * element or it is the last element and we are allowed to
         * follow symlinks, resolve the symlink.
         */
        if ((nch.ncp->nc_flag & NCF_ISSYMLINK) &&
            (*ptr || (nd->nl_flags & NLC_FOLLOW))
        ) {
            if (nd->nl_loopcnt++ >= MAXSYMLINKS) {
                error = ELOOP;
                if (last_element)
                        cache_unlock(&nch);
                cache_drop_and_cache(&nch, nd->nl_elmno);
                break;
            }

            /*
             * Check for a generation change.
             *
             * NOTE: On generation changes we must at a minimum cycle
             *       the lock.  Here we get or have the lock so we are
             *       ok.
             */
            if (last_element == 0)
                cache_lock_maybe_shared(&nch, 1);

            if ((nch.ncp->nc_generation - nch_gen) & ~1) {
                if (nlookup_debug & 1) {
                    kprintf("nlookup: symlink: GEN CHANGE %d\n",
                            (nch.ncp->nc_generation - nch_gen));
                }
                gen_changed = 1;
            }

            error = nreadsymlink(nd, &nch, &nlc);
            cache_put(&nch);
            if (error)
                break;

            /*
             * Concatenate trailing path elements onto the returned symlink.
             * Note that if the path component (ptr) is not exhausted, it
             * will being with a '/', so we do not have to add another one.
             *
             * The symlink may not be empty.
             */
            len = strlen(ptr);
            if (nlc.nlc_namelen == 0 || nlc.nlc_namelen + len >= MAXPATHLEN) {
                error = nlc.nlc_namelen ? ENAMETOOLONG : ENOENT;
                objcache_put(namei_oc, nlc.nlc_nameptr);
                break;
            }
            bcopy(ptr, nlc.nlc_nameptr + nlc.nlc_namelen, len + 1);

            if (path_reset) {
                if (nd->nl_flags & NLC_HASBUF)
                    objcache_put(namei_oc, nd->nl_path);
            } else {
                path_reset = nd->nl_path;
            }
            nd->nl_path = nlc.nlc_nameptr;
            nd->nl_flags |= NLC_HASBUF;
            ptr = nd->nl_path;
            /* nl_gen has not changed */

            /*
             * Go back up to the top to resolve any initial '/'s in the
             * symlink.
             */
            continue;
        }
        
        /*
         * If the element is a directory and we are crossing a mount point,
         * Locate the mount.
         */
        while ((nch.ncp->nc_flag & NCF_ISMOUNTPT) && 
            (nd->nl_flags & NLC_NOCROSSMOUNT) == 0 &&
            (mp = cache_findmount(&nch)) != NULL
        ) {
            struct vnode *tdp;
            int vfs_do_busy = 0;

            /*
             * VFS must be busied before the namecache entry is locked,
             * but we don't want to waste time calling vfs_busy() if the
             * mount point is already resolved.
             */
again:
            /*
             * Check for a generation change.
             *
             * NOTE: On generation changes we must at a minimum cycle
             *       the lock.  So get and release the lock if we
             *       do not have it.
             */
            if ((nch.ncp->nc_generation - nch_gen) & ~1) {
                if (last_element == 0) {
                    cache_lock_maybe_shared(&nch, 1);
                    cache_unlock(&nch);
                }
                if (nlookup_debug & 1) {
                    kprintf("nlookup: mountpt: GEN CHANGE %d\n",
                            (nch.ncp->nc_generation - nch_gen));
                }
                gen_changed = 1;
            }
            if (last_element)
                    cache_unlock(&nch);
            cache_drop_and_cache(&nch, nd->nl_elmno);

            if (vfs_do_busy) {
                while (vfs_busy(mp, 0)) {
                    if (mp->mnt_kern_flag & MNTK_UNMOUNT) {
                        kprintf("nlookup: warning umount race avoided\n");
                        cache_dropmount(mp);
                        error = EBUSY;
                        vfs_do_busy = 0;
                        goto double_break;
                    }
                }
            }

