xnu-792.tar.gz

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

/*
 * Copyright (c) 2000-2004 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This 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 OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * Copyright (c) 1994 Jan-Simon Pendry
 * Copyright (c) 1994
 *      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_subr.c        8.20 (Berkeley) 5/20/95
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/vnode_internal.h>
#include <sys/namei.h>
#include <sys/malloc.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/queue.h>
#include <sys/mount_internal.h>
#include <sys/stat.h>
#include <sys/ubc.h>
#include <sys/uio_internal.h>
#include <miscfs/union/union.h>

#if DIAGNOSTIC
#include <sys/proc.h>
#endif

/* must be power of two, otherwise change UNION_HASH() */
#define NHASH 32

/* unsigned int ... */
#define UNION_HASH(u, l) \
        (((((unsigned long) (u)) + ((unsigned long) l)) >> 8) & (NHASH-1))

static LIST_HEAD(unhead, union_node) unhead[NHASH];
static int unvplock[NHASH];

int
union_init()
{
        int i;

        for (i = 0; i < NHASH; i++)
                LIST_INIT(&unhead[i]);
        bzero((caddr_t) unvplock, sizeof(unvplock));
}

static int
union_list_lock(ix)
        int ix;
{

        if (unvplock[ix] & UN_LOCKED) {
                unvplock[ix] |= UN_WANT;
                sleep((caddr_t) &unvplock[ix], PINOD);
                return (1);
        }

        unvplock[ix] |= UN_LOCKED;

        return (0);
}

static void
union_list_unlock(ix)
        int ix;
{

        unvplock[ix] &= ~UN_LOCKED;

        if (unvplock[ix] & UN_WANT) {
                unvplock[ix] &= ~UN_WANT;
                wakeup((caddr_t) &unvplock[ix]);
        }
}

void
union_updatevp(un, uppervp, lowervp)
        struct union_node *un;
        struct vnode *uppervp;
        struct vnode *lowervp;
{
        int ohash = UNION_HASH(un->un_uppervp, un->un_lowervp);
        int nhash = UNION_HASH(uppervp, lowervp);
        int docache = (lowervp != NULLVP || uppervp != NULLVP);
        int lhash, uhash;

        /*
         * Ensure locking is ordered from lower to higher
         * to avoid deadlocks.
         */
        if (nhash < ohash) {
                lhash = nhash;
                uhash = ohash;
        } else {
                lhash = ohash;
                uhash = nhash;
        }

        if (lhash != uhash)
                while (union_list_lock(lhash))
                        continue;

        while (union_list_lock(uhash))
                continue;

        if (ohash != nhash || !docache) {
                if (un->un_flags & UN_CACHED) {
                        un->un_flags &= ~UN_CACHED;
                        LIST_REMOVE(un, un_cache);
                }
        }

        if (ohash != nhash)
                union_list_unlock(ohash);

        if (un->un_lowervp != lowervp) {
                if (un->un_lowervp) {
                        vnode_put(un->un_lowervp);
                        if (un->un_path) {
                                _FREE(un->un_path, M_TEMP);
                                un->un_path = 0;
                        }
                        if (un->un_dirvp) {
                                vnode_put(un->un_dirvp);
                                un->un_dirvp = NULLVP;
                        }
                }
                un->un_lowervp = lowervp;
                un->un_lowersz = VNOVAL;
        }

        if (un->un_uppervp != uppervp) {
                if (un->un_uppervp)
                        vnode_put(un->un_uppervp);

                un->un_uppervp = uppervp;
                un->un_uppersz = VNOVAL;
        }

        if (docache && (ohash != nhash)) {
                LIST_INSERT_HEAD(&unhead[nhash], un, un_cache);
                un->un_flags |= UN_CACHED;
        }

        union_list_unlock(nhash);
}

void
union_newlower(un, lowervp)
        struct union_node *un;
        struct vnode *lowervp;
{

        union_updatevp(un, un->un_uppervp, lowervp);
}

void
union_newupper(un, uppervp)
        struct union_node *un;
        struct vnode *uppervp;
{

        union_updatevp(un, uppervp, un->un_lowervp);
}

/*
 * Keep track of size changes in the underlying vnodes.
 * If the size changes, then callback to the vm layer
 * giving priority to the upper layer size.
 */
void
union_newsize(vp, uppersz, lowersz)
        struct vnode *vp;
        off_t uppersz, lowersz;
{
        struct union_node *un;
        off_t sz;

