File:  [DragonFly] / src / sys / kern / vfs_bio.c
Revision 1.26: download - view: text, annotated - select for diffs
Wed May 19 22:52:58 2004 UTC (10 years, 3 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) 1994,1997 John S. Dyson
 * All rights reserved.
 *
 * 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 immediately at the beginning of the file, without modification,
 *    this list of conditions, and the following disclaimer.
 * 2. Absolutely no warranty of function or purpose is made by the author
 *		John S. Dyson.
 *
 * $FreeBSD: src/sys/kern/vfs_bio.c,v 1.242.2.20 2003/05/28 18:38:10 alc Exp $
 * $DragonFly: src/sys/kern/vfs_bio.c,v 1.26 2004/05/19 22:52:58 dillon Exp $
 */

/*
 * this file contains a new buffer I/O scheme implementing a coherent
 * VM object and buffer cache scheme.  Pains have been taken to make
 * sure that the performance degradation associated with schemes such
 * as this is not realized.
 *
 * Author:  John S. Dyson
 * Significant help during the development and debugging phases
 * had been provided by David Greenman, also of the FreeBSD core team.
 *
 * see man buf(9) for more info.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/buf.h>
#include <sys/conf.h>
#include <sys/eventhandler.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/proc.h>
#include <sys/reboot.h>
#include <sys/resourcevar.h>
#include <sys/sysctl.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <sys/proc.h>
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_kern.h>
#include <vm/vm_pageout.h>
#include <vm/vm_page.h>
#include <vm/vm_object.h>
#include <vm/vm_extern.h>
#include <vm/vm_map.h>
#include <sys/buf2.h>
#include <vm/vm_page2.h>

static MALLOC_DEFINE(M_BIOBUF, "BIO buffer", "BIO buffer");

struct	bio_ops bioops;		/* I/O operation notification */

struct buf *buf;		/* buffer header pool */
struct swqueue bswlist;

static void vm_hold_free_pages(struct buf * bp, vm_offset_t from,
		vm_offset_t to);
static void vm_hold_load_pages(struct buf * bp, vm_offset_t from,
		vm_offset_t to);
static void vfs_page_set_valid(struct buf *bp, vm_ooffset_t off,
			       int pageno, vm_page_t m);
static void vfs_clean_pages(struct buf * bp);
static void vfs_setdirty(struct buf *bp);
static void vfs_vmio_release(struct buf *bp);
static void vfs_backgroundwritedone(struct buf *bp);
static int flushbufqueues(void);

static int bd_request;

static void buf_daemon (void);
/*
 * bogus page -- for I/O to/from partially complete buffers
 * this is a temporary solution to the problem, but it is not
 * really that bad.  it would be better to split the buffer
 * for input in the case of buffers partially already in memory,
 * but the code is intricate enough already.
 */
vm_page_t bogus_page;
int vmiodirenable = TRUE;
int runningbufspace;
struct lwkt_token buftimetoken;  /* Interlock on setting prio and timo */

static vm_offset_t bogus_offset;

static int bufspace, maxbufspace,
	bufmallocspace, maxbufmallocspace, lobufspace, hibufspace;
static int bufreusecnt, bufdefragcnt, buffreekvacnt;
static int needsbuffer;
static int lorunningspace, hirunningspace, runningbufreq;
static int numdirtybuffers, lodirtybuffers, hidirtybuffers;
static int numfreebuffers, lofreebuffers, hifreebuffers;
static int getnewbufcalls;
static int getnewbufrestarts;

SYSCTL_INT(_vfs, OID_AUTO, numdirtybuffers, CTLFLAG_RD,
	&numdirtybuffers, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, lodirtybuffers, CTLFLAG_RW,
	&lodirtybuffers, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, hidirtybuffers, CTLFLAG_RW,
	&hidirtybuffers, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, numfreebuffers, CTLFLAG_RD,
	&numfreebuffers, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, lofreebuffers, CTLFLAG_RW,
	&lofreebuffers, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, hifreebuffers, CTLFLAG_RW,
	&hifreebuffers, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, runningbufspace, CTLFLAG_RD,
	&runningbufspace, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, lorunningspace, CTLFLAG_RW,
	&lorunningspace, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, hirunningspace, CTLFLAG_RW,
	&hirunningspace, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, maxbufspace, CTLFLAG_RD,
	&maxbufspace, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, hibufspace, CTLFLAG_RD,
	&hibufspace, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, lobufspace, CTLFLAG_RD,
	&lobufspace, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, bufspace, CTLFLAG_RD,
	&bufspace, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, maxmallocbufspace, CTLFLAG_RW,
	&maxbufmallocspace, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, bufmallocspace, CTLFLAG_RD,
	&bufmallocspace, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, getnewbufcalls, CTLFLAG_RW,
	&getnewbufcalls, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, getnewbufrestarts, CTLFLAG_RW,
	&getnewbufrestarts, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, vmiodirenable, CTLFLAG_RW,
	&vmiodirenable, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, bufdefragcnt, CTLFLAG_RW,
	&bufdefragcnt, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, buffreekvacnt, CTLFLAG_RW,
	&buffreekvacnt, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, bufreusecnt, CTLFLAG_RW,
	&bufreusecnt, 0, "");

/*
 * Disable background writes for now.  There appear to be races in the 
 * flags tests and locking operations as well as races in the completion
 * code modifying the original bp (origbp) without holding a lock, assuming
 * splbio protection when there might not be splbio protection.
 */
static int dobkgrdwrite = 0;
SYSCTL_INT(_debug, OID_AUTO, dobkgrdwrite, CTLFLAG_RW, &dobkgrdwrite, 0,
	"Do background writes (honoring the BV_BKGRDWRITE flag)?");

static int bufhashmask;
static int bufhashshift;
static LIST_HEAD(bufhashhdr, buf) *bufhashtbl, invalhash;
struct bqueues bufqueues[BUFFER_QUEUES] = { { 0 } };
char *buf_wmesg = BUF_WMESG;

extern int vm_swap_size;

#define VFS_BIO_NEED_ANY	0x01	/* any freeable buffer */
#define VFS_BIO_NEED_DIRTYFLUSH	0x02	/* waiting for dirty buffer flush */
#define VFS_BIO_NEED_FREE	0x04	/* wait for free bufs, hi hysteresis */
#define VFS_BIO_NEED_BUFSPACE	0x08	/* wait for buf space, lo hysteresis */

/*
 * Buffer hash table code.  Note that the logical block scans linearly, which
 * gives us some L1 cache locality.
 */

static __inline 
struct bufhashhdr *
bufhash(struct vnode *vnp, daddr_t bn)
{
	u_int64_t hashkey64;
	int hashkey; 
	
	/*
	 * A variation on the Fibonacci hash that Knuth credits to
	 * R. W. Floyd, see Knuth's _Art of Computer Programming,
	 * Volume 3 / Sorting and Searching_
	 *
         * We reduce the argument to 32 bits before doing the hash to
	 * avoid the need for a slow 64x64 multiply on 32 bit platforms.
	 *
	 * sizeof(struct vnode) is 168 on i386, so toss some of the lower
	 * bits of the vnode address to reduce the key range, which
	 * improves the distribution of keys across buckets.
	 *
	 * The file system cylinder group blocks are very heavily
	 * used.  They are located at invervals of fbg, which is
	 * on the order of 89 to 94 * 2^10, depending on other
	 * filesystem parameters, for a 16k block size.  Smaller block
	 * sizes will reduce fpg approximately proportionally.  This
	 * will cause the cylinder group index to be hashed using the
	 * lower bits of the hash multiplier, which will not distribute
	 * the keys as uniformly in a classic Fibonacci hash where a
	 * relatively small number of the upper bits of the result
	 * are used.  Using 2^16 as a close-enough approximation to
	 * fpg, split the hash multiplier in half, with the upper 16
	 * bits being the inverse of the golden ratio, and the lower
	 * 16 bits being a fraction between 1/3 and 3/7 (closer to
	 * 3/7 in this case), that gives good experimental results.
	 */
	hashkey64 = ((u_int64_t)(uintptr_t)vnp >> 3) + (u_int64_t)bn;
	hashkey = (((u_int32_t)(hashkey64 + (hashkey64 >> 32)) * 0x9E376DB1u) >>
	    bufhashshift) & bufhashmask;
	return(&bufhashtbl[hashkey]);
}

/*
 *	numdirtywakeup:
 *
 *	If someone is blocked due to there being too many dirty buffers,
 *	and numdirtybuffers is now reasonable, wake them up.
 */

static __inline void
numdirtywakeup(int level)
{
	if (numdirtybuffers <= level) {
		if (needsbuffer & VFS_BIO_NEED_DIRTYFLUSH) {
			needsbuffer &= ~VFS_BIO_NEED_DIRTYFLUSH;
			wakeup(&needsbuffer);
		}
	}
}

/*
 *	bufspacewakeup:
 *
 *	Called when buffer space is potentially available for recovery.
 *	getnewbuf() will block on this flag when it is unable to free 
 *	sufficient buffer space.  Buffer space becomes recoverable when 
 *	bp's get placed back in the queues.
 */

static __inline void
bufspacewakeup(void)
{
	/*
	 * If someone is waiting for BUF space, wake them up.  Even
	 * though we haven't freed the kva space yet, the waiting
	 * process will be able to now.
	 */
	if (needsbuffer & VFS_BIO_NEED_BUFSPACE) {
		needsbuffer &= ~VFS_BIO_NEED_BUFSPACE;
		wakeup(&needsbuffer);
	}
}

/*
 * runningbufwakeup() - in-progress I/O accounting.
 *
 */
static __inline void
runningbufwakeup(struct buf *bp)
{
	if (bp->b_runningbufspace) {
		runningbufspace -= bp->b_runningbufspace;
		bp->b_runningbufspace = 0;
		if (runningbufreq && runningbufspace <= lorunningspace) {
			runningbufreq = 0;
			wakeup(&runningbufreq);
		}
	}
}

/*
 *	bufcountwakeup:
 *
 *	Called when a buffer has been added to one of the free queues to
 *	account for the buffer and to wakeup anyone waiting for free buffers.
 *	This typically occurs when large amounts of metadata are being handled
 *	by the buffer cache ( else buffer space runs out first, usually ).
 */

static __inline void
bufcountwakeup(void) 
{
	++numfreebuffers;
	if (needsbuffer) {
		needsbuffer &= ~VFS_BIO_NEED_ANY;
		if (numfreebuffers >= hifreebuffers)
			needsbuffer &= ~VFS_BIO_NEED_FREE;
		wakeup(&needsbuffer);
	}
}

