/*-
 * Copyright (c) 1994 Jan-Simon Pendry
 * Copyright (c) 1994
 *      The Regents of the University of California.  All rights reserved.
 * Copyright (c) 2005, 2006 Masanori Ozawa <ozawa@ongs.co.jp>, ONGS Inc.
 * Copyright (c) 2006 Daichi Goto <daichi@freebsd.org>
 *
 * This code is derived from software contributed to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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.
 * 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.
 *
 *      @(#)union_subr.c        8.20 (Berkeley) 5/20/95
 * $FreeBSD: src/sys/fs/unionfs/union_subr.c,v 1.99 2008/01/24 12:34:27 attilio Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/dirent.h>
#include <sys/fcntl.h>
#include <sys/filedesc.h>
#include <sys/stat.h>
#include <sys/kauth.h>
#include <sys/resourcevar.h>

#include <fs/unionfs/unionfs.h>

MALLOC_DEFINE(M_UNIONFSPATH, "UNIONFS path", "UNIONFS path private part");

/*
 * Make a new or get existing unionfs node.
 * 
 * uppervp and lowervp should be unlocked. Because if new unionfs vnode is
 * locked, uppervp or lowervp is locked too. In order to prevent dead lock,
 * you should not lock plurality simultaneously.
 */
int
unionfs_nodeget(struct mount *mp, struct vnode *uppervp,
                struct vnode *lowervp, struct vnode *dvp,
                struct vnode **vpp, struct componentname *cnp)
{
        struct unionfs_mount *ump;
        struct unionfs_node *unp;
        struct vnode   *vp;
        int             error;
        const char      *path;

        ump = MOUNTTOUNIONFSMOUNT(mp);
        path = (cnp ? cnp->cn_nameptr : NULL);

        if (uppervp == NULLVP && lowervp == NULLVP)
                panic("unionfs_nodeget: upper and lower is null");

        /* If it has no ISLASTCN flag, path check is skipped. */
        if (cnp && !(cnp->cn_flags & ISLASTCN))
                path = NULL;

        if ((uppervp == NULLVP || ump->um_uppervp != uppervp) ||
            (lowervp == NULLVP || ump->um_lowervp != lowervp)) {
                if (dvp == NULLVP)
                        return (EINVAL);
        }

        /*
         * Get a new vnode and share the lock with upper layer vnode,
         * unless layers are inverted.
         */
        vnode_t *svp = (uppervp != NULLVP) ? uppervp : lowervp;
        error = vcache_get(mp, svp, sizeof(svp), &vp);
        if (error != 0) {
                return (error);
        }
        if (dvp != NULLVP)
                vref(dvp);
        if (uppervp != NULLVP)
                vref(uppervp);
        if (lowervp != NULLVP)
                vref(lowervp);

        unp = kmem_zalloc(sizeof(*unp), KM_SLEEP);
        unp->un_vnode = vp;
        unp->un_uppervp = uppervp;
        unp->un_lowervp = lowervp;
        unp->un_dvp = dvp;

        if (path != NULL) {
                unp->un_path = (char *)
                    malloc(cnp->cn_namelen +1, M_UNIONFSPATH, M_WAITOK|M_ZERO);
                memcpy(unp->un_path, cnp->cn_nameptr, cnp->cn_namelen);
                unp->un_path[cnp->cn_namelen] = '\0';
        }
        vp->v_type = (uppervp != NULLVP ? uppervp->v_type : lowervp->v_type);
        vp->v_data = unp;
        uvm_vnp_setsize(vp, 0);

        if ((uppervp != NULLVP && ump->um_uppervp == uppervp) &&
            (lowervp != NULLVP && ump->um_lowervp == lowervp))
                vp->v_vflag |= VV_ROOT;

        *vpp = vp;

        return (0);
}

/*
 * Clean up the unionfs node.
 */
void
unionfs_noderem(struct vnode *vp)
{
        struct unionfs_node *unp;
        struct unionfs_node_status *unsp;
        struct vnode   *lvp;
        struct vnode   *uvp;