        /* only interested in regular files */
        if (vp->v_type != VREG)
                return;

        un = VTOUNION(vp);
        sz = VNOVAL;

        if ((uppersz != VNOVAL) && (un->un_uppersz != uppersz)) {
                un->un_uppersz = uppersz;
                if (sz == VNOVAL)
                        sz = un->un_uppersz;
        }

        if ((lowersz != VNOVAL) && (un->un_lowersz != lowersz)) {
                un->un_lowersz = lowersz;
                if (sz == VNOVAL)
                        sz = un->un_lowersz;
        }

        if (sz != VNOVAL) {
#ifdef UNION_DIAGNOSTIC
                printf("union: %s size now %ld\n",
                        uppersz != VNOVAL ? "upper" : "lower", (long) sz);
#endif
                ubc_setsize(vp, sz);
        }
}

/*
 * allocate a union_node/vnode pair.  the vnode is
 * referenced and locked.  the new vnode is returned
 * via (vpp).  (mp) is the mountpoint of the union filesystem,
 * (dvp) is the parent directory where the upper layer object
 * should exist (but doesn't) and (cnp) is the componentname
 * information which is partially copied to allow the upper
 * layer object to be created at a later time.  (uppervp)
 * and (lowervp) reference the upper and lower layer objects
 * being mapped.  either, but not both, can be nil.
 * if supplied, (uppervp) is locked.
 * the reference is either maintained in the new union_node
 * object which is allocated, or they are vnode_put'd.
 *
 * all union_nodes are maintained on a singly-linked
 * list.  new nodes are only allocated when they cannot
 * be found on this list.  entries on the list are
 * removed when the vfs reclaim entry is called.
 *
 * a single lock is kept for the entire list.  this is
 * needed because the getnewvnode() function can block
 * waiting for a vnode to become free, in which case there
 * may be more than one process trying to get the same
 * vnode.  this lock is only taken if we are going to
 * call getnewvnode, since the kernel itself is single-threaded.
 *
 * if an entry is found on the list, then call vnode_get() to
 * take a reference.  this is done because there may be
 * zero references to it and so it needs to removed from
 * the vnode free list.
 */
int
union_allocvp(vpp, mp, undvp, dvp, cnp, uppervp, lowervp, docache)
        struct vnode **vpp;
        struct mount *mp;
        struct vnode *undvp;            /* parent union vnode */
        struct vnode *dvp;              /* may be null */
        struct componentname *cnp;      /* may be null */
        struct vnode *uppervp;          /* may be null */
        struct vnode *lowervp;          /* may be null */
        int docache;
{
        int error;
        struct union_node *un;
        struct union_node **pp;
        struct vnode *xlowervp = NULLVP;
        struct union_mount *um = MOUNTTOUNIONMOUNT(mp);
        int hash;
        int markroot;
        int try;
        struct union_node *unp;
        struct vnode_fsparam vfsp;
        enum vtype vtype;

        if (uppervp == NULLVP && lowervp == NULLVP)
                panic("union: unidentifiable allocation");

        if (uppervp && lowervp && (uppervp->v_type != lowervp->v_type)) {
                xlowervp = lowervp;
                lowervp = NULLVP;
        }

