xnu-792.18.15.tar.gz

[apple/xnu.git] / bsd / miscfs / union / union_vnops.c

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 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
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/kauth.h>
#include <sys/file.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/vnode_internal.h>
#include <sys/mount_internal.h>
#include <sys/namei.h>
#include <sys/malloc.h>
#include <sys/buf_internal.h>
#include <sys/queue.h>
#include <sys/lock.h>
#include <miscfs/union/union.h>
#include <vfs/vfs_support.h>
#include <sys/ubc.h>
#include <sys/uio_internal.h>

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

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

        un->un_flags |= UN_ULOCK;
}

static int
union_lookup1(struct vnode *udvp, struct vnode **dvpp, struct vnode **vpp,
        struct componentname *cnp)
{
        int error;
        vfs_context_t ctx = cnp->cn_context;
        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;
                        vnode_put(tdvp);
                        vnode_get(dvp);
                }
        }

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

        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, LK_NOWAIT)) {
                        vnode_put(dvp);
                        return(ENOENT);
                }
                error = VFS_ROOT(mp, &tdvp, ctx);
                vfs_unbusy(mp);
                if (error) {
                        vnode_put(dvp);
                        return (error);
                }

                vnode_put(dvp);
                dvp = tdvp;
        }

        *vpp = dvp;
        return (0);
}

int
union_lookup(
        struct vnop_lookup_args /* {
                struct vnodeop_desc *a_desc;
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
                vfs_context_t a_context;
        } */ *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;
        vfs_context_t ctx = cnp->cn_context;
        struct proc *p = vfs_context_proc(ctx);
        int lockparent = cnp->cn_flags & LOCKPARENT;
        struct union_mount *um = MOUNTTOUNIONMOUNT(dvp->v_mount);
        kauth_cred_t saved_cred;
        int iswhiteout;
        struct vnode_attr va;

#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);
                vnode_get(dvp);

                return (0);
        }
#endif

        cnp->cn_flags |= LOCKPARENT;

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

        /*
         * 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);
                uerror = union_lookup1(um->um_uppervp, &upperdvp,
                                        &uppervp, cnp);
                /*if (uppervp == upperdvp)
                        dun->un_flags |= UN_KLOCK;*/

                if (cnp->cn_consume != 0) {
                        *ap->a_vpp = uppervp;
                        if (!lockparent)
                                cnp->cn_flags &= ~LOCKPARENT;
                        return (uerror);
                }
                if (uerror == ENOENT || uerror == EJUSTRETURN) {
                        if (cnp->cn_flags & ISWHITEOUT) {
                                iswhiteout = 1;
                        } else if (lowerdvp != NULLVP) {
                                VATTR_INIT(&va);
                                VATTR_WANTED(&va, va_flags);
                                lerror = vnode_getattr(upperdvp, &va, ap->a_context);
                                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 vnode_put whatever we got
         * back from the upper layer and return the lower vnode
         * instead.
         */
        if (lowerdvp != NULLVP && !iswhiteout) {
                int nameiop;

                /*
                 * 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) {
                        /* XXX BOGUS */
                        saved_cred = cnp->cn_context->vc_ucred;
                        cnp->cn_context->vc_ucred = um->um_cred;
                        lerror = union_lookup1(um->um_lowervp, &lowerdvp,
                                        &lowervp, cnp);
                        cnp->cn_context->vc_ucred = saved_cred;
                } else {
                        lerror = union_lookup1(um->um_lowervp, &lowerdvp,
                                        &lowervp, cnp);
                }
                cnp->cn_nameiop = nameiop;

                if (cnp->cn_consume != 0) {
                        if (uppervp != NULLVP) {
                                vnode_put(uppervp);
                                uppervp = NULLVP;
                        }
                        *ap->a_vpp = lowervp;
                        if (!lockparent)
                                cnp->cn_flags &= ~LOCKPARENT;
                        return (lerror);
                }
        } else {
                lerror = ENOENT;
                if ((cnp->cn_flags & ISDOTDOT) && dun->un_pvp != NULLVP) {
                        lowervp = LOWERVP(dun->un_pvp);
                        if (lowervp != NULLVP) {
                                vnode_get(lowervp);
                                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)) {
                return (uerror);
        }

