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[netbsd-mini2440.git] / sys / fs / union / union_subr.c

/*      $NetBSD: union_subr.c,v 1.34 2008/12/17 20:51:35 cegger Exp $   */

/*
 * 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. 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
 */

/*
 * Copyright (c) 1994 Jan-Simon Pendry
 *
 * 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/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: union_subr.c,v 1.34 2008/12/17 20:51:35 cegger Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/vnode.h>
#include <sys/namei.h>
#include <sys/malloc.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/queue.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/kauth.h>

#include <uvm/uvm_extern.h>

#include <fs/union/union.h>

/* 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];

static int union_list_lock(int);
static void union_list_unlock(int);
void union_updatevp(struct union_node *, struct vnode *, struct vnode *);
static int union_relookup(struct union_mount *, struct vnode *,
                               struct vnode **, struct componentname *,
                               struct componentname *, const char *, int);
int union_vn_close(struct vnode *, int, kauth_cred_t, struct lwp *);
static void union_dircache_r(struct vnode *, struct vnode ***, int *);
struct vnode *union_dircache(struct vnode *, struct lwp *);

void
union_init(void)
{
        int i;

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

/*
 * Free global unionfs resources.
 */
void
union_done(void)
{

        /* Make sure to unset the readdir hook. */
        vn_union_readdir_hook = NULL;
}

static int
union_list_lock(int ix)
{

        if (unvplock[ix] & UN_LOCKED) {
                unvplock[ix] |= UN_WANTED;
                (void) tsleep(&unvplock[ix], PINOD, "unionlk", 0);
                return (1);
        }

        unvplock[ix] |= UN_LOCKED;

        return (0);
}

static void
union_list_unlock(int ix)
{

        unvplock[ix] &= ~UN_LOCKED;

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

void
union_updatevp(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) {
                        vrele(un->un_lowervp);
                        if (un->un_path) {
                                free(un->un_path, M_TEMP);
                                un->un_path = 0;
                        }
                        if (un->un_dirvp) {
                                vrele(un->un_dirvp);
                                un->un_dirvp = NULLVP;
                        }
                }
                un->un_lowervp = lowervp;
                un->un_lowersz = VNOVAL;
        }

        if (un->un_uppervp != uppervp) {
                if (un->un_uppervp)
                        vrele(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(struct union_node *un, struct vnode *lowervp)
{

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

void
union_newupper(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(struct vnode *vp, off_t uppersz, off_t lowersz)
{
        struct union_node *un;
        off_t sz;

        /* only interested in regular files */
        if (vp->v_type != VREG) {
                uvm_vnp_setsize(vp, 0);
                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 %qd\n",
                    uppersz != VNOVAL ? "upper" : "lower", sz);
#endif
                uvm_vnp_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 vrele'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 vget() 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(
        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 vattr va;
        struct union_node *un = NULL;
        struct vnode *xlowervp = NULLVP;
        struct union_mount *um = MOUNTTOUNIONMOUNT(mp);
        voff_t uppersz, lowersz;
        int hash = 0;
        int vflag, iflag;
        int try;

        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) */
        iflag = VI_LAYER;
        vflag = 0;
        if ((uppervp == um->um_uppervp) &&
            ((lowervp == NULLVP) || lowervp == um->um_lowervp)) {
                if (lowervp == NULLVP) {
                        lowervp = um->um_lowervp;
                        if (lowervp != NULLVP)
                                vref(lowervp);
                }
                iflag = 0;
                vflag = VV_ROOT;
        }

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 (vget(UNIONTOV(un), 0)) {
                                        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 vrele'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).
                         */
#ifdef DIAGNOSTIC
                        if ((un->un_flags & UN_LOCKED) == 0)
                                panic("union: . not locked");
                        else if (curproc && un->un_pid != curproc->p_pid &&
                                    un->un_pid > -1 && curproc->p_pid > -1)
                                panic("union: allocvp not lock owner");
#endif
                } else {
                        if (un->un_flags & UN_LOCKED) {
                                vrele(UNIONTOV(un));
                                un->un_flags |= UN_WANTED;
                                (void) tsleep(&un->un_flags, PINOD,
                                    "unionalloc", 0);
                                goto loop;
                        }
                        un->un_flags |= UN_LOCKED;

#ifdef DIAGNOSTIC
                        if (curproc)
                                un->un_pid = curproc->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) {
                        vrele(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;
                                un->un_path = malloc(cnp->cn_namelen+1,
                                                M_TEMP, M_WAITOK);
                                memcpy(un->un_path, cnp->cn_nameptr,
                                                cnp->cn_namelen);
                                un->un_path[cnp->cn_namelen] = '\0';
                                vref(dvp);
                                un->un_dirvp = dvp;
                        }
                } else if (lowervp) {
                        vrele(lowervp);
                }
                *vpp = UNIONTOV(un);
                return (0);
        }

        uppersz = lowersz = VNOVAL;
        if (uppervp != NULLVP)
                if (VOP_GETATTR(uppervp, &va, FSCRED) == 0)
                        uppersz = va.va_size;
        if (lowervp != NULLVP)
                if (VOP_GETATTR(lowervp, &va, FSCRED) == 0)
                        lowersz = va.va_size;