        /* detect the root vnode (and aliases) */
        markroot = 0;
        if ((uppervp == um->um_uppervp) &&
            ((lowervp == NULLVP) || lowervp == um->um_lowervp)) {
                if (lowervp == NULLVP) {
                        lowervp = um->um_lowervp;
                        if (lowervp != NULLVP)
                                vnode_get(lowervp);
                }
                markroot = VROOT;
        }

loop:
        if (!docache) {
                un = 0;
        } else for (try = 0; try < 3; try++) {
                switch (try) {
                case 0:
                        if (lowervp == NULLVP)
                                continue;
                        hash = UNION_HASH(uppervp, lowervp);
                        break;

                case 1:
                        if (uppervp == NULLVP)
                                continue;
                        hash = UNION_HASH(uppervp, NULLVP);
                        break;

                case 2:
                        if (lowervp == NULLVP)
                                continue;
                        hash = UNION_HASH(NULLVP, lowervp);
                        break;
                }

                while (union_list_lock(hash))
                        continue;

                for (un = unhead[hash].lh_first; un != 0;
                                        un = un->un_cache.le_next) {
                        if ((un->un_lowervp == lowervp ||
                             un->un_lowervp == NULLVP) &&
                            (un->un_uppervp == uppervp ||
                             un->un_uppervp == NULLVP) &&
                            (UNIONTOV(un)->v_mount == mp)) {
                                if (vnode_get(UNIONTOV(un))) {
                                        union_list_unlock(hash);
                                        goto loop;
                                }
                                break;
                        }
                }

                union_list_unlock(hash);

                if (un)
                        break;
        }

        if (un) {
                /*
                 * Obtain a lock on the union_node.
                 * uppervp is locked, though un->un_uppervp
                 * may not be.  this doesn't break the locking
                 * hierarchy since in the case that un->un_uppervp
                 * is not yet locked it will be vnode_put'd and replaced
                 * with uppervp.
                 */

                if ((dvp != NULLVP) && (uppervp == dvp)) {
                        /*
                         * Access ``.'', so (un) will already
                         * be locked.  Since this process has
                         * the lock on (uppervp) no other
                         * process can hold the lock on (un).
                         */
#if DIAGNOSTIC
                        if ((un->un_flags & UN_LOCKED) == 0)
                                panic("union: . not locked");
                        else if (current_proc() && un->un_pid != current_proc()->p_pid &&
                                    un->un_pid > -1 && current_proc()->p_pid > -1)
                                panic("union: allocvp not lock owner");
#endif
                } else {
                        if (un->un_flags & UN_LOCKED) {
                                vnode_put(UNIONTOV(un));
                                un->un_flags |= UN_WANT;
                                sleep((caddr_t) &un->un_flags, PINOD);
                                goto loop;
                        }
                        un->un_flags |= UN_LOCKED;

#if DIAGNOSTIC
                        if (current_proc())
                                un->un_pid = current_proc()->p_pid;
                        else
                                un->un_pid = -1;
#endif
                }

                /*
                 * At this point, the union_node is locked,
                 * un->un_uppervp may not be locked, and uppervp
                 * is locked or nil.
                 */

                /*
                 * Save information about the upper layer.
                 */
                if (uppervp != un->un_uppervp) {
                        union_newupper(un, uppervp);
                } else if (uppervp) {
                        vnode_put(uppervp);
                }

                if (un->un_uppervp) {
                        un->un_flags |= UN_ULOCK;
                        un->un_flags &= ~UN_KLOCK;
                }

                /*
                 * Save information about the lower layer.
                 * This needs to keep track of pathname
                 * and directory information which union_vn_create
                 * might need.
                 */
                if (lowervp != un->un_lowervp) {
                        union_newlower(un, lowervp);
                        if (cnp && (lowervp != NULLVP)) {
                                un->un_hash = cnp->cn_hash;
                                MALLOC(un->un_path, caddr_t, cnp->cn_namelen+1,
                                                M_TEMP, M_WAITOK);
                                bcopy(cnp->cn_nameptr, un->un_path,
                                                cnp->cn_namelen);
                                un->un_path[cnp->cn_namelen] = '\0';
                                vnode_get(dvp);
                                un->un_dirvp = dvp;
                        }
                } else if (lowervp) {
                        vnode_put(lowervp);
                }
                *vpp = UNIONTOV(un);
                return (0);
        }