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

                        if (uerror) {
                                if (lowervp != NULLVP) {
                                        vnode_put(lowervp);
                                        lowervp = NULLVP;
                                }
                                return (uerror);
                        }
                }
        }
        error = union_allocvp(ap->a_vpp, dvp->v_mount, dvp, upperdvp, cnp,
                              uppervp, lowervp, 1);

        if (error) {
                if (uppervp != NULLVP)
                        vnode_put(uppervp);
                if (lowervp != NULLVP)
                        vnode_put(lowervp);
        }

        return (error);
}

int
union_create(
        struct vnop_create_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
                struct vnode_attr *a_vap;
                vfs_context_t a_context;
        } */ *ap)
{
        struct union_node *un = VTOUNION(ap->a_dvp);
        struct vnode *dvp = un->un_uppervp;
        struct componentname *cnp = ap->a_cnp;
        vfs_context_t ctx = cnp->cn_context;
        struct proc *p = vfs_context_proc(ctx);

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

                FIXUP(un, p);

                un->un_flags |= UN_KLOCK;
                mp = ap->a_dvp->v_mount;

                /* note that this is a direct passthrough to the filesystem */
                error = VNOP_CREATE(dvp, &vp, cnp, ap->a_vap, ap->a_context);
                if (error)
                        return (error);

                error = union_allocvp(ap->a_vpp, mp, NULLVP, NULLVP, cnp, vp,
                                NULLVP, 1);
                if (error)
                        vnode_put(vp);
                return (error);
        }
        return (EROFS);
}

int
union_whiteout(
        struct vnop_whiteout_args /* {
                struct vnode *a_dvp;
                struct componentname *a_cnp;
                int a_flags;
                vfs_context_t a_context;
        } */ *ap)
{
        struct union_node *un = VTOUNION(ap->a_dvp);
        struct componentname *cnp = ap->a_cnp;
        vfs_context_t ctx = cnp->cn_context;
        struct proc *p = vfs_context_proc(ctx);

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

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

int
union_mknod(
        struct vnop_mknod_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
                struct vnode_attr *a_vap;
                vfs_context_t a_context;
        } */ *ap)
{
        struct union_node *un = VTOUNION(ap->a_dvp);
        struct vnode *dvp = un->un_uppervp;
        struct componentname *cnp = ap->a_cnp;
        vfs_context_t ctx = cnp->cn_context;
        struct proc *p = vfs_context_proc(ctx);

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

                FIXUP(un, p);

                un->un_flags |= UN_KLOCK;
                mp = ap->a_dvp->v_mount;

                /* note that this is a direct passthrough to the filesystem */
                error = VNOP_MKNOD(dvp, &vp, cnp, ap->a_vap, ap->a_context);
                if (error)
                        return (error);

                if (vp != NULLVP) {
                        error = union_allocvp(ap->a_vpp, mp, NULLVP, NULLVP,
                                        cnp, vp, NULLVP, 1);
                        if (error)
                                vnode_put(vp);
                }
                return (error);
        }
        return (EROFS);
}

int
union_open(
        struct vnop_open_args /* {
                struct vnodeop_desc *a_desc;
                struct vnode *a_vp;
                int a_mode;
                vfs_context_t a_context;
        } */ *ap)
{
        struct union_node *un = VTOUNION(ap->a_vp);
        struct vnode *tvp;
        int mode = ap->a_mode;
        kauth_cred_t cred = vfs_context_ucred(ap->a_context);
        struct proc *p = vfs_context_proc(ap->a_context);
        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 = VNOP_OPEN(un->un_uppervp, mode, ap->a_context);
                        return (error);
                }

                /*
                 * Just open the lower vnode
                 */
                un->un_openl++;

                error = VNOP_OPEN(tvp, mode, ap->a_context);

                return (error);
        }

        FIXUP(un, p);

        error = VNOP_OPEN(tvp, mode, ap->a_context);

        return (error);
}

int
union_close(ap)
        struct vnop_close_args /* {
                struct vnode *a_vp;
                int  a_fflag;
                vfs_context_t a_context;
        } */ *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(vnop_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.
 */
int
union_access(
        struct vnop_access_args /* {
                struct vnodeop_desc *a_desc;
                struct vnode *a_vp;
                int a_action;
                vfs_context_t a_context;
        } */ *ap)
{
        struct union_node *un = VTOUNION(ap->a_vp);
        struct proc *p = vfs_context_proc(ap->a_context);
        int error = EACCES;
        struct vnode *vp;

        if ((vp = un->un_uppervp) != NULLVP) {
                FIXUP(un, p);
                ap->a_vp = vp;
                return (VCALL(vp, VOFFSET(vnop_access), ap));
        }

        if ((vp = un->un_lowervp) != NULLVP) {
                ap->a_vp = vp;
                error = VCALL(vp, VOFFSET(vnop_access), ap);
                if (error == 0) {
                        struct union_mount *um = MOUNTTOUNIONMOUNT(vp->v_mount);