        /*
         * Use the interlock to protect the clearing of v_data to
         * prevent faults in unionfs_lock().
         */
        unp = VTOUNIONFS(vp);
        lvp = unp->un_lowervp;
        uvp = unp->un_uppervp;
        unp->un_lowervp = unp->un_uppervp = NULLVP;
        vp->v_data = NULL;
        
        if (lvp != NULLVP)
                vrele(lvp);
        if (uvp != NULLVP)
                vrele(uvp);
        if (unp->un_dvp != NULLVP) {
                vrele(unp->un_dvp);
                unp->un_dvp = NULLVP;
        }
        if (unp->un_path) {
                free(unp->un_path, M_UNIONFSPATH);
                unp->un_path = NULL;
        }

        while ((unsp = LIST_FIRST(&(unp->un_unshead))) != NULL) {
                LIST_REMOVE(unsp, uns_list);
                free(unsp, M_TEMP);
        }
        kmem_free(unp, sizeof(*unp));
}

/*
 * Get the unionfs node status.
 * You need exclusive lock this vnode.
 */
void
unionfs_get_node_status(struct unionfs_node *unp,
                        struct unionfs_node_status **unspp)
{
        struct unionfs_node_status *unsp;
        pid_t pid;
        lwpid_t lid;

        KASSERT(NULL != unspp);
        KASSERT(VOP_ISLOCKED(UNIONFSTOV(unp)) == LK_EXCLUSIVE);

        pid = curproc->p_pid;
        lid = curlwp->l_lid;

        LIST_FOREACH(unsp, &(unp->un_unshead), uns_list) {
                if (unsp->uns_pid == pid && unsp->uns_lid == lid) {
                        *unspp = unsp;
                        return;
                }
        }

        /* create a new unionfs node status */
        unsp = kmem_zalloc(sizeof(*unsp), KM_SLEEP);
        unsp->uns_pid = pid;
        unsp->uns_lid = lid;
        LIST_INSERT_HEAD(&(unp->un_unshead), unsp, uns_list);

        *unspp = unsp;
}

/*
 * Remove the unionfs node status, if you can.
 * You need exclusive lock this vnode.
 */
void
unionfs_tryrem_node_status(struct unionfs_node *unp,
                           struct unionfs_node_status *unsp)
{
        KASSERT(NULL != unsp);
        KASSERT(VOP_ISLOCKED(UNIONFSTOV(unp)) == LK_EXCLUSIVE);

        if (0 < unsp->uns_lower_opencnt || 0 < unsp->uns_upper_opencnt)
                return;

        LIST_REMOVE(unsp, uns_list);
        kmem_free(unsp, sizeof(*unsp));
}

/*
 * Create upper node attr.
 */
void
unionfs_create_uppervattr_core(struct unionfs_mount *ump,
                               struct vattr *lva,
                               struct vattr *uva)
{
        vattr_null(uva);
        uva->va_type = lva->va_type;
        uva->va_atime = lva->va_atime;
        uva->va_mtime = lva->va_mtime;
        uva->va_ctime = lva->va_ctime;

        switch (ump->um_copymode) {
        case UNIONFS_TRANSPARENT:
                uva->va_mode = lva->va_mode;
                uva->va_uid = lva->va_uid;
                uva->va_gid = lva->va_gid;
                break;
        case UNIONFS_MASQUERADE:
                if (ump->um_uid == lva->va_uid) {
                        uva->va_mode = lva->va_mode & 077077;
                        uva->va_mode |= (lva->va_type == VDIR ? ump->um_udir : ump->um_ufile) & 0700;
                        uva->va_uid = lva->va_uid;
                        uva->va_gid = lva->va_gid;
                } else {
                        uva->va_mode = (lva->va_type == VDIR ? ump->um_udir : ump->um_ufile);
                        uva->va_uid = ump->um_uid;
                        uva->va_gid = ump->um_gid;
                }
                break;
        default:                /* UNIONFS_TRADITIONAL */
                uva->va_mode = 0777 & ~curproc->p_cwdi->cwdi_cmask;
                uva->va_uid = ump->um_uid;
                uva->va_gid = ump->um_gid;
                break;
        }
}