        if (docache) {
                /*
                 * otherwise lock the vp list while we call getnewvnode
                 * since that can block.
                 */ 
                hash = UNION_HASH(uppervp, lowervp);

                if (union_list_lock(hash))
                        goto loop;
        }

        MALLOC(unp, void *, sizeof(struct union_node), M_TEMP, M_WAITOK);

        if (uppervp)
                vtype = uppervp->v_type;
        else
                vtype = lowervp->v_type;
        //bzero(&vfsp, sizeof(struct vnode_fsparam));
        vfsp.vnfs_mp = mp;
        vfsp.vnfs_vtype = vtype;
        vfsp.vnfs_str = "unionfs";
        vfsp.vnfs_dvp = dvp;
        vfsp.vnfs_fsnode = unp;
        vfsp.vnfs_cnp = cnp;
        vfsp.vnfs_vops = union_vnodeop_p;
        vfsp.vnfs_rdev = 0;
        vfsp.vnfs_filesize = 0;
        vfsp.vnfs_flags = VNFS_NOCACHE | VNFS_CANTCACHE;
        vfsp.vnfs_marksystem = 0;
        vfsp.vnfs_markroot = markroot;

        error = vnode_create(VNCREATE_FLAVOR, VCREATESIZE, &vfsp, vpp);
        if (error) {
                FREE(unp, M_TEMP);
                if (uppervp) {
                        vnode_put(uppervp);
                }
                if (lowervp)
                        vnode_put(lowervp);

                goto out;
        }

        (*vpp)->v_tag = VT_UNION;
        un = VTOUNION(*vpp);
        un->un_vnode = *vpp;
        un->un_uppervp = uppervp;
        un->un_uppersz = VNOVAL;
        un->un_lowervp = lowervp;
        un->un_lowersz = VNOVAL;
        un->un_pvp = undvp;
        if (undvp != NULLVP)
                vnode_get(undvp);
        un->un_dircache = 0;
        un->un_openl = 0;
        un->un_flags = UN_LOCKED;
        if (un->un_uppervp)
                un->un_flags |= UN_ULOCK;
#if DIAGNOSTIC
        if (current_proc())
                un->un_pid = current_proc()->p_pid;
        else
                un->un_pid = -1;
#endif
        if (cnp && (lowervp != NULLVP)) {
                un->un_hash = cnp->cn_hash;
                un->un_path = _MALLOC(cnp->cn_namelen+1, M_TEMP, M_WAITOK);
                bcopy(cnp->cn_nameptr, un->un_path, cnp->cn_namelen);
                un->un_path[cnp->cn_namelen] = '\0';
                vnode_get(dvp);
                un->un_dirvp = dvp;
        } else {
                un->un_hash = 0;
                un->un_path = 0;
                un->un_dirvp = 0;
        }

        if (docache) {
                LIST_INSERT_HEAD(&unhead[hash], un, un_cache);
                un->un_flags |= UN_CACHED;
        }

        if (xlowervp)
                vnode_put(xlowervp);

out:
        if (docache)
                union_list_unlock(hash);

        return (error);
}

int
union_freevp(vp)
        struct vnode *vp;
{
        struct union_node *un = VTOUNION(vp);

        if (un->un_flags & UN_CACHED) {
                un->un_flags &= ~UN_CACHED;
                LIST_REMOVE(un, un_cache);
        }

        if (un->un_pvp != NULLVP)
                vnode_put(un->un_pvp);
        if (un->un_uppervp != NULLVP)
                vnode_put(un->un_uppervp);
        if (un->un_lowervp != NULLVP)
                vnode_put(un->un_lowervp);
        if (un->un_dirvp != NULLVP)
                vnode_put(un->un_dirvp);
        if (un->un_path)
                _FREE(un->un_path, M_TEMP);

