freebsd-src/sys/fs/unionfs/union_vnops.c

/*
 * Copyright (c) 1992, 1993, 1994, 1995 Jan-Simon Pendry.
 * Copyright (c) 1992, 1993, 1994, 1995
 *	The Regents of the University of California.  All rights reserved.
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)union_vnops.c	8.32 (Berkeley) 6/23/95
 * $Id: union_vnops.c,v 1.59 1998/12/14 05:00:59 dillon Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/fcntl.h>
#include <sys/stat.h>
#include <sys/kernel.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/malloc.h>
#include <sys/buf.h>
#include <sys/lock.h>
#include <miscfs/union/union.h>

#define FIXUP(un, p) { \
	if (((un)->un_flags & UN_ULOCK) == 0) { \
		union_fixup(un, p); \
	} \
}

static int	union_abortop __P((struct vop_abortop_args *ap));
static int	union_access __P((struct vop_access_args *ap));
static int	union_advlock __P((struct vop_advlock_args *ap));
static int	union_bmap __P((struct vop_bmap_args *ap));
static int	union_close __P((struct vop_close_args *ap));
static int	union_create __P((struct vop_create_args *ap));
static void	union_fixup __P((struct union_node *un, struct proc *p));
static int	union_fsync __P((struct vop_fsync_args *ap));
static int	union_getattr __P((struct vop_getattr_args *ap));
static int	union_inactive __P((struct vop_inactive_args *ap));
static int	union_ioctl __P((struct vop_ioctl_args *ap));
static int	union_islocked __P((struct vop_islocked_args *ap));
static int	union_lease __P((struct vop_lease_args *ap));
static int	union_link __P((struct vop_link_args *ap));
static int	union_lock __P((struct vop_lock_args *ap));
static int	union_lookup __P((struct vop_lookup_args *ap));
static int	union_lookup1 __P((struct vnode *udvp, struct vnode **dvpp,
				   struct vnode **vpp,
				   struct componentname *cnp));
static int	union_mkdir __P((struct vop_mkdir_args *ap));
static int	union_mknod __P((struct vop_mknod_args *ap));
static int	union_mmap __P((struct vop_mmap_args *ap));
static int	union_open __P((struct vop_open_args *ap));
static int	union_pathconf __P((struct vop_pathconf_args *ap));
static int	union_print __P((struct vop_print_args *ap));
static int	union_read __P((struct vop_read_args *ap));
static int	union_readdir __P((struct vop_readdir_args *ap));
static int	union_readlink __P((struct vop_readlink_args *ap));
static int	union_reclaim __P((struct vop_reclaim_args *ap));
static int	union_remove __P((struct vop_remove_args *ap));
static int	union_rename __P((struct vop_rename_args *ap));
static int	union_revoke __P((struct vop_revoke_args *ap));
static int	union_rmdir __P((struct vop_rmdir_args *ap));
static int	union_poll __P((struct vop_poll_args *ap));
static int	union_setattr __P((struct vop_setattr_args *ap));
static int	union_strategy __P((struct vop_strategy_args *ap));
static int	union_symlink __P((struct vop_symlink_args *ap));
static int	union_unlock __P((struct vop_unlock_args *ap));
static int	union_whiteout __P((struct vop_whiteout_args *ap));
static int	union_write __P((struct vop_read_args *ap));

static void
union_fixup(un, p)
	struct union_node *un;
	struct proc *p;
{

	vn_lock(un->un_uppervp, LK_EXCLUSIVE | LK_RETRY, p);
	un->un_flags |= UN_ULOCK;
}

static int
union_lookup1(udvp, dvpp, vpp, cnp)
	struct vnode *udvp;
	struct vnode **dvpp;
	struct vnode **vpp;
	struct componentname *cnp;
{
	int error;
	struct proc *p = cnp->cn_proc;
	struct vnode *tdvp;
	struct vnode *dvp;
	struct mount *mp;

	dvp = *dvpp;

	/*
	 * If stepping up the directory tree, check for going
	 * back across the mount point, in which case do what
	 * lookup would do by stepping back down the mount
	 * hierarchy.
	 */
	if (cnp->cn_flags & ISDOTDOT) {
		while ((dvp != udvp) && (dvp->v_flag & VROOT)) {
			/*
			 * Don't do the NOCROSSMOUNT check
			 * at this level.  By definition,
			 * union fs deals with namespaces, not
			 * filesystems.
			 */
			tdvp = dvp;
			*dvpp = dvp = dvp->v_mount->mnt_vnodecovered;
			vput(tdvp);
			VREF(dvp);
			vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY, p);
		}
	}

        error = VOP_LOOKUP(dvp, &tdvp, cnp);
	if (error)
		return (error);

	/*
	 * The parent directory will have been unlocked, unless lookup
	 * found the last component.  In which case, re-lock the node
	 * here to allow it to be unlocked again (phew) in union_lookup.
	 */
	if (dvp != tdvp && !(cnp->cn_flags & ISLASTCN))
		vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY, p);

	dvp = tdvp;

	/*
	 * Lastly check if the current node is a mount point in
	 * which case walk up the mount hierarchy making sure not to
	 * bump into the root of the mount tree (ie. dvp != udvp).
	 */
	while (dvp != udvp && (dvp->v_type == VDIR) &&
	       (mp = dvp->v_mountedhere)) {

		if (vfs_busy(mp, 0, 0, p))
			continue;

		error = VFS_ROOT(mp, &tdvp);
		vfs_unbusy(mp, p);
		if (error) {
			vput(dvp);
			return (error);
		}

		vput(dvp);
		dvp = tdvp;
	}

	*vpp = dvp;
	return (0);
}

static int
union_lookup(ap)
	struct vop_lookup_args /* {
		struct vnodeop_desc *a_desc;
		struct vnode *a_dvp;
		struct vnode **a_vpp;
		struct componentname *a_cnp;
	} */ *ap;
{
	int error;
	int uerror, lerror;
	struct vnode *uppervp, *lowervp;
	struct vnode *upperdvp, *lowerdvp;
	struct vnode *dvp = ap->a_dvp;
	struct union_node *dun = VTOUNION(dvp);
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;
	int lockparent = cnp->cn_flags & LOCKPARENT;
	struct union_mount *um = MOUNTTOUNIONMOUNT(dvp->v_mount);
	struct ucred *saved_cred = NULL;
	int iswhiteout;
	struct vattr va;


	/*
	 * Disallow write attemps to the filesystem mounted read-only.
	 */
	if ((cnp->cn_flags & ISLASTCN) && (dvp->v_mount->mnt_flag & MNT_RDONLY) &&
		(cnp->cn_nameiop == DELETE || cnp->cn_nameiop == RENAME))
		return (EROFS);