            /*
             * We don't need to lock the nch unless the entry is unresolved
             * or this is the last element.
             */
            if (last_element)
                cache_get_maybe_shared(&mp->mnt_ncmountpt, &nch,
                                       wantsexcllock(nd, 1));
            else
                cache_copy(&mp->mnt_ncmountpt, &nch);
            nch_gen = nch.ncp->nc_generation & ~3;

            if (nch.ncp->nc_flag & NCF_UNRESOLVED) {
                if (last_element == 0)
                    cache_lock(&nch);
                if (nch.ncp->nc_flag & NCF_UNRESOLVED) {
                    if (vfs_do_busy == 0) {
                        vfs_do_busy = 1;
                        if (last_element == 0)
                            cache_unlock(&nch);
                        goto again;
                    }
                    error = VFS_ROOT(mp, &tdp);
                    vfs_unbusy(mp);
                    vfs_do_busy = 0;
                    if (keeperror(nd, error)) {
                        cache_dropmount(mp);
                        if (last_element == 0)
                            cache_unlock(&nch);
                        break;
                    }
                    if (error == 0) {
                        cache_setvp(&nch, tdp);
                        nch_gen = nch.ncp->nc_generation & ~3;
                        vput(tdp);
                    }
                }
                if (last_element == 0)
                    cache_unlock(&nch);
            }
            if (vfs_do_busy)
                vfs_unbusy(mp);
            cache_dropmount(mp);
        }

        /*
         * Break out on error
         */
        if (keeperror(nd, error)) {
            if (last_element)
                    cache_unlock(&nch);
            cache_drop_and_cache(&nch, nd->nl_elmno);
double_break:
            break;
        }
            
        /*
         * Skip any slashes to get to the next element.  If there 
         * are any slashes at all the current element must be a
         * directory or, in the create case, intended to become a directory.
         * If it isn't we break without incrementing ptr and fall through
         * to the failure case below.
         */
        while (*ptr == '/') {
            if ((nch.ncp->nc_flag & NCF_ISDIR) == 0 && 
                !(nd->nl_flags & NLC_WILLBEDIR)
            ) {
                break;
            }
            ++ptr;
        }

        /*
         * Continuation case: additional elements and the current
         * element is a directory.
         */
        if (*ptr && (nch.ncp->nc_flag & NCF_ISDIR)) {
            /*
             * Check for a generation change.
             *
             * NOTE: On generation changes we must at a minimum cycle
             *       the lock.  So get and release the lock if we
             *       do not have it.
             */
            if ((nch.ncp->nc_generation - nch_gen) & ~1) {
                if (last_element == 0) {
                    cache_lock_maybe_shared(&nch, 1);
                    cache_unlock(&nch);
                }
                if (nlookup_debug & 1) {
                    kprintf("nlookup: next: GEN CHANGE %d\n",
                            (nch.ncp->nc_generation - nch_gen));
                }
                gen_changed = 1;
            }
            cache_drop_and_cache(&nd->nl_nch, nd->nl_elmno);
            if (last_element)
                    cache_unlock(&nch);
            /*nchislocked = 0; not needed */
            KKASSERT((nd->nl_flags & NLC_NCPISLOCKED) == 0);
            nd->nl_nch = nch;
            nl_gen = nch_gen;
            continue;
        }

        /*
         * Check for a generation change.
         *
         * NOTE: On generation changes we must at a minimum cycle
         *           the lock.  So get and release the lock if we
         *           do not have it.
         */
        if ((nch.ncp->nc_generation - nch_gen) & ~1) {
            if (nlookup_debug & 1) {
                if (last_element == 0) {
                    cache_lock_maybe_shared(&nch, 1);
                    cache_unlock(&nch);
                }
                kprintf("nlookup: final: GEN CHANGE %d\n",
                        (nch.ncp->nc_generation - nch_gen));
                gen_changed = 1;
            }
        }

        /*
         * Failure case: additional elements and the current element
         * is not a directory
         */
        if (*ptr) {
            if (last_element)
                    cache_unlock(&nch);
            cache_drop_and_cache(&nch, nd->nl_elmno);
            error = ENOTDIR;
            break;
        }

