Fix a buffer cache deadlock which can occur when simulated disk devices

[dragonfly.git] / sys / dev / disk / vn / vn.c

/*
 * Copyright (c) 1988 University of Utah.
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * the Systems Programming Group of the University of Utah Computer
 * Science Department.
 *
 * 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.
 *
 * from: Utah Hdr: vn.c 1.13 94/04/02
 *
 *      from: @(#)vn.c  8.6 (Berkeley) 4/1/94
 * $FreeBSD: src/sys/dev/vn/vn.c,v 1.105.2.4 2001/11/18 07:11:00 dillon Exp $
 * $DragonFly: src/sys/dev/disk/vn/vn.c,v 1.38 2008/07/01 02:02:53 dillon Exp $
 */

/*
 * Vnode disk driver.
 *
 * Block/character interface to a vnode.  Allows one to treat a file
 * as a disk (e.g. build a filesystem in it, mount it, etc.).
 *
 * NOTE 1: There is a security issue involved with this driver.
 * Once mounted all access to the contents of the "mapped" file via
 * the special file is controlled by the permissions on the special
 * file, the protection of the mapped file is ignored (effectively,
 * by using root credentials in all transactions).
 *
 * NOTE 2: Doesn't interact with leases, should it?
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/nlookup.h>
#include <sys/buf.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/vnode.h>
#include <sys/fcntl.h>
#include <sys/conf.h>
#include <sys/diskslice.h>
#include <sys/disk.h>
#include <sys/stat.h>
#include <sys/module.h>
#include <sys/vnioctl.h>

#include <vm/vm.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pager.h>
#include <vm/vm_pageout.h>
#include <vm/swap_pager.h>
#include <vm/vm_extern.h>
#include <vm/vm_zone.h>

static  d_ioctl_t       vnioctl;
static  d_open_t        vnopen;
static  d_close_t       vnclose;
static  d_psize_t       vnsize;
static  d_strategy_t    vnstrategy;

#define CDEV_MAJOR 43

#define VN_BSIZE_BEST   8192

/*
 * dev_ops
 *      D_DISK          we want to look like a disk
 *      D_CANFREE       We support BUF_CMD_FREEBLKS
 */

static struct dev_ops vn_ops = {
        { "vn", CDEV_MAJOR, D_DISK | D_CANFREE },
        .d_open =       vnopen,
        .d_close =      vnclose,
        .d_read =       physread,
        .d_write =      physwrite,
        .d_ioctl =      vnioctl,
        .d_strategy =   vnstrategy,
        .d_psize =      vnsize
};

struct vn_softc {
        int             sc_unit;
        int             sc_flags;       /* flags                        */
        u_int64_t       sc_size;        /* size of vn, sc_secsize scale */
        int             sc_secsize;     /* sector size                  */
        struct diskslices *sc_slices;   /* XXX fields from struct disk  */
        struct disk_info sc_info;       /* XXX fields from struct disk  */
        struct vnode    *sc_vp;         /* vnode if not NULL            */
        vm_object_t     sc_object;      /* backing object if not NULL   */
        struct ucred    *sc_cred;       /* credentials                  */
        int              sc_maxactive;  /* max # of active requests     */
        struct buf       sc_tab;        /* transfer queue               */
        u_long           sc_options;    /* options                      */
        cdev_t           sc_devlist;    /* devices that refer to this unit */
        SLIST_ENTRY(vn_softc) sc_list;
};

static SLIST_HEAD(, vn_softc) vn_list;

/* sc_flags */
#define VNF_INITED      0x01
#define VNF_READONLY    0x02

static u_long   vn_options;

#define IFOPT(vn,opt) if (((vn)->sc_options|vn_options) & (opt))
#define TESTOPT(vn,opt) (((vn)->sc_options|vn_options) & (opt))

static int      vnsetcred (struct vn_softc *vn, struct ucred *cred);
static void     vnclear (struct vn_softc *vn);
static int      vnget (cdev_t dev, struct vn_softc *vn , struct vn_user *vnu);
static int      vn_modevent (module_t, int, void *);
static int      vniocattach_file (struct vn_softc *, struct vn_ioctl *, cdev_t dev, int flag, struct ucred *cred);
static int      vniocattach_swap (struct vn_softc *, struct vn_ioctl *, cdev_t dev, int flag, struct ucred *cred);

static  int
vnclose(struct dev_close_args *ap)
{
        cdev_t dev = ap->a_head.a_dev;
        struct vn_softc *vn = dev->si_drv1;