#ifdef notyet
	if (cnp->cn_namelen == 3 &&
			cnp->cn_nameptr[2] == '.' &&
			cnp->cn_nameptr[1] == '.' &&
			cnp->cn_nameptr[0] == '.') {
		dvp = *ap->a_vpp = LOWERVP(ap->a_dvp);
		if (dvp == NULLVP)
			return (ENOENT);
		VREF(dvp);
		vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY, p);
		if (!lockparent || !(cnp->cn_flags & ISLASTCN))
			VOP_UNLOCK(ap->a_dvp, 0, p);
		return (0);
	}
#endif

	cnp->cn_flags |= LOCKPARENT;

	upperdvp = dun->un_uppervp;
	lowerdvp = dun->un_lowervp;
	uppervp = NULLVP;
	lowervp = NULLVP;
	iswhiteout = 0;

	if (cnp->cn_flags & ISDOTDOT) {
		if (upperdvp != NULL)
			VREF(upperdvp);
		if (lowerdvp != NULL)
			VREF(lowerdvp);
	}

	/*
	 * do the lookup in the upper level.
	 * if that level comsumes additional pathnames,
	 * then assume that something special is going
	 * on and just return that vnode.
	 */
	if (upperdvp != NULLVP) {
		FIXUP(dun, p);
		/*
		 * If we're doing `..' in the underlying filesystem,
		 * we must drop our lock on the union node before
		 * going up the tree in the lower file system--if we block
		 * on the lowervp lock, and that's held by someone else
		 * coming down the tree and who's waiting for our lock,
		 * we would be hosed.
		 */
		if (cnp->cn_flags & ISDOTDOT) {
			/* retain lock on underlying VP: */
			dun->un_flags |= UN_KLOCK;
			VOP_UNLOCK(dvp, 0, p);
		}
		uerror = union_lookup1(um->um_uppervp, &upperdvp,
					&uppervp, cnp);
		/*
		 * Disallow write attemps to the filesystem mounted read-only.
		 */
		if (uerror == EJUSTRETURN && (cnp->cn_flags & ISLASTCN) &&
			(dvp->v_mount->mnt_flag & MNT_RDONLY) &&
			(cnp->cn_nameiop == CREATE || cnp->cn_nameiop == RENAME)) {
			if (!lockparent)
				cnp->cn_flags &= ~LOCKPARENT;
			return (EROFS);
		}
			
		if (cnp->cn_flags & ISDOTDOT) {
			if (dun->un_uppervp == upperdvp) {
				/*
				 * We got the underlying bugger back locked...
				 * now take back the union node lock.  Since we
				 * hold the uppervp lock, we can diddle union
				 * locking flags at will. :)
				 */
				dun->un_flags |= UN_ULOCK;
			}
			/*
			 * If upperdvp got swapped out, it means we did
			 * some mount point magic, and we do not have
			 * dun->un_uppervp locked currently--so we get it
			 * locked here (don't set the UN_ULOCK flag).
			 */
			vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY, p);
		}

		/*if (uppervp == upperdvp)
			dun->un_flags |= UN_KLOCK;*/

		if (cnp->cn_consume != 0) {
			*ap->a_vpp = uppervp;
			if (!lockparent)
				cnp->cn_flags &= ~LOCKPARENT;
			error = uerror;
			goto out;
		}
		if (uerror == ENOENT || uerror == EJUSTRETURN) {
			if (cnp->cn_flags & ISWHITEOUT) {
				iswhiteout = 1;
			} else if (lowerdvp != NULLVP) {
				lerror = VOP_GETATTR(upperdvp, &va,
					cnp->cn_cred, cnp->cn_proc);
				if (lerror == 0 && (va.va_flags & OPAQUE))
					iswhiteout = 1;
			}
		}
	} else {
		uerror = ENOENT;
	}

	/*
	 * in a similar way to the upper layer, do the lookup
	 * in the lower layer.   this time, if there is some
	 * component magic going on, then vput whatever we got
	 * back from the upper layer and return the lower vnode
	 * instead.
	 */
	if (lowerdvp != NULLVP && !iswhiteout) {
		int nameiop;

		vn_lock(lowerdvp, LK_EXCLUSIVE | LK_RETRY, p);

		/*
		 * Only do a LOOKUP on the bottom node, since
		 * we won't be making changes to it anyway.
		 */
		nameiop = cnp->cn_nameiop;
		cnp->cn_nameiop = LOOKUP;
		if (um->um_op == UNMNT_BELOW) {
			saved_cred = cnp->cn_cred;
			cnp->cn_cred = um->um_cred;
		}
		/*
		 * We shouldn't have to worry about locking interactions
		 * between the lower layer and our union layer (w.r.t.
		 * `..' processing) because we don't futz with lowervp
		 * locks in the union-node instantiation code path.
		 */
		lerror = union_lookup1(um->um_lowervp, &lowerdvp,
				&lowervp, cnp);
		if (um->um_op == UNMNT_BELOW)
			cnp->cn_cred = saved_cred;
		cnp->cn_nameiop = nameiop;

		if (lowervp != lowerdvp)
			VOP_UNLOCK(lowerdvp, 0, p);

		if (cnp->cn_consume != 0 || lerror == EACCES) {
			if (lerror == EACCES)
				lowervp = NULLVP;
			if (uppervp != NULLVP) {
				if (uppervp == upperdvp)
					vrele(uppervp);
				else
					vput(uppervp);
				uppervp = NULLVP;
			}
			*ap->a_vpp = lowervp;
			if (!lockparent)
				cnp->cn_flags &= ~LOCKPARENT;
			error = lerror;
			goto out;
		}
	} else {
		lerror = ENOENT;
		if ((cnp->cn_flags & ISDOTDOT) && dun->un_pvp != NULLVP) {
			lowervp = LOWERVP(dun->un_pvp);
			if (lowervp != NULLVP) {
				VREF(lowervp);
				vn_lock(lowervp, LK_EXCLUSIVE | LK_RETRY, p);
				lerror = 0;
			}
		}
	}

	if (!lockparent)
		cnp->cn_flags &= ~LOCKPARENT;

	/*
	 * at this point, we have uerror and lerror indicating
	 * possible errors with the lookups in the upper and lower
	 * layers.  additionally, uppervp and lowervp are (locked)
	 * references to existing vnodes in the upper and lower layers.
	 *
	 * there are now three cases to consider.
	 * 1. if both layers returned an error, then return whatever
	 *    error the upper layer generated.
	 *
	 * 2. if the top layer failed and the bottom layer succeeded
	 *    then two subcases occur.
	 *    a.  the bottom vnode is not a directory, in which
	 *	  case just return a new union vnode referencing
	 *	  an empty top layer and the existing bottom layer.
	 *    b.  the bottom vnode is a directory, in which case
	 *	  create a new directory in the top-level and
	 *	  continue as in case 3.
	 *
	 * 3. if the top layer succeeded then return a new union
	 *    vnode referencing whatever the new top layer and
	 *    whatever the bottom layer returned.
	 */

	*ap->a_vpp = NULLVP;

	/* case 1. */
	if ((uerror != 0) && (lerror != 0)) {
		error = uerror;
		goto out;
	}