        /*
         * Successful lookup of last element.
         *
         * Check permissions if the target exists.  If the target does not
         * exist directory permissions were already tested in the early
         * completion code above.
         *
         * nd->nl_flags will be adjusted on return with NLC_APPENDONLY
         * if the file is marked append-only, and NLC_STICKY if the directory
         * containing the file is sticky.
         */
        KKASSERT(last_element);

        if (nch.ncp->nc_vp && (nd->nl_flags & NLC_ALLCHKS)) {
            error = naccess(nd, &nch, &nch_gen, nd->nl_flags | dflags,
                            nd->nl_cred, NULL, 1);
            if (keeperror(nd, error)) {
                cache_put(&nch);
                break;
            }
        }

        /*
         * Termination: no more elements.
         *
         * Check to see if the immediate parent has been destroyed.  This race
         * can occur because the element lookup must temporarily unlock
         * the parent.  If so, do a retry.
         */
        if (nch.ncp->nc_parent &&
            (nch.ncp->nc_parent->nc_flag & NCF_DESTROYED)) {
                doretry = TRUE;
        }

        /*
         * Termination: no more elements.
         *
         * If NLC_REFDVP is set acquire a referenced parent dvp.  Typically
         * used for mkdir/mknod/ncreate/nremove/unlink/rename.
         *
         * If a mount-point transition occurs due to ncp being a mount point,
         * or a null-mount, nl_dvp will be set to NULL and an error code of
         * 0 will be returned.  A NULL nc_parent is not necessarily the only
         * indication of a mount-point as null-mounts will also tend to have
         * a non-null nc_parent.
         *
         * nch is locked, standard lock order for the namecache is
         * child-to-parent so we can safely lock its parent.  We can
         * just use cache_dvpref().
         */
        if ((nd->nl_flags & NLC_REFDVP) &&
            (doretry == FALSE || inretry == TRUE)) {
                if (nch.ncp->nc_parent) {
                        error = cache_resolve_dvp(&nch, nd->nl_cred,
                                                  &nd->nl_dvp);
                        if (error) {
                                if (nlookup_debug & 1) {
                                    kprintf("Parent directory lost during "
                                            "nlookup: %s/%s (%08x/%08x)\n",
                                            nch.ncp->nc_parent->nc_name,
                                            nch.ncp->nc_name,
                                            nch.ncp->nc_parent->nc_flag,
                                            nch.ncp->nc_flag);
                                }
                                cache_put(&nch);
                                error = EINVAL;
                                break;
                        }

                        /*
                         * Mount-point, nl_dvp should remain NULL, error 0,
                         * caller won't be able to use the results so leave
                         * the ncp referenced but unlocked.
                         */
                        if (nd->nl_dvp == NULL) {
                                cache_put(&nch);
                                break;
                        }

                        /*
                         * Good directory, fall through to drop-and-cache
                         * below
                         */
                        /* */
                } else {
                        /*
                         * Mount-point, nl_dvp should remain NULL, error 0,
                         * caller won't be able to use the results so leave
                         * the ncp referenced but unlocked.
                         */
                        error = 0;
                        cache_put(&nch);
                        break;
                }
        }

        /*
         * ncp left with lock+ref on break, set NLC_NCPISLOCKED flag
         */
        cache_drop_and_cache(&nd->nl_nch, nd->nl_elmno);
        nd->nl_nch = nch;
        nd->nl_flags |= NLC_NCPISLOCKED;
        nl_gen = nch_gen;
        error = 0;
        break;
    }

    /*
     * Force a retry (up to max_retries) if nl_gen is incorrect
     *
     * NOTE: On generation changes we must at a minimum cycle
     *       the lock.   In this case we have one so we are ok.
     */
    if (nd->nl_nch.ncp && (nd->nl_nch.ncp->nc_generation - nl_gen) & ~1) {
        if (nlookup_debug & 1) {
            kprintf("nlookup: DONE error %d: GEN CHANGE ON \"%s\" "
                    "%d (retries %d)\n",
                    error,
                    nd->nl_nch.ncp->nc_name,
                    (nd->nl_nch.ncp->nc_generation - nl_gen),
                    max_retries);
        }
        gen_changed = 1;
    }
    if (gen_changed) {
        if (max_retries) {
            --max_retries;
            doretry = TRUE;
            inretry = FALSE;
        } else {
            error = EINVAL;
        }
    }