        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;
        }

        error = getnewvnode(VT_UNION, mp, union_vnodeop_p, vpp);
        if (error) {
                if (uppervp) {
                        if (dvp == uppervp)
                                vrele(uppervp);
                        else
                                vput(uppervp);
                }
                if (lowervp)
                        vrele(lowervp);

                goto out;
        }

        (*vpp)->v_data = malloc(sizeof(struct union_node), M_TEMP, M_WAITOK);

        (*vpp)->v_vflag |= vflag;
        (*vpp)->v_iflag |= iflag;
        (*vpp)->v_vnlock = NULL;        /* Make upper layers call VOP_LOCK */
        if (uppervp)
                (*vpp)->v_type = uppervp->v_type;
        else
                (*vpp)->v_type = lowervp->v_type;
        un = VTOUNION(*vpp);
        un->un_vnode = *vpp;
        un->un_uppervp = uppervp;
        un->un_lowervp = lowervp;
        un->un_pvp = undvp;
        if (undvp != NULLVP)
                vref(undvp);
        un->un_dircache = 0;
        un->un_openl = 0;
        un->un_flags = UN_LOCKED;

        un->un_uppersz = VNOVAL;
        un->un_lowersz = VNOVAL;
        union_newsize(*vpp, uppersz, lowersz);

        if (un->un_uppervp)
                un->un_flags |= UN_ULOCK;
#ifdef DIAGNOSTIC
        if (curproc)
                un->un_pid = curproc->p_pid;
        else
                un->un_pid = -1;
#endif
        if (dvp && cnp && (lowervp != NULLVP)) {
                un->un_hash = cnp->cn_hash;
                un->un_path = malloc(cnp->cn_namelen+1, M_TEMP, M_WAITOK);
                memcpy(un->un_path, cnp->cn_nameptr, cnp->cn_namelen);
                un->un_path[cnp->cn_namelen] = '\0';
                vref(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)
                vrele(xlowervp);

out:
        if (docache)
                union_list_unlock(hash);

        return (error);
}

int
union_freevp(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)
                vrele(un->un_pvp);
        if (un->un_uppervp != NULLVP)
                vrele(un->un_uppervp);
        if (un->un_lowervp != NULLVP)
                vrele(un->un_lowervp);
        if (un->un_dirvp != NULLVP)
                vrele(un->un_dirvp);
        if (un->un_path)
                free(un->un_path, M_TEMP);

        free(vp->v_data, M_TEMP);
        vp->v_data = NULL;

        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 lwp *l)
{
        char *tbuf;
        struct uio uio;
        struct iovec iov;
        int error = 0;

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

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

        VOP_UNLOCK(fvp, 0);                     /* XXX */
        vn_lock(fvp, LK_EXCLUSIVE | LK_RETRY);  /* XXX */
        VOP_UNLOCK(tvp, 0);                     /* XXX */
        vn_lock(tvp, LK_EXCLUSIVE | LK_RETRY);  /* XXX */

        tbuf = malloc(MAXBSIZE, M_TEMP, M_WAITOK);

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

                uio.uio_iov = &iov;
                uio.uio_iovcnt = 1;
                iov.iov_base = tbuf;
                iov.iov_len = MAXBSIZE;
                uio.uio_resid = iov.iov_len;
                uio.uio_rw = UIO_READ;
                error = VOP_READ(fvp, &uio, 0, cred);

                if (error == 0) {
                        uio.uio_iov = &iov;
                        uio.uio_iovcnt = 1;
                        iov.iov_base = tbuf;
                        iov.iov_len = MAXBSIZE - uio.uio_resid;
                        uio.uio_offset = offset;
                        uio.uio_rw = UIO_WRITE;
                        uio.uio_resid = iov.iov_len;

                        if (uio.uio_resid == 0)
                                break;

                        do {
                                error = VOP_WRITE(tvp, &uio, 0, cred);
                        } while ((uio.uio_resid > 0) && (error == 0));
                }

        } while (error == 0);

        free(tbuf, 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 lwp *l)
{
        int error;
        struct vnode *lvp, *uvp;
        struct vattr lvattr, uvattr;