	/* case 2. */
	if (uerror != 0 /* && (lerror == 0) */ ) {
		if (lowervp->v_type == VDIR) { /* case 2b. */
			dun->un_flags &= ~UN_ULOCK;
			VOP_UNLOCK(upperdvp, 0, p);
			uerror = union_mkshadow(um, upperdvp, cnp, &uppervp);
			vn_lock(upperdvp, LK_EXCLUSIVE | LK_RETRY, p);
			dun->un_flags |= UN_ULOCK;

			if (uerror) {
				if (lowervp != NULLVP) {
					vput(lowervp);
					lowervp = NULLVP;
				}
				error = uerror;
				goto out;
			}
		}
	}

	if (lowervp != NULLVP)
		VOP_UNLOCK(lowervp, 0, p);

	error = union_allocvp(ap->a_vpp, dvp->v_mount, dvp, upperdvp, cnp,
			      uppervp, lowervp, 1);

	if (error) {
		if (uppervp != NULLVP)
			vput(uppervp);
		if (lowervp != NULLVP)
			vrele(lowervp);
	} else {
		if (*ap->a_vpp != dvp)
			if (!lockparent || !(cnp->cn_flags & ISLASTCN))
				VOP_UNLOCK(dvp, 0, p);
#ifdef DIAGNOSTIC
        if (cnp->cn_namelen == 1 &&
            cnp->cn_nameptr[0] == '.' &&
            *ap->a_vpp != dvp) {
            panic("union_lookup returning . (%p) not same as startdir (%p)",
				  ap->a_vpp, dvp);
		}
#endif
	}

out:
    if (cnp->cn_flags & ISDOTDOT) {
        if (upperdvp != NULL)
            vrele(upperdvp);
        if (lowerdvp != NULL)
            vrele(lowerdvp);
    }

	return (error);
}

static int
union_create(ap)
	struct vop_create_args /* {
		struct vnode *a_dvp;
		struct vnode **a_vpp;
		struct componentname *a_cnp;
		struct vattr *a_vap;
	} */ *ap;
{
	struct union_node *dun = VTOUNION(ap->a_dvp);
	struct vnode *dvp = dun->un_uppervp;
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;

	if (dvp != NULLVP) {
		struct vnode *vp;
		struct mount *mp;
		int error;

		FIXUP(dun, p);

		dun->un_flags |= UN_KLOCK;
		VOP_UNLOCK(ap->a_dvp, 0, p);
		error = VOP_CREATE(dvp, &vp, cnp, ap->a_vap);
		if (error) {
			dun->un_flags |= UN_ULOCK;
			return (error);
		}

		mp = ap->a_dvp->v_mount;
		VOP_UNLOCK(dvp, 0, p);
		error = union_allocvp(ap->a_vpp, mp, NULLVP, NULLVP, cnp, vp,
				NULLVP, 1);
		if (error)
			vput(vp);
		vn_lock(ap->a_dvp, LK_EXCLUSIVE| LK_RETRY, p);
		return (error);
	}

	return (EROFS);
}

static int
union_whiteout(ap)
	struct vop_whiteout_args /* {
		struct vnode *a_dvp;
		struct componentname *a_cnp;
		int a_flags;
	} */ *ap;
{
	struct union_node *un = VTOUNION(ap->a_dvp);
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;

	if (un->un_uppervp == NULLVP)
		return (EOPNOTSUPP);

	FIXUP(un, p);
	return (VOP_WHITEOUT(un->un_uppervp, cnp, ap->a_flags));
}

static int
union_mknod(ap)
	struct vop_mknod_args /* {
		struct vnode *a_dvp;
		struct vnode **a_vpp;
		struct componentname *a_cnp;
		struct vattr *a_vap;
	} */ *ap;
{
	struct union_node *dun = VTOUNION(ap->a_dvp);
	struct vnode *dvp = dun->un_uppervp;
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;

	if (dvp != NULLVP) {
		struct vnode *vp;
		struct mount *mp;
		int error;

		FIXUP(dun, p);

		dun->un_flags |= UN_KLOCK;
		VOP_UNLOCK(ap->a_dvp, 0, p);
		error = VOP_MKNOD(dvp, &vp, cnp, ap->a_vap);
		if (error) {
			dun->un_flags |= UN_ULOCK;
			return (error);
		}

		if (vp != NULLVP) {
			mp = ap->a_dvp->v_mount;
			VOP_UNLOCK(dvp, 0, p);
			error = union_allocvp(ap->a_vpp, mp, NULLVP, NULLVP,
					cnp, vp, NULLVP, 1);
			if (error)
				vput(vp);
			vn_lock(ap->a_dvp, LK_EXCLUSIVE| LK_RETRY, p);
		} else {
			dun->un_flags |= UN_ULOCK;
		}
		return (error);
	}

	return (EROFS);
}

static int
union_open(ap)
	struct vop_open_args /* {
		struct vnodeop_desc *a_desc;
		struct vnode *a_vp;
		int a_mode;
		struct ucred *a_cred;
		struct proc *a_p;
	} */ *ap;
{
	struct union_node *un = VTOUNION(ap->a_vp);
	struct vnode *tvp;
	int mode = ap->a_mode;
	struct ucred *cred = ap->a_cred;
	struct proc *p = ap->a_p;
	int error;

	/*
	 * If there is an existing upper vp then simply open that.
	 */
	tvp = un->un_uppervp;
	if (tvp == NULLVP) {
		/*
		 * If the lower vnode is being opened for writing, then
		 * copy the file contents to the upper vnode and open that,
		 * otherwise can simply open the lower vnode.
		 */
		tvp = un->un_lowervp;
		if ((ap->a_mode & FWRITE) && (tvp->v_type == VREG)) {
			error = union_copyup(un, (mode&O_TRUNC) == 0, cred, p);
			if (error == 0)
				error = VOP_OPEN(un->un_uppervp, mode, cred, p);
			return (error);
		}

		/*
		 * Just open the lower vnode
		 */
		un->un_openl++;
		vn_lock(tvp, LK_EXCLUSIVE | LK_RETRY, p);
		error = VOP_OPEN(tvp, mode, cred, p);
		VOP_UNLOCK(tvp, 0, p);

		return (error);
	}

	FIXUP(un, p);

	error = VOP_OPEN(tvp, mode, cred, p);

	return (error);
}

static int
union_close(ap)
	struct vop_close_args /* {
		struct vnode *a_vp;
		int  a_fflag;
		struct ucred *a_cred;
		struct proc *a_p;
	} */ *ap;
{
	struct union_node *un = VTOUNION(ap->a_vp);
	struct vnode *vp;

	if ((vp = un->un_uppervp) == NULLVP) {
#ifdef UNION_DIAGNOSTIC
		if (un->un_openl <= 0)
			panic("union: un_openl cnt");
#endif
		--un->un_openl;
		vp = un->un_lowervp;
	}

	ap->a_vp = vp;
	return (VCALL(vp, VOFFSET(vop_close), ap));
}

/*
 * Check access permission on the union vnode.
 * The access check being enforced is to check
 * against both the underlying vnode, and any
 * copied vnode.  This ensures that no additional
 * file permissions are given away simply because
 * the user caused an implicit file copy.
 */
static int
union_access(ap)
	struct vop_access_args /* {
		struct vnodeop_desc *a_desc;
		struct vnode *a_vp;
		int a_mode;
		struct ucred *a_cred;
		struct proc *a_p;
	} */ *ap;
{
	struct union_node *un = VTOUNION(ap->a_vp);
	struct proc *p = ap->a_p;
	int error = EACCES;
	struct vnode *vp;
	struct vnode *savedvp;