    /*
     * We are done / or possibly retry
     */
    if (hit)
        ++gd->gd_nchstats->ncs_longhits;
    else
        ++gd->gd_nchstats->ncs_longmiss;

    if (nd->nl_flags & NLC_NCPISLOCKED)
        KKASSERT(cache_lockstatus(&nd->nl_nch) > 0);

    /*
     * Reset nd->nl_path if necessary (due to softlinks).  We want to return
     * nl_path to its original state before retrying or returning.
     */
    if (path_reset) {
        if (nd->nl_flags & NLC_HASBUF) {
            objcache_put(namei_oc, nd->nl_path);
            nd->nl_flags &= ~NLC_HASBUF;
        }
        nd->nl_path = path_reset;
        nd->nl_flags |= saveflag & NLC_HASBUF;
        path_reset = NULL;
    }

    /*
     * Retry the whole thing if doretry flag is set, but only once.
     *
     * autofs(5) may mount another filesystem under its root directory
     * while resolving a path.
     *
     * NFS might return ESTALE
     */
    if (doretry && !inretry) {
        if (nlookup_debug & 2)
            kprintf("nlookup: errno %d retry %s\n", error, nd->nl_path);
        inretry = TRUE;

        /*
         * Clean up nd->nl_nch and reset to base directory
         */
        if (nd->nl_flags & NLC_NCPISLOCKED) {
                cache_unlock(&nd->nl_nch);
                nd->nl_flags &= ~NLC_NCPISLOCKED;
        }
        cache_drop(&nd->nl_nch);
        cache_copy(nd->nl_basench, &nd->nl_nch);

        nd->nl_elmno = 0;
        nd->nl_flags |= saveflag;

        goto nlookup_start;
    }

    /*
     * NOTE: If NLC_CREATE was set the ncp may represent a negative hit
     * (ncp->nc_error will be ENOENT), but we will still return an error
     * code of 0.
     */
    return(error);
}

/*
 * Resolve a mount point's glue ncp.  This ncp connects creates the illusion
 * of continuity in the namecache tree by connecting the ncp related to the
 * vnode under the mount to the ncp related to the mount's root vnode.
 *
 * If no error occured a locked, ref'd ncp is stored in *ncpp.
 */
int
nlookup_mp(struct mount *mp, struct nchandle *nch)
{
    struct vnode *vp;
    int error;

    error = 0;
    cache_get(&mp->mnt_ncmountpt, nch);
    if (nch->ncp->nc_flag & NCF_UNRESOLVED) {
        while (vfs_busy(mp, 0))
            ;
        error = VFS_ROOT(mp, &vp);
        vfs_unbusy(mp);
        if (error) {
            cache_put(nch);
        } else {
            cache_setvp(nch, vp);
            vput(vp);
        }
    }
    return(error);
}

/*
 * Read the contents of a symlink, allocate a path buffer out of the
 * namei_oc and initialize the supplied nlcomponent with the result.
 *
 * If an error occurs no buffer will be allocated or returned in the nlc.
 */
int
nreadsymlink(struct nlookupdata *nd, struct nchandle *nch, 
                struct nlcomponent *nlc)
{
    struct vnode *vp;
    struct iovec aiov;
    struct uio auio;
    int linklen;
    int error;
    char *cp;

    nlc->nlc_nameptr = NULL;
    nlc->nlc_namelen = 0;
    if (nch->ncp->nc_vp == NULL)
        return(ENOENT);
    if ((error = cache_vget(nch, nd->nl_cred, LK_SHARED, &vp)) != 0)
        return(error);
    cp = objcache_get(namei_oc, M_WAITOK);
    aiov.iov_base = cp;
    aiov.iov_len = MAXPATHLEN;
    auio.uio_iov = &aiov;
    auio.uio_iovcnt = 1;
    auio.uio_offset = 0;
    auio.uio_rw = UIO_READ;
    auio.uio_segflg = UIO_SYSSPACE;
    auio.uio_td = nd->nl_td;
    auio.uio_resid = MAXPATHLEN - 1;
    error = VOP_READLINK(vp, &auio, nd->nl_cred);
    if (error)
        goto fail;
    linklen = MAXPATHLEN - 1 - auio.uio_resid;
    if (varsym_enable) {
        linklen = varsymreplace(cp, linklen, MAXPATHLEN - 1);
        if (linklen < 0) {
            error = ENAMETOOLONG;
            goto fail;
        }
    }
    cp[linklen] = 0;
    nlc->nlc_nameptr = cp;
    nlc->nlc_namelen = linklen;
    vput(vp);
    return(0);
fail:
    objcache_put(namei_oc, cp);
    vput(vp);
    return(error);
}