        IFOPT(vn, VN_LABELS)
                if (vn->sc_slices != NULL)
                        dsclose(dev, ap->a_devtype, vn->sc_slices);
        return (0);
}

/*
 * Called only when si_drv1 is NULL.  Locate the associated vn node and
 * attach the device to it.
 */
static struct vn_softc *
vnfindvn(cdev_t dev)
{
        int unit;
        struct vn_softc *vn;

        unit = dkunit(dev);
        SLIST_FOREACH(vn, &vn_list, sc_list) {
                if (vn->sc_unit == unit) {
                        dev->si_drv1 = vn;
                        dev->si_drv2 = vn->sc_devlist;
                        vn->sc_devlist = dev;
                        reference_dev(dev);
                        break;
                }
        }
        if (vn == NULL) {
                vn = kmalloc(sizeof *vn, M_DEVBUF, M_WAITOK | M_ZERO);
                vn->sc_unit = unit;
                dev->si_drv1 = vn;
                vn->sc_devlist = make_dev(&vn_ops, 0, UID_ROOT,
                                        GID_OPERATOR, 0640, "vn%d", unit);
                if (vn->sc_devlist->si_drv1 == NULL) {
                        reference_dev(vn->sc_devlist);
                        vn->sc_devlist->si_drv1 = vn;
                        vn->sc_devlist->si_drv2 = NULL;
                }
                if (vn->sc_devlist != dev) {
                        dev->si_drv1 = vn;
                        dev->si_drv2 = vn->sc_devlist;
                        vn->sc_devlist = dev;
                        reference_dev(dev);
                }
                SLIST_INSERT_HEAD(&vn_list, vn, sc_list);
        }
        return (vn);
}

static  int
vnopen(struct dev_open_args *ap)
{
        cdev_t dev = ap->a_head.a_dev;
        struct vn_softc *vn;
        struct disk_info *info;

        /*
         * Locate preexisting device
         */

        if ((vn = dev->si_drv1) == NULL)
                vn = vnfindvn(dev);

        /*
         * Update si_bsize fields for device.  This data will be overriden by
         * the slice/parition code for vn accesses through partitions, and
         * used directly if you open the 'whole disk' device.
         *
         * si_bsize_best must be reinitialized in case VN has been 
         * reconfigured, plus make it at least VN_BSIZE_BEST for efficiency.
         */
        dev->si_bsize_phys = vn->sc_secsize;
        dev->si_bsize_best = vn->sc_secsize;
        if (dev->si_bsize_best < VN_BSIZE_BEST)
                dev->si_bsize_best = VN_BSIZE_BEST;

        if ((ap->a_oflags & FWRITE) && (vn->sc_flags & VNF_READONLY))
                return (EACCES);

        IFOPT(vn, VN_FOLLOW)
                kprintf("vnopen(%s, 0x%x, 0x%x)\n",
                    devtoname(dev), ap->a_oflags, ap->a_devtype);

        /*
         * Initialize label
         */

        IFOPT(vn, VN_LABELS) {
                if (vn->sc_flags & VNF_INITED) {
                        info = &vn->sc_info;
                        bzero(info, sizeof(*info));
                        info->d_media_blksize = vn->sc_secsize;
                        info->d_media_blocks = vn->sc_size;
                        /*
                         * reserve mbr sector for backwards compatibility
                         * when no slices exist.
                         */
                        info->d_dsflags = DSO_COMPATMBR;

                        info->d_secpertrack = 32;
                        info->d_nheads = 64 / (vn->sc_secsize / DEV_BSIZE);
                        info->d_secpercyl = info->d_secpertrack *
                                            info->d_nheads;
                        info->d_ncylinders = vn->sc_size / info->d_secpercyl;