	/*
	 * Disallow write attempts on filesystems mounted read-only.
	 */
	if (ap->a_mode & VWRITE && (ap->a_vp->v_mount->mnt_flag & MNT_RDONLY)) {
		switch (ap->a_vp->v_type) {
		case VREG: 
		case VDIR:
		case VLNK:
			return (EROFS);
		default:
			break;
		}
	}
	if ((vp = un->un_uppervp) != NULLVP) {
		FIXUP(un, p);
		ap->a_vp = vp;
		return (VCALL(vp, VOFFSET(vop_access), ap));
	}

	if ((vp = un->un_lowervp) != NULLVP) {
		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, p);
		savedvp = ap->a_vp;
		ap->a_vp = vp;
		error = VCALL(vp, VOFFSET(vop_access), ap);
		if (error == 0) {
			struct union_mount *um = MOUNTTOUNIONMOUNT(savedvp->v_mount);

			if (um->um_op == UNMNT_BELOW) {
				ap->a_cred = um->um_cred;
				error = VCALL(vp, VOFFSET(vop_access), ap);
			}
		}
		VOP_UNLOCK(vp, 0, p);
		if (error)
			return (error);
	}

	return (error);
}

/*
 * We handle getattr only to change the fsid and
 * track object sizes
 */
static int
union_getattr(ap)
	struct vop_getattr_args /* {
		struct vnode *a_vp;
		struct vattr *a_vap;
		struct ucred *a_cred;
		struct proc *a_p;
	} */ *ap;
{
	int error;
	struct union_node *un = VTOUNION(ap->a_vp);
	struct vnode *vp = un->un_uppervp;
	struct proc *p = ap->a_p;
	struct vattr *vap;
	struct vattr va;


	/*
	 * Some programs walk the filesystem hierarchy by counting
	 * links to directories to avoid stat'ing all the time.
	 * This means the link count on directories needs to be "correct".
	 * The only way to do that is to call getattr on both layers
	 * and fix up the link count.  The link count will not necessarily
	 * be accurate but will be large enough to defeat the tree walkers.
	 */

	vap = ap->a_vap;

	vp = un->un_uppervp;
	if (vp != NULLVP) {
		/*
		 * It's not clear whether VOP_GETATTR is to be
		 * called with the vnode locked or not.  stat() calls
		 * it with (vp) locked, and fstat calls it with
		 * (vp) unlocked.
		 * In the mean time, compensate here by checking
		 * the union_node's lock flag.
		 */
		if (un->un_flags & UN_LOCKED)
			FIXUP(un, p);

		error = VOP_GETATTR(vp, vap, ap->a_cred, ap->a_p);
		if (error)
			return (error);
		union_newsize(ap->a_vp, vap->va_size, VNOVAL);
	}

	if (vp == NULLVP) {
		vp = un->un_lowervp;
	} else if (vp->v_type == VDIR && un->un_lowervp != NULLVP) {
		vp = un->un_lowervp;
		vap = &va;
	} else {
		vp = NULLVP;
	}

	if (vp != NULLVP) {
		error = VOP_GETATTR(vp, vap, ap->a_cred, ap->a_p);
		if (error)
			return (error);
		union_newsize(ap->a_vp, VNOVAL, vap->va_size);
	}

	if ((vap != ap->a_vap) && (vap->va_type == VDIR))
		ap->a_vap->va_nlink += vap->va_nlink;

	ap->a_vap->va_fsid = ap->a_vp->v_mount->mnt_stat.f_fsid.val[0];
	return (0);
}

static int
union_setattr(ap)
	struct vop_setattr_args /* {
		struct vnode *a_vp;
		struct vattr *a_vap;
		struct ucred *a_cred;
		struct proc *a_p;
	} */ *ap;
{
	struct union_node *un = VTOUNION(ap->a_vp);
	struct proc *p = ap->a_p;
	struct vattr *vap = ap->a_vap;
	int error;

	/*
	 * Disallow write attempts on filesystems mounted read-only.
	 */
	if ((ap->a_vp->v_mount->mnt_flag & MNT_RDONLY) &&
		(vap->va_flags != VNOVAL || vap->va_uid != (uid_t)VNOVAL ||
		 vap->va_gid != (gid_t)VNOVAL || vap->va_atime.tv_sec != VNOVAL ||
		 vap->va_mtime.tv_sec != VNOVAL || vap->va_mode != (mode_t)VNOVAL))
		return (EROFS);

	/*
	 * Handle case of truncating lower object to zero size,
	 * by creating a zero length upper object.  This is to
	 * handle the case of open with O_TRUNC and O_CREAT.
	 */
	if ((un->un_uppervp == NULLVP) &&
	    /* assert(un->un_lowervp != NULLVP) */
	    (un->un_lowervp->v_type == VREG)) {
		error = union_copyup(un, (ap->a_vap->va_size != 0),
						ap->a_cred, ap->a_p);
		if (error)
			return (error);
	}

	/*
	 * Try to set attributes in upper layer,
	 * otherwise return read-only filesystem error.
	 */
	if (un->un_uppervp != NULLVP) {
		FIXUP(un, p);
		error = VOP_SETATTR(un->un_uppervp, ap->a_vap,
					ap->a_cred, ap->a_p);
		if ((error == 0) && (ap->a_vap->va_size != VNOVAL))
			union_newsize(ap->a_vp, ap->a_vap->va_size, VNOVAL);
	} else {
		error = EROFS;
	}

	return (error);
}

static int
union_read(ap)
	struct vop_read_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		int  a_ioflag;
		struct ucred *a_cred;
	} */ *ap;
{
	int error;
	struct proc *p = ap->a_uio->uio_procp;
	struct vnode *vp = OTHERVP(ap->a_vp);
	int dolock = (vp == LOWERVP(ap->a_vp));

	if (dolock)
		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, p);
	else
		FIXUP(VTOUNION(ap->a_vp), p);
	error = VOP_READ(vp, ap->a_uio, ap->a_ioflag, ap->a_cred);
	if (dolock)
		VOP_UNLOCK(vp, 0, p);