/*
 * Check access [XXX cache vattr!] [XXX quota]
 *
 * Generally check the NLC_* access bits.   All specified bits must pass
 * for this function to return 0.
 *
 * The file does not have to exist when checking NLC_CREATE or NLC_RENAME_DST
 * access, otherwise it must exist.  No error is returned in this case.
 *
 * The file must not exist if NLC_EXCL is specified.
 *
 * Directory permissions in general are tested for NLC_CREATE if the file
 * does not exist, NLC_DELETE if the file does exist, and NLC_RENAME_DST
 * whether the file exists or not.
 *
 * The directory sticky bit is tested for NLC_DELETE and NLC_RENAME_DST,
 * the latter is only tested if the target exists.
 *
 * The passed ncp must be referenced and locked.  If it is already resolved
 * it may be locked shared but otherwise should be locked exclusively.
 */

#define S_WXOK_MASK     (S_IRUSR|S_IXUSR|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH)
#define S_XOK_MASK      (S_IXUSR|S_IXGRP|S_IXOTH)

static int
naccess(struct nlookupdata *nd, struct nchandle *nch, u_int *genp, int nflags,
        struct ucred *cred, int *nflagsp, int nchislocked)
{
    struct vnode *vp;
    struct vattr_lite lva;
    struct namecache *ncp;
    int error;
    int cflags;

    ncp = nch->ncp;

again:
    /*
     * We need a resolved entry.  If the entry is not resolved we need
     * to lock and resolve it.  If it is already resolved, our ref should
     * prevent normal evictions (as long as we tested the lock race above).
     *
     * If the ncp was locked by the caller and left unresolved, it must
     * have been locked exclusively.
     */
    if (ncp->nc_flag & NCF_UNRESOLVED) {
        if (nchislocked == 0) {
            cache_lock(nch);
            nchislocked = 2;
        }
        cache_resolve(nch, genp, cred);
        ncp = nch->ncp;
    }
    error = ncp->nc_error;

    /*
     * Only unresolved entries should return this error (though maybe
     * in-filesystem sockets can too).   XXX check filetype for VSOCK.
     */
    if (error == ENOTCONN) {
        if (nchislocked == 0) {
            if (nlookup_debug & 4) {
                kprintf("ncp %p %08x %d %s: Warning, unexpected state, "
                        "forcing lock\n",
                        ncp, ncp->nc_flag, ncp->nc_error, ncp->nc_name);
                print_backtrace(-1);
            }
            cache_lock(nch);
            nchislocked = 2;
            goto again;
        }
        if (nlookup_debug & 4) {
            kprintf("ncp %p %08x %d %s: Warning, unexpected state\n",
                    ncp, ncp->nc_flag, ncp->nc_error, ncp->nc_name);
            print_backtrace(-1);
        }
    }

    /*
     * Directory permissions checks.  Silently ignore ENOENT if these
     * tests pass.  It isn't an error.
     *
     * We can safely resolve ncp->nc_parent because ncp is currently
     * locked.
     *
     * We set nl_dir_error if an error occurs checking directory perms
     * for an intermediate directory.
     */
    if (nflags & (NLC_CREATE | NLC_DELETE | NLC_RENAME_SRC | NLC_RENAME_DST)) {
        if (((nflags & NLC_CREATE) && ncp->nc_vp == NULL) ||
            ((nflags & NLC_DELETE) && ncp->nc_vp != NULL) ||
            ((nflags & NLC_RENAME_SRC) && ncp->nc_vp != NULL) ||
            (nflags & NLC_RENAME_DST)
        ) {
            struct nchandle par;