                        if (um->um_op == UNMNT_BELOW) {
                                /* XXX fix me */
                        //      ap->a_cred = um->um_cred;
                                error = VCALL(vp, VOFFSET(vnop_access), ap);
                        }
                }
                if (error)
                        return (error);
        }

        return (error);
}

/*
 * We handle getattr only to change the fsid and
 * track object sizes
 */
int
union_getattr(ap)
        struct vnop_getattr_args /* {
                struct vnode *a_vp;
                struct vnode_attr *a_vap;
                vfs_context_t a_context;
        } */ *ap;
{
        int error;
        struct union_node *un = VTOUNION(ap->a_vp);
        struct vnode *vp = un->un_uppervp;
        struct proc *p = vfs_context_proc(ap->a_context);
        struct vnode_attr *vap;
        struct vnode_attr 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 vnop_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 = vnode_getattr(vp, vap, ap->a_context);
                if (error)
                        return (error);
                union_newsize(ap->a_vp, vap->va_data_size, VNOVAL);
        }

        if (vp == NULLVP) {
                vp = un->un_lowervp;
        } else if (vp->v_type == VDIR) {
                vp = un->un_lowervp;
                VATTR_INIT(&va);
                /* all we want from the lower node is the link count */
                VATTR_WANTED(&va, va_nlink);
                vap = &va;
        } else {
                vp = NULLVP;
        }

        if (vp != NULLVP) {
                error = vnode_getattr(vp, vap, ap->a_context);
                if (error)
                        return (error);
                union_newsize(ap->a_vp, VNOVAL, vap->va_data_size);
        }

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

        VATTR_RETURN(ap->a_vap, va_fsid, ap->a_vp->v_mount->mnt_vfsstat.f_fsid.val[0]);
        return (0);
}

int
union_setattr(ap)
        struct vnop_setattr_args /* {
                struct vnode *a_vp;
                struct vnode_attr *a_vap;
                vfs_context_t a_context;
        } */ *ap;
{
        struct union_node *un = VTOUNION(ap->a_vp);
        struct proc *p = vfs_context_proc(ap->a_context);
        kauth_cred_t cred = vfs_context_ucred(ap->a_context);
        int error;

        /*
         * 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 (VATTR_IS_ACTIVE(ap->a_vap, va_data_size) &&
            (un->un_uppervp == NULLVP) &&
            /* assert(un->un_lowervp != NULLVP) */
            (un->un_lowervp->v_type == VREG)) {
                error = union_copyup(un, (ap->a_vap->va_data_size != 0), cred, 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 = vnode_setattr(un->un_uppervp, ap->a_vap, ap->a_context);
                if ((error == 0) && VATTR_IS_ACTIVE(ap->a_vap, va_data_size))
                        union_newsize(ap->a_vp, ap->a_vap->va_data_size, VNOVAL);
        } else {
                error = EROFS;
        }

        return (error);
}

int
union_read(ap)
        struct vnop_read_args /* {
                struct vnode *a_vp;
                struct uio *a_uio;
                int  a_ioflag;
                vfs_context_t a_context;
        } */ *ap;
{
        int error;
        struct proc *p = vfs_context_proc(ap->a_context);
        struct vnode *vp = OTHERVP(ap->a_vp);
        int dolock = (vp == LOWERVP(ap->a_vp));

        if (!dolock)
                FIXUP(VTOUNION(ap->a_vp), p);
        error = VNOP_READ(vp, ap->a_uio, ap->a_ioflag, ap->a_context);

        /*
         * 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);
}

int
union_write(ap)
        struct vnop_read_args /* {
                struct vnode *a_vp;
                struct uio *a_uio;
                int  a_ioflag;
                vfs_context_t a_context;
        } */ *ap;
{
        int error;
        struct vnode *vp;
        struct union_node *un = VTOUNION(ap->a_vp);
        struct proc *p = vfs_context_proc(ap->a_context);

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

        FIXUP(un, p);
        error = VNOP_WRITE(vp, ap->a_uio, ap->a_ioflag, ap->a_context);