	/*
	 * XXX
	 * perhaps the size of the underlying object has changed under
	 * our feet.  take advantage of the offset information present
	 * in the uio structure.
	 */
	if (error == 0) {
		struct union_node *un = VTOUNION(ap->a_vp);
		off_t cur = ap->a_uio->uio_offset;

		if (vp == un->un_uppervp) {
			if (cur > un->un_uppersz)
				union_newsize(ap->a_vp, cur, VNOVAL);
		} else {
			if (cur > un->un_lowersz)
				union_newsize(ap->a_vp, VNOVAL, cur);
		}
	}

	return (error);
}

static int
union_write(ap)
	struct vop_read_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		int  a_ioflag;
		struct ucred *a_cred;
	} */ *ap;
{
	int error;
	struct vnode *vp;
	struct union_node *un = VTOUNION(ap->a_vp);
	struct proc *p = ap->a_uio->uio_procp;

	vp = UPPERVP(ap->a_vp);
	if (vp == NULLVP)
		panic("union: missing upper layer in write");

	FIXUP(un, p);
	error = VOP_WRITE(vp, ap->a_uio, ap->a_ioflag, ap->a_cred);

	/*
	 * the size of the underlying object may be changed by the
	 * write.
	 */
	if (error == 0) {
		off_t cur = ap->a_uio->uio_offset;

		if (cur > un->un_uppersz)
			union_newsize(ap->a_vp, cur, VNOVAL);
	}

	return (error);
}

static int
union_lease(ap)
	struct vop_lease_args /* {
		struct vnode *a_vp;
		struct proc *a_p;
		struct ucred *a_cred;
		int a_flag;
	} */ *ap;
{
	register struct vnode *ovp = OTHERVP(ap->a_vp);

	ap->a_vp = ovp;
	return (VCALL(ovp, VOFFSET(vop_lease), ap));
}

static int
union_ioctl(ap)
	struct vop_ioctl_args /* {
		struct vnode *a_vp;
		int  a_command;
		caddr_t  a_data;
		int  a_fflag;
		struct ucred *a_cred;
		struct proc *a_p;
	} */ *ap;
{
	register struct vnode *ovp = OTHERVP(ap->a_vp);

	ap->a_vp = ovp;
	return (VCALL(ovp, VOFFSET(vop_ioctl), ap));
}

static int
union_poll(ap)
	struct vop_poll_args /* {
		struct vnode *a_vp;
		int  a_events;
		struct ucred *a_cred;
		struct proc *a_p;
	} */ *ap;
{
	register struct vnode *ovp = OTHERVP(ap->a_vp);

	ap->a_vp = ovp;
	return (VCALL(ovp, VOFFSET(vop_poll), ap));
}

static int
union_revoke(ap)
	struct vop_revoke_args /* {
		struct vnode *a_vp;
		int a_flags;
		struct proc *a_p;
	} */ *ap;
{
	struct vnode *vp = ap->a_vp;

	if (UPPERVP(vp))
		VOP_REVOKE(UPPERVP(vp), ap->a_flags);
	if (LOWERVP(vp))
		VOP_REVOKE(LOWERVP(vp), ap->a_flags);
	vgone(vp);
	return (0);
}

static int
union_mmap(ap)
	struct vop_mmap_args /* {
		struct vnode *a_vp;
		int  a_fflags;
		struct ucred *a_cred;
		struct proc *a_p;
	} */ *ap;
{
	register struct vnode *ovp = OTHERVP(ap->a_vp);

	ap->a_vp = ovp;
	return (VCALL(ovp, VOFFSET(vop_mmap), ap));
}

static int
union_fsync(ap)
	struct vop_fsync_args /* {
		struct vnode *a_vp;
		struct ucred *a_cred;
		int  a_waitfor;
		struct proc *a_p;
	} */ *ap;
{
	int error = 0;
	struct proc *p = ap->a_p;
	struct vnode *targetvp = OTHERVP(ap->a_vp);
	struct union_node *un;

	if (targetvp != NULLVP) {
		int dolock = (targetvp == LOWERVP(ap->a_vp));

		un = VTOUNION(ap->a_vp);
		if (dolock)
			vn_lock(targetvp, LK_EXCLUSIVE | LK_RETRY, p);
		else  {
			un = VTOUNION(ap->a_vp);
			if ((un->un_flags & UN_ULOCK) == 0 &&
			    targetvp->v_data != NULL &&
			    ((struct lock *)targetvp->v_data)->lk_lockholder
			        == curproc->p_pid &&
			    VOP_ISLOCKED(targetvp) != 0)
				return 0;   /* XXX */

			FIXUP(un, p);
		}

		error = VOP_FSYNC(targetvp, ap->a_cred, ap->a_waitfor, p);
		if (dolock)
			VOP_UNLOCK(targetvp, 0, p);
	}

	return (error);
}

static int
union_remove(ap)
	struct vop_remove_args /* {
		struct vnode *a_dvp;
		struct vnode *a_vp;
		struct componentname *a_cnp;
	} */ *ap;
{
	struct union_node *dun = VTOUNION(ap->a_dvp);
	struct union_node *un = VTOUNION(ap->a_vp);
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;
	int error;

	if (dun->un_uppervp == NULLVP)
		panic("union remove: null upper vnode");

	if (un->un_uppervp != NULLVP) {
		struct vnode *dvp = dun->un_uppervp;
		struct vnode *vp = un->un_uppervp;

		FIXUP(dun, p);
		dun->un_flags |= UN_KLOCK;
		VOP_UNLOCK(ap->a_dvp, 0, p);
		FIXUP(un, p);
		un->un_flags |= UN_KLOCK;
		VOP_UNLOCK(ap->a_vp, 0, p);

		if (union_dowhiteout(un, cnp->cn_cred, p))
			cnp->cn_flags |= DOWHITEOUT;
		error = VOP_REMOVE(dvp, vp, cnp);
#if 0
		/* XXX */
		if (!error)
			union_removed_upper(un);
#endif
		dun->un_flags |= UN_ULOCK;
		un->un_flags |= UN_ULOCK;
	} else {
		FIXUP(dun, p);
		error = union_mkwhiteout(
			MOUNTTOUNIONMOUNT(UNIONTOV(dun)->v_mount),
			dun->un_uppervp, ap->a_cnp, un->un_path);
	}

	return (error);
}

static int
union_link(ap)
	struct vop_link_args /* {
		struct vnode *a_tdvp;
		struct vnode *a_vp;
		struct componentname *a_cnp;
	} */ *ap;
{
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;
	struct union_node *dun = VTOUNION(ap->a_tdvp);
	struct vnode *vp;
	struct vnode *tdvp;
	int error = 0;


	if (ap->a_tdvp->v_op != ap->a_vp->v_op) {
		vp = ap->a_vp;
	} else {
		struct union_node *tun = VTOUNION(ap->a_vp);
		if (tun->un_uppervp == NULLVP) {
			vn_lock(ap->a_vp, LK_EXCLUSIVE | LK_RETRY, p);
			if (dun->un_uppervp == tun->un_dirvp) {
				dun->un_flags &= ~UN_ULOCK;
				VOP_UNLOCK(dun->un_uppervp, 0, p);
			}
			error = union_copyup(tun, 1, cnp->cn_cred, p);
			if (dun->un_uppervp == tun->un_dirvp) {
				vn_lock(dun->un_uppervp,
						LK_EXCLUSIVE | LK_RETRY, p);
				dun->un_flags |= UN_ULOCK;
			}
			VOP_UNLOCK(ap->a_vp, 0, p);
		}
		vp = tun->un_uppervp;
	}

	tdvp = dun->un_uppervp;
	if (tdvp == NULLVP)
		error = EROFS;

	if (error)
		return (error);