/*
 *	waitrunningbufspace()
 *
 *	runningbufspace is a measure of the amount of I/O currently
 *	running.  This routine is used in async-write situations to
 *	prevent creating huge backups of pending writes to a device.
 *	Only asynchronous writes are governed by this function.  
 *
 *	Reads will adjust runningbufspace, but will not block based on it.
 *	The read load has a side effect of reducing the allowed write load.
 *
 *	This does NOT turn an async write into a sync write.  It waits
 *	for earlier writes to complete and generally returns before the
 *	caller's write has reached the device.
 */
static __inline void
waitrunningbufspace(void)
{
	while (runningbufspace > hirunningspace) {
		int s;

		s = splbio();	/* fix race against interrupt/biodone() */
		++runningbufreq;
		tsleep(&runningbufreq, 0, "wdrain", 0);
		splx(s);
	}
}

/*
 *	vfs_buf_test_cache:
 *
 *	Called when a buffer is extended.  This function clears the B_CACHE
 *	bit if the newly extended portion of the buffer does not contain
 *	valid data.
 */
static __inline__
void
vfs_buf_test_cache(struct buf *bp,
		  vm_ooffset_t foff, vm_offset_t off, vm_offset_t size,
		  vm_page_t m)
{
	if (bp->b_flags & B_CACHE) {
		int base = (foff + off) & PAGE_MASK;
		if (vm_page_is_valid(m, base, size) == 0)
			bp->b_flags &= ~B_CACHE;
	}
}

static __inline__
void
bd_wakeup(int dirtybuflevel)
{
	if (bd_request == 0 && numdirtybuffers >= dirtybuflevel) {
		bd_request = 1;
		wakeup(&bd_request);
	}
}

/*
 * bd_speedup - speedup the buffer cache flushing code
 */

static __inline__
void
bd_speedup(void)
{
	bd_wakeup(1);
}

/*
 * Initialize buffer headers and related structures. 
 */

caddr_t
bufhashinit(caddr_t vaddr)
{
	/* first, make a null hash table */
	bufhashshift = 29;
	for (bufhashmask = 8; bufhashmask < nbuf / 4; bufhashmask <<= 1)
		bufhashshift--;
	bufhashtbl = (void *)vaddr;
	vaddr = vaddr + sizeof(*bufhashtbl) * bufhashmask;
	--bufhashmask;
	return(vaddr);
}

void
bufinit(void)
{
	struct buf *bp;
	int i;

	TAILQ_INIT(&bswlist);
	LIST_INIT(&invalhash);
	lwkt_token_init(&buftimetoken);

	for (i = 0; i <= bufhashmask; i++)
		LIST_INIT(&bufhashtbl[i]);

	/* next, make a null set of free lists */
	for (i = 0; i < BUFFER_QUEUES; i++)
		TAILQ_INIT(&bufqueues[i]);

	/* finally, initialize each buffer header and stick on empty q */
	for (i = 0; i < nbuf; i++) {
		bp = &buf[i];
		bzero(bp, sizeof *bp);
		bp->b_flags = B_INVAL;	/* we're just an empty header */
		bp->b_dev = NODEV;
		bp->b_qindex = QUEUE_EMPTY;
		bp->b_xflags = 0;
		LIST_INIT(&bp->b_dep);
		BUF_LOCKINIT(bp);
		TAILQ_INSERT_TAIL(&bufqueues[QUEUE_EMPTY], bp, b_freelist);
		LIST_INSERT_HEAD(&invalhash, bp, b_hash);
	}

	/*
	 * maxbufspace is the absolute maximum amount of buffer space we are 
	 * allowed to reserve in KVM and in real terms.  The absolute maximum
	 * is nominally used by buf_daemon.  hibufspace is the nominal maximum
	 * used by most other processes.  The differential is required to 
	 * ensure that buf_daemon is able to run when other processes might 
	 * be blocked waiting for buffer space.
	 *
	 * maxbufspace is based on BKVASIZE.  Allocating buffers larger then
	 * this may result in KVM fragmentation which is not handled optimally
	 * by the system.
	 */
	maxbufspace = nbuf * BKVASIZE;
	hibufspace = imax(3 * maxbufspace / 4, maxbufspace - MAXBSIZE * 10);
	lobufspace = hibufspace - MAXBSIZE;

	lorunningspace = 512 * 1024;
	hirunningspace = 1024 * 1024;

/*
 * Limit the amount of malloc memory since it is wired permanently into
 * the kernel space.  Even though this is accounted for in the buffer
 * allocation, we don't want the malloced region to grow uncontrolled.
 * The malloc scheme improves memory utilization significantly on average
 * (small) directories.
 */
	maxbufmallocspace = hibufspace / 20;

/*
 * Reduce the chance of a deadlock occuring by limiting the number
 * of delayed-write dirty buffers we allow to stack up.
 */
	hidirtybuffers = nbuf / 4 + 20;
	numdirtybuffers = 0;
/*
 * To support extreme low-memory systems, make sure hidirtybuffers cannot
 * eat up all available buffer space.  This occurs when our minimum cannot
 * be met.  We try to size hidirtybuffers to 3/4 our buffer space assuming
 * BKVASIZE'd (8K) buffers.
 */
	while (hidirtybuffers * BKVASIZE > 3 * hibufspace / 4) {
		hidirtybuffers >>= 1;
	}
	lodirtybuffers = hidirtybuffers / 2;

/*
 * Try to keep the number of free buffers in the specified range,
 * and give special processes (e.g. like buf_daemon) access to an 
 * emergency reserve.
 */
	lofreebuffers = nbuf / 18 + 5;
	hifreebuffers = 2 * lofreebuffers;
	numfreebuffers = nbuf;

/*
 * Maximum number of async ops initiated per buf_daemon loop.  This is
 * somewhat of a hack at the moment, we really need to limit ourselves
 * based on the number of bytes of I/O in-transit that were initiated
 * from buf_daemon.
 */

	bogus_offset = kmem_alloc_pageable(kernel_map, PAGE_SIZE);
	bogus_page = vm_page_alloc(kernel_object,
			((bogus_offset - VM_MIN_KERNEL_ADDRESS) >> PAGE_SHIFT),
			VM_ALLOC_NORMAL);
	vmstats.v_wire_count++;

}

/*
 * bfreekva() - free the kva allocation for a buffer.
 *
 *	Must be called at splbio() or higher as this is the only locking for
 *	buffer_map.
 *
 *	Since this call frees up buffer space, we call bufspacewakeup().
 */
static void
bfreekva(struct buf * bp)
{
	int count;

	if (bp->b_kvasize) {
		++buffreekvacnt;
		count = vm_map_entry_reserve(MAP_RESERVE_COUNT);
		vm_map_lock(buffer_map);
		bufspace -= bp->b_kvasize;
		vm_map_delete(buffer_map,
		    (vm_offset_t) bp->b_kvabase,
		    (vm_offset_t) bp->b_kvabase + bp->b_kvasize,
		    &count
		);
		vm_map_unlock(buffer_map);
		vm_map_entry_release(count);
		bp->b_kvasize = 0;
		bufspacewakeup();
	}
}

/*
 *	bremfree:
 *
 *	Remove the buffer from the appropriate free list.
 */
void
bremfree(struct buf * bp)
{
	int s = splbio();
	int old_qindex = bp->b_qindex;

	if (bp->b_qindex != QUEUE_NONE) {
		KASSERT(BUF_REFCNT(bp) == 1, ("bremfree: bp %p not locked",bp));
		TAILQ_REMOVE(&bufqueues[bp->b_qindex], bp, b_freelist);
		bp->b_qindex = QUEUE_NONE;
	} else {
		if (BUF_REFCNT(bp) <= 1)
			panic("bremfree: removing a buffer not on a queue");
	}

	/*
	 * Fixup numfreebuffers count.  If the buffer is invalid or not
	 * delayed-write, and it was on the EMPTY, LRU, or AGE queues,
	 * the buffer was free and we must decrement numfreebuffers.
	 */
	if ((bp->b_flags & B_INVAL) || (bp->b_flags & B_DELWRI) == 0) {
		switch(old_qindex) {
		case QUEUE_DIRTY:
		case QUEUE_CLEAN:
		case QUEUE_EMPTY:
		case QUEUE_EMPTYKVA:
			--numfreebuffers;
			break;
		default:
			break;
		}
	}
	splx(s);
}


/*
 * Get a buffer with the specified data.  Look in the cache first.  We
 * must clear B_ERROR and B_INVAL prior to initiating I/O.  If B_CACHE
 * is set, the buffer is valid and we do not have to do anything ( see
 * getblk() ).
 */
int
bread(struct vnode * vp, daddr_t blkno, int size, struct buf ** bpp)
{
	struct buf *bp;

	bp = getblk(vp, blkno, size, 0, 0);
	*bpp = bp;

	/* if not found in cache, do some I/O */
	if ((bp->b_flags & B_CACHE) == 0) {
		KASSERT(!(bp->b_flags & B_ASYNC), ("bread: illegal async bp %p", bp));
		bp->b_flags |= B_READ;
		bp->b_flags &= ~(B_ERROR | B_INVAL);
		vfs_busy_pages(bp, 0);
		VOP_STRATEGY(vp, bp);
		return (biowait(bp));
	}
	return (0);
}

/*
 * Operates like bread, but also starts asynchronous I/O on
 * read-ahead blocks.  We must clear B_ERROR and B_INVAL prior
 * to initiating I/O . If B_CACHE is set, the buffer is valid 
 * and we do not have to do anything.
 */
int
breadn(struct vnode * vp, daddr_t blkno, int size, daddr_t * rablkno,
	int *rabsize, int cnt, struct buf ** bpp)
{
	struct buf *bp, *rabp;
	int i;
	int rv = 0, readwait = 0;

	*bpp = bp = getblk(vp, blkno, size, 0, 0);