/*
 * Create upper node attr.
 */
int
unionfs_create_uppervattr(struct unionfs_mount *ump,
                          struct vnode *lvp,
                          struct vattr *uva,
                          kauth_cred_t cred)
{
        int             error;
        struct vattr    lva;

        if ((error = VOP_GETATTR(lvp, &lva, cred)))
                return (error);

        unionfs_create_uppervattr_core(ump, &lva, uva);

        return (error);
}

/*
 * relookup
 * 
 * dvp should be locked on entry and will be locked on return.
 * 
 * If an error is returned, *vpp will be invalid, otherwise it will hold a
 * locked, referenced vnode. If *vpp == dvp then remember that only one
 * LK_EXCLUSIVE lock is held.
 */
static int
unionfs_relookup(struct vnode *dvp, struct vnode **vpp,
                 struct componentname *cnp, struct componentname *cn,
                 char **pnbuf_ret,
                 const char *path, int pathlen, u_long nameiop)
{
        int     error;
        char *pnbuf;

        cn->cn_namelen = pathlen;
        pnbuf = PNBUF_GET();
        memcpy(pnbuf, path, pathlen);
        pnbuf[pathlen] = '\0';

        cn->cn_nameiop = nameiop;
        cn->cn_flags = (LOCKPARENT | LOCKLEAF | ISLASTCN);
        cn->cn_cred = cnp->cn_cred;

        cn->cn_nameptr = pnbuf;

        if (nameiop == DELETE)
                cn->cn_flags |= (cnp->cn_flags & DOWHITEOUT);

        vref(dvp);
        VOP_UNLOCK(dvp);

        if ((error = relookup(dvp, vpp, cn, 0))) {
                PNBUF_PUT(pnbuf);
                *pnbuf_ret = NULL;
                vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY);
        } else {
                *pnbuf_ret = pnbuf;
                vrele(dvp);
        }

        return (error);
}

/*
 * relookup for CREATE namei operation.
 *
 * dvp is unionfs vnode. dvp should be locked.
 *
 * If it called 'unionfs_copyfile' function by unionfs_link etc,
 * VOP_LOOKUP information is broken.
 * So it need relookup in order to create link etc.
 */
int
unionfs_relookup_for_create(struct vnode *dvp, struct componentname *cnp)
{
        int     error;
        struct vnode *udvp;
        struct vnode *vp;
        struct componentname cn;
        char *pnbuf;

        udvp = UNIONFSVPTOUPPERVP(dvp);
        vp = NULLVP;

        error = unionfs_relookup(udvp, &vp, cnp, &cn, &pnbuf,
            cnp->cn_nameptr,
            strlen(cnp->cn_nameptr), CREATE);
        if (error)
                return (error);

        if (vp != NULLVP) {
                if (udvp == vp)
                        vrele(vp);
                else
                        vput(vp);

                error = EEXIST;
        }

        PNBUF_PUT(pnbuf);

        if (!error) {
                cnp->cn_flags = cn.cn_flags;
        }

        return (error);
}

/*
 * relookup for DELETE namei operation.
 *
 * dvp is unionfs vnode. dvp should be locked.
 */
int
unionfs_relookup_for_delete(struct vnode *dvp, struct componentname *cnp)
{
        int     error;
        struct vnode *udvp;
        struct vnode *vp;
        struct componentname cn;
        char *pnbuf;

        udvp = UNIONFSVPTOUPPERVP(dvp);
        vp = NULLVP;

        error = unionfs_relookup(udvp, &vp, cnp, &cn, &pnbuf, cnp->cn_nameptr,
            strlen(cnp->cn_nameptr), DELETE);
        if (error)
                return (error);

        if (vp == NULLVP)
                error = ENOENT;
        else {
                if (udvp == vp)
                        vrele(vp);
                else
                        vput(vp);
        }