	FIXUP(dun, p);
	dun->un_flags |= UN_KLOCK;
	VOP_UNLOCK(ap->a_tdvp, 0, p);

	error = VOP_LINK(tdvp, vp, cnp);

	dun->un_flags |= UN_ULOCK;

	return (error);
}

static int
union_rename(ap)
	struct vop_rename_args  /* {
		struct vnode *a_fdvp;
		struct vnode *a_fvp;
		struct componentname *a_fcnp;
		struct vnode *a_tdvp;
		struct vnode *a_tvp;
		struct componentname *a_tcnp;
	} */ *ap;
{
	int error;

	struct vnode *fdvp = ap->a_fdvp;
	struct vnode *fvp = ap->a_fvp;
	struct vnode *tdvp = ap->a_tdvp;
	struct vnode *tvp = ap->a_tvp;

	if (fdvp->v_op == union_vnodeop_p) {	/* always true */
		struct union_node *un = VTOUNION(fdvp);
		if (un->un_uppervp == NULLVP) {
			/*
			 * this should never happen in normal
			 * operation but might if there was
			 * a problem creating the top-level shadow
			 * directory.
			 */
			error = EXDEV;
			goto bad;
		}

		fdvp = un->un_uppervp;
		VREF(fdvp);
		vrele(ap->a_fdvp);
	}

	if (fvp->v_op == union_vnodeop_p) {	/* always true */
		struct union_node *un = VTOUNION(fvp);
		if (un->un_uppervp == NULLVP) {
			/* XXX: should do a copyup */
			error = EXDEV;
			goto bad;
		}

		if (un->un_lowervp != NULLVP)
			ap->a_fcnp->cn_flags |= DOWHITEOUT;

		fvp = un->un_uppervp;
		VREF(fvp);
		vrele(ap->a_fvp);
	}

	if (tdvp->v_op == union_vnodeop_p) {
		struct union_node *un = VTOUNION(tdvp);
		if (un->un_uppervp == NULLVP) {
			/*
			 * this should never happen in normal
			 * operation but might if there was
			 * a problem creating the top-level shadow
			 * directory.
			 */
			error = EXDEV;
			goto bad;
		}

		tdvp = un->un_uppervp;
		VREF(tdvp);
		un->un_flags |= UN_KLOCK;
		vput(ap->a_tdvp);
	}

	if (tvp != NULLVP && tvp->v_op == union_vnodeop_p) {
		struct union_node *un = VTOUNION(tvp);

		tvp = un->un_uppervp;
		if (tvp != NULLVP) {
			VREF(tvp);
			un->un_flags |= UN_KLOCK;
		}
		vput(ap->a_tvp);
	}

	return (VOP_RENAME(fdvp, fvp, ap->a_fcnp, tdvp, tvp, ap->a_tcnp));

bad:
	vrele(fdvp);
	vrele(fvp);
	vput(tdvp);
	if (tvp != NULLVP)
		vput(tvp);

	return (error);
}

static int
union_mkdir(ap)
	struct vop_mkdir_args /* {
		struct vnode *a_dvp;
		struct vnode **a_vpp;
		struct componentname *a_cnp;
		struct vattr *a_vap;
	} */ *ap;
{
	struct union_node *dun = VTOUNION(ap->a_dvp);
	struct vnode *dvp = dun->un_uppervp;
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;

	if (dvp != NULLVP) {
		struct vnode *vp;
		int error;

		FIXUP(dun, p);
		dun->un_flags |= UN_KLOCK;
		VOP_UNLOCK(ap->a_dvp, 0, p);
		error = VOP_MKDIR(dvp, &vp, cnp, ap->a_vap);
		if (error) {
			dun->un_flags |= UN_ULOCK;
			return (error);
		}

		VOP_UNLOCK(dvp, 0, p);
		error = union_allocvp(ap->a_vpp, ap->a_dvp->v_mount, ap->a_dvp,
				NULLVP, cnp, vp, NULLVP, 1);
		if (error)
			vput(vp);
		vn_lock(ap->a_dvp, LK_EXCLUSIVE| LK_RETRY, p);

		return (error);
	}

	return (EROFS);
}

static int
union_rmdir(ap)
	struct vop_rmdir_args /* {
		struct vnode *a_dvp;
		struct vnode *a_vp;
		struct componentname *a_cnp;
	} */ *ap;
{
	struct union_node *dun = VTOUNION(ap->a_dvp);
	struct union_node *un = VTOUNION(ap->a_vp);
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;
	int error;

	if (dun->un_uppervp == NULLVP)
		panic("union rmdir: null upper vnode");

	if (un->un_uppervp != NULLVP) {
		struct vnode *dvp = dun->un_uppervp;
		struct vnode *vp = un->un_uppervp;

		FIXUP(dun, p);
		dun->un_flags |= UN_KLOCK;
		VOP_UNLOCK(ap->a_dvp, 0, p);
		FIXUP(un, p);
		un->un_flags |= UN_KLOCK;
		VOP_UNLOCK(ap->a_vp, 0, p);

		if (union_dowhiteout(un, cnp->cn_cred, p))
			cnp->cn_flags |= DOWHITEOUT;
		error = VOP_RMDIR(dvp, vp, ap->a_cnp);
#if 0
		/* XXX */
		if (!error)
			union_removed_upper(un);
#endif
		dun->un_flags |= UN_ULOCK;
		un->un_flags |= UN_ULOCK;
	} else {
		FIXUP(dun, p);
		error = union_mkwhiteout(
			MOUNTTOUNIONMOUNT(UNIONTOV(dun)->v_mount),
			dun->un_uppervp, ap->a_cnp, un->un_path);
	}

	return (error);
}

static int
union_symlink(ap)
	struct vop_symlink_args /* {
		struct vnode *a_dvp;
		struct vnode **a_vpp;
		struct componentname *a_cnp;
		struct vattr *a_vap;
		char *a_target;
	} */ *ap;
{
	struct union_node *dun = VTOUNION(ap->a_dvp);
	struct vnode *dvp = dun->un_uppervp;
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;

	if (dvp != NULLVP) {
		struct vnode *vp;
		int error;