	/* if not found in cache, do some I/O */
	if ((bp->b_flags & B_CACHE) == 0) {
		bp->b_flags |= B_READ;
		bp->b_flags &= ~(B_ERROR | B_INVAL);
		vfs_busy_pages(bp, 0);
		VOP_STRATEGY(vp, bp);
		++readwait;
	}

	for (i = 0; i < cnt; i++, rablkno++, rabsize++) {
		if (inmem(vp, *rablkno))
			continue;
		rabp = getblk(vp, *rablkno, *rabsize, 0, 0);

		if ((rabp->b_flags & B_CACHE) == 0) {
			rabp->b_flags |= B_READ | B_ASYNC;
			rabp->b_flags &= ~(B_ERROR | B_INVAL);
			vfs_busy_pages(rabp, 0);
			BUF_KERNPROC(rabp);
			VOP_STRATEGY(vp, rabp);
		} else {
			brelse(rabp);
		}
	}

	if (readwait) {
		rv = biowait(bp);
	}
	return (rv);
}

/*
 * Write, release buffer on completion.  (Done by iodone
 * if async).  Do not bother writing anything if the buffer
 * is invalid.
 *
 * Note that we set B_CACHE here, indicating that buffer is
 * fully valid and thus cacheable.  This is true even of NFS
 * now so we set it generally.  This could be set either here 
 * or in biodone() since the I/O is synchronous.  We put it
 * here.
 */
int
bwrite(struct buf * bp)
{
	int oldflags, s;
	struct buf *newbp;

	if (bp->b_flags & B_INVAL) {
		brelse(bp);
		return (0);
	}

	oldflags = bp->b_flags;

	if (BUF_REFCNT(bp) == 0)
		panic("bwrite: buffer is not busy???");
	s = splbio();
	/*
	 * If a background write is already in progress, delay
	 * writing this block if it is asynchronous. Otherwise
	 * wait for the background write to complete.
	 */
	if (bp->b_xflags & BX_BKGRDINPROG) {
		if (bp->b_flags & B_ASYNC) {
			splx(s);
			bdwrite(bp);
			return (0);
		}
		bp->b_xflags |= BX_BKGRDWAIT;
		tsleep(&bp->b_xflags, 0, "biord", 0);
		if (bp->b_xflags & BX_BKGRDINPROG)
			panic("bwrite: still writing");
	}

	/* Mark the buffer clean */
	bundirty(bp);

	/*
	 * If this buffer is marked for background writing and we
	 * do not have to wait for it, make a copy and write the
	 * copy so as to leave this buffer ready for further use.
	 *
	 * This optimization eats a lot of memory.  If we have a page
	 * or buffer shortfull we can't do it.
	 */
	if (dobkgrdwrite &&
	    (bp->b_xflags & BX_BKGRDWRITE) &&
	    (bp->b_flags & B_ASYNC) &&
	    !vm_page_count_severe() &&
	    !buf_dirty_count_severe()) {
		if (bp->b_flags & B_CALL)
			panic("bwrite: need chained iodone");

		/* get a new block */
		newbp = geteblk(bp->b_bufsize);

		/* set it to be identical to the old block */
		memcpy(newbp->b_data, bp->b_data, bp->b_bufsize);
		bgetvp(bp->b_vp, newbp);
		newbp->b_lblkno = bp->b_lblkno;
		newbp->b_blkno = bp->b_blkno;
		newbp->b_offset = bp->b_offset;
		newbp->b_iodone = vfs_backgroundwritedone;
		newbp->b_flags |= B_ASYNC | B_CALL;
		newbp->b_flags &= ~B_INVAL;

		/* move over the dependencies */
		if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_movedeps)
			(*bioops.io_movedeps)(bp, newbp);

		/*
		 * Initiate write on the copy, release the original to
		 * the B_LOCKED queue so that it cannot go away until
		 * the background write completes. If not locked it could go
		 * away and then be reconstituted while it was being written.
		 * If the reconstituted buffer were written, we could end up
		 * with two background copies being written at the same time.
		 */
		bp->b_xflags |= BX_BKGRDINPROG;
		bp->b_flags |= B_LOCKED;
		bqrelse(bp);
		bp = newbp;
	}

	bp->b_flags &= ~(B_READ | B_DONE | B_ERROR);
	bp->b_flags |= B_WRITEINPROG | B_CACHE;

	bp->b_vp->v_numoutput++;
	vfs_busy_pages(bp, 1);

	/*
	 * Normal bwrites pipeline writes
	 */
	bp->b_runningbufspace = bp->b_bufsize;
	runningbufspace += bp->b_runningbufspace;

	splx(s);
	if (oldflags & B_ASYNC)
		BUF_KERNPROC(bp);
	VOP_STRATEGY(bp->b_vp, bp);

	if ((oldflags & B_ASYNC) == 0) {
		int rtval = biowait(bp);
		brelse(bp);
		return (rtval);
	} else if ((oldflags & B_NOWDRAIN) == 0) {
		/*
		 * don't allow the async write to saturate the I/O
		 * system.  Deadlocks can occur only if a device strategy
		 * routine (like in VN) turns around and issues another
		 * high-level write, in which case B_NOWDRAIN is expected
		 * to be set.   Otherwise we will not deadlock here because
		 * we are blocking waiting for I/O that is already in-progress
		 * to complete.
		 */
		waitrunningbufspace();
	}

	return (0);
}

/*
 * Complete a background write started from bwrite.
 */
static void
vfs_backgroundwritedone(bp)
	struct buf *bp;
{
	struct buf *origbp;

	/*
	 * Find the original buffer that we are writing.
	 */
	if ((origbp = gbincore(bp->b_vp, bp->b_lblkno)) == NULL)
		panic("backgroundwritedone: lost buffer");
	/*
	 * Process dependencies then return any unfinished ones.
	 */
	if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_complete)
		(*bioops.io_complete)(bp);
	if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_movedeps)
		(*bioops.io_movedeps)(bp, origbp);
	/*
	 * Clear the BX_BKGRDINPROG flag in the original buffer
	 * and awaken it if it is waiting for the write to complete.
	 * If BX_BKGRDINPROG is not set in the original buffer it must
	 * have been released and re-instantiated - which is not legal.
	 */
	KASSERT((origbp->b_xflags & BX_BKGRDINPROG), ("backgroundwritedone: lost buffer2"));
	origbp->b_xflags &= ~BX_BKGRDINPROG;
	if (origbp->b_xflags & BX_BKGRDWAIT) {
		origbp->b_xflags &= ~BX_BKGRDWAIT;
		wakeup(&origbp->b_xflags);
	}
	/*
	 * Clear the B_LOCKED flag and remove it from the locked
	 * queue if it currently resides there.
	 */
	origbp->b_flags &= ~B_LOCKED;
	if (BUF_LOCK(origbp, LK_EXCLUSIVE | LK_NOWAIT) == 0) {
		bremfree(origbp);
		bqrelse(origbp);
	}
	/*
	 * This buffer is marked B_NOCACHE, so when it is released
	 * by biodone, it will be tossed. We mark it with B_READ
	 * to avoid biodone doing a second vwakeup.
	 */
	bp->b_flags |= B_NOCACHE | B_READ;
	bp->b_flags &= ~(B_CACHE | B_CALL | B_DONE);
	bp->b_iodone = 0;
	biodone(bp);
}

/*
 * Delayed write. (Buffer is marked dirty).  Do not bother writing
 * anything if the buffer is marked invalid.
 *
 * Note that since the buffer must be completely valid, we can safely
 * set B_CACHE.  In fact, we have to set B_CACHE here rather then in
 * biodone() in order to prevent getblk from writing the buffer
 * out synchronously.
 */
void
bdwrite(struct buf * bp)
{
	if (BUF_REFCNT(bp) == 0)
		panic("bdwrite: buffer is not busy");

	if (bp->b_flags & B_INVAL) {
		brelse(bp);
		return;
	}
	bdirty(bp);

	/*
	 * Set B_CACHE, indicating that the buffer is fully valid.  This is
	 * true even of NFS now.
	 */
	bp->b_flags |= B_CACHE;

	/*
	 * This bmap keeps the system from needing to do the bmap later,
	 * perhaps when the system is attempting to do a sync.  Since it
	 * is likely that the indirect block -- or whatever other datastructure
	 * that the filesystem needs is still in memory now, it is a good
	 * thing to do this.  Note also, that if the pageout daemon is
	 * requesting a sync -- there might not be enough memory to do
	 * the bmap then...  So, this is important to do.
	 */
	if (bp->b_lblkno == bp->b_blkno) {
		VOP_BMAP(bp->b_vp, bp->b_lblkno, NULL, &bp->b_blkno, NULL, NULL);
	}

	/*
	 * Set the *dirty* buffer range based upon the VM system dirty pages.
	 */
	vfs_setdirty(bp);

	/*
	 * We need to do this here to satisfy the vnode_pager and the
	 * pageout daemon, so that it thinks that the pages have been
	 * "cleaned".  Note that since the pages are in a delayed write
	 * buffer -- the VFS layer "will" see that the pages get written
	 * out on the next sync, or perhaps the cluster will be completed.
	 */
	vfs_clean_pages(bp);
	bqrelse(bp);

	/*
	 * Wakeup the buffer flushing daemon if we have a lot of dirty
	 * buffers (midpoint between our recovery point and our stall
	 * point).
	 */
	bd_wakeup((lodirtybuffers + hidirtybuffers) / 2);

	/*
	 * note: we cannot initiate I/O from a bdwrite even if we wanted to,
	 * due to the softdep code.
	 */
}

/*
 *	bdirty:
 *
 *	Turn buffer into delayed write request.  We must clear B_READ and
 *	B_RELBUF, and we must set B_DELWRI.  We reassign the buffer to 
 *	itself to properly update it in the dirty/clean lists.  We mark it
 *	B_DONE to ensure that any asynchronization of the buffer properly
 *	clears B_DONE ( else a panic will occur later ).  
 *
 *	bdirty() is kinda like bdwrite() - we have to clear B_INVAL which
 *	might have been set pre-getblk().  Unlike bwrite/bdwrite, bdirty()
 *	should only be called if the buffer is known-good.
 *
 *	Since the buffer is not on a queue, we do not update the numfreebuffers
 *	count.
 *
 *	Must be called at splbio().
 *	The buffer must be on QUEUE_NONE.
 */
void
bdirty(bp)
	struct buf *bp;
{
	KASSERT(bp->b_qindex == QUEUE_NONE, ("bdirty: buffer %p still on queue %d", bp, bp->b_qindex));
	bp->b_flags &= ~(B_READ|B_RELBUF);

	if ((bp->b_flags & B_DELWRI) == 0) {
		bp->b_flags |= B_DONE | B_DELWRI;
		reassignbuf(bp, bp->b_vp);
		++numdirtybuffers;
		bd_wakeup((lodirtybuffers + hidirtybuffers) / 2);
	}
}

