File:  [DragonFly] / src / sys / dev / disk / vn / vn.c
Revision 1.10: download - view: text, annotated - select for diffs
Wed May 19 22:52:42 2004 UTC (10 years, 5 months ago) by dillon
Branches: MAIN
CVS tags: HEAD
Device layer rollup commit.

* cdevsw_add() is now required.  cdevsw_add() and cdevsw_remove() may specify
  a mask/match indicating the range of supported minor numbers.  Multiple
  cdevsw_add()'s using the same major number, but distinctly different
  ranges, may be issued.  All devices that failed to call cdevsw_add() before
  now do.

* cdevsw_remove() now automatically marks all devices within its supported
  range as being destroyed.

* vnode->v_rdev is no longer resolved when the vnode is created.  Instead,
  only v_udev (a newly added field) is resolved.  v_rdev is resolved when
  the vnode is opened and cleared on the last close.

* A great deal of code was making rather dubious assumptions with regards
  to the validity of devices associated with vnodes, primarily due to
  the persistence of a device structure due to being indexed by (major, minor)
  instead of by (cdevsw, major, minor).  In particular, if you run a program
  which connects to a USB device and then you pull the USB device and plug
  it back in, the vnode subsystem will continue to believe that the device
  is open when, in fact, it isn't (because it was destroyed and recreated).

  In particular, note that all the VFS mount procedures now check devices
  via v_udev instead of v_rdev prior to calling VOP_OPEN(), since v_rdev
  is NULL prior to the first open.

* The disk layer's device interaction has been rewritten.  The disk layer
  (i.e. the slice and disklabel management layer) no longer overloads
  its data onto the device structure representing the underlying physical
  disk.  Instead, the disk layer uses the new cdevsw_add() functionality
  to register its own cdevsw using the underlying device's major number,
  and simply does NOT register the underlying device's cdevsw.  No
  confusion is created because the device hash is now based on
  (cdevsw,major,minor) rather then (major,minor).

  NOTE: This also means that underlying raw disk devices may use the entire
  device minor number instead of having to reserve the bits used by the disk
  layer, and also means that can we (theoretically) stack a fully
  disklabel-supported 'disk' on top of any block device.

* The new reference counting scheme prevents this by associating a device
  with a cdevsw and disconnecting the device from its cdevsw when the cdevsw
  is removed.  Additionally, all udev2dev() lookups run through the cdevsw
  mask/match and only successfully find devices still associated with an
  active cdevsw.

* Major work on MFS:  MFS no longer shortcuts vnode and device creation.  It
  now creates a real vnode and a real device and implements real open and
  close VOPs.  Additionally, due to the disk layer changes, MFS is no longer
  limited to 255 mounts.  The new limit is 16 million.  Since MFS creates a
  real device node, mount_mfs will now create a real /dev/mfs<PID> device
  that can be read from userland (e.g. so you can dump an MFS filesystem).

* BUF AND DEVICE STRATEGY changes.  The struct buf contains a b_dev field.
  In order to properly handle stacked devices we now require that the b_dev
  field be initialized before the device strategy routine is called.  This
  required some additional work in various VFS implementations.  To enforce
  this requirement, biodone() now sets b_dev to NODEV.  The new disk layer
  will adjust b_dev before forwarding a request to the actual physical
  device.

* A bug in the ISO CD boot sequence which resulted in a panic has been fixed.

Testing by: lots of people, but David Rhodus found the most aggregious bugs.

/*
 * 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 1.10 2004/05/19 22:52:42 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: This uses the VOP_BMAP/VOP_STRATEGY interface to the vnode
 * instead of a simple VOP_RDWR.  We do this to avoid distorting the
 * local buffer cache.
 *
 * NOTE 2: 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 3: 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/namei.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/disklabel.h>
#include <sys/diskslice.h>
#include <sys/stat.h>
#include <sys/conf.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

/*
 * cdevsw
 *	D_DISK		we want to look like a disk
 *	D_CANFREE	We support B_FREEBUF
 */

static struct cdevsw vn_cdevsw = {
	/* name */	"vn",
	/* maj */	CDEV_MAJOR,
	/* flags */	D_DISK|D_CANFREE,
	/* port */	NULL,
	/* clone */	NULL,