        PNBUF_PUT(pnbuf);

        if (!error) {
                cnp->cn_flags = cn.cn_flags;
        }

        return (error);
}

/*
 * relookup for RENAME namei operation.
 *
 * dvp is unionfs vnode. dvp should be locked.
 */
int
unionfs_relookup_for_rename(struct vnode *dvp, struct componentname *cnp)
{
        int error;
        struct vnode *udvp;
        struct vnode *vp;
        struct componentname cn;
        char *pnbuf;

        udvp = UNIONFSVPTOUPPERVP(dvp);
        vp = NULLVP;

        error = unionfs_relookup(udvp, &vp, cnp, &cn, &pnbuf, cnp->cn_nameptr,
            strlen(cnp->cn_nameptr), RENAME);
        if (error)
                return (error);

        if (vp != NULLVP) {
                if (udvp == vp)
                        vrele(vp);
                else
                        vput(vp);
        }

        PNBUF_PUT(pnbuf);

        if (!error) {
                cnp->cn_flags = cn.cn_flags;
        }

        return (error);

}

/*
 * Update the unionfs_node.
 * 
 * uvp is new locked upper vnode. unionfs vnode's lock will be exchanged to the
 * uvp's lock and lower's lock will be unlocked.
 */
static void
unionfs_node_update(struct unionfs_node *unp, struct vnode *uvp)
{
        struct vnode   *vp;
        struct vnode   *lvp;

        vp = UNIONFSTOV(unp);
        lvp = unp->un_lowervp;

        /*
         * lock update
         */
        mutex_enter(vp->v_interlock);
        unp->un_uppervp = uvp;
        KASSERT(VOP_ISLOCKED(lvp) == LK_EXCLUSIVE);
        mutex_exit(vp->v_interlock);
}

/*
 * Create a new shadow dir.
 * 
 * udvp should be locked on entry and will be locked on return.
 * 
 * If no error returned, unp will be updated.
 */
int
unionfs_mkshadowdir(struct unionfs_mount *ump, struct vnode *udvp,
                    struct unionfs_node *unp, struct componentname *cnp)
{
        int             error;
        struct vnode   *lvp;
        struct vnode   *uvp;
        struct vattr    va;
        struct vattr    lva;
        struct componentname cn;
        char *pnbuf;

        if (unp->un_uppervp != NULLVP)
                return (EEXIST);

        lvp = unp->un_lowervp;
        uvp = NULLVP;

        memset(&cn, 0, sizeof(cn));

        if ((error = VOP_GETATTR(lvp, &lva, cnp->cn_cred)))
                goto unionfs_mkshadowdir_abort;

        if ((error = unionfs_relookup(udvp, &uvp, cnp, &cn, &pnbuf,
                        cnp->cn_nameptr, cnp->cn_namelen, CREATE)))
                goto unionfs_mkshadowdir_abort;
        if (uvp != NULLVP) {
                if (udvp == uvp)
                        vrele(uvp);
                else
                        vput(uvp);

                error = EEXIST;
                goto unionfs_mkshadowdir_free_out;
        }

        unionfs_create_uppervattr_core(ump, &lva, &va);

        error = VOP_MKDIR(udvp, &uvp, &cn, &va);

        if (!error) {
                unionfs_node_update(unp, uvp);