                        return (dsopen(dev, ap->a_devtype, 0,
                                        &vn->sc_slices, info));
                }
                if (dkslice(dev) != WHOLE_DISK_SLICE ||
                    dkpart(dev) != WHOLE_SLICE_PART ||
                    ap->a_devtype != S_IFCHR) {
                        return (ENXIO);
                }
        }
        return(0);
}

/*
 *      vnstrategy:
 *
 *      Run strategy routine for VN device.  We use VOP_READ/VOP_WRITE calls
 *      for vnode-backed vn's, and the new vm_pager_strategy() call for
 *      vm_object-backed vn's.
 *
 *      Currently B_ASYNC is only partially handled - for OBJT_SWAP I/O only.
 */
static int
vnstrategy(struct dev_strategy_args *ap)
{
        cdev_t dev = ap->a_head.a_dev;
        struct bio *bio = ap->a_bio;
        struct buf *bp;
        struct bio *nbio;
        int unit;
        struct vn_softc *vn;
        int error;

        unit = dkunit(dev);
        if ((vn = dev->si_drv1) == NULL)
                vn = vnfindvn(dev);

        bp = bio->bio_buf;

        IFOPT(vn, VN_DEBUG)
                kprintf("vnstrategy(%p): unit %d\n", bp, unit);

        if ((vn->sc_flags & VNF_INITED) == 0) {
                bp->b_error = ENXIO;
                bp->b_flags |= B_ERROR;
                biodone(bio);
                return(0);
        }

        bp->b_resid = bp->b_bcount;

        IFOPT(vn, VN_LABELS) {
                /*
                 * The vnode device is using disk/slice label support.
                 *
                 * The dscheck() function is called for validating the
                 * slices that exist ON the vnode device itself, and
                 * translate the "slice-relative" block number, again.
                 * dscheck() will call biodone() and return NULL if
                 * we are at EOF or beyond the device size.
                 */
                if (vn->sc_slices == NULL) {
                        nbio = bio;
                } else if ((nbio = dscheck(dev, bio, vn->sc_slices)) == NULL) {
                        goto done;
                }
        } else {
                int64_t pbn;    /* in sc_secsize chunks */
                long sz;        /* in sc_secsize chunks */

                /*
                 * Check for required alignment.  Transfers must be a valid
                 * multiple of the sector size.
                 */
                if (bp->b_bcount % vn->sc_secsize != 0 ||
                    bio->bio_offset % vn->sc_secsize != 0) {
                        goto bad;
                }

                pbn = bio->bio_offset / vn->sc_secsize;
                sz = howmany(bp->b_bcount, vn->sc_secsize);

                /*
                 * Check for an illegal pbn or EOF truncation
                 */
                if (pbn < 0)
                        goto bad;
                if (pbn + sz > vn->sc_size) {
                        if (pbn > vn->sc_size || (bp->b_flags & B_BNOCLIP))
                                goto bad;
                        if (pbn == vn->sc_size) {
                                bp->b_resid = bp->b_bcount;
                                bp->b_flags |= B_INVAL;
                                goto done;
                        }
                        bp->b_bcount = (vn->sc_size - pbn) * vn->sc_secsize;
                }
                nbio = push_bio(bio);
                nbio->bio_offset = pbn * vn->sc_secsize;
        }

        /*
         * Use the translated nbio from this point on
         */
        if (vn->sc_vp && bp->b_cmd == BUF_CMD_FREEBLKS) {
                /*
                 * Freeblks is not handled for vnode-backed elements yet.
                 */
                bp->b_resid = 0;
                /* operation complete */
        } else if (vn->sc_vp) {
                /*
                 * VNODE I/O
                 *
                 * If an error occurs, we set B_ERROR but we do not set 
                 * B_INVAL because (for a write anyway), the buffer is 
                 * still valid.
                 */
                struct uio auio;
                struct iovec aiov;

                bzero(&auio, sizeof(auio));