		FIXUP(dun, p);
		dun->un_flags |= UN_KLOCK;
		VOP_UNLOCK(ap->a_dvp, 0, p);
		error = VOP_SYMLINK(dvp, &vp, cnp, ap->a_vap, ap->a_target);
		dun->un_flags |= UN_ULOCK;
		*ap->a_vpp = NULLVP;
		return (error);
	}

	return (EROFS);
}

/*
 * union_readdir works in concert with getdirentries and
 * readdir(3) to provide a list of entries in the unioned
 * directories.  getdirentries is responsible for walking
 * down the union stack.  readdir(3) is responsible for
 * eliminating duplicate names from the returned data stream.
 */
static int
union_readdir(ap)
	struct vop_readdir_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		struct ucred *a_cred;
		int *a_eofflag;
		u_long *a_cookies;
		int a_ncookies;
	} */ *ap;
{
	struct union_node *un = VTOUNION(ap->a_vp);
	struct vnode *uvp = un->un_uppervp;
	struct proc *p = ap->a_uio->uio_procp;

	if (uvp == NULLVP)
		return (0);

	FIXUP(un, p);
	ap->a_vp = uvp;
	return (VCALL(uvp, VOFFSET(vop_readdir), ap));
}

static int
union_readlink(ap)
	struct vop_readlink_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		struct ucred *a_cred;
	} */ *ap;
{
	int error;
	struct uio *uio = ap->a_uio;
	struct proc *p = uio->uio_procp;
	struct vnode *vp = OTHERVP(ap->a_vp);
	int dolock = (vp == LOWERVP(ap->a_vp));

	if (dolock)
		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, p);
	else
		FIXUP(VTOUNION(ap->a_vp), p);
	ap->a_vp = vp;
	error = VCALL(vp, VOFFSET(vop_readlink), ap);
	if (dolock)
		VOP_UNLOCK(vp, 0, p);

	return (error);
}

static int
union_abortop(ap)
	struct vop_abortop_args /* {
		struct vnode *a_dvp;
		struct componentname *a_cnp;
	} */ *ap;
{
	int error;
	struct componentname *cnp = ap->a_cnp;
	struct proc *p = cnp->cn_proc;
	struct vnode *vp = OTHERVP(ap->a_dvp);
	struct union_node *un = VTOUNION(ap->a_dvp);
	int islocked = un->un_flags & UN_LOCKED;
	int dolock = (vp == LOWERVP(ap->a_dvp));

	if (islocked) {
		if (dolock)
			vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, p);
		else
			FIXUP(VTOUNION(ap->a_dvp), p);
	}
	ap->a_dvp = vp;
	error = VCALL(vp, VOFFSET(vop_abortop), ap);
	if (islocked && dolock)
		VOP_UNLOCK(vp, 0, p);

	return (error);
}

static int
union_inactive(ap)
	struct vop_inactive_args /* {
		struct vnode *a_vp;
		struct proc *a_p;
	} */ *ap;
{
	struct vnode *vp = ap->a_vp;
	struct proc *p = ap->a_p;
	struct union_node *un = VTOUNION(vp);
	struct vnode **vpp;

	/*
	 * Do nothing (and _don't_ bypass).
	 * Wait to vrele lowervp until reclaim,
	 * so that until then our union_node is in the
	 * cache and reusable.
	 *
	 * NEEDSWORK: Someday, consider inactive'ing
	 * the lowervp and then trying to reactivate it
	 * with capabilities (v_id)
	 * like they do in the name lookup cache code.
	 * That's too much work for now.
	 */

	if (un->un_dircache != 0) {
		for (vpp = un->un_dircache; *vpp != NULLVP; vpp++)
			vrele(*vpp);
		free(un->un_dircache, M_TEMP);
		un->un_dircache = 0;
	}

	VOP_UNLOCK(vp, 0, p);

	if ((un->un_flags & UN_CACHED) == 0)
		vgone(vp);

	return (0);
}

static int
union_reclaim(ap)
	struct vop_reclaim_args /* {
		struct vnode *a_vp;
	} */ *ap;
{

	union_freevp(ap->a_vp);

	return (0);
}

static int
union_lock(ap)
	struct vop_lock_args *ap;
{
	struct vnode *vp = ap->a_vp;
	struct proc *p = ap->a_p;
	int flags = ap->a_flags;
	struct union_node *un;
	int error;

	vop_nolock(ap);
	/*
	 * Need to do real lockmgr-style locking here.
	 * in the mean time, draining won't work quite right,
	 * which could lead to a few race conditions.
	 * the following test was here, but is not quite right, we
	 * still need to take the lock:
	if ((flags & LK_TYPE_MASK) == LK_DRAIN)
		return (0);
	 */
	flags &= ~LK_INTERLOCK;

start:
	un = VTOUNION(vp);

	if (un->un_uppervp != NULLVP) {
		if (((un->un_flags & UN_ULOCK) == 0) &&
		    (vp->v_usecount != 0)) {
			error = vn_lock(un->un_uppervp, flags, p);
			if (error)
				return (error);
			un->un_flags |= UN_ULOCK;
		}
#ifdef DIAGNOSTIC
		if (un->un_flags & UN_KLOCK) {
			vprint("dangling upper lock", vp);
			panic("union: dangling upper lock");
		}
#endif
	}

	if (un->un_flags & UN_LOCKED) {
#ifdef DIAGNOSTIC
		if (curproc && un->un_pid == curproc->p_pid &&
			    un->un_pid > -1 && curproc->p_pid > -1)
			panic("union: locking against myself");
#endif
		un->un_flags |= UN_WANT;
		tsleep((caddr_t)&un->un_flags, PINOD, "unionlk2", 0);
		goto start;
	}

#ifdef DIAGNOSTIC
	if (curproc)
		un->un_pid = curproc->p_pid;
	else
		un->un_pid = -1;
#endif

	un->un_flags |= UN_LOCKED;
	return (0);
}

/*
 * When operations want to vput() a union node yet retain a lock on
 * the upper vnode (say, to do some further operations like link(),
 * mkdir(), ...), they set UN_KLOCK on the union node, then call
 * vput() which calls VOP_UNLOCK() and comes here.  union_unlock()
 * unlocks the union node (leaving the upper vnode alone), clears the
 * KLOCK flag, and then returns to vput().  The caller then does whatever
 * is left to do with the upper vnode, and ensures that it gets unlocked.
 *
 * If UN_KLOCK isn't set, then the upper vnode is unlocked here.
 */
static int
union_unlock(ap)
	struct vop_unlock_args /* {
		struct vnode *a_vp;
		int a_flags;
		struct proc *a_p;
	} */ *ap;
{
	struct union_node *un = VTOUNION(ap->a_vp);
	struct proc *p = ap->a_p;

#ifdef DIAGNOSTIC
	if ((un->un_flags & UN_LOCKED) == 0)
		panic("union: unlock unlocked node");
	if (curproc && un->un_pid != curproc->p_pid &&
			curproc->p_pid > -1 && un->un_pid > -1)
		panic("union: unlocking other process's union node");
#endif

	un->un_flags &= ~UN_LOCKED;

	if ((un->un_flags & (UN_ULOCK|UN_KLOCK)) == UN_ULOCK)
		VOP_UNLOCK(un->un_uppervp, 0, p);

	un->un_flags &= ~(UN_ULOCK|UN_KLOCK);

	if (un->un_flags & UN_WANT) {
		un->un_flags &= ~UN_WANT;
		wakeup((caddr_t) &un->un_flags);
	}