            if (nchislocked == 0) {
                cache_lock_maybe_shared(nch, 0);
                nchislocked = 2;
                goto again;
            }
            if ((par.ncp = ncp->nc_parent) == NULL) {
                if (error != EAGAIN) {
                    error = EINVAL;
                    ++nd->nl_dir_error;
                }
            } else if (error == 0 || error == ENOENT) {
                u_int dummy_gen = 0;

                par.mount = nch->mount;
                cache_hold(&par);
                cache_lock_maybe_shared(&par, 0);
                error = naccess(nd, &par, &dummy_gen, NLC_WRITE, cred, NULL, 1);
                cache_put(&par);
                if (error)
                        ++nd->nl_dir_error;
            }
        }
    }

    /*
     * NLC_EXCL check.  Target file must not exist.
     */
    if (error == 0 && (nflags & NLC_EXCL) && ncp->nc_vp != NULL)
        error = EEXIST;

    /*
     * Try to short-cut the vnode operation for intermediate directory
     * components.  This is a major SMP win because it avoids having
     * to execute a lot of code for intermediate directory components,
     * including shared refs and locks on intermediate directory vnodes.
     *
     * We can only do this if the caller does not need nflagsp.
     */
    if (error == 0 && nflagsp == NULL &&
        nflags == NLC_EXEC && (ncp->nc_flag & NCF_WXOK)) {
        if (nchislocked == 2)
                cache_unlock(nch);
        return 0;
    }

    /*
     * Get the vnode attributes so we can do the rest of our checks.
     *
     * NOTE: We only call naccess_lva() if the target exists.
     */
    if (error == 0) {
        if (nchislocked == 0) {
            cache_lock_maybe_shared(nch, 0);
            nchislocked = 2;
        }
#if 0
        error = cache_vget(nch, cred, LK_SHARED, &vp);
#else
        error = cache_vref(nch, cred, &vp);
#endif
        if (error == ENOENT) {
            /*
             * Silently zero-out ENOENT if creating or renaming
             * (rename target).  It isn't an error.
             */
            if (nflags & (NLC_CREATE | NLC_RENAME_DST))
                error = 0;
        } else if (error == 0) {
            /*
             * Get the vnode attributes and check for illegal O_TRUNC
             * requests and read-only mounts.
             *
             * NOTE: You can still open devices on read-only mounts for
             *       writing.
             *
             * NOTE: creates/deletes/renames are handled by the NLC_WRITE
             *       check on the parent directory above.
             *
             * XXX cache the va in the namecache or in the vnode
             */
            error = VOP_GETATTR_LITE(vp, &lva);
            if (error == 0 && (nflags & NLC_TRUNCATE)) {
                switch(lva.va_type) {
                case VREG:
                case VDATABASE:
                case VCHR:
                case VBLK:
                case VFIFO:
                    break;
                case VDIR:
                    error = EISDIR;
                    break;
                default:
                    error = EINVAL;
                    break;
                }
            }
            if (error == 0 && (nflags & NLC_WRITE) && vp->v_mount &&
                (vp->v_mount->mnt_flag & MNT_RDONLY)
            ) {
                switch(lva.va_type) {
                case VDIR:
                case VLNK:
                case VREG:
                case VDATABASE:
                    error = EROFS;
                    break;
                default:
                    break;
                }
            }
#if 0
            vput(vp);
#else
            vrele(vp);
#endif

            /*
             * Check permissions based on file attributes.  The passed
             * flags (*nflagsp) are modified with feedback based on
             * special attributes and requirements.
             */
            if (error == 0) {
                /*
                 * Adjust the returned (*nflagsp) if non-NULL.
                 */
                if (nflagsp) {
                    if ((lva.va_mode & VSVTX) && lva.va_uid != cred->cr_uid)
                        *nflagsp |= NLC_STICKY;
                    if (lva.va_flags & APPEND)
                        *nflagsp |= NLC_APPENDONLY;
                    if (lva.va_flags & IMMUTABLE)
                        *nflagsp |= NLC_IMMUTABLE;
                }