                aiov.iov_base = bp->b_data;
                aiov.iov_len = bp->b_bcount;
                auio.uio_iov = &aiov;
                auio.uio_iovcnt = 1;
                auio.uio_offset = nbio->bio_offset;
                auio.uio_segflg = UIO_SYSSPACE;
                if (bp->b_cmd == BUF_CMD_READ)
                        auio.uio_rw = UIO_READ;
                else
                        auio.uio_rw = UIO_WRITE;
                auio.uio_resid = bp->b_bcount;
                auio.uio_td = curthread;
                vn_lock(vn->sc_vp, LK_EXCLUSIVE | LK_RETRY);
                if (bp->b_cmd == BUF_CMD_READ)
                        error = VOP_READ(vn->sc_vp, &auio, IO_DIRECT | IO_RECURSE, vn->sc_cred);
                else
                        error = VOP_WRITE(vn->sc_vp, &auio, IO_DIRECT | IO_RECURSE, vn->sc_cred);
                vn_unlock(vn->sc_vp);
                bp->b_resid = auio.uio_resid;
                if (error) {
                        bp->b_error = error;
                        bp->b_flags |= B_ERROR;
                }
                /* operation complete */
        } else if (vn->sc_object) {
                /*
                 * OBJT_SWAP I/O (handles read, write, freebuf)
                 *
                 * We have nothing to do if freeing  blocks on a reserved
                 * swap area, othrewise execute the op.
                 */
                if (bp->b_cmd == BUF_CMD_FREEBLKS && TESTOPT(vn, VN_RESERVE)) {
                        bp->b_resid = 0;
                        /* operation complete */
                } else {
                        vm_pager_strategy(vn->sc_object, nbio);
                        return(0);
                        /* NOT REACHED */
                }
        } else {
                bp->b_resid = bp->b_bcount;
                bp->b_flags |= B_ERROR | B_INVAL;
                bp->b_error = EINVAL;
                /* operation complete */
        }
        biodone(nbio);
        return(0);

        /*
         * Shortcuts / check failures on the original bio (not nbio).
         */
bad:
        bp->b_error = EINVAL;
        bp->b_flags |= B_ERROR | B_INVAL;
done:
        biodone(bio);
        return(0);
}

/* ARGSUSED */
static  int
vnioctl(struct dev_ioctl_args *ap)
{
        cdev_t dev = ap->a_head.a_dev;
        struct vn_softc *vn;
        struct vn_ioctl *vio;
        int error;
        u_long *f;

        vn = dev->si_drv1;
        IFOPT(vn,VN_FOLLOW) {
                kprintf("vnioctl(%s, 0x%lx, %p, 0x%x): unit %d\n",
                    devtoname(dev), ap->a_cmd, ap->a_data, ap->a_fflag,
                    dkunit(dev));
        }

        switch (ap->a_cmd) {
        case VNIOCATTACH:
        case VNIOCDETACH:
        case VNIOCGSET:
        case VNIOCGCLEAR:
        case VNIOCGET:
        case VNIOCUSET:
        case VNIOCUCLEAR:
                goto vn_specific;
        }

        IFOPT(vn,VN_LABELS) {
                if (vn->sc_slices != NULL) {
                        error = dsioctl(dev, ap->a_cmd, ap->a_data,
                                        ap->a_fflag,
                                        &vn->sc_slices, &vn->sc_info);
                        if (error != ENOIOCTL)
                                return (error);
                }
                if (dkslice(dev) != WHOLE_DISK_SLICE ||
                    dkpart(dev) != WHOLE_SLICE_PART)
                        return (ENOTTY);
        }

    vn_specific:

        error = suser_cred(ap->a_cred, 0);
        if (error)
                return (error);

        vio = (struct vn_ioctl *)ap->a_data;
        f = (u_long*)ap->a_data;

        switch (ap->a_cmd) {
        case VNIOCATTACH:
                if (vn->sc_flags & VNF_INITED)
                        return(EBUSY);

                if (vio->vn_file == NULL)
                        error = vniocattach_swap(vn, vio, dev, ap->a_fflag, ap->a_cred);
                else
                        error = vniocattach_file(vn, vio, dev, ap->a_fflag, ap->a_cred);
                break;