        /*
         * 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);
}


int
union_ioctl(ap)
        struct vnop_ioctl_args /* {
                struct vnode *a_vp;
                int  a_command;
                caddr_t  a_data;
                int  a_fflag;
                vfs_context_t a_context;
        } */ *ap;
{
        register struct vnode *ovp = OTHERVP(ap->a_vp);

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

int
union_select(ap)
        struct vnop_select_args /* {
                struct vnode *a_vp;
                int  a_which;
                int  a_fflags;
                void * a_wql;
                vfs_context_t a_context;
        } */ *ap;
{
        register struct vnode *ovp = OTHERVP(ap->a_vp);

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

int
union_revoke(ap)
        struct vnop_revoke_args /* {
                struct vnode *a_vp;
                int a_flags;
                vfs_context_t a_context;
        } */ *ap;
{
        struct vnode *vp = ap->a_vp;

        if (UPPERVP(vp))
                VNOP_REVOKE(UPPERVP(vp), ap->a_flags, ap->a_context);
        if (LOWERVP(vp))
                VNOP_REVOKE(LOWERVP(vp), ap->a_flags, ap->a_context);
        vnode_reclaim(vp);
}

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

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

int
union_fsync(
        struct vnop_fsync_args /* {
                struct vnode *a_vp;
                int  a_waitfor;
                vfs_context_t a_context;
        } */ *ap)
{
        int error = 0;
        struct proc *p = vfs_context_proc(ap->a_context);
        struct vnode *targetvp = OTHERVP(ap->a_vp);

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

                if (!dolock)
                        FIXUP(VTOUNION(ap->a_vp), p);
                error = VNOP_FSYNC(targetvp, ap->a_waitfor, ap->a_context);
        }

        return (error);
}

int
union_remove(
        struct vnop_remove_args /* {
                struct vnode *a_dvp;
                struct vnode *a_vp;
                struct componentname *a_cnp;
                vfs_context_t a_context;
        } */ *ap)
{
        int error;
        struct union_node *dun = VTOUNION(ap->a_dvp);
        struct union_node *un = VTOUNION(ap->a_vp);
        struct componentname *cnp = ap->a_cnp;
        vfs_context_t ctx = cnp->cn_context;
        struct proc *p = vfs_context_proc(ctx);

        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;
                FIXUP(un, p);
                un->un_flags |= UN_KLOCK;

                if (union_dowhiteout(un, cnp->cn_context))
                        cnp->cn_flags |= DOWHITEOUT;
                error = VNOP_REMOVE(dvp, vp, cnp, 0, ap->a_context);
                if (!error)
                        union_removed_upper(un);
        } else {
                FIXUP(dun, p);
                error = union_mkwhiteout(
                        MOUNTTOUNIONMOUNT(UNIONTOV(dun)->v_mount),
                        dun->un_uppervp, ap->a_cnp, un->un_path);
        }

        return (error);
}

int
union_link(
        struct vnop_link_args /* {
                struct vnode *a_vp;
                struct vnode *a_tdvp;
                struct componentname *a_cnp;
                vfs_context_t a_context;
        } */ *ap)
{
        int error = 0;
        struct componentname *cnp = ap->a_cnp;
        vfs_context_t ctx = cnp->cn_context;
        struct proc *p = vfs_context_proc(ctx);
        struct union_node *un;
        struct vnode *vp;
        struct vnode *tdvp;

        un = VTOUNION(ap->a_tdvp);

        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) {
                        if (un->un_uppervp == tun->un_dirvp) {
                                un->un_flags &= ~UN_ULOCK;
                        }
                        error = union_copyup(tun, 1, vfs_context_ucred(ctx), p);
                        if (un->un_uppervp == tun->un_dirvp) {
                                un->un_flags |= UN_ULOCK;
                        }
                }
                vp = tun->un_uppervp;
        }
        tdvp = un->un_uppervp;
        if (tdvp == NULLVP)
                error = EROFS;

        if (error) {
                return (error);
        }

        FIXUP(un, p);
        vnode_get(tdvp);
        un->un_flags |= UN_KLOCK;

        return (VNOP_LINK(vp, tdvp, cnp, ap->a_context));
}

int
union_rename(ap)
        struct vnop_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;
                vfs_context_t a_context;
        } */ *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;
                vnode_get(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;
                vnode_get(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;
                vnode_get(tdvp);
                un->un_flags |= UN_KLOCK;
        }