                /*
                 * XXX The bug which cannot set uid/gid was corrected.
                 * Ignore errors.   XXXNETBSD Why is this done as root?
                 */
                va.va_type = VNON;
                VOP_SETATTR(uvp, &va, lwp0.l_cred);
        }

unionfs_mkshadowdir_free_out:
        PNBUF_PUT(pnbuf);

unionfs_mkshadowdir_abort:

        return (error);
}

/*
 * Create a new whiteout.
 * 
 * dvp should be locked on entry and will be locked on return.
 */
int
unionfs_mkwhiteout(struct vnode *dvp, struct componentname *cnp, const char *path)
{
        int             error;
        struct vnode   *wvp;
        struct componentname cn;
        char *pnbuf;

        if (path == NULL)
                path = cnp->cn_nameptr;

        wvp = NULLVP;
        if ((error = unionfs_relookup(dvp, &wvp, cnp, &cn, &pnbuf,
                        path, strlen(path), CREATE)))
                return (error);
        if (wvp != NULLVP) {
                PNBUF_PUT(pnbuf);
                if (dvp == wvp)
                        vrele(wvp);
                else
                        vput(wvp);

                return (EEXIST);
        }

        PNBUF_PUT(pnbuf);

        return (error);
}

/*
 * Create a new vnode for create a new shadow file.
 * 
 * If an error is returned, *vpp will be invalid, otherwise it will hold a
 * locked, referenced and opened vnode.
 * 
 * unp is never updated.
 */
static int
unionfs_vn_create_on_upper(struct vnode **vpp, struct vnode *udvp,
                           struct unionfs_node *unp, struct vattr *uvap)
{
        struct unionfs_mount *ump;
        struct vnode   *vp;
        struct vnode   *lvp;
        kauth_cred_t    cred;
        struct vattr    lva;
        int             fmode;
        int             error;
        struct componentname cn;
        char *pnbuf;

        ump = MOUNTTOUNIONFSMOUNT(UNIONFSTOV(unp)->v_mount);
        vp = NULLVP;
        lvp = unp->un_lowervp;
        cred = kauth_cred_get();
        fmode = FFLAGS(O_WRONLY | O_CREAT | O_TRUNC | O_EXCL);
        error = 0;

        if ((error = VOP_GETATTR(lvp, &lva, cred)) != 0)
                return (error);
        unionfs_create_uppervattr_core(ump, &lva, uvap);

        if (unp->un_path == NULL)
                panic("unionfs: un_path is null");

        cn.cn_namelen = strlen(unp->un_path);
        pnbuf = PNBUF_GET();
        memcpy(pnbuf, unp->un_path, cn.cn_namelen + 1);
        cn.cn_nameiop = CREATE;
        cn.cn_flags = (LOCKPARENT | LOCKLEAF | ISLASTCN);
        cn.cn_cred = cred;
        cn.cn_nameptr = pnbuf;

        vref(udvp);
        if ((error = relookup(udvp, &vp, &cn, 0)) != 0)
                goto unionfs_vn_create_on_upper_free_out2;
        vrele(udvp);

        if (vp != NULLVP) {
                if (vp == udvp)
                        vrele(vp);
                else
                        vput(vp);
                error = EEXIST;
                goto unionfs_vn_create_on_upper_free_out1;
        }

        if ((error = VOP_CREATE(udvp, &vp, &cn, uvap)) != 0)
                goto unionfs_vn_create_on_upper_free_out1;

        if ((error = VOP_OPEN(vp, fmode, cred)) != 0) {
                vput(vp);
                goto unionfs_vn_create_on_upper_free_out1;
        }
        vp->v_writecount++;
        *vpp = vp;

unionfs_vn_create_on_upper_free_out1:
        VOP_UNLOCK(udvp);

unionfs_vn_create_on_upper_free_out2:
        PNBUF_PUT(pnbuf);

        return (error);
}

/*
 * Copy from lvp to uvp.
 * 
 * lvp and uvp should be locked and opened on entry and will be locked and
 * opened on return.
 */
static int
unionfs_copyfile_core(struct vnode *lvp, struct vnode *uvp,
                      kauth_cred_t cred)
{
        int             error;
        off_t           offset;
        int             count;
        int             bufoffset;
        char           *buf;
        struct uio      uio;
        struct iovec    iov;

        error = 0;
        memset(&uio, 0, sizeof(uio));
        UIO_SETUP_SYSSPACE(&uio);
        uio.uio_offset = 0;