#ifdef DIAGNOSTIC
	un->un_pid = 0;
#endif
	vop_nounlock(ap);

	return (0);
}

static int
union_bmap(ap)
	struct vop_bmap_args /* {
		struct vnode *a_vp;
		daddr_t  a_bn;
		struct vnode **a_vpp;
		daddr_t *a_bnp;
		int *a_runp;
		int *a_runb;
	} */ *ap;
{
	int error;
	struct proc *p = curproc;		/* XXX */
	struct vnode *vp = OTHERVP(ap->a_vp);
	int dolock = (vp == LOWERVP(ap->a_vp));

	if (dolock)
		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, p);
	else
		FIXUP(VTOUNION(ap->a_vp), p);
	ap->a_vp = vp;
	error = VCALL(vp, VOFFSET(vop_bmap), ap);
	if (dolock)
		VOP_UNLOCK(vp, 0, p);

	return (error);
}

static int
union_print(ap)
	struct vop_print_args /* {
		struct vnode *a_vp;
	} */ *ap;
{
	struct vnode *vp = ap->a_vp;

	printf("\ttag VT_UNION, vp=%p, uppervp=%p, lowervp=%p\n",
			vp, UPPERVP(vp), LOWERVP(vp));
	if (UPPERVP(vp) != NULLVP)
		vprint("union: upper", UPPERVP(vp));
	if (LOWERVP(vp) != NULLVP)
		vprint("union: lower", LOWERVP(vp));

	return (0);
}

static int
union_islocked(ap)
	struct vop_islocked_args /* {
		struct vnode *a_vp;
	} */ *ap;
{

	return ((VTOUNION(ap->a_vp)->un_flags & UN_LOCKED) ? 1 : 0);
}

static int
union_pathconf(ap)
	struct vop_pathconf_args /* {
		struct vnode *a_vp;
		int a_name;
		int *a_retval;
	} */ *ap;
{
	int error;
	struct proc *p = curproc;		/* XXX */
	struct vnode *vp = OTHERVP(ap->a_vp);
	int dolock = (vp == LOWERVP(ap->a_vp));

	if (dolock)
		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, p);
	else
		FIXUP(VTOUNION(ap->a_vp), p);
	ap->a_vp = vp;
	error = VCALL(vp, VOFFSET(vop_pathconf), ap);
	if (dolock)
		VOP_UNLOCK(vp, 0, p);

	return (error);
}

static int
union_advlock(ap)
	struct vop_advlock_args /* {
		struct vnode *a_vp;
		caddr_t  a_id;
		int  a_op;
		struct flock *a_fl;
		int  a_flags;
	} */ *ap;
{
	register struct vnode *ovp = OTHERVP(ap->a_vp);

	ap->a_vp = ovp;
	return (VCALL(ovp, VOFFSET(vop_advlock), ap));
}


/*
 * XXX - vop_strategy must be hand coded because it has no
 * vnode in its arguments.
 * This goes away with a merged VM/buffer cache.
 */
static int
union_strategy(ap)
	struct vop_strategy_args /* {
		struct vnode *a_vp;
		struct buf *a_bp;
	} */ *ap;
{
	struct buf *bp = ap->a_bp;
	int error;
	struct vnode *savedvp;

	savedvp = bp->b_vp;
	bp->b_vp = OTHERVP(bp->b_vp);

#ifdef DIAGNOSTIC
	if (bp->b_vp == NULLVP)
		panic("union_strategy: nil vp");
	if (((bp->b_flags & B_READ) == 0) &&
	    (bp->b_vp == LOWERVP(savedvp)))
		panic("union_strategy: writing to lowervp");
#endif

	error = VOP_STRATEGY(bp->b_vp, bp);
	bp->b_vp = savedvp;

	return (error);
}

/*
 * Global vfs data structures
 */
vop_t **union_vnodeop_p;
static struct vnodeopv_entry_desc union_vnodeop_entries[] = {
	{ &vop_default_desc,		(vop_t *) vop_defaultop },
	{ &vop_abortop_desc,		(vop_t *) union_abortop },
	{ &vop_access_desc,		(vop_t *) union_access },
	{ &vop_advlock_desc,		(vop_t *) union_advlock },
	{ &vop_bmap_desc,		(vop_t *) union_bmap },
	{ &vop_close_desc,		(vop_t *) union_close },
	{ &vop_create_desc,		(vop_t *) union_create },
	{ &vop_fsync_desc,		(vop_t *) union_fsync },
	{ &vop_getattr_desc,		(vop_t *) union_getattr },
	{ &vop_inactive_desc,		(vop_t *) union_inactive },
	{ &vop_ioctl_desc,		(vop_t *) union_ioctl },
	{ &vop_islocked_desc,		(vop_t *) union_islocked },
	{ &vop_lease_desc,		(vop_t *) union_lease },
	{ &vop_link_desc,		(vop_t *) union_link },
	{ &vop_lock_desc,		(vop_t *) union_lock },
	{ &vop_lookup_desc,		(vop_t *) union_lookup },
	{ &vop_mkdir_desc,		(vop_t *) union_mkdir },
	{ &vop_mknod_desc,		(vop_t *) union_mknod },
	{ &vop_mmap_desc,		(vop_t *) union_mmap },
	{ &vop_open_desc,		(vop_t *) union_open },
	{ &vop_pathconf_desc,		(vop_t *) union_pathconf },
	{ &vop_poll_desc,		(vop_t *) union_poll },
	{ &vop_print_desc,		(vop_t *) union_print },
	{ &vop_read_desc,		(vop_t *) union_read },
	{ &vop_readdir_desc,		(vop_t *) union_readdir },
	{ &vop_readlink_desc,		(vop_t *) union_readlink },
	{ &vop_reclaim_desc,		(vop_t *) union_reclaim },
	{ &vop_remove_desc,		(vop_t *) union_remove },
	{ &vop_rename_desc,		(vop_t *) union_rename },
	{ &vop_revoke_desc,		(vop_t *) union_revoke },
	{ &vop_rmdir_desc,		(vop_t *) union_rmdir },
	{ &vop_setattr_desc,		(vop_t *) union_setattr },
	{ &vop_strategy_desc,		(vop_t *) union_strategy },
	{ &vop_symlink_desc,		(vop_t *) union_symlink },
	{ &vop_unlock_desc,		(vop_t *) union_unlock },
	{ &vop_whiteout_desc,		(vop_t *) union_whiteout },
	{ &vop_write_desc,		(vop_t *) union_write },
	{ NULL, NULL }
};
static struct vnodeopv_desc union_vnodeop_opv_desc =
	{ &union_vnodeop_p, union_vnodeop_entries };

VNODEOP_SET(union_vnodeop_opv_desc);