/*
 *	bundirty:
 *
 *	Clear B_DELWRI for buffer.
 *
 *	Since the buffer is not on a queue, we do not update the numfreebuffers
 *	count.
 *	
 *	Must be called at splbio().
 *	The buffer must be on QUEUE_NONE.
 */

void
bundirty(bp)
	struct buf *bp;
{
	KASSERT(bp->b_qindex == QUEUE_NONE, ("bundirty: buffer %p still on queue %d", bp, bp->b_qindex));

	if (bp->b_flags & B_DELWRI) {
		bp->b_flags &= ~B_DELWRI;
		reassignbuf(bp, bp->b_vp);
		--numdirtybuffers;
		numdirtywakeup(lodirtybuffers);
	}
	/*
	 * Since it is now being written, we can clear its deferred write flag.
	 */
	bp->b_flags &= ~B_DEFERRED;
}

/*
 *	bawrite:
 *
 *	Asynchronous write.  Start output on a buffer, but do not wait for
 *	it to complete.  The buffer is released when the output completes.
 *
 *	bwrite() ( or the VOP routine anyway ) is responsible for handling 
 *	B_INVAL buffers.  Not us.
 */
void
bawrite(struct buf * bp)
{
	bp->b_flags |= B_ASYNC;
	(void) VOP_BWRITE(bp->b_vp, bp);
}

/*
 *	bowrite:
 *
 *	Ordered write.  Start output on a buffer, and flag it so that the 
 *	device will write it in the order it was queued.  The buffer is 
 *	released when the output completes.  bwrite() ( or the VOP routine
 *	anyway ) is responsible for handling B_INVAL buffers.
 */
int
bowrite(struct buf * bp)
{
	bp->b_flags |= B_ORDERED | B_ASYNC;
	return (VOP_BWRITE(bp->b_vp, bp));
}

/*
 *	bwillwrite:
 *
 *	Called prior to the locking of any vnodes when we are expecting to
 *	write.  We do not want to starve the buffer cache with too many
 *	dirty buffers so we block here.  By blocking prior to the locking
 *	of any vnodes we attempt to avoid the situation where a locked vnode
 *	prevents the various system daemons from flushing related buffers.
 */

void
bwillwrite(void)
{
	if (numdirtybuffers >= hidirtybuffers) {
		int s;

		s = splbio();
		while (numdirtybuffers >= hidirtybuffers) {
			bd_wakeup(1);
			needsbuffer |= VFS_BIO_NEED_DIRTYFLUSH;
			tsleep(&needsbuffer, 0, "flswai", 0);
		}
		splx(s);
	}
}

/*
 * Return true if we have too many dirty buffers.
 */
int
buf_dirty_count_severe(void)
{
	return(numdirtybuffers >= hidirtybuffers);
}

/*
 *	brelse:
 *
 *	Release a busy buffer and, if requested, free its resources.  The
 *	buffer will be stashed in the appropriate bufqueue[] allowing it
 *	to be accessed later as a cache entity or reused for other purposes.
 */
void
brelse(struct buf * bp)
{
	int s;

	KASSERT(!(bp->b_flags & (B_CLUSTER|B_PAGING)), ("brelse: inappropriate B_PAGING or B_CLUSTER bp %p", bp));

	s = splbio();

	if (bp->b_flags & B_LOCKED)
		bp->b_flags &= ~B_ERROR;

	if ((bp->b_flags & (B_READ | B_ERROR | B_INVAL)) == B_ERROR) {
		/*
		 * Failed write, redirty.  Must clear B_ERROR to prevent
		 * pages from being scrapped.  If B_INVAL is set then
		 * this case is not run and the next case is run to 
		 * destroy the buffer.  B_INVAL can occur if the buffer
		 * is outside the range supported by the underlying device.
		 */
		bp->b_flags &= ~B_ERROR;
		bdirty(bp);
	} else if ((bp->b_flags & (B_NOCACHE | B_INVAL | B_ERROR | B_FREEBUF)) ||
	    (bp->b_bufsize <= 0)) {
		/*
		 * Either a failed I/O or we were asked to free or not
		 * cache the buffer.
		 */
		bp->b_flags |= B_INVAL;
		if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_deallocate)
			(*bioops.io_deallocate)(bp);
		if (bp->b_flags & B_DELWRI) {
			--numdirtybuffers;
			numdirtywakeup(lodirtybuffers);
		}
		bp->b_flags &= ~(B_DELWRI | B_CACHE | B_FREEBUF);
		if ((bp->b_flags & B_VMIO) == 0) {
			if (bp->b_bufsize)
				allocbuf(bp, 0);
			if (bp->b_vp)
				brelvp(bp);
		}
	}

	/*
	 * We must clear B_RELBUF if B_DELWRI is set.  If vfs_vmio_release() 
	 * is called with B_DELWRI set, the underlying pages may wind up
	 * getting freed causing a previous write (bdwrite()) to get 'lost'
	 * because pages associated with a B_DELWRI bp are marked clean.
	 * 
	 * We still allow the B_INVAL case to call vfs_vmio_release(), even
	 * if B_DELWRI is set.
	 *
	 * If B_DELWRI is not set we may have to set B_RELBUF if we are low
	 * on pages to return pages to the VM page queues.
	 */
	if (bp->b_flags & B_DELWRI)
		bp->b_flags &= ~B_RELBUF;
	else if (vm_page_count_severe() && !(bp->b_xflags & BX_BKGRDINPROG))
		bp->b_flags |= B_RELBUF;

	/*
	 * VMIO buffer rundown.  It is not very necessary to keep a VMIO buffer
	 * constituted, not even NFS buffers now.  Two flags effect this.  If
	 * B_INVAL, the struct buf is invalidated but the VM object is kept
	 * around ( i.e. so it is trivial to reconstitute the buffer later ).
	 *
	 * If B_ERROR or B_NOCACHE is set, pages in the VM object will be
	 * invalidated.  B_ERROR cannot be set for a failed write unless the
	 * buffer is also B_INVAL because it hits the re-dirtying code above.
	 *
	 * Normally we can do this whether a buffer is B_DELWRI or not.  If
	 * the buffer is an NFS buffer, it is tracking piecemeal writes or
	 * the commit state and we cannot afford to lose the buffer. If the
	 * buffer has a background write in progress, we need to keep it
	 * around to prevent it from being reconstituted and starting a second
	 * background write.
	 */
	if ((bp->b_flags & B_VMIO)
	    && !(bp->b_vp->v_tag == VT_NFS &&
		 !vn_isdisk(bp->b_vp, NULL) &&
		 (bp->b_flags & B_DELWRI))
	    ) {

		int i, j, resid;
		vm_page_t m;
		off_t foff;
		vm_pindex_t poff;
		vm_object_t obj;
		struct vnode *vp;

		vp = bp->b_vp;

		/*
		 * Get the base offset and length of the buffer.  Note that 
		 * in the VMIO case if the buffer block size is not
		 * page-aligned then b_data pointer may not be page-aligned.
		 * But our b_pages[] array *IS* page aligned.
		 *
		 * block sizes less then DEV_BSIZE (usually 512) are not 
		 * supported due to the page granularity bits (m->valid,
		 * m->dirty, etc...). 
		 *
		 * See man buf(9) for more information
		 */

		resid = bp->b_bufsize;
		foff = bp->b_offset;

		for (i = 0; i < bp->b_npages; i++) {
			m = bp->b_pages[i];
			vm_page_flag_clear(m, PG_ZERO);
			/*
			 * If we hit a bogus page, fixup *all* of them
			 * now.  Note that we left these pages wired
			 * when we removed them so they had better exist,
			 * and they cannot be ripped out from under us so
			 * no splvm() protection is necessary.
			 */
			if (m == bogus_page) {
				VOP_GETVOBJECT(vp, &obj);
				poff = OFF_TO_IDX(bp->b_offset);

				for (j = i; j < bp->b_npages; j++) {
					vm_page_t mtmp;

					mtmp = bp->b_pages[j];
					if (mtmp == bogus_page) {
						mtmp = vm_page_lookup(obj, poff + j);
						if (!mtmp) {
							panic("brelse: page missing");
						}
						bp->b_pages[j] = mtmp;
					}
				}

				if ((bp->b_flags & B_INVAL) == 0) {
					pmap_qenter(trunc_page((vm_offset_t)bp->b_data), bp->b_pages, bp->b_npages);
				}
				m = bp->b_pages[i];
			}

			/*
			 * Invalidate the backing store if B_NOCACHE is set
			 * (e.g. used with vinvalbuf()).  If this is NFS
			 * we impose a requirement that the block size be
			 * a multiple of PAGE_SIZE and create a temporary
			 * hack to basically invalidate the whole page.  The
			 * problem is that NFS uses really odd buffer sizes
			 * especially when tracking piecemeal writes and
			 * it also vinvalbuf()'s a lot, which would result
			 * in only partial page validation and invalidation
			 * here.  If the file page is mmap()'d, however,
			 * all the valid bits get set so after we invalidate
			 * here we would end up with weird m->valid values
			 * like 0xfc.  nfs_getpages() can't handle this so
			 * we clear all the valid bits for the NFS case
			 * instead of just some of them.
			 *
			 * The real bug is the VM system having to set m->valid
			 * to VM_PAGE_BITS_ALL for faulted-in pages, which
			 * itself is an artifact of the whole 512-byte
			 * granular mess that exists to support odd block 
			 * sizes and UFS meta-data block sizes (e.g. 6144).
			 * A complete rewrite is required.
			 */
			if (bp->b_flags & (B_NOCACHE|B_ERROR)) {
				int poffset = foff & PAGE_MASK;
				int presid;

				presid = PAGE_SIZE - poffset;
				if (bp->b_vp->v_tag == VT_NFS &&
				    bp->b_vp->v_type == VREG) {
					; /* entire page */
				} else if (presid > resid) {
					presid = resid;
				}
				KASSERT(presid >= 0, ("brelse: extra page"));
				vm_page_set_invalid(m, poffset, presid);
			}
			resid -= PAGE_SIZE - (foff & PAGE_MASK);
			foff = (foff + PAGE_SIZE) & ~(off_t)PAGE_MASK;
		}

		if (bp->b_flags & (B_INVAL | B_RELBUF))
			vfs_vmio_release(bp);

	} else if (bp->b_flags & B_VMIO) {

		if (bp->b_flags & (B_INVAL | B_RELBUF))
			vfs_vmio_release(bp);

	}
			
	if (bp->b_qindex != QUEUE_NONE)
		panic("brelse: free buffer onto another queue???");
	if (BUF_REFCNT(bp) > 1) {
		/* Temporary panic to verify exclusive locking */
		/* This panic goes away when we allow shared refs */
		panic("brelse: multiple refs");
		/* do not release to free list */
		BUF_UNLOCK(bp);
		splx(s);
		return;
	}