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

                tvp = un->un_uppervp;
                if (tvp != NULLVP) {
                        vnode_get(tvp);
                        un->un_flags |= UN_KLOCK;
                }
        }

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

bad:
        return (error);
}

int
union_mkdir(
        struct vnop_mkdir_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
                struct vnode_attr *a_vap;
                vfs_context_t a_context;
        } */ *ap)
{
        struct union_node *un = VTOUNION(ap->a_dvp);
        struct vnode *dvp = un->un_uppervp;
        struct componentname *cnp = ap->a_cnp;
        vfs_context_t ctx = cnp->cn_context;
        struct proc *p = vfs_context_proc(ctx);

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

                FIXUP(un, p);
                un->un_flags |= UN_KLOCK;

                /* note that this is a direct fallthrough to the filesystem */
                error = VNOP_MKDIR(dvp, &vp, cnp, ap->a_vap, ap->a_context);
                if (error)
                        return (error);

                error = union_allocvp(ap->a_vpp, ap->a_dvp->v_mount, ap->a_dvp,
                                NULLVP, cnp, vp, NULLVP, 1);
                if (error)
                        vnode_put(vp);
                return (error);
        }
        return (EROFS);
}

int
union_rmdir(
        struct vnop_rmdir_args /* {
                struct vnode *a_dvp;
                struct vnode *a_vp;
                struct componentname *a_cnp;
                vfs_context_t a_context;
        } */ *ap)
{
        int error;
        struct union_node *dun = VTOUNION(ap->a_dvp);
        struct union_node *un = VTOUNION(ap->a_vp);
        struct componentname *cnp = ap->a_cnp;
        vfs_context_t ctx = cnp->cn_context;
        struct proc *p = vfs_context_proc(ctx);

        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);
                vnode_get(dvp);
                dun->un_flags |= UN_KLOCK;
                FIXUP(un, p);
                vnode_get(vp);
                un->un_flags |= UN_KLOCK;

                if (union_dowhiteout(un, cnp->cn_context))
                        cnp->cn_flags |= DOWHITEOUT;
                error = VNOP_RMDIR(dvp, vp, ap->a_cnp, ap->a_context);
                if (!error)
                        union_removed_upper(un);
        } else {
                FIXUP(dun, p);
                error = union_mkwhiteout(
                        MOUNTTOUNIONMOUNT(UNIONTOV(dun)->v_mount),
                        dun->un_uppervp, ap->a_cnp, un->un_path);
        }
        return (error);
}

int
union_symlink(
        struct vnop_symlink_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
                struct vnode_attr *a_vap;
                char *a_target;
                vfs_context_t a_context;
        } */ *ap)
{
        struct union_node *un = VTOUNION(ap->a_dvp);
        struct vnode *dvp = un->un_uppervp;
        struct componentname *cnp = ap->a_cnp;
        vfs_context_t ctx = cnp->cn_context;
        struct proc *p = vfs_context_proc(ctx);

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

                FIXUP(un, p);
                un->un_flags |= UN_KLOCK;

                error = VNOP_SYMLINK(dvp, &vp, cnp, ap->a_vap, ap->a_target, ap->a_context);
                *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.
 */
int
union_readdir(ap)
        struct vnop_readdir_args /* {
                struct vnodeop_desc *a_desc;
                struct vnode *a_vp;
                struct uio *a_uio;
                int a_flags;
                int *a_eofflag;
                int *a_numdirent;
                vfs_context_t a_context;
        } */ *ap;
{
        struct union_node *un = VTOUNION(ap->a_vp);
        struct vnode *uvp = un->un_uppervp;
        struct proc *p = vfs_context_proc(ap->a_context);

        if (ap->a_flags & (VNODE_READDIR_EXTENDED | VNODE_READDIR_REQSEEKOFF))
                return (EINVAL);

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

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

int
union_readlink(ap)
        struct vnop_readlink_args /* {
                struct vnode *a_vp;
                struct uio *a_uio;
                vfs_context_t a_context;
        } */ *ap;
{
        int error;
        struct uio *uio = ap->a_uio;
        struct proc *p = vfs_context_proc(ap->a_context);
        struct vnode *vp = OTHERVP(ap->a_vp);
        int dolock = (vp == LOWERVP(ap->a_vp));

        if (!dolock)
                FIXUP(VTOUNION(ap->a_vp), p);
        ap->a_vp = vp;
        error = VCALL(vp, VOFFSET(vnop_readlink), ap);

        return (error);
}

int
union_inactive(
        struct vnop_inactive_args /* {
                struct vnode *a_vp;
                vfs_context_t a_context;
        } */ *ap)
{
        struct vnode *vp = ap->a_vp;
        struct union_node *un = VTOUNION(vp);
        struct vnode **vpp;