        FREE(vp->v_data, M_TEMP);
        vp->v_data = 0;

        return (0);
}

/*
 * copyfile.  copy the vnode (fvp) to the vnode (tvp)
 * using a sequence of reads and writes.  both (fvp)
 * and (tvp) are locked on entry and exit.
 */
int
union_copyfile(struct vnode *fvp, struct vnode *tvp, kauth_cred_t cred,
        struct proc *p)
{
        char *bufp;
        struct uio uio;
        struct iovec_32 iov;
        struct vfs_context context;
        int error = 0;

        /*
         * strategy:
         * allocate a buffer of size MAXPHYSIO.
         * loop doing reads and writes, keeping track
         * of the current uio offset.
         * give up at the first sign of trouble.
         */

        context.vc_proc = p;
        context.vc_ucred = cred;

#if 1   /* LP64todo - can't use new segment flags until the drivers are ready */
        uio.uio_segflg = UIO_SYSSPACE;
#else
        uio.uio_segflg = UIO_SYSSPACE32;
#endif 
        uio.uio_offset = 0;

        bufp = _MALLOC(MAXPHYSIO, M_TEMP, M_WAITOK);

        /* ugly loop follows... */
        do {
                off_t offset = uio.uio_offset;

                uio.uio_iovs.iov32p = &iov;
                uio.uio_iovcnt = 1;
                iov.iov_base = (uintptr_t)bufp;
                iov.iov_len = MAXPHYSIO;
                uio_setresid(&uio, iov.iov_len);
                uio.uio_rw = UIO_READ;
                error = VNOP_READ(fvp, &uio, 0, &context);

                if (error == 0) {
                        uio.uio_iovs.iov32p = &iov;
                        uio.uio_iovcnt = 1;
                        iov.iov_base = (uintptr_t)bufp;
                        iov.iov_len = MAXPHYSIO - uio_resid(&uio);
                        uio.uio_offset = offset;
                        uio.uio_rw = UIO_WRITE;
                        uio_setresid(&uio, iov.iov_len);

                        if (uio_resid(&uio) == 0)
                                break;

                        do {
                                error = VNOP_WRITE(tvp, &uio, 0, &context);
                        } while ((uio_resid(&uio) > 0) && (error == 0));
                }

        } while (error == 0);

        _FREE(bufp, M_TEMP);
        return (error);
}

/*
 * (un) is assumed to be locked on entry and remains
 * locked on exit.
 */
int
union_copyup(struct union_node *un, int docopy, kauth_cred_t cred,
        struct proc *p)
{
        int error;
        struct vnode *lvp, *uvp;
        struct vfs_context context;

        error = union_vn_create(&uvp, un, p);
        if (error)
                return (error);

        context.vc_proc = p;
        context.vc_ucred = cred;

        /* at this point, uppervp is locked */
        union_newupper(un, uvp);
        un->un_flags |= UN_ULOCK;

        lvp = un->un_lowervp;

        if (docopy) {
                /*
                 * XX - should not ignore errors
                 * from vnop_close
                 */
                error = VNOP_OPEN(lvp, FREAD, &context);
                if (error == 0) {
                        error = union_copyfile(lvp, uvp, cred, p);
                        (void) VNOP_CLOSE(lvp, FREAD, &context);
                }
#ifdef UNION_DIAGNOSTIC
                if (error == 0)
                        uprintf("union: copied up %s\n", un->un_path);
#endif

        }
        un->un_flags &= ~UN_ULOCK;
        union_vn_close(uvp, FWRITE, cred, p);
        un->un_flags |= UN_ULOCK;