	/* open */	vnopen,
	/* close */	vnclose,
	/* read */	physread,
	/* write */	physwrite,
	/* ioctl */	vnioctl,
	/* poll */	nopoll,
	/* mmap */	nommap,
	/* strategy */	vnstrategy,
	/* dump */	nodump,
	/* psize */	vnsize
};

#define	getvnbuf()	\
	((struct buf *)malloc(sizeof(struct buf), M_DEVBUF, M_WAITOK))

#define putvnbuf(bp)	\
	free((caddr_t)(bp), M_DEVBUF)

struct vn_softc {
	int		sc_unit;
	int		sc_flags;	/* flags 			*/
	int		sc_size;	/* size of vn, sc_secsize scale	*/
	int		sc_secsize;	/* sector size			*/
	struct diskslices *sc_slices;
	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 			*/
	dev_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	vn_modevent (module_t, int, void *);
static int 	vniocattach_file (struct vn_softc *, struct vn_ioctl *, dev_t dev, int flag, struct thread *p);
static int 	vniocattach_swap (struct vn_softc *, struct vn_ioctl *, dev_t dev, int flag, struct thread *p);

static	int
vnclose(dev_t dev, int flags, int mode, struct thread *td)
{
	struct vn_softc *vn = dev->si_drv1;

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

static struct vn_softc *
vnfindvn(dev_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_drv2 = vn->sc_devlist;
			vn->sc_devlist = dev;
			reference_dev(dev);
			dev->si_drv1 = vn;
			break;
		}
	}
	if (vn == NULL) {
		vn = malloc(sizeof *vn, M_DEVBUF, M_WAITOK | M_ZERO);
		vn->sc_unit = unit;
		dev->si_drv1 = vn;
		vn->sc_devlist = make_dev(&vn_cdevsw, 0, UID_ROOT,
					GID_OPERATOR, 0640, "vn%d", unit);
		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(dev_t dev, int flags, int mode, struct thread *td)
{
	struct vn_softc *vn;

	/*
	 * 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 ((flags & FWRITE) && (vn->sc_flags & VNF_READONLY))
		return (EACCES);

	IFOPT(vn, VN_FOLLOW)
		printf("vnopen(%s, 0x%x, 0x%x, %p)\n",
		    devtoname(dev), flags, mode, (void *)td);

	/*
	 * Initialize label
	 */

	IFOPT(vn, VN_LABELS) {
		if (vn->sc_flags & VNF_INITED) {
			struct disklabel label;

			/* Build label for whole disk. */
			bzero(&label, sizeof label);
			label.d_secsize = vn->sc_secsize;
			label.d_nsectors = 32;
			label.d_ntracks = 64 / (vn->sc_secsize / DEV_BSIZE);
			label.d_secpercyl = label.d_nsectors * label.d_ntracks;
			label.d_ncylinders = vn->sc_size / label.d_secpercyl;
			label.d_secperunit = vn->sc_size;
			label.d_partitions[RAW_PART].p_size = vn->sc_size;

			return (dsopen(dev, mode, 0, &vn->sc_slices, &label));
		}
		if (dkslice(dev) != WHOLE_DISK_SLICE ||
		    dkpart(dev) != RAW_PART ||
		    mode != 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.
 *
 *	NOTE: bp->b_blkno is DEV_BSIZE'd.  We must generate bp->b_pblkno for
 *	our uio or vn_pager_strategy() call that is vn->sc_secsize'd
 */

static	void
vnstrategy(struct buf *bp)
{
	int unit;
	struct vn_softc *vn;
	int error;

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

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

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

	bp->b_resid = bp->b_bcount;

	IFOPT(vn, VN_LABELS) {
		if (vn->sc_slices != NULL && dscheck(bp, vn->sc_slices) <= 0) {
			bp->b_flags |= B_INVAL;
			biodone(bp);
			return;
		}
	} else {
		int 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 ||
		    bp->b_blkno % (vn->sc_secsize / DEV_BSIZE) != 0) {
			bp->b_error = EINVAL;
			bp->b_flags |= B_ERROR | B_INVAL;
			biodone(bp);
			return;
		}

		pbn = bp->b_blkno / (vn->sc_secsize / DEV_BSIZE);
		sz = howmany(bp->b_bcount, vn->sc_secsize);