        /*
         * Do nothing (and _don't_ bypass).
         * Wait to vnode_put 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++)
                        vnode_put(*vpp);
                _FREE(un->un_dircache, M_TEMP);
                un->un_dircache = 0;
        }

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

        return (0);
}

int
union_reclaim(ap)
        struct vnop_reclaim_args /* {
                struct vnode *a_vp;
                vfs_context_t a_context;
        } */ *ap;
{

        union_freevp(ap->a_vp);

        return (0);
}

int
union_blockmap(ap)
        struct vnop_blockmap_args /* {
                struct vnode *a_vp;
                off_t a_offset;    
                size_t a_size;
                daddr64_t *a_bpn;
                size_t *a_run;
                void *a_poff;
                int a_flags;
        } */ *ap;
{
        int error;
        struct proc *p = current_proc();                /* XXX */
        struct vnode *vp = OTHERVP(ap->a_vp);
        int dolock = (vp == LOWERVP(ap->a_vp));

        if (!dolock)
                FIXUP(VTOUNION(ap->a_vp), p);
        ap->a_vp = vp;
        error = VCALL(vp, VOFFSET(vnop_blockmap), ap);

        return (error);
}

int
union_pathconf(ap)
        struct vnop_pathconf_args /* {
                struct vnode *a_vp;
                int a_name;
                int *a_retval;
                vfs_context_t a_context;
        } */ *ap;
{
        int error;
        struct proc *p = current_proc();                /* XXX */
        struct vnode *vp = OTHERVP(ap->a_vp);
        int dolock = (vp == LOWERVP(ap->a_vp));

        if (!dolock)
                FIXUP(VTOUNION(ap->a_vp), p);
        ap->a_vp = vp;
        error = VCALL(vp, VOFFSET(vnop_pathconf), ap);

        return (error);
}

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

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


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

        savedvp = buf_vnode(bp);
        buf_setvnode(bp, OTHERVP(savedvp));

#if DIAGNOSTIC
        if (buf_vnode(bp) == NULLVP)
                panic("union_strategy: nil vp");
        if (((buf_flags(bp) & B_READ) == 0) &&
            (buf_vnode(bp) == LOWERVP(savedvp)))
                panic("union_strategy: writing to lowervp");
#endif

        error = VNOP_STRATEGY(bp);
        buf_setvnode(bp, savedvp);

        return (error);
}

/* Pagein */
int
union_pagein(ap)
        struct vnop_pagein_args /* {
                struct vnode    *a_vp,
                upl_t           a_pl,
                vm_offset_t     a_pl_offset,
                off_t           a_f_offset,
                size_t          a_size,
                int             a_flags
                vfs_context_t   a_context;
        } */ *ap;
{
        int error;
        struct vnode *vp = OTHERVP(ap->a_vp);

        error = VNOP_PAGEIN(vp, ap->a_pl, ap->a_pl_offset, ap->a_f_offset,
                            ap->a_size, ap->a_flags, ap->a_context);

        /*
         * 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_f_offset + (off_t)ap->a_pl_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);
}

/* Pageout  */
int
union_pageout(ap)
        struct vnop_pageout_args /* {
                struct vnode    *a_vp,
                upl_t           a_pl,
                vm_offset_t     a_pl_offset,
                off_t           a_f_offset,
                size_t          a_size,
                int             a_flags
                vfs_context_t   a_context;
        } */ *ap;
{
        int error;
        struct vnode *vp;
        struct union_node *un = VTOUNION(ap->a_vp);

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

        error = VNOP_PAGEOUT(vp, ap->a_pl, ap->a_pl_offset, ap->a_f_offset,
                             ap->a_size, ap->a_flags, ap->a_context);