        case VNIOCDETACH:
                if ((vn->sc_flags & VNF_INITED) == 0)
                        return(ENXIO);
                /*
                 * XXX handle i/o in progress.  Return EBUSY, or wait, or
                 * flush the i/o.
                 * XXX handle multiple opens of the device.  Return EBUSY,
                 * or revoke the fd's.
                 * How are these problems handled for removable and failing
                 * hardware devices? (Hint: They are not)
                 */
                vnclear(vn);
                IFOPT(vn, VN_FOLLOW)
                        kprintf("vnioctl: CLRed\n");
                break;

        case VNIOCGET:
                error = vnget(dev, vn, (struct vn_user *) ap->a_data);
                break;

        case VNIOCGSET:
                vn_options |= *f;
                *f = vn_options;
                break;

        case VNIOCGCLEAR:
                vn_options &= ~(*f);
                *f = vn_options;
                break;

        case VNIOCUSET:
                vn->sc_options |= *f;
                *f = vn->sc_options;
                break;

        case VNIOCUCLEAR:
                vn->sc_options &= ~(*f);
                *f = vn->sc_options;
                break;

        default:
                error = ENOTTY;
                break;
        }
        return(error);
}

/*
 *      vniocattach_file:
 *
 *      Attach a file to a VN partition.  Return the size in the vn_size
 *      field.
 */

static int
vniocattach_file(struct vn_softc *vn, struct vn_ioctl *vio, cdev_t dev,
                 int flag, struct ucred *cred)
{
        struct vattr vattr;
        struct nlookupdata nd;
        int error, flags;
        struct vnode *vp;

        flags = FREAD|FWRITE;
        error = nlookup_init(&nd, vio->vn_file, 
                                UIO_USERSPACE, NLC_FOLLOW|NLC_LOCKVP);
        if (error)
                return (error);
        if ((error = vn_open(&nd, NULL, flags, 0)) != 0) {
                if (error != EACCES && error != EPERM && error != EROFS)
                        goto done;
                flags &= ~FWRITE;
                nlookup_done(&nd);
                error = nlookup_init(&nd, vio->vn_file, UIO_USERSPACE, NLC_FOLLOW|NLC_LOCKVP);
                if (error)
                        return (error);
                if ((error = vn_open(&nd, NULL, flags, 0)) != 0)
                        goto done;
        }
        vp = nd.nl_open_vp;
        if (vp->v_type != VREG ||
            (error = VOP_GETATTR(vp, &vattr))) {
                if (error == 0)
                        error = EINVAL;
                goto done;
        }
        vn_unlock(vp);
        vn->sc_secsize = DEV_BSIZE;
        vn->sc_vp = vp;
        nd.nl_open_vp = NULL;

        /*
         * If the size is specified, override the file attributes.  Note that
         * the vn_size argument is in PAGE_SIZE sized blocks.
         */
        if (vio->vn_size)
                vn->sc_size = vio->vn_size * PAGE_SIZE / vn->sc_secsize;
        else
                vn->sc_size = vattr.va_size / vn->sc_secsize;
        error = vnsetcred(vn, cred);
        if (error) {
                vn->sc_vp = NULL;
                vn_close(vp, flags);
                goto done;
        }
        vn->sc_flags |= VNF_INITED;
        if (flags == FREAD)
                vn->sc_flags |= VNF_READONLY;
        IFOPT(vn, VN_LABELS) {
                /*
                 * Reopen so that `ds' knows which devices are open.
                 * If this is the first VNIOCSET, then we've
                 * guaranteed that the device is the cdev and that
                 * no other slices or labels are open.  Otherwise,
                 * we rely on VNIOCCLR not being abused.
                 */
                error = dev_dopen(dev, flag, S_IFCHR, cred);
                if (error)
                        vnclear(vn);
        }
        IFOPT(vn, VN_FOLLOW)
                kprintf("vnioctl: SET vp %p size %llx blks\n",
                       vn->sc_vp, vn->sc_size);
done:
        nlookup_done(&nd);
        return(error);
}