        buf = kmem_alloc(MAXBSIZE, KM_SLEEP);
        while (error == 0) {
                offset = uio.uio_offset;

                uio.uio_iov = &iov;
                uio.uio_iovcnt = 1;
                iov.iov_base = buf;
                iov.iov_len = MAXBSIZE;
                uio.uio_resid = iov.iov_len;
                uio.uio_rw = UIO_READ;

                if ((error = VOP_READ(lvp, &uio, 0, cred)) != 0)
                        break;
                if ((count = MAXBSIZE - uio.uio_resid) == 0)
                        break;

                bufoffset = 0;
                while (bufoffset < count) {
                        uio.uio_iov = &iov;
                        uio.uio_iovcnt = 1;
                        iov.iov_base = buf + bufoffset;
                        iov.iov_len = count - bufoffset;
                        uio.uio_offset = offset + bufoffset;
                        uio.uio_resid = iov.iov_len;
                        uio.uio_rw = UIO_WRITE;

                        if ((error = VOP_WRITE(uvp, &uio, 0, cred)) != 0)
                                break;

                        bufoffset += (count - bufoffset) - uio.uio_resid;
                }

                uio.uio_offset = offset + bufoffset;
        }

        kmem_free(buf, MAXBSIZE);

        return (error);
}

/*
 * Copy file from lower to upper.
 * 
 * If you need copy of the contents, set 1 to docopy. Otherwise, set 0 to
 * docopy.
 * 
 * If no error returned, unp will be updated.
 */
int
unionfs_copyfile(struct unionfs_node *unp, int docopy, kauth_cred_t cred)
{
        int             error;
        struct vnode   *udvp;
        struct vnode   *lvp;
        struct vnode   *uvp;
        struct vattr    uva;

        lvp = unp->un_lowervp;
        uvp = NULLVP;

        if ((UNIONFSTOV(unp)->v_mount->mnt_flag & MNT_RDONLY))
                return (EROFS);
        if (unp->un_dvp == NULLVP)
                return (EINVAL);
        if (unp->un_uppervp != NULLVP)
                return (EEXIST);
        udvp = VTOUNIONFS(unp->un_dvp)->un_uppervp;
        if (udvp == NULLVP)
                return (EROFS);
        if ((udvp->v_mount->mnt_flag & MNT_RDONLY))
                return (EROFS);

        error = VOP_ACCESS(lvp, VREAD, cred);
        if (error != 0)
                return (error);

        error = unionfs_vn_create_on_upper(&uvp, udvp, unp, &uva);
        if (error != 0)
                return (error);

        if (docopy != 0) {
                error = VOP_OPEN(lvp, FREAD, cred);
                if (error == 0) {
                        error = unionfs_copyfile_core(lvp, uvp, cred);
                        VOP_CLOSE(lvp, FREAD, cred);
                }
        }
        VOP_CLOSE(uvp, FWRITE, cred);
        uvp->v_writecount--;

        if (error == 0) {
                /* Reset the attributes. Ignore errors. */
                uva.va_type = VNON;
                VOP_SETATTR(uvp, &uva, cred);
        }

        unionfs_node_update(unp, uvp);

        return (error);
}

/*
 * It checks whether vp can rmdir. (check empty)
 *
 * vp is unionfs vnode.
 * vp should be locked.
 */
int
unionfs_check_rmdir(struct vnode *vp, kauth_cred_t cred)
{
        int             error;
        int             eofflag;
        int             lookuperr;
        struct vnode   *uvp;
        struct vnode   *lvp;
        struct vnode   *tvp;
        struct vattr    va;
        struct componentname cn;
        /*
         * The size of buf needs to be larger than DIRBLKSIZ.
         */
        char            buf[256 * 6];
        struct dirent  *dp;
        struct dirent  *edp;
        struct uio      uio;
        struct iovec    iov;

        KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE);

        eofflag = 0;
        uvp = UNIONFSVPTOUPPERVP(vp);
        lvp = UNIONFSVPTOLOWERVP(vp);