		/*
		 * If out of bounds return an error.  If at the EOF point,
		 * simply read or write less.
		 */
		if (pbn < 0 || pbn >= vn->sc_size) {
			if (pbn != vn->sc_size) {
				bp->b_error = EINVAL;
				bp->b_flags |= B_ERROR | B_INVAL;
			}
			biodone(bp);
			return;
		}

		/*
		 * If the request crosses EOF, truncate the request.
		 */
		if (pbn + sz > vn->sc_size) {
			bp->b_bcount = (vn->sc_size - pbn) * vn->sc_secsize;
			bp->b_resid = bp->b_bcount;
		}
		bp->b_pblkno = pbn;
	}

	if (vn->sc_vp && (bp->b_flags & B_FREEBUF)) {
		/*
		 * Not handled for vnode-backed element yet.
		 */
		biodone(bp);
	} 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 = (vm_ooffset_t)bp->b_pblkno * vn->sc_secsize;
		auio.uio_segflg = UIO_SYSSPACE;
		if( bp->b_flags & B_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, NULL, LK_EXCLUSIVE | LK_RETRY, curthread);
		if (bp->b_flags & B_READ)
			error = VOP_READ(vn->sc_vp, &auio, IO_DIRECT, vn->sc_cred);
		else
			error = VOP_WRITE(vn->sc_vp, &auio, IO_NOWDRAIN, vn->sc_cred);
		VOP_UNLOCK(vn->sc_vp, NULL, 0, curthread);
		bp->b_resid = auio.uio_resid;

		if (error) {
			bp->b_error = error;
			bp->b_flags |= B_ERROR;
		}
		biodone(bp);
	} else if (vn->sc_object) {
		/*
		 * OBJT_SWAP I/O
		 *
		 * ( handles read, write, freebuf )
		 *
		 * Note: if we pre-reserved swap, B_FREEBUF is disabled
		 */
		KASSERT((bp->b_bufsize & (vn->sc_secsize - 1)) == 0,
		    ("vnstrategy: buffer %p too small for physio", bp));

		if ((bp->b_flags & B_FREEBUF) && TESTOPT(vn, VN_RESERVE)) {
			biodone(bp);
		} else {
			vm_pager_strategy(vn->sc_object, bp);
		}
	} else {
		bp->b_flags |= B_ERROR;
		bp->b_error = EINVAL;
		biodone(bp);
	}
}

/* ARGSUSED */
static	int
vnioctl(dev_t dev, u_long cmd, caddr_t data, int flag, struct thread *td)
{
	struct vn_softc *vn;
	struct vn_ioctl *vio;
	int error;
	u_long *f;

	vn = dev->si_drv1;
	IFOPT(vn,VN_FOLLOW)
		printf("vnioctl(%s, 0x%lx, %p, 0x%x, %p): unit %d\n",
		    devtoname(dev), cmd, (void *)data, flag, (void *)td,
		    dkunit(dev));

	switch (cmd) {
	case VNIOCATTACH:
	case VNIOCDETACH:
	case VNIOCGSET:
	case VNIOCGCLEAR:
	case VNIOCUSET:
	case VNIOCUCLEAR:
		goto vn_specific;
	}

	IFOPT(vn,VN_LABELS) {
		if (vn->sc_slices != NULL) {
			error = dsioctl(dev, cmd, data, flag, &vn->sc_slices);
			if (error != ENOIOCTL)
				return (error);
		}
		if (dkslice(dev) != WHOLE_DISK_SLICE ||
		    dkpart(dev) != RAW_PART)
			return (ENOTTY);
	}

    vn_specific:

	error = suser(td);
	if (error)
		return (error);

	vio = (struct vn_ioctl *)data;
	f = (u_long*)data;
	switch (cmd) {

	case VNIOCATTACH:
		if (vn->sc_flags & VNF_INITED)
			return(EBUSY);

		if (vio->vn_file == NULL)
			error = vniocattach_swap(vn, vio, dev, flag, td);
		else
			error = vniocattach_file(vn, vio, dev, flag, td);
		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)
			printf("vnioctl: CLRed\n");
		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(vn, vio, dev, flag, td)
	struct vn_softc *vn;
	struct vn_ioctl *vio;
	dev_t dev;
	int flag;
	struct thread *td;
{
	struct vattr vattr;
	struct nameidata nd;
	int error, flags;
	struct proc *p = td->td_proc;