        /*
         * Subsequent IOs will go to the top layer, so
         * call close on the lower vnode and open on the
         * upper vnode to ensure that the filesystem keeps
         * its references counts right.  This doesn't do
         * the right thing with (cred) and (FREAD) though.
         * Ignoring error returns is not right, either.
         */
        if (error == 0) {
                int i;

                for (i = 0; i < un->un_openl; i++) {
                        (void) VNOP_CLOSE(lvp, FREAD, &context);
                        (void) VNOP_OPEN(uvp, FREAD, &context);
                }
                un->un_openl = 0;
        }

        return (error);

}

static int
union_relookup(um, dvp, vpp, cnp, cn, path, pathlen)
        struct union_mount *um;
        struct vnode *dvp;
        struct vnode **vpp;
        struct componentname *cnp;
        struct componentname *cn;
        char *path;
        int pathlen;
{
        int error;

        /*
         * A new componentname structure must be faked up because
         * there is no way to know where the upper level cnp came
         * from or what it is being used for.  This must duplicate
         * some of the work done by NDINIT, some of the work done
         * by namei, some of the work done by lookup and some of
         * the work done by vnop_lookup when given a CREATE flag.
         * Conclusion: Horrible.
         */
        cn->cn_namelen = pathlen;
        cn->cn_pnbuf = _MALLOC_ZONE(cn->cn_namelen+1, M_NAMEI, M_WAITOK);
        cn->cn_pnlen = cn->cn_namelen+1;
        bcopy(path, cn->cn_pnbuf, cn->cn_namelen);
        cn->cn_pnbuf[cn->cn_namelen] = '\0';

        cn->cn_nameiop = CREATE;
        cn->cn_flags = (LOCKPARENT|HASBUF|SAVENAME|SAVESTART|ISLASTCN);
#ifdef XXX_HELP_ME
        cn->cn_proc = cnp->cn_proc;
        if (um->um_op == UNMNT_ABOVE)
                cn->cn_cred = cnp->cn_cred;
        else
                cn->cn_cred = um->um_cred;
#endif
        cn->cn_context = cnp->cn_context;       /* XXX !UNMNT_ABOVE  case ??? */
        cn->cn_nameptr = cn->cn_pnbuf;
        cn->cn_hash = cnp->cn_hash;
        cn->cn_consume = cnp->cn_consume;

        vnode_get(dvp);
        error = relookup(dvp, vpp, cn);
        if (!error)
                vnode_put(dvp);

        return (error);
}

/*
 * Create a shadow directory in the upper layer.
 * The new vnode is returned locked.
 *
 * (um) points to the union mount structure for access to the
 * the mounting process's credentials.
 * (dvp) is the directory in which to create the shadow directory.
 * it is unlocked on entry and exit.
 * (cnp) is the componentname to be created.
 * (vpp) is the returned newly created shadow directory, which
 * is returned locked.
 */
int
union_mkshadow(um, dvp, cnp, vpp)
        struct union_mount *um;
        struct vnode *dvp;
        struct componentname *cnp;
        struct vnode **vpp;
{
        int error;
        struct vnode_attr va;
        struct componentname cn;

        error = union_relookup(um, dvp, vpp, cnp, &cn,
                        cnp->cn_nameptr, cnp->cn_namelen);
        if (error)
                return (error);

        if (*vpp) {
                vnode_put(*vpp);
                *vpp = NULLVP;
                return (EEXIST);
        }

        /*
         * policy: when creating the shadow directory in the
         * upper layer, create it owned by the user who did
         * the mount, group from parent directory, and mode
         * 777 modified by umask (ie mostly identical to the
         * mkdir syscall).  (jsp, kb)
         */
        VATTR_INIT(&va);
        VATTR_SET(&va, va_type, VDIR);
        VATTR_SET(&va, va_mode, um->um_cmode);

        error = vn_create(dvp, vpp, &cn, &va, 0, cnp->cn_context);
        return (error);
}