        /* check opaque */
        if ((error = VOP_GETATTR(uvp, &va, cred)) != 0)
                return (error);
        if (va.va_flags & OPAQUE)
                return (0);

        /* open vnode */
        if ((error = VOP_ACCESS(vp, VEXEC|VREAD, cred)) != 0)
                return (error);
        if ((error = VOP_OPEN(vp, FREAD, cred)) != 0)
                return (error);

        UIO_SETUP_SYSSPACE(&uio);
        uio.uio_rw = UIO_READ;
        uio.uio_offset = 0;

        while (!error && !eofflag) {
                iov.iov_base = buf;
                iov.iov_len = sizeof(buf);
                uio.uio_iov = &iov;
                uio.uio_iovcnt = 1;
                uio.uio_resid = iov.iov_len;

                error = VOP_READDIR(lvp, &uio, cred, &eofflag, NULL, NULL);
                if (error)
                        break;

                edp = (struct dirent*)&buf[sizeof(buf) - uio.uio_resid];
                for (dp = (struct dirent*)buf; !error && dp < edp;
                     dp = (struct dirent*)((char *)dp + dp->d_reclen)) {
                        if (dp->d_type == DT_WHT ||
                            (dp->d_namlen == 1 && dp->d_name[0] == '.') ||
                            (dp->d_namlen == 2 && !memcmp(dp->d_name, "..", 2)))
                                continue;

                        cn.cn_namelen = dp->d_namlen;
                        cn.cn_nameptr = dp->d_name;
                        cn.cn_nameiop = LOOKUP;
                        cn.cn_flags = (LOCKPARENT | LOCKLEAF | RDONLY | ISLASTCN);
                        cn.cn_cred = cred;

                        /*
                         * check entry in lower.
                         * Sometimes, readdir function returns
                         * wrong entry.
                         */
                        lookuperr = VOP_LOOKUP(lvp, &tvp, &cn);

                        if (!lookuperr)
                                vput(tvp);
                        else
                                continue; /* skip entry */

                        /*
                         * check entry
                         * If it has no exist/whiteout entry in upper,
                         * directory is not empty.
                         */
                        cn.cn_flags = (LOCKPARENT | LOCKLEAF | RDONLY | ISLASTCN);
                        lookuperr = VOP_LOOKUP(uvp, &tvp, &cn);

                        if (!lookuperr)
                                vput(tvp);

                        /* ignore exist or whiteout entry */
                        if (!lookuperr ||
                            (lookuperr == ENOENT && (cn.cn_flags & ISWHITEOUT)))
                                continue;

                        error = ENOTEMPTY;
                }
        }

        /* close vnode */
        VOP_CLOSE(vp, FREAD, cred);

        return (error);
}

#ifdef DIAGNOSTIC

struct vnode   *
unionfs_checkuppervp(struct vnode *vp, const char *fil, int lno)
{
        struct unionfs_node *unp;

        unp = VTOUNIONFS(vp);

#ifdef notyet
        if (vp->v_op != unionfs_vnodeop_p) {
                printf("unionfs_checkuppervp: on non-unionfs-node.\n");
#ifdef KDB
                kdb_enter(KDB_WHY_UNIONFS,
                    "unionfs_checkuppervp: on non-unionfs-node.\n");
#endif
                panic("unionfs_checkuppervp");
        };
#endif
        return (unp->un_uppervp);
}

struct vnode   *
unionfs_checklowervp(struct vnode *vp, const char *fil, int lno)
{
        struct unionfs_node *unp;

        unp = VTOUNIONFS(vp);

#ifdef notyet
        if (vp->v_op != unionfs_vnodeop_p) {
                printf("unionfs_checklowervp: on non-unionfs-node.\n");
#ifdef KDB
                kdb_enter(KDB_WHY_UNIONFS,
                    "unionfs_checklowervp: on non-unionfs-node.\n");
#endif
                panic("unionfs_checklowervp");
        };
#endif
        return (unp->un_lowervp);
}
#endif