                /*
                 * NCF_WXOK can be set for world-searchable directories.
                 *
                 * XXX When we implement capabilities this code would also
                 * need a cap check, or only set the flag if there are no
                 * capabilities.
                 */
                cflags = 0;
                if (lva.va_type == VDIR &&
                    (lva.va_mode & S_WXOK_MASK) == S_WXOK_MASK) {
                        cflags |= NCF_WXOK;
                }
                if ((lva.va_mode & S_XOK_MASK) == 0)
                        cflags |= NCF_NOTX;

                /*
                 * Track swapcache management flags in the namecache.
                 *
                 * Calculate the flags based on the current vattr_lite info
                 * and recalculate the inherited flags from the parent
                 * (the original cache linkage may have occurred without
                 * getattrs and thus have stale flags).
                 */
                if (lva.va_flags & SF_NOCACHE)
                        cflags |= NCF_SF_NOCACHE;
                if (lva.va_flags & UF_CACHE)
                        cflags |= NCF_UF_CACHE;
                if (ncp->nc_parent) {
                        if (ncp->nc_parent->nc_flag &
                            (NCF_SF_NOCACHE | NCF_SF_PNOCACHE)) {
                                cflags |= NCF_SF_PNOCACHE;
                        }
                        if (ncp->nc_parent->nc_flag &
                            (NCF_UF_CACHE | NCF_UF_PCACHE)) {
                                cflags |= NCF_UF_PCACHE;
                        }
                }

                /*
                 * We're not supposed to update nc_flag when holding a shared
                 * lock, but we allow the case for certain flags.  Note that
                 * holding an exclusive lock allows updating nc_flag without
                 * atomics.  nc_flag is not allowe to be updated at all unless
                 * a shared or exclusive lock is held.
                 */
                atomic_clear_short(&ncp->nc_flag,
                                   (NCF_SF_NOCACHE | NCF_UF_CACHE |
                                   NCF_SF_PNOCACHE | NCF_UF_PCACHE |
                                   NCF_WXOK | NCF_NOTX) & ~cflags);
                atomic_set_short(&ncp->nc_flag, cflags);

                /*
                 * Process general access.
                 */
                error = naccess_lva(&lva, nflags, cred);
            }
        }
    }
    if (nchislocked == 2)
        cache_unlock(nch);
    return(error);
}

/*
 * Check the requested access against the given vattr using cred.
 */
int
naccess_lva(struct vattr_lite *lvap, int nflags, struct ucred *cred)
{
    int i;
    int vmode;

    /*
     * Test the immutable bit.  Creations, deletions, renames (source
     * or destination) are not allowed.  chown/chmod/other is also not
     * allowed but is handled by SETATTR.  Hardlinks to the immutable
     * file are allowed.
     *
     * If the directory is set to immutable then creations, deletions,
     * renames (source or dest) and hardlinks to files within the directory
     * are not allowed, and regular files opened through the directory may
     * not be written to or truncated (unless a special device).
     *
     * NOTE!  New hardlinks to immutable files work but new hardlinks to
     * files, immutable or not, sitting inside an immutable directory are
     * not allowed.  As always if the file is hardlinked via some other
     * path additional hardlinks may be possible even if the file is marked
     * immutable.  The sysop needs to create a closure by checking the hard
     * link count.  Once closure is achieved you are good, and security
     * scripts should check link counts anyway.
     *
     * Writes and truncations are only allowed on special devices.
     */
    if ((lvap->va_flags & IMMUTABLE) || (nflags & NLC_IMMUTABLE)) {
        if ((nflags & NLC_IMMUTABLE) && (nflags & NLC_HLINK))
            return (EPERM);
        if (nflags & (NLC_CREATE | NLC_DELETE |
                      NLC_RENAME_SRC | NLC_RENAME_DST)) {
            return (EPERM);
        }
        if (nflags & (NLC_WRITE | NLC_TRUNCATE)) {
            switch(lvap->va_type) {
            case VDIR:
                return (EISDIR);
            case VLNK:
            case VREG:
            case VDATABASE:
                return (EPERM);
            default:
                break;
            }
        }
    }