/*
 *      vniocattach_swap:
 *
 *      Attach swap backing store to a VN partition of the size specified
 *      in vn_size.
 */

static int
vniocattach_swap(struct vn_softc *vn, struct vn_ioctl *vio, cdev_t dev,
                 int flag, struct ucred *cred)
{
        int error;

        /*
         * Range check.  Disallow negative sizes or any size less then the
         * size of a page.  Then round to a page.
         */

        if (vio->vn_size <= 0)
                return(EDOM);

        /*
         * Allocate an OBJT_SWAP object.
         *
         * sc_secsize is PAGE_SIZE'd
         *
         * vio->vn_size is in PAGE_SIZE'd chunks.
         * sc_size must be in PAGE_SIZE'd chunks.  
         * Note the truncation.
         */

        vn->sc_secsize = PAGE_SIZE;
        vn->sc_size = vio->vn_size;
        vn->sc_object = vm_pager_allocate(OBJT_SWAP, NULL,
                                          vn->sc_secsize * (off_t)vio->vn_size,
                                          VM_PROT_DEFAULT, 0);
        IFOPT(vn, VN_RESERVE) {
                if (swap_pager_reserve(vn->sc_object, 0, vn->sc_size) < 0) {
                        vm_pager_deallocate(vn->sc_object);
                        vn->sc_object = NULL;
                        return(EDOM);
                }
        }
        vn->sc_flags |= VNF_INITED;

        error = vnsetcred(vn, cred);
        if (error == 0) {
                IFOPT(vn, VN_LABELS) {
                        /*
                         * Reopen so that `ds' knows which devices are open.
                         * If this is the first VNIOCSET, then we've
                         * guaranteed that the device is the cdev and that
                         * no other slices or labels are open.  Otherwise,
                         * we rely on VNIOCCLR not being abused.
                         */
                        error = dev_dopen(dev, flag, S_IFCHR, cred);
                }
        }
        if (error == 0) {
                IFOPT(vn, VN_FOLLOW) {
                        kprintf("vnioctl: SET vp %p size %llx\n",
                               vn->sc_vp, vn->sc_size);
                }
        }
        if (error)
                vnclear(vn);
        return(error);
}

/*
 * Duplicate the current processes' credentials.  Since we are called only
 * as the result of a SET ioctl and only root can do that, any future access
 * to this "disk" is essentially as root.  Note that credentials may change
 * if some other uid can write directly to the mapped file (NFS).
 */
int
vnsetcred(struct vn_softc *vn, struct ucred *cred)
{
        char *tmpbuf;
        int error = 0;

        /*
         * Set credits in our softc
         */

        if (vn->sc_cred)
                crfree(vn->sc_cred);
        vn->sc_cred = crdup(cred);

        /*
         * Horrible kludge to establish credentials for NFS  XXX.
         */

        if (vn->sc_vp) {
                struct uio auio;
                struct iovec aiov;

                tmpbuf = kmalloc(vn->sc_secsize, M_TEMP, M_WAITOK);
                bzero(&auio, sizeof(auio));

                aiov.iov_base = tmpbuf;
                aiov.iov_len = vn->sc_secsize;
                auio.uio_iov = &aiov;
                auio.uio_iovcnt = 1;
                auio.uio_offset = 0;
                auio.uio_rw = UIO_READ;
                auio.uio_segflg = UIO_SYSSPACE;
                auio.uio_resid = aiov.iov_len;
                vn_lock(vn->sc_vp, LK_EXCLUSIVE | LK_RETRY);
                error = VOP_READ(vn->sc_vp, &auio, 0, vn->sc_cred);
                vn_unlock(vn->sc_vp);
                kfree(tmpbuf, M_TEMP);
        }
        return (error);
}

void
vnclear(struct vn_softc *vn)
{
        IFOPT(vn, VN_FOLLOW)
                kprintf("vnclear(%p): vp=%p\n", vn, vn->sc_vp);
        if (vn->sc_slices != NULL)
                dsgone(&vn->sc_slices);
        vn->sc_flags &= ~VNF_INITED;
        if (vn->sc_vp != NULL) {
                vn_close(vn->sc_vp,
                    (vn->sc_flags & VNF_READONLY) ?  FREAD : (FREAD|FWRITE));
                vn->sc_vp = NULL;
        }
        vn->sc_flags &= ~VNF_READONLY;
        if (vn->sc_cred) {
                crfree(vn->sc_cred);
                vn->sc_cred = NULL;
        }
        if (vn->sc_object != NULL) {
                vm_pager_deallocate(vn->sc_object);
                vn->sc_object = NULL;
        }
        vn->sc_size = 0;
}