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

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

        return (error);
}

/* Blktooff derives file offset for the given logical block number */
int
union_blktooff(ap)
        struct vnop_blktooff_args /* {
                struct vnode *a_vp;
                daddr64_t a_lblkno;
                off_t *a_offset;    
        } */ *ap;
{
        int error;
        struct vnode *vp = OTHERVP(ap->a_vp);

        error = VNOP_BLKTOOFF(vp, ap->a_lblkno, ap->a_offset);

        return(error);
}

/* offtoblk derives file offset for the given logical block number */
int
union_offtoblk(ap)
        struct vnop_offtoblk_args /* {
                struct vnode *a_vp;
                off_t a_offset;    
                daddr64_t *a_lblkno;
        } */ *ap;
{
        int error;
        struct vnode *vp = OTHERVP(ap->a_vp);

        error = VNOP_OFFTOBLK(vp, ap->a_offset, ap->a_lblkno);

        return(error);
}

#define VOPFUNC int (*)(void *)

/*
 * Global vfs data structures
 */
int (**union_vnodeop_p)(void *);
struct vnodeopv_entry_desc union_vnodeop_entries[] = {
        { &vnop_default_desc, (VOPFUNC)vn_default_error },
        { &vnop_lookup_desc, (VOPFUNC)union_lookup },           /* lookup */
        { &vnop_create_desc, (VOPFUNC)union_create },           /* create */
        { &vnop_whiteout_desc, (VOPFUNC)union_whiteout },       /* whiteout */
        { &vnop_mknod_desc, (VOPFUNC)union_mknod },             /* mknod */
        { &vnop_open_desc, (VOPFUNC)union_open },               /* open */
        { &vnop_close_desc, (VOPFUNC)union_close },             /* close */
        { &vnop_access_desc, (VOPFUNC)union_access },           /* access */
        { &vnop_getattr_desc, (VOPFUNC)union_getattr },         /* getattr */
        { &vnop_setattr_desc, (VOPFUNC)union_setattr },         /* setattr */
        { &vnop_read_desc, (VOPFUNC)union_read },               /* read */
        { &vnop_write_desc, (VOPFUNC)union_write },             /* write */
        { &vnop_ioctl_desc, (VOPFUNC)union_ioctl },             /* ioctl */
        { &vnop_select_desc, (VOPFUNC)union_select },           /* select */
        { &vnop_revoke_desc, (VOPFUNC)union_revoke },           /* revoke */
        { &vnop_mmap_desc, (VOPFUNC)union_mmap },               /* mmap */
        { &vnop_fsync_desc, (VOPFUNC)union_fsync },             /* fsync */
        { &vnop_remove_desc, (VOPFUNC)union_remove },           /* remove */
        { &vnop_link_desc, (VOPFUNC)union_link },               /* link */
        { &vnop_rename_desc, (VOPFUNC)union_rename },           /* rename */
        { &vnop_mkdir_desc, (VOPFUNC)union_mkdir },             /* mkdir */
        { &vnop_rmdir_desc, (VOPFUNC)union_rmdir },             /* rmdir */
        { &vnop_symlink_desc, (VOPFUNC)union_symlink },         /* symlink */
        { &vnop_readdir_desc, (VOPFUNC)union_readdir },         /* readdir */
        { &vnop_readlink_desc, (VOPFUNC)union_readlink },       /* readlink */
        { &vnop_inactive_desc, (VOPFUNC)union_inactive },       /* inactive */
        { &vnop_reclaim_desc, (VOPFUNC)union_reclaim },         /* reclaim */
        { &vnop_strategy_desc, (VOPFUNC)union_strategy },       /* strategy */
        { &vnop_pathconf_desc, (VOPFUNC)union_pathconf },       /* pathconf */
        { &vnop_advlock_desc, (VOPFUNC)union_advlock },         /* advlock */
#ifdef notdef
        { &vnop_bwrite_desc, (VOPFUNC)union_bwrite },           /* bwrite */
#endif
        { &vnop_pagein_desc, (VOPFUNC)union_pagein },           /* Pagein */
        { &vnop_pageout_desc, (VOPFUNC)union_pageout },         /* Pageout */
        { &vnop_copyfile_desc, (VOPFUNC)err_copyfile },         /* Copyfile */
        { &vnop_blktooff_desc, (VOPFUNC)union_blktooff },       /* blktooff */
        { &vnop_offtoblk_desc, (VOPFUNC)union_offtoblk },       /* offtoblk */
        { &vnop_blockmap_desc, (VOPFUNC)union_blockmap },       /* blockmap */
        { (struct vnodeop_desc*)NULL, (int(*)())NULL }
};
struct vnodeopv_desc union_vnodeop_opv_desc =
        { &union_vnodeop_p, union_vnodeop_entries };