	KKASSERT(p != NULL);

	flags = FREAD|FWRITE;
	NDINIT(&nd, NAMEI_LOOKUP, CNP_FOLLOW, UIO_USERSPACE, vio->vn_file, td);
	error = vn_open(&nd, flags, 0);
	if (error) {
		if (error != EACCES && error != EPERM && error != EROFS)
			return (error);
		flags &= ~FWRITE;
		NDINIT(&nd, NAMEI_LOOKUP, CNP_FOLLOW,
			UIO_USERSPACE, vio->vn_file, td);
		error = vn_open(&nd, flags, 0);
		if (error)
			return (error);
	}
	NDFREE(&nd, NDF_ONLY_PNBUF);
	if (nd.ni_vp->v_type != VREG ||
	    (error = VOP_GETATTR(nd.ni_vp, &vattr, td))) {
		VOP_UNLOCK(nd.ni_vp, NULL, 0, td);
		(void) vn_close(nd.ni_vp, flags, td);
		return (error ? error : EINVAL);
	}
	VOP_UNLOCK(nd.ni_vp, NULL, 0, td);
	vn->sc_secsize = DEV_BSIZE;
	vn->sc_vp = nd.ni_vp;

	/*
	 * 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 = (quad_t)vio->vn_size * PAGE_SIZE / vn->sc_secsize;
	else
		vn->sc_size = vattr.va_size / vn->sc_secsize;
	error = vnsetcred(vn, p->p_ucred);
	if (error) {
		(void) vn_close(nd.ni_vp, flags, td);
		return(error);
	}
	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 = vnopen(dev, flag, S_IFCHR, td);
		if (error)
			vnclear(vn);
	}
	IFOPT(vn, VN_FOLLOW)
		printf("vnioctl: SET vp %p size %x blks\n",
		       vn->sc_vp, vn->sc_size);
	return(0);
}

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

static int
vniocattach_swap(vn, vio, dev, flag, td)
	struct vn_softc *vn;
	struct vn_ioctl *vio;
	dev_t dev;
	int flag;
	struct thread *td;
{
	int error;
	struct proc *p = td->td_proc;

	KKASSERT(p != NULL);
	/*
	 * 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 * (vm_ooffset_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, p->p_ucred);
	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 = vnopen(dev, flag, S_IFCHR, td);
		}
	}
	if (error == 0) {
		IFOPT(vn, VN_FOLLOW) {
			printf("vnioctl: SET vp %p size %x\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 = malloc(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, NULL, LK_EXCLUSIVE | LK_RETRY, curthread);
		error = VOP_READ(vn->sc_vp, &auio, 0, vn->sc_cred);
		VOP_UNLOCK(vn->sc_vp, NULL, 0, curthread);
		free(tmpbuf, M_TEMP);
	}
	return (error);
}

void
vnclear(struct vn_softc *vn)
{
	struct thread *td = curthread;		/* XXX */

	IFOPT(vn, VN_FOLLOW)
		printf("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) {
		(void)vn_close(vn->sc_vp, vn->sc_flags & VNF_READONLY ?
		    FREAD : (FREAD|FWRITE), td);
		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;
}

static	int
vnsize(dev_t dev)
{
	struct vn_softc *vn;

	vn = dev->si_drv1;
	if (!vn)
		return(-1);
	if ((vn->sc_flags & VNF_INITED) == 0)
		return(-1);

	return(vn->sc_size);
}

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

	switch (type) {
	case MOD_LOAD:
		cdevsw_add(&vn_cdevsw, 0, 0);
		break;
	case MOD_UNLOAD:
		/* fall through */
	case MOD_SHUTDOWN:
		for (;;) {
			vn = SLIST_FIRST(&vn_list);
			if (!vn)
				break;
			SLIST_REMOVE_HEAD(&vn_list, sc_list);
			if (vn->sc_flags & VNF_INITED)
				vnclear(vn);
			/* Cleanup all dev_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);
			}
			free(vn, M_DEVBUF);
		}
		cdevsw_remove(&vn_cdevsw, -1, 0);
		break;
	default:
		break;
	}
	return 0;
}

DEV_MODULE(vn, vn_modevent, 0);