	/* enqueue */

	/* buffers with no memory */
	if (bp->b_bufsize == 0) {
		bp->b_flags |= B_INVAL;
		bp->b_xflags &= ~BX_BKGRDWRITE;
		if (bp->b_xflags & BX_BKGRDINPROG)
			panic("losing buffer 1");
		if (bp->b_kvasize) {
			bp->b_qindex = QUEUE_EMPTYKVA;
		} else {
			bp->b_qindex = QUEUE_EMPTY;
		}
		TAILQ_INSERT_HEAD(&bufqueues[bp->b_qindex], bp, b_freelist);
		LIST_REMOVE(bp, b_hash);
		LIST_INSERT_HEAD(&invalhash, bp, b_hash);
		bp->b_dev = NODEV;
	/* buffers with junk contents */
	} else if (bp->b_flags & (B_ERROR | B_INVAL | B_NOCACHE | B_RELBUF)) {
		bp->b_flags |= B_INVAL;
		bp->b_xflags &= ~BX_BKGRDWRITE;
		if (bp->b_xflags & BX_BKGRDINPROG)
			panic("losing buffer 2");
		bp->b_qindex = QUEUE_CLEAN;
		TAILQ_INSERT_HEAD(&bufqueues[QUEUE_CLEAN], bp, b_freelist);
		LIST_REMOVE(bp, b_hash);
		LIST_INSERT_HEAD(&invalhash, bp, b_hash);
		bp->b_dev = NODEV;

	/* buffers that are locked */
	} else if (bp->b_flags & B_LOCKED) {
		bp->b_qindex = QUEUE_LOCKED;
		TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LOCKED], bp, b_freelist);

	/* remaining buffers */
	} else {
		switch(bp->b_flags & (B_DELWRI|B_AGE)) {
		case B_DELWRI | B_AGE:
		    bp->b_qindex = QUEUE_DIRTY;
		    TAILQ_INSERT_HEAD(&bufqueues[QUEUE_DIRTY], bp, b_freelist);
		    break;
		case B_DELWRI:
		    bp->b_qindex = QUEUE_DIRTY;
		    TAILQ_INSERT_TAIL(&bufqueues[QUEUE_DIRTY], bp, b_freelist);
		    break;
		case B_AGE:
		    bp->b_qindex = QUEUE_CLEAN;
		    TAILQ_INSERT_HEAD(&bufqueues[QUEUE_CLEAN], bp, b_freelist);
		    break;
		default:
		    bp->b_qindex = QUEUE_CLEAN;
		    TAILQ_INSERT_TAIL(&bufqueues[QUEUE_CLEAN], bp, b_freelist);
		    break;
		}
	}

	/*
	 * If B_INVAL, clear B_DELWRI.  We've already placed the buffer
	 * on the correct queue.
	 */
	if ((bp->b_flags & (B_INVAL|B_DELWRI)) == (B_INVAL|B_DELWRI))
		bundirty(bp);

	/*
	 * Fixup numfreebuffers count.  The bp is on an appropriate queue
	 * unless locked.  We then bump numfreebuffers if it is not B_DELWRI.
	 * We've already handled the B_INVAL case ( B_DELWRI will be clear
	 * if B_INVAL is set ).
	 */

	if ((bp->b_flags & B_LOCKED) == 0 && !(bp->b_flags & B_DELWRI))
		bufcountwakeup();

	/*
	 * Something we can maybe free or reuse
	 */
	if (bp->b_bufsize || bp->b_kvasize)
		bufspacewakeup();

	/* unlock */
	BUF_UNLOCK(bp);
	bp->b_flags &= ~(B_ORDERED | B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF |
			B_DIRECT | B_NOWDRAIN);
	splx(s);
}

/*
 * Release a buffer back to the appropriate queue but do not try to free
 * it.  The buffer is expected to be used again soon.
 *
 * bqrelse() is used by bdwrite() to requeue a delayed write, and used by
 * biodone() to requeue an async I/O on completion.  It is also used when
 * known good buffers need to be requeued but we think we may need the data
 * again soon.
 *
 * XXX we should be able to leave the B_RELBUF hint set on completion.
 */
void
bqrelse(struct buf * bp)
{
	int s;

	s = splbio();

	KASSERT(!(bp->b_flags & (B_CLUSTER|B_PAGING)), ("bqrelse: inappropriate B_PAGING or B_CLUSTER bp %p", bp));

	if (bp->b_qindex != QUEUE_NONE)
		panic("bqrelse: free buffer onto another queue???");
	if (BUF_REFCNT(bp) > 1) {
		/* do not release to free list */
		panic("bqrelse: multiple refs");
		BUF_UNLOCK(bp);
		splx(s);
		return;
	}
	if (bp->b_flags & B_LOCKED) {
		bp->b_flags &= ~B_ERROR;
		bp->b_qindex = QUEUE_LOCKED;
		TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LOCKED], bp, b_freelist);
		/* buffers with stale but valid contents */
	} else if (bp->b_flags & B_DELWRI) {
		bp->b_qindex = QUEUE_DIRTY;
		TAILQ_INSERT_TAIL(&bufqueues[QUEUE_DIRTY], bp, b_freelist);
	} else if (vm_page_count_severe()) {
		/*
		 * We are too low on memory, we have to try to free the
		 * buffer (most importantly: the wired pages making up its
		 * backing store) *now*.
		 */
		splx(s);
		brelse(bp);
		return;
	} else {
		bp->b_qindex = QUEUE_CLEAN;
		TAILQ_INSERT_TAIL(&bufqueues[QUEUE_CLEAN], bp, b_freelist);
	}

	if ((bp->b_flags & B_LOCKED) == 0 &&
	    ((bp->b_flags & B_INVAL) || !(bp->b_flags & B_DELWRI))) {
		bufcountwakeup();
	}

	/*
	 * Something we can maybe free or reuse.
	 */
	if (bp->b_bufsize && !(bp->b_flags & B_DELWRI))
		bufspacewakeup();

	/* unlock */
	BUF_UNLOCK(bp);
	bp->b_flags &= ~(B_ORDERED | B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF);
	splx(s);
}

static void
vfs_vmio_release(bp)
	struct buf *bp;
{
	int i, s;
	vm_page_t m;

	s = splvm();
	for (i = 0; i < bp->b_npages; i++) {
		m = bp->b_pages[i];
		bp->b_pages[i] = NULL;
		/*
		 * In order to keep page LRU ordering consistent, put
		 * everything on the inactive queue.
		 */
		vm_page_unwire(m, 0);
		/*
		 * We don't mess with busy pages, it is
		 * the responsibility of the process that
		 * busied the pages to deal with them.
		 */
		if ((m->flags & PG_BUSY) || (m->busy != 0))
			continue;
			
		if (m->wire_count == 0) {
			vm_page_flag_clear(m, PG_ZERO);
			/*
			 * Might as well free the page if we can and it has
			 * no valid data.  We also free the page if the
			 * buffer was used for direct I/O.
			 */
			if ((bp->b_flags & B_ASYNC) == 0 && !m->valid && m->hold_count == 0) {
				vm_page_busy(m);
				vm_page_protect(m, VM_PROT_NONE);
				vm_page_free(m);
			} else if (bp->b_flags & B_DIRECT) {
				vm_page_try_to_free(m);
			} else if (vm_page_count_severe()) {
				vm_page_try_to_cache(m);
			}
		}
	}
	splx(s);
	pmap_qremove(trunc_page((vm_offset_t) bp->b_data), bp->b_npages);
	if (bp->b_bufsize) {
		bufspacewakeup();
		bp->b_bufsize = 0;
	}
	bp->b_npages = 0;
	bp->b_flags &= ~B_VMIO;
	if (bp->b_vp)
		brelvp(bp);
}

/*
 * Check to see if a block is currently memory resident.
 */
struct buf *
gbincore(struct vnode * vp, daddr_t blkno)
{
	struct buf *bp;
	struct bufhashhdr *bh;

	bh = bufhash(vp, blkno);

	/* Search hash chain */
	LIST_FOREACH(bp, bh, b_hash) {
		/* hit */
		if (bp->b_vp == vp && bp->b_lblkno == blkno &&
		    (bp->b_flags & B_INVAL) == 0) {
			break;
		}
	}
	return (bp);
}

/*
 *	vfs_bio_awrite:
 *
 *	Implement clustered async writes for clearing out B_DELWRI buffers.
 *	This is much better then the old way of writing only one buffer at
 *	a time.  Note that we may not be presented with the buffers in the 
 *	correct order, so we search for the cluster in both directions.
 */
int
vfs_bio_awrite(struct buf * bp)
{
	int i;
	int j;
	daddr_t lblkno = bp->b_lblkno;
	struct vnode *vp = bp->b_vp;
	int s;
	int ncl;
	struct buf *bpa;
	int nwritten;
	int size;
	int maxcl;

	s = splbio();
	/*
	 * right now we support clustered writing only to regular files.  If
	 * we find a clusterable block we could be in the middle of a cluster
	 * rather then at the beginning.
	 */
	if ((vp->v_type == VREG) && 
	    (vp->v_mount != 0) && /* Only on nodes that have the size info */
	    (bp->b_flags & (B_CLUSTEROK | B_INVAL)) == B_CLUSTEROK) {

		size = vp->v_mount->mnt_stat.f_iosize;
		maxcl = MAXPHYS / size;

		for (i = 1; i < maxcl; i++) {
			if ((bpa = gbincore(vp, lblkno + i)) &&
			    BUF_REFCNT(bpa) == 0 &&
			    ((bpa->b_flags & (B_DELWRI | B_CLUSTEROK | B_INVAL)) ==
			    (B_DELWRI | B_CLUSTEROK)) &&
			    (bpa->b_bufsize == size)) {
				if ((bpa->b_blkno == bpa->b_lblkno) ||
				    (bpa->b_blkno !=
				     bp->b_blkno + ((i * size) >> DEV_BSHIFT)))
					break;
			} else {
				break;
			}
		}
		for (j = 1; i + j <= maxcl && j <= lblkno; j++) {
			if ((bpa = gbincore(vp, lblkno - j)) &&
			    BUF_REFCNT(bpa) == 0 &&
			    ((bpa->b_flags & (B_DELWRI | B_CLUSTEROK | B_INVAL)) ==
			    (B_DELWRI | B_CLUSTEROK)) &&
			    (bpa->b_bufsize == size)) {
				if ((bpa->b_blkno == bpa->b_lblkno) ||
				    (bpa->b_blkno !=
				     bp->b_blkno - ((j * size) >> DEV_BSHIFT)))
					break;
			} else {
				break;
			}
		}
		--j;
		ncl = i + j;
		/*
		 * this is a possible cluster write
		 */
		if (ncl != 1) {
			nwritten = cluster_wbuild(vp, size, lblkno - j, ncl);
			splx(s);
			return nwritten;
		}
	}