    /*
     * Test the no-unlink and append-only bits for opens, rename targets,
     * and deletions.  These bits are not tested for creations or
     * rename sources.
     *
     * Unlike FreeBSD we allow a file with APPEND set to be renamed.
     * If you do not wish this you must also set NOUNLINK.
     *
     * If the governing directory is marked APPEND-only it implies
     * NOUNLINK for all entries in the directory.
     */
    if (((lvap->va_flags & NOUNLINK) || (nflags & NLC_APPENDONLY)) &&
        (nflags & (NLC_DELETE | NLC_RENAME_SRC | NLC_RENAME_DST))
    ) {
        return (EPERM);
    }

    /*
     * A file marked append-only may not be deleted but can be renamed.
     */
    if ((lvap->va_flags & APPEND) &&
        (nflags & (NLC_DELETE | NLC_RENAME_DST))
    ) {
        return (EPERM);
    }

    /*
     * A file marked append-only which is opened for writing must also
     * be opened O_APPEND.
     */
    if ((lvap->va_flags & APPEND) && (nflags & (NLC_OPEN | NLC_TRUNCATE))) {
        if (nflags & NLC_TRUNCATE)
            return (EPERM);
        if ((nflags & (NLC_OPEN | NLC_WRITE)) == (NLC_OPEN | NLC_WRITE)) {
            if ((nflags & NLC_APPEND) == 0)
                return (EPERM);
        }
    }

    /*
     * root gets universal access
     */
    if (cred->cr_uid == 0)
        return(0);

    /*
     * Check owner perms.
     *
     * If NLC_OWN is set the owner of the file is allowed no matter when
     * the owner-mode bits say (utimes).
     */
    vmode = 0;
    if (nflags & NLC_READ)
        vmode |= S_IRUSR;
    if (nflags & NLC_WRITE)
        vmode |= S_IWUSR;
    if (nflags & NLC_EXEC)
        vmode |= S_IXUSR;

    if (cred->cr_uid == lvap->va_uid) {
        if ((nflags & NLC_OWN) == 0) {
            if ((vmode & lvap->va_mode) != vmode)
                return(EACCES);
        }
        return(0);
    }

    /*
     * If NLC_STICKY is set only the owner may delete or rename a file.
     * This bit is typically set on /tmp.
     *
     * Note that the NLC_READ/WRITE/EXEC bits are not typically set in
     * the specific delete or rename case.  For deletions and renames we
     * usually just care about directory permissions, not file permissions.
     */
    if ((nflags & NLC_STICKY) &&
        (nflags & (NLC_RENAME_SRC | NLC_RENAME_DST | NLC_DELETE))) {
        return(EACCES);
    }

    /*
     * Check group perms
     */
    vmode >>= 3;
    for (i = 0; i < cred->cr_ngroups; ++i) {
        if (lvap->va_gid == cred->cr_groups[i]) {
            if ((vmode & lvap->va_mode) != vmode)
                return(EACCES);
            return(0);
        }
    }

    /*
     * Check world perms
     */
    vmode >>= 3;
    if ((vmode & lvap->va_mode) != vmode)
        return(EACCES);
    return(0);
}

/*
 * Long-term (10-second interval) statistics collection
 */
static
uint64_t
collect_nlookup_callback(int n)
{
        static uint64_t last_total;
        uint64_t save;
        uint64_t total;

        total = 0;
        for (n = 0; n < ncpus; ++n) {
                globaldata_t gd = globaldata_find(n);
                struct nchstats *sp;

                if ((sp = gd->gd_nchstats) != NULL)
                        total += sp->ncs_longhits + sp->ncs_longmiss;
        }
        save = total;
        total = total - last_total;
        last_total = save;

        return total;
}

static
void
nlookup_collect_init(void *dummy __unused)
{
        kcollect_register(KCOLLECT_NLOOKUP, "nlookup", collect_nlookup_callback,
                          KCOLLECT_SCALE(KCOLLECT_NLOOKUP_FORMAT, 0));
}
SYSINIT(collect_nlookup, SI_SUB_PROP, SI_ORDER_ANY, nlookup_collect_init, 0);