/*
 *      vnget:
 *
 *      populate a struct vn_user for the VNIOCGET ioctl.
 *      interface conventions defined in sys/sys/vnioctl.h.
 */

static int
vnget(cdev_t dev, struct vn_softc *vn, struct vn_user *vnu)
{
        int error, found = 0; 
        char *freepath, *fullpath;
        struct vattr vattr;

        if (vnu->vnu_unit == -1) {
                vnu->vnu_unit = dkunit(dev);
        }
        else if (vnu->vnu_unit < 0)
                return (EINVAL);

        SLIST_FOREACH(vn, &vn_list, sc_list) {

                if(vn->sc_unit != vnu->vnu_unit)
                        continue;

                found = 1;

                if (vn->sc_flags & VNF_INITED && vn->sc_vp != NULL) {

                        /* note: u_cred checked in vnioctl above */
                        error = VOP_GETATTR(vn->sc_vp, &vattr);
                        if (error) {
                                kprintf("vnget: VOP_GETATTR for %p failed\n",
                                        vn->sc_vp);
                                return (error);
                        }

                        error = vn_fullpath(curproc, vn->sc_vp,
                                                &fullpath, &freepath);

                        if (error) {
                                kprintf("vnget: unable to resolve vp %p\n",
                                        vn->sc_vp);
                                return(error);
                        }
                        
                        strlcpy(vnu->vnu_file, fullpath,
                                sizeof(vnu->vnu_file));
                        kfree(freepath, M_TEMP);
                        vnu->vnu_dev = vattr.va_fsid;
                        vnu->vnu_ino = vattr.va_fileid;

                } 
                else if (vn->sc_flags & VNF_INITED && vn->sc_object != NULL){

                        strlcpy(vnu->vnu_file, _VN_USER_SWAP,
                                sizeof(vnu->vnu_file));
                        vnu->vnu_size = vn->sc_size;
                        vnu->vnu_secsize = vn->sc_secsize;

                } else {

                        bzero(vnu->vnu_file, sizeof(vnu->vnu_file));
                        vnu->vnu_dev = 0;
                        vnu->vnu_ino = 0;

                }
                break;
        }

        if (!found)
                return(ENXIO);

        return(0);
}

static int
vnsize(struct dev_psize_args *ap)
{
        cdev_t dev = ap->a_head.a_dev;
        struct vn_softc *vn;

        vn = dev->si_drv1;
        if (!vn)
                return(ENXIO);
        if ((vn->sc_flags & VNF_INITED) == 0)
                return(ENXIO);
        ap->a_result = (int64_t)vn->sc_size;
        return(0);
}

static int 
vn_modevent(module_t mod, int type, void *data)
{
        struct vn_softc *vn;
        cdev_t dev;

        switch (type) {
        case MOD_LOAD:
                dev_ops_add(&vn_ops, 0, 0);
                break;
        case MOD_UNLOAD:
                /* fall through */
        case MOD_SHUTDOWN:
                while ((vn = SLIST_FIRST(&vn_list)) != NULL) {
                        SLIST_REMOVE_HEAD(&vn_list, sc_list);
                        if (vn->sc_flags & VNF_INITED)
                                vnclear(vn);
                        /* Cleanup all cdev_t's that refer to this unit */
                        while ((dev = vn->sc_devlist) != NULL) {
                                vn->sc_devlist = dev->si_drv2;
                                dev->si_drv1 = dev->si_drv2 = NULL;
                                destroy_dev(dev);
                        }
                        kfree(vn, M_DEVBUF);
                }
                dev_ops_remove(&vn_ops, 0, 0);
                break;
        default:
                break;
        }
        return 0;
}

DEV_MODULE(vn, vn_modevent, 0);