	BUF_LOCK(bp, LK_EXCLUSIVE);
	bremfree(bp);
	bp->b_flags |= B_ASYNC;

	splx(s);
	/*
	 * default (old) behavior, writing out only one block
	 *
	 * XXX returns b_bufsize instead of b_bcount for nwritten?
	 */
	nwritten = bp->b_bufsize;
	(void) VOP_BWRITE(bp->b_vp, bp);

	return nwritten;
}

/*
 *	getnewbuf:
 *
 *	Find and initialize a new buffer header, freeing up existing buffers 
 *	in the bufqueues as necessary.  The new buffer is returned locked.
 *
 *	Important:  B_INVAL is not set.  If the caller wishes to throw the
 *	buffer away, the caller must set B_INVAL prior to calling brelse().
 *
 *	We block if:
 *		We have insufficient buffer headers
 *		We have insufficient buffer space
 *		buffer_map is too fragmented ( space reservation fails )
 *		If we have to flush dirty buffers ( but we try to avoid this )
 *
 *	To avoid VFS layer recursion we do not flush dirty buffers ourselves.
 *	Instead we ask the buf daemon to do it for us.  We attempt to
 *	avoid piecemeal wakeups of the pageout daemon.
 */

static struct buf *
getnewbuf(int slpflag, int slptimeo, int size, int maxsize)
{
	struct buf *bp;
	struct buf *nbp;
	int defrag = 0;
	int nqindex;
	static int flushingbufs;

	/*
	 * We can't afford to block since we might be holding a vnode lock,
	 * which may prevent system daemons from running.  We deal with
	 * low-memory situations by proactively returning memory and running
	 * async I/O rather then sync I/O.
	 */
	
	++getnewbufcalls;
	--getnewbufrestarts;
restart:
	++getnewbufrestarts;

	/*
	 * Setup for scan.  If we do not have enough free buffers,
	 * we setup a degenerate case that immediately fails.  Note
	 * that if we are specially marked process, we are allowed to
	 * dip into our reserves.
	 *
	 * The scanning sequence is nominally:  EMPTY->EMPTYKVA->CLEAN
	 *
	 * We start with EMPTYKVA.  If the list is empty we backup to EMPTY.
	 * However, there are a number of cases (defragging, reusing, ...)
	 * where we cannot backup.
	 */
	nqindex = QUEUE_EMPTYKVA;
	nbp = TAILQ_FIRST(&bufqueues[QUEUE_EMPTYKVA]);

	if (nbp == NULL) {
		/*
		 * If no EMPTYKVA buffers and we are either
		 * defragging or reusing, locate a CLEAN buffer
		 * to free or reuse.  If bufspace useage is low
		 * skip this step so we can allocate a new buffer.
		 */
		if (defrag || bufspace >= lobufspace) {
			nqindex = QUEUE_CLEAN;
			nbp = TAILQ_FIRST(&bufqueues[QUEUE_CLEAN]);
		}

		/*
		 * If we could not find or were not allowed to reuse a
		 * CLEAN buffer, check to see if it is ok to use an EMPTY
		 * buffer.  We can only use an EMPTY buffer if allocating
		 * its KVA would not otherwise run us out of buffer space.
		 */
		if (nbp == NULL && defrag == 0 &&
		    bufspace + maxsize < hibufspace) {
			nqindex = QUEUE_EMPTY;
			nbp = TAILQ_FIRST(&bufqueues[QUEUE_EMPTY]);
		}
	}

	/*
	 * Run scan, possibly freeing data and/or kva mappings on the fly
	 * depending.
	 */

	while ((bp = nbp) != NULL) {
		int qindex = nqindex;

		/*
		 * Calculate next bp ( we can only use it if we do not block
		 * or do other fancy things ).
		 */
		if ((nbp = TAILQ_NEXT(bp, b_freelist)) == NULL) {
			switch(qindex) {
			case QUEUE_EMPTY:
				nqindex = QUEUE_EMPTYKVA;
				if ((nbp = TAILQ_FIRST(&bufqueues[QUEUE_EMPTYKVA])))
					break;
				/* fall through */
			case QUEUE_EMPTYKVA:
				nqindex = QUEUE_CLEAN;
				if ((nbp = TAILQ_FIRST(&bufqueues[QUEUE_CLEAN])))
					break;
				/* fall through */
			case QUEUE_CLEAN:
				/*
				 * nbp is NULL. 
				 */
				break;
			}
		}

		/*
		 * Sanity Checks
		 */
		KASSERT(bp->b_qindex == qindex, ("getnewbuf: inconsistant queue %d bp %p", qindex, bp));

		/*
		 * Note: we no longer distinguish between VMIO and non-VMIO
		 * buffers.
		 */

		KASSERT((bp->b_flags & B_DELWRI) == 0, ("delwri buffer %p found in queue %d", bp, qindex));

		/*
		 * If we are defragging then we need a buffer with 
		 * b_kvasize != 0.  XXX this situation should no longer
		 * occur, if defrag is non-zero the buffer's b_kvasize
		 * should also be non-zero at this point.  XXX
		 */
		if (defrag && bp->b_kvasize == 0) {
			printf("Warning: defrag empty buffer %p\n", bp);
			continue;
		}

		/*
		 * Start freeing the bp.  This is somewhat involved.  nbp
		 * remains valid only for QUEUE_EMPTY[KVA] bp's.
		 */

		if (BUF_LOCK(bp, LK_EXCLUSIVE | LK_NOWAIT) != 0)
			panic("getnewbuf: locked buf");
		bremfree(bp);

		if (qindex == QUEUE_CLEAN) {
			if (bp->b_flags & B_VMIO) {
				bp->b_flags &= ~B_ASYNC;
				vfs_vmio_release(bp);
			}
			if (bp->b_vp)
				brelvp(bp);
		}

		/*
		 * NOTE:  nbp is now entirely invalid.  We can only restart
		 * the scan from this point on.
		 *
		 * Get the rest of the buffer freed up.  b_kva* is still
		 * valid after this operation.
		 */

		if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_deallocate)
			(*bioops.io_deallocate)(bp);
		if (bp->b_xflags & BX_BKGRDINPROG)
			panic("losing buffer 3");
		LIST_REMOVE(bp, b_hash);
		LIST_INSERT_HEAD(&invalhash, bp, b_hash);

		/*
		 * spl protection not required when scrapping a buffer's
		 * contents because it is already wired.
		 */
		if (bp->b_bufsize)
			allocbuf(bp, 0);

		bp->b_flags = 0;
		bp->b_xflags = 0;
		bp->b_dev = NODEV;
		bp->b_vp = NULL;
		bp->b_blkno = bp->b_lblkno = 0;
		bp->b_offset = NOOFFSET;
		bp->b_iodone = 0;
		bp->b_error = 0;
		bp->b_resid = 0;
		bp->b_bcount = 0;
		bp->b_npages = 0;
		bp->b_dirtyoff = bp->b_dirtyend = 0;

		LIST_INIT(&bp->b_dep);

		/*
		 * If we are defragging then free the buffer.
		 */
		if (defrag) {
			bp->b_flags |= B_INVAL;
			bfreekva(bp);
			brelse(bp);
			defrag = 0;
			goto restart;
		}

		/*
		 * If we are overcomitted then recover the buffer and its
		 * KVM space.  This occurs in rare situations when multiple
		 * processes are blocked in getnewbuf() or allocbuf().
		 */
		if (bufspace >= hibufspace)
			flushingbufs = 1;
		if (flushingbufs && bp->b_kvasize != 0) {
			bp->b_flags |= B_INVAL;
			bfreekva(bp);
			brelse(bp);
			goto restart;
		}
		if (bufspace < lobufspace)
			flushingbufs = 0;
		break;
	}

	/*
	 * If we exhausted our list, sleep as appropriate.  We may have to
	 * wakeup various daemons and write out some dirty buffers.
	 *
	 * Generally we are sleeping due to insufficient buffer space.
	 */

	if (bp == NULL) {
		int flags;
		char *waitmsg;

		if (defrag) {
			flags = VFS_BIO_NEED_BUFSPACE;
			waitmsg = "nbufkv";
		} else if (bufspace >= hibufspace) {
			waitmsg = "nbufbs";
			flags = VFS_BIO_NEED_BUFSPACE;
		} else {
			waitmsg = "newbuf";
			flags = VFS_BIO_NEED_ANY;
		}

		bd_speedup();	/* heeeelp */

		needsbuffer |= flags;
		while (needsbuffer & flags) {
			if (tsleep(&needsbuffer, slpflag, waitmsg, slptimeo))
				return (NULL);
		}
	} else {
		/*
		 * We finally have a valid bp.  We aren't quite out of the
		 * woods, we still have to reserve kva space.  In order
		 * to keep fragmentation sane we only allocate kva in
		 * BKVASIZE chunks.
		 */
		maxsize = (maxsize + BKVAMASK) & ~BKVAMASK;

		if (maxsize != bp->b_kvasize) {
			vm_offset_t addr = 0;
			int count;

			bfreekva(bp);

			count = vm_map_entry_reserve(MAP_RESERVE_COUNT);
			vm_map_lock(buffer_map);

			if (vm_map_findspace(buffer_map,
				    vm_map_min(buffer_map), maxsize,
				    maxsize, &addr)) {
				/*
				 * Uh oh.  Buffer map is to fragmented.  We
				 * must defragment the map.
				 */
				vm_map_unlock(buffer_map);
				vm_map_entry_release(count);
				++bufdefragcnt;
				defrag = 1;
				bp->b_flags |= B_INVAL;
				brelse(bp);
				goto restart;
			}
			if (addr) {
				vm_map_insert(buffer_map, &count,
					NULL, 0,
					addr, addr + maxsize,
					VM_PROT_ALL, VM_PROT_ALL, MAP_NOFAULT);

				bp->b_kvabase = (caddr_t) addr;
				bp->b_kvasize = maxsize;
				bufspace += bp->b_kvasize;
				++bufreusecnt;
			}
			vm_map_unlock(buffer_map);
			vm_map_entry_release(count);
		}
		bp->b_data = bp->b_kvabase;
	}
	return(bp);
}