/*
 * Create a whiteout entry in the upper layer.
 *
 * (um) points to the union mount structure for access to the
 * the mounting process's credentials.
 * (dvp) is the directory in which to create the whiteout.
 * it is locked on entry and exit.
 * (cnp) is the componentname to be created.
 */
int
union_mkwhiteout(um, dvp, cnp, path)
        struct union_mount *um;
        struct vnode *dvp;
        struct componentname *cnp;
        char *path;
{
        int error;
        struct vnode *wvp;
        struct componentname cn;

        error = union_relookup(um, dvp, &wvp, cnp, &cn, path, strlen(path));
        if (error) {
                return (error);
        }
        if (wvp) {
                vnode_put(dvp);
                vnode_put(wvp);
                return (EEXIST);
        }

        error = VNOP_WHITEOUT(dvp, &cn, CREATE, cnp->cn_context);

        vnode_put(dvp);

        return (error);
}

/*
 * union_vn_create: creates and opens a new shadow file
 * on the upper union layer.  this function is similar
 * in spirit to calling vn_open but it avoids calling namei().
 * the problem with calling namei is that a) it locks too many
 * things, and b) it doesn't start at the "right" directory,
 * whereas relookup is told where to start.
 */
int
union_vn_create(vpp, un, p)
        struct vnode **vpp;
        struct union_node *un;
        struct proc *p;
{
        struct vnode *vp;
        kauth_cred_t cred = p->p_ucred;
        struct vnode_attr vat;
        struct vnode_attr *vap = &vat;
        struct vfs_context context;
        int fmode = FFLAGS(O_WRONLY|O_CREAT|O_TRUNC|O_EXCL);
        int error;
        int cmode = UN_FILEMODE & ~p->p_fd->fd_cmask;
        char *cp;
        struct componentname cn;

        *vpp = NULLVP;

        context.vc_proc = p;
        context.vc_ucred = p->p_ucred;

        /*
         * Build a new componentname structure (for the same
         * reasons outlines in union_mkshadow).
         * The difference here is that the file is owned by
         * the current user, rather than by the person who
         * did the mount, since the current user needs to be
         * able to write the file (that's why it is being
         * copied in the first place).
         */
        cn.cn_namelen = strlen(un->un_path);
        cn.cn_pnbuf = (caddr_t) _MALLOC_ZONE(cn.cn_namelen+1,
                                                M_NAMEI, M_WAITOK);
        cn.cn_pnlen = cn.cn_namelen+1;
        bcopy(un->un_path, cn.cn_pnbuf, cn.cn_namelen+1);
        cn.cn_nameiop = CREATE;
        cn.cn_flags = (LOCKPARENT|HASBUF|SAVENAME|SAVESTART|ISLASTCN);
        cn.cn_context = &context;
        cn.cn_nameptr = cn.cn_pnbuf;
        cn.cn_hash = un->un_hash;
        cn.cn_consume = 0;

        vnode_get(un->un_dirvp);
        if (error = relookup(un->un_dirvp, &vp, &cn))
                return (error);
        vnode_put(un->un_dirvp);

        if (vp) {
                vnode_put(un->un_dirvp);
                vnode_put(vp);
                return (EEXIST);
        }

        /*
         * Good - there was no race to create the file
         * so go ahead and create it.  The permissions
         * on the file will be 0666 modified by the
         * current user's umask.  Access to the file, while
         * it is unioned, will require access to the top *and*
         * bottom files.  Access when not unioned will simply
         * require access to the top-level file.
         *
         * TODO: confirm choice of access permissions.
         *       decide on authorisation behaviour
         */
        