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

        /* 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 VOP_CLOSE
                 */
                vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);

                error = VOP_GETATTR(lvp, &lvattr, cred);
                if (error == 0)
                        error = VOP_OPEN(lvp, FREAD, cred);
                if (error == 0) {
                        error = union_copyfile(lvp, uvp, cred, l);
                        (void) VOP_CLOSE(lvp, FREAD, cred);
                }
                if (error == 0) {
                        /* Copy permissions up too */
                        vattr_null(&uvattr);
                        uvattr.va_mode = lvattr.va_mode;
                        uvattr.va_flags = lvattr.va_flags;
                        error = VOP_SETATTR(uvp, &uvattr, cred);
                }
                VOP_UNLOCK(lvp, 0);
#ifdef UNION_DIAGNOSTIC
                if (error == 0)
                        uprintf("union: copied up %s\n", un->un_path);
#endif

        }
        union_vn_close(uvp, FWRITE, cred, l);

        /*
         * 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;

                vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
                for (i = 0; i < un->un_openl; i++) {
                        (void) VOP_CLOSE(lvp, FREAD, cred);
                        (void) VOP_OPEN(uvp, FREAD, cred);
                }
                un->un_openl = 0;
                VOP_UNLOCK(lvp, 0);
        }

        return (error);

}

static int
union_relookup(
        struct union_mount *um,
        struct vnode *dvp,
        struct vnode **vpp,
        struct componentname *cnp,
        struct componentname *cn,
        const 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 VOP_LOOKUP when given a CREATE flag.
         * Conclusion: Horrible.
         *
         * The pathname buffer will be PNBUF_PUT'd by VOP_MKDIR.
         */
        cn->cn_namelen = pathlen;
        if ((cn->cn_namelen + 1) > MAXPATHLEN)
                return (ENAMETOOLONG);
        cn->cn_pnbuf = PNBUF_GET();
        memcpy(cn->cn_pnbuf, path, cn->cn_namelen);
        cn->cn_pnbuf[cn->cn_namelen] = '\0';

        cn->cn_nameiop = CREATE;
        cn->cn_flags = (LOCKPARENT|HASBUF|SAVENAME|ISLASTCN);
        if (um->um_op == UNMNT_ABOVE)
                cn->cn_cred = cnp->cn_cred;
        else
                cn->cn_cred = um->um_cred;
        cn->cn_nameptr = cn->cn_pnbuf;
        cn->cn_hash = cnp->cn_hash;
        cn->cn_consume = cnp->cn_consume;

        error = relookup(dvp, vpp, cn);
        if (error) {
                PNBUF_PUT(cn->cn_pnbuf);
                cn->cn_pnbuf = 0;
        }

        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.
 *
 * N.B. We still attempt to create shadow directories even if the union
 * is mounted read-only, which is a little nonintuitive.
 */
int
union_mkshadow(struct union_mount *um, struct vnode *dvp,
        struct componentname *cnp, struct vnode **vpp)
{
        int error;
        struct vattr va;
        struct componentname cn;

        vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY);
        error = union_relookup(um, dvp, vpp, cnp, &cn,
                        cnp->cn_nameptr, cnp->cn_namelen);
        if (error) {
                VOP_UNLOCK(dvp, 0);
                return (error);
        }

        if (*vpp) {
                VOP_ABORTOP(dvp, &cn);
                if (dvp != *vpp)
                        VOP_UNLOCK(dvp, 0);
                vput(*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_null(&va);
        va.va_type = VDIR;
        va.va_mode = um->um_cmode;

        vref(dvp);
        error = VOP_MKDIR(dvp, vpp, &cn, &va);
        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(struct union_mount *um, struct vnode *dvp,
        struct componentname *cnp, char *path)
{
        int error;
        struct vnode *wvp;
        struct componentname cn;

        VOP_UNLOCK(dvp, 0);
        vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY);
        error = union_relookup(um, dvp, &wvp, cnp, &cn, path, strlen(path));
        if (error)
                return (error);

        if (wvp) {
                VOP_ABORTOP(dvp, &cn);
                if (dvp != wvp)
                        VOP_UNLOCK(dvp, 0);
                vput(wvp);
                return (EEXIST);
        }

        error = VOP_WHITEOUT(dvp, &cn, CREATE);
        if (error)
                VOP_ABORTOP(dvp, &cn);

        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(struct vnode **vpp, struct union_node *un, struct lwp *l)
{
        struct vnode *vp;
        kauth_cred_t cred = l->l_cred;
        struct vattr vat;
        struct vattr *vap = &vat;
        int fmode = FFLAGS(O_WRONLY|O_CREAT|O_TRUNC|O_EXCL);
        int error;
        int cmode = UN_FILEMODE & ~l->l_proc->p_cwdi->cwdi_cmask;
        struct componentname cn;

        *vpp = NULLVP;