/*
 *	buf_daemon:
 *
 *	buffer flushing daemon.  Buffers are normally flushed by the
 *	update daemon but if it cannot keep up this process starts to
 *	take the load in an attempt to prevent getnewbuf() from blocking.
 */

static struct thread *bufdaemonthread;

static struct kproc_desc buf_kp = {
	"bufdaemon",
	buf_daemon,
	&bufdaemonthread
};
SYSINIT(bufdaemon, SI_SUB_KTHREAD_BUF, SI_ORDER_FIRST, kproc_start, &buf_kp)

static void
buf_daemon()
{
	int s;

	/*
	 * This process needs to be suspended prior to shutdown sync.
	 */
	EVENTHANDLER_REGISTER(shutdown_pre_sync, shutdown_kproc,
	    bufdaemonthread, SHUTDOWN_PRI_LAST);

	/*
	 * This process is allowed to take the buffer cache to the limit
	 */
	s = splbio();

	for (;;) {
		kproc_suspend_loop();

		/*
		 * Do the flush.  Limit the amount of in-transit I/O we
		 * allow to build up, otherwise we would completely saturate
		 * the I/O system.  Wakeup any waiting processes before we
		 * normally would so they can run in parallel with our drain.
		 */
		while (numdirtybuffers > lodirtybuffers) {
			if (flushbufqueues() == 0)
				break;
			waitrunningbufspace();
			numdirtywakeup((lodirtybuffers + hidirtybuffers) / 2);
		}

		/*
		 * Only clear bd_request if we have reached our low water
		 * mark.  The buf_daemon normally waits 5 seconds and
		 * then incrementally flushes any dirty buffers that have
		 * built up, within reason.
		 *
		 * If we were unable to hit our low water mark and couldn't
		 * find any flushable buffers, we sleep half a second. 
		 * Otherwise we loop immediately.
		 */
		if (numdirtybuffers <= lodirtybuffers) {
			/*
			 * We reached our low water mark, reset the
			 * request and sleep until we are needed again.
			 * The sleep is just so the suspend code works.
			 */
			bd_request = 0;
			tsleep(&bd_request, 0, "psleep", hz);
		} else {
			/*
			 * We couldn't find any flushable dirty buffers but
			 * still have too many dirty buffers, we
			 * have to sleep and try again.  (rare)
			 */
			tsleep(&bd_request, 0, "qsleep", hz / 2);
		}
	}
}

/*
 *	flushbufqueues:
 *
 *	Try to flush a buffer in the dirty queue.  We must be careful to
 *	free up B_INVAL buffers instead of write them, which NFS is 
 *	particularly sensitive to.
 */

static int
flushbufqueues(void)
{
	struct buf *bp;
	int r = 0;

	bp = TAILQ_FIRST(&bufqueues[QUEUE_DIRTY]);

	while (bp) {
		KASSERT((bp->b_flags & B_DELWRI), ("unexpected clean buffer %p", bp));
		if ((bp->b_flags & B_DELWRI) != 0 &&
		    (bp->b_xflags & BX_BKGRDINPROG) == 0) {
			if (bp->b_flags & B_INVAL) {
				if (BUF_LOCK(bp, LK_EXCLUSIVE | LK_NOWAIT) != 0)
					panic("flushbufqueues: locked buf");
				bremfree(bp);
				brelse(bp);
				++r;
				break;
			}
			if (LIST_FIRST(&bp->b_dep) != NULL &&
			    bioops.io_countdeps &&
			    (bp->b_flags & B_DEFERRED) == 0 &&
			    (*bioops.io_countdeps)(bp, 0)) {
				TAILQ_REMOVE(&bufqueues[QUEUE_DIRTY],
				    bp, b_freelist);
				TAILQ_INSERT_TAIL(&bufqueues[QUEUE_DIRTY],
				    bp, b_freelist);
				bp->b_flags |= B_DEFERRED;
				bp = TAILQ_FIRST(&bufqueues[QUEUE_DIRTY]);
				continue;
			}
			vfs_bio_awrite(bp);
			++r;
			break;
		}
		bp = TAILQ_NEXT(bp, b_freelist);
	}
	return (r);
}

/*
 * Check to see if a block is currently memory resident.
 */
struct buf *
incore(struct vnode * vp, daddr_t blkno)
{
	struct buf *bp;

	int s = splbio();
	bp = gbincore(vp, blkno);
	splx(s);
	return (bp);
}

/*
 * Returns true if no I/O is needed to access the associated VM object.
 * This is like incore except it also hunts around in the VM system for
 * the data.
 *
 * Note that we ignore vm_page_free() races from interrupts against our
 * lookup, since if the caller is not protected our return value will not
 * be any more valid then otherwise once we splx().
 */
int
inmem(struct vnode * vp, daddr_t blkno)
{
	vm_object_t obj;
	vm_offset_t toff, tinc, size;
	vm_page_t m;
	vm_ooffset_t off;

	if (incore(vp, blkno))
		return 1;
	if (vp->v_mount == NULL)
		return 0;
	if (VOP_GETVOBJECT(vp, &obj) != 0 || (vp->v_flag & VOBJBUF) == 0)
 		return 0;

	size = PAGE_SIZE;
	if (size > vp->v_mount->mnt_stat.f_iosize)
		size = vp->v_mount->mnt_stat.f_iosize;
	off = (vm_ooffset_t)blkno * (vm_ooffset_t)vp->v_mount->mnt_stat.f_iosize;

	for (toff = 0; toff < vp->v_mount->mnt_stat.f_iosize; toff += tinc) {
		m = vm_page_lookup(obj, OFF_TO_IDX(off + toff));
		if (!m)
			return 0;
		tinc = size;
		if (tinc > PAGE_SIZE - ((toff + off) & PAGE_MASK))
			tinc = PAGE_SIZE - ((toff + off) & PAGE_MASK);
		if (vm_page_is_valid(m,
		    (vm_offset_t) ((toff + off) & PAGE_MASK), tinc) == 0)
			return 0;
	}
	return 1;
}

/*
 *	vfs_setdirty:
 *
 *	Sets the dirty range for a buffer based on the status of the dirty
 *	bits in the pages comprising the buffer.
 *
 *	The range is limited to the size of the buffer.
 *
 *	This routine is primarily used by NFS, but is generalized for the
 *	B_VMIO case.
 */
static void
vfs_setdirty(struct buf *bp) 
{
	int i;
	vm_object_t object;

	/*
	 * Degenerate case - empty buffer
	 */

	if (bp->b_bufsize == 0)
		return;

	/*
	 * We qualify the scan for modified pages on whether the
	 * object has been flushed yet.  The OBJ_WRITEABLE flag
	 * is not cleared simply by protecting pages off.
	 */

	if ((bp->b_flags & B_VMIO) == 0)
		return;

	object = bp->b_pages[0]->object;

	if ((object->flags & OBJ_WRITEABLE) && !(object->flags & OBJ_MIGHTBEDIRTY))
		printf("Warning: object %p writeable but not mightbedirty\n", object);
	if (!(object->flags & OBJ_WRITEABLE) && (object->flags & OBJ_MIGHTBEDIRTY))
		printf("Warning: object %p mightbedirty but not writeable\n", object);

	if (object->flags & (OBJ_MIGHTBEDIRTY|OBJ_CLEANING)) {
		vm_offset_t boffset;
		vm_offset_t eoffset;

		/*
		 * test the pages to see if they have been modified directly
		 * by users through the VM system.
		 */
		for (i = 0; i < bp->b_npages; i++) {
			vm_page_flag_clear(bp->b_pages[i], PG_ZERO);
			vm_page_test_dirty(bp->b_pages[i]);
		}

		/*
		 * Calculate the encompassing dirty range, boffset and eoffset,
		 * (eoffset - boffset) bytes.
		 */

		for (i = 0; i < bp->b_npages; i++) {
			if (bp->b_pages[i]->dirty)
				break;
		}
		boffset = (i << PAGE_SHIFT) - (bp->b_offset & PAGE_MASK);

		for (i = bp->b_npages - 1; i >= 0; --i) {
			if (bp->b_pages[i]->dirty) {
				break;
			}
		}
		eoffset = ((i + 1) << PAGE_SHIFT) - (bp->b_offset & PAGE_MASK);

		/*
		 * Fit it to the buffer.
		 */

		if (eoffset > bp->b_bcount)
			eoffset = bp->b_bcount;

		/*
		 * If we have a good dirty range, merge with the existing
		 * dirty range.
		 */

		if (boffset < eoffset) {
			if (bp->b_dirtyoff > boffset)
				bp->b_dirtyoff = boffset;
			if (bp->b_dirtyend < eoffset)
				bp->b_dirtyend = eoffset;
		}
	}
}

/*
 *	getblk:
 *
 *	Get a block given a specified block and offset into a file/device.
 *	The buffers B_DONE bit will be cleared on return, making it almost
 * 	ready for an I/O initiation.  B_INVAL may or may not be set on 
 *	return.  The caller should clear B_INVAL prior to initiating a
 *	READ.
 *
 *	For a non-VMIO buffer, B_CACHE is set to the opposite of B_INVAL for
 *	an existing buffer.
 *
 *	For a VMIO buffer, B_CACHE is modified according to the backing VM.
 *	If getblk()ing a previously 0-sized invalid buffer, B_CACHE is set
 *	and then cleared based on the backing VM.  If the previous buffer is
 *	non-0-sized but invalid, B_CACHE will be cleared.
 *
 *	If getblk() must create a new buffer, the new buffer is returned with
 *	both B_INVAL and B_CACHE clear unless it is a VMIO buffer, in which
 *	case it is returned with B_INVAL clear and B_CACHE set based on the
 *	backing VM.
 *
 *	getblk() also forces a VOP_BWRITE() for any B_DELWRI buffer whos
 *	B_CACHE bit is clear.
 *	
 *	What this means, basically, is that the caller should use B_CACHE to
 *	determine whether the buffer is fully valid or not and should clear
 *	B_INVAL prior to issuing a read.  If the caller intends to validate
 *	the buffer by loading its data area with something, the caller needs
 *	to clear B_INVAL.  If the caller does this without issuing an I/O, 
 *	the caller should set B_CACHE ( as an optimization ), else the caller
 *	should issue the I/O and biodone() will set B_CACHE if the I/O was
 *	a write attempt or if it was a successfull read.  If the caller 
 *	intends to issue a READ, the caller must clear B_INVAL and B_ERROR
 *	prior to issuing the READ.  biodone() will *not* clear B_INVAL.
 */
struct buf *
getblk(struct vnode * vp, daddr_t blkno, int size, int slpflag, int slptimeo)
{
	struct buf *bp;
	int s;
	struct bufhashhdr *bh;

	if (size > MAXBSIZE)
		panic("getblk: size(%d) > MAXBSIZE(%d)", size, MAXBSIZE);

	s = splbio();
loop:
	/*
	 * Block if we are low on buffers.   Certain processes are allowed
	 * to completely exhaust the buffer cache.
         *
         * If this check ever becomes a bottleneck it may be better to
         * move it into the else, when gbincore() fails.  At the moment
         * it isn't a problem.
	 *
	 * XXX remove, we cannot afford to block anywhere if holding a vnode
	 * lock in low-memory situation, so take it to the max.
         */
	if (numfreebuffers == 0) {
		if (!curproc)
			return NULL;
		needsbuffer |= VFS_BIO_NEED_ANY;
		tsleep(&needsbuffer, slpflag, "newbuf", slptimeo);
	}

	if ((bp = gbincore(vp, blkno))) {
		/*
		 * Buffer is in-core.  If the buffer is not busy, it must
		 * be on a queue.
		 */

		if (BUF_LOCK(bp, LK_EXCLUSIVE | LK_NOWAIT)) {
			if (BUF_TIMELOCK(bp, LK_EXCLUSIVE | LK_SLEEPFAIL,
			    "getblk", slpflag, slptimeo) == ENOLCK)
				goto loop;
			splx(s);
			return (struct buf *) NULL;
		}