        VATTR_INIT(vap);
        VATTR_SET(vap, va_type, VREG);
        VATTR_SET(vap, va_mode, cmode);

        if (error = vn_create(un->un_dirvp, &vp, &cn, vap, 0, &context))
                return (error);

        if (error = VNOP_OPEN(vp, fmode, &context)) {
                vnode_put(vp);
                return (error);
        }

        vnode_lock(vp);
        if (++vp->v_writecount <= 0)
                panic("union: v_writecount");
        vnode_unlock(vp);
        *vpp = vp;
        return (0);
}

int
union_vn_close(struct vnode *vp, int fmode, kauth_cred_t cred,
        struct proc *p)
{
        struct vfs_context context;

        context.vc_proc = p;
        context.vc_ucred = cred;

        if (fmode & FWRITE) {
                vnode_lock(vp);
                --vp->v_writecount;
                vnode_unlock(vp);
        }
        return (VNOP_CLOSE(vp, fmode, &context));
}

void
union_removed_upper(un)
        struct union_node *un;
{
        struct proc *p = current_proc();        /* XXX */

        union_newupper(un, NULLVP);
        if (un->un_flags & UN_CACHED) {
                un->un_flags &= ~UN_CACHED;
                LIST_REMOVE(un, un_cache);
        }

        if (un->un_flags & UN_ULOCK) {
                un->un_flags &= ~UN_ULOCK;
        }
}

#if 0
struct vnode *
union_lowervp(vp)
        struct vnode *vp;
{
        struct union_node *un = VTOUNION(vp);

        if ((un->un_lowervp != NULLVP) &&
            (vp->v_type == un->un_lowervp->v_type)) {
                if (vnode_get(un->un_lowervp) == 0)
                        return (un->un_lowervp);
        }

        return (NULLVP);
}
#endif

/*
 * determine whether a whiteout is needed
 * during a remove/rmdir operation.
 */
int
union_dowhiteout(struct union_node *un, vfs_context_t ctx)
{
        struct vnode_attr va;

        if (un->un_lowervp != NULLVP)
                return (1);

        VATTR_INIT(&va);
        VATTR_WANTED(&va, va_flags);
        if (vnode_getattr(un->un_uppervp, &va, ctx) == 0 &&
            (va.va_flags & OPAQUE))
                return (1);

        return (0);
}

static void
union_dircache_r(vp, vppp, cntp)
        struct vnode *vp;
        struct vnode ***vppp;
        int *cntp;
{
        struct union_node *un;

        if (vp->v_op != union_vnodeop_p) {
                if (vppp) {
                        vnode_get(vp);
                        *(*vppp)++ = vp;
                        if (--(*cntp) == 0)
                                panic("union: dircache table too small");
                } else {
                        (*cntp)++;
                }

                return;
        }

        un = VTOUNION(vp);
        if (un->un_uppervp != NULLVP)
                union_dircache_r(un->un_uppervp, vppp, cntp);
        if (un->un_lowervp != NULLVP)
                union_dircache_r(un->un_lowervp, vppp, cntp);
}

struct vnode *
union_dircache(vp, p)
        struct vnode *vp;
        struct proc *p;
{
        int count;
        struct vnode *nvp;
        struct vnode **vpp;
        struct vnode **dircache;
        struct union_node *un;
        int error;

        dircache = VTOUNION(vp)->un_dircache;

        nvp = NULLVP;

        if (dircache == 0) {
                count = 0;
                union_dircache_r(vp, 0, &count);
                count++;
                dircache = (struct vnode **)
                                _MALLOC(count * sizeof(struct vnode *),
                                        M_TEMP, M_WAITOK);
                vpp = dircache;
                union_dircache_r(vp, &vpp, &count);
                *vpp = NULLVP;
                vpp = dircache + 1;
        } else {
                vpp = dircache;
                do {
                        if (*vpp++ == VTOUNION(vp)->un_uppervp)
                                break;
                } while (*vpp != NULLVP);
        }

        if (*vpp == NULLVP)
                goto out;

        vnode_get(*vpp);
        error = union_allocvp(&nvp, vp->v_mount, NULLVP, NULLVP, 0, *vpp, NULLVP, 0);
        if (error)
                goto out;

        VTOUNION(vp)->un_dircache = 0;
        un = VTOUNION(nvp);
        un->un_dircache = dircache;

out:
        return (nvp);
}