        /*
         * 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);
        if ((cn.cn_namelen + 1) > MAXPATHLEN)
                return (ENAMETOOLONG);
        cn.cn_pnbuf = PNBUF_GET();
        memcpy(cn.cn_pnbuf, un->un_path, cn.cn_namelen+1);
        cn.cn_nameiop = CREATE;
        cn.cn_flags = (LOCKPARENT|HASBUF|SAVENAME|ISLASTCN);
        cn.cn_cred = l->l_cred;
        cn.cn_nameptr = cn.cn_pnbuf;
        cn.cn_hash = un->un_hash;
        cn.cn_consume = 0;

        vn_lock(un->un_dirvp, LK_EXCLUSIVE | LK_RETRY);
        error = relookup(un->un_dirvp, &vp, &cn);
        if (error) {
                VOP_UNLOCK(un->un_dirvp, 0);
                return (error);
        }

        if (vp) {
                VOP_ABORTOP(un->un_dirvp, &cn);
                if (un->un_dirvp != vp)
                        VOP_UNLOCK(un->un_dirvp, 0);
                vput(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.
         */
        vattr_null(vap);
        vap->va_type = VREG;
        vap->va_mode = cmode;
        vref(un->un_dirvp);
        if ((error = VOP_CREATE(un->un_dirvp, &vp, &cn, vap)) != 0)
                return (error);

        if ((error = VOP_OPEN(vp, fmode, cred)) != 0) {
                vput(vp);
                return (error);
        }

        vp->v_writecount++;
        *vpp = vp;
        return (0);
}

int
union_vn_close(struct vnode *vp, int fmode, kauth_cred_t cred, struct lwp *l)
{

        if (fmode & FWRITE)
                --vp->v_writecount;
        return (VOP_CLOSE(vp, fmode, cred));
}

void
union_removed_upper(struct union_node *un)
{
#if 1
        /*
         * We do not set the uppervp to NULLVP here, because lowervp
         * may also be NULLVP, so this routine would end up creating
         * a bogus union node with no upper or lower VP (that causes
         * pain in many places that assume at least one VP exists).
         * Since we've removed this node from the cache hash chains,
         * it won't be found again.  When all current holders
         * release it, union_inactive() will vgone() it.
         */
        union_diruncache(un);
#else
        union_newupper(un, NULLVP);
#endif

        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;
                VOP_UNLOCK(un->un_uppervp, 0);
        }
}

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

        if ((un->un_lowervp != NULLVP) &&
            (vp->v_type == un->un_lowervp->v_type)) {
                if (vget(un->un_lowervp, 0) == 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, kauth_cred_t cred)
{
        struct vattr va;

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

        if (VOP_GETATTR(un->un_uppervp, &va, cred) == 0 &&
            (va.va_flags & OPAQUE))
                return (1);

        return (0);
}

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

        if (vp->v_op != union_vnodeop_p) {
                if (vppp) {
                        vref(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(struct vnode *vp, struct lwp *l)
{
        int cnt;
        struct vnode *nvp = NULLVP;
        struct vnode **vpp;
        struct vnode **dircache;
        int error;

        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
        dircache = VTOUNION(vp)->un_dircache;

        nvp = NULLVP;

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

        if (*vpp == NULLVP)
                goto out;

        vn_lock(*vpp, LK_EXCLUSIVE | LK_RETRY);
        vref(*vpp);
        error = union_allocvp(&nvp, vp->v_mount, NULLVP, NULLVP, 0, *vpp, NULLVP, 0);
        if (!error) {
                VTOUNION(vp)->un_dircache = 0;
                VTOUNION(nvp)->un_dircache = dircache;
        }

out:
        VOP_UNLOCK(vp, 0);
        return (nvp);
}

void
union_diruncache(struct union_node *un)
{
        struct vnode **vpp;

        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;
        }
}

/*
 * This hook is called from vn_readdir() to switch to lower directory
 * entry after the upper directory is read.
 */
int
union_readdirhook(struct vnode **vpp, struct file *fp, struct lwp *l)
{
        struct vnode *vp = *vpp, *lvp;
        struct vattr va;
        int error;

        if (vp->v_op != union_vnodeop_p)
                return (0);

        if ((lvp = union_dircache(vp, l)) == NULLVP)
                return (0);

        /*
         * If the directory is opaque,
         * then don't show lower entries
         */
        error = VOP_GETATTR(vp, &va, fp->f_cred);
        if (error || (va.va_flags & OPAQUE)) {
                vput(lvp);
                return (error);
        }

        error = VOP_OPEN(lvp, FREAD, fp->f_cred);
        if (error) {
                vput(lvp);
                return (error);
        }
        VOP_UNLOCK(lvp, 0);
        fp->f_data = lvp;
        fp->f_offset = 0;
        error = vn_close(vp, FREAD, fp->f_cred);
        if (error)
                return (error);
        *vpp = lvp;
        return (0);
}