		/*
		 * The buffer is locked.  B_CACHE is cleared if the buffer is 
		 * invalid.  Ohterwise, for a non-VMIO buffer, B_CACHE is set
		 * and for a VMIO buffer B_CACHE is adjusted according to the
		 * backing VM cache.
		 */
		if (bp->b_flags & B_INVAL)
			bp->b_flags &= ~B_CACHE;
		else if ((bp->b_flags & (B_VMIO | B_INVAL)) == 0)
			bp->b_flags |= B_CACHE;
		bremfree(bp);

		/*
		 * check for size inconsistancies for non-VMIO case.
		 */

		if (bp->b_bcount != size) {
			if ((bp->b_flags & B_VMIO) == 0 ||
			    (size > bp->b_kvasize)) {
				if (bp->b_flags & B_DELWRI) {
					bp->b_flags |= B_NOCACHE;
					VOP_BWRITE(bp->b_vp, bp);
				} else {
					if ((bp->b_flags & B_VMIO) &&
					   (LIST_FIRST(&bp->b_dep) == NULL)) {
						bp->b_flags |= B_RELBUF;
						brelse(bp);
					} else {
						bp->b_flags |= B_NOCACHE;
						VOP_BWRITE(bp->b_vp, bp);
					}
				}
				goto loop;
			}
		}

		/*
		 * If the size is inconsistant in the VMIO case, we can resize
		 * the buffer.  This might lead to B_CACHE getting set or
		 * cleared.  If the size has not changed, B_CACHE remains
		 * unchanged from its previous state.
		 */

		if (bp->b_bcount != size)
			allocbuf(bp, size);

		KASSERT(bp->b_offset != NOOFFSET, 
		    ("getblk: no buffer offset"));

		/*
		 * A buffer with B_DELWRI set and B_CACHE clear must
		 * be committed before we can return the buffer in
		 * order to prevent the caller from issuing a read
		 * ( due to B_CACHE not being set ) and overwriting
		 * it.
		 *
		 * Most callers, including NFS and FFS, need this to
		 * operate properly either because they assume they
		 * can issue a read if B_CACHE is not set, or because
		 * ( for example ) an uncached B_DELWRI might loop due 
		 * to softupdates re-dirtying the buffer.  In the latter
		 * case, B_CACHE is set after the first write completes,
		 * preventing further loops.
		 *
		 * NOTE!  b*write() sets B_CACHE.  If we cleared B_CACHE
		 * above while extending the buffer, we cannot allow the
		 * buffer to remain with B_CACHE set after the write
		 * completes or it will represent a corrupt state.  To
		 * deal with this we set B_NOCACHE to scrap the buffer
		 * after the write.
		 *
		 * We might be able to do something fancy, like setting
		 * B_CACHE in bwrite() except if B_DELWRI is already set,
		 * so the below call doesn't set B_CACHE, but that gets real
		 * confusing.  This is much easier.
		 */

		if ((bp->b_flags & (B_CACHE|B_DELWRI)) == B_DELWRI) {
			bp->b_flags |= B_NOCACHE;
			VOP_BWRITE(bp->b_vp, bp);
			goto loop;
		}

		splx(s);
		bp->b_flags &= ~B_DONE;
	} else {
		/*
		 * Buffer is not in-core, create new buffer.  The buffer
		 * returned by getnewbuf() is locked.  Note that the returned
		 * buffer is also considered valid (not marked B_INVAL).
		 */
		int bsize, maxsize, vmio;
		off_t offset;

		if (vn_isdisk(vp, NULL))
			bsize = DEV_BSIZE;
		else if (vp->v_mountedhere)
			bsize = vp->v_mountedhere->mnt_stat.f_iosize;
		else if (vp->v_mount)
			bsize = vp->v_mount->mnt_stat.f_iosize;
		else
			bsize = size;

		offset = (off_t)blkno * bsize;
		vmio = (VOP_GETVOBJECT(vp, NULL) == 0) && (vp->v_flag & VOBJBUF);
		maxsize = vmio ? size + (offset & PAGE_MASK) : size;
		maxsize = imax(maxsize, bsize);

		if ((bp = getnewbuf(slpflag, slptimeo, size, maxsize)) == NULL) {
			if (slpflag || slptimeo) {
				splx(s);
				return NULL;
			}
			goto loop;
		}

		/*
		 * This code is used to make sure that a buffer is not
		 * created while the getnewbuf routine is blocked.
		 * This can be a problem whether the vnode is locked or not.
		 * If the buffer is created out from under us, we have to
		 * throw away the one we just created.  There is now window
		 * race because we are safely running at splbio() from the
		 * point of the duplicate buffer creation through to here,
		 * and we've locked the buffer.
		 */
		if (gbincore(vp, blkno)) {
			bp->b_flags |= B_INVAL;
			brelse(bp);
			goto loop;
		}

		/*
		 * Insert the buffer into the hash, so that it can
		 * be found by incore.
		 */
		bp->b_blkno = bp->b_lblkno = blkno;
		bp->b_offset = offset;

		bgetvp(vp, bp);
		LIST_REMOVE(bp, b_hash);
		bh = bufhash(vp, blkno);
		LIST_INSERT_HEAD(bh, bp, b_hash);

		/*
		 * set B_VMIO bit.  allocbuf() the buffer bigger.  Since the
		 * buffer size starts out as 0, B_CACHE will be set by
		 * allocbuf() for the VMIO case prior to it testing the
		 * backing store for validity.
		 */

		if (vmio) {
			bp->b_flags |= B_VMIO;
#if defined(VFS_BIO_DEBUG)
			if (vn_canvmio(vp) != TRUE)
				printf("getblk: vmioing file type %d???\n", vp->v_type);
#endif
		} else {
			bp->b_flags &= ~B_VMIO;
		}

		allocbuf(bp, size);

		splx(s);
		bp->b_flags &= ~B_DONE;
	}
	return (bp);
}

/*
 * Get an empty, disassociated buffer of given size.  The buffer is initially
 * set to B_INVAL.
 *
 * spl protection is not required for the allocbuf() call because races are
 * impossible here.
 */
struct buf *
geteblk(int size)
{
	struct buf *bp;
	int s;
	int maxsize;

	maxsize = (size + BKVAMASK) & ~BKVAMASK;

	s = splbio();
	while ((bp = getnewbuf(0, 0, size, maxsize)) == 0);
	splx(s);
	allocbuf(bp, size);
	bp->b_flags |= B_INVAL;	/* b_dep cleared by getnewbuf() */
	return (bp);
}


/*
 * This code constitutes the buffer memory from either anonymous system
 * memory (in the case of non-VMIO operations) or from an associated
 * VM object (in the case of VMIO operations).  This code is able to
 * resize a buffer up or down.
 *
 * Note that this code is tricky, and has many complications to resolve
 * deadlock or inconsistant data situations.  Tread lightly!!! 
 * There are B_CACHE and B_DELWRI interactions that must be dealt with by 
 * the caller.  Calling this code willy nilly can result in the loss of data.
 *
 * allocbuf() only adjusts B_CACHE for VMIO buffers.  getblk() deals with
 * B_CACHE for the non-VMIO case.
 *
 * This routine does not need to be called at splbio() but you must own the
 * buffer.
 */
int
allocbuf(struct buf *bp, int size)
{
	int newbsize, mbsize;
	int i;

	if (BUF_REFCNT(bp) == 0)
		panic("allocbuf: buffer not busy");

	if (bp->b_kvasize < size)
		panic("allocbuf: buffer too small");

	if ((bp->b_flags & B_VMIO) == 0) {
		caddr_t origbuf;
		int origbufsize;
		/*
		 * Just get anonymous memory from the kernel.  Don't
		 * mess with B_CACHE.
		 */
		mbsize = (size + DEV_BSIZE - 1) & ~(DEV_BSIZE - 1);
#if !defined(NO_B_MALLOC)
		if (bp->b_flags & B_MALLOC)
			newbsize = mbsize;
		else
#endif
			newbsize = round_page(size);

		if (newbsize < bp->b_bufsize) {
#if !defined(NO_B_MALLOC)
			/*
			 * malloced buffers are not shrunk
			 */
			if (bp->b_flags & B_MALLOC) {
				if (newbsize) {
					bp->b_bcount = size;
				} else {
					free(bp->b_data, M_BIOBUF);
					if (bp->b_bufsize) {
						bufmallocspace -= bp->b_bufsize;
						bufspacewakeup();
						bp->b_bufsize = 0;
					}
					bp->b_data = bp->b_kvabase;
					bp->b_bcount = 0;
					bp->b_flags &= ~B_MALLOC;
				}
				return 1;
			}		
#endif
			vm_hold_free_pages(
			    bp,
			    (vm_offset_t) bp->b_data + newbsize,
			    (vm_offset_t) bp->b_data + bp->b_bufsize);
		} else if (newbsize > bp->b_bufsize) {
#if !defined(NO_B_MALLOC)
			/*
			 * We only use malloced memory on the first allocation.
			 * and revert to page-allocated memory when the buffer
			 * grows.
			 */
			if ( (bufmallocspace < maxbufmallocspace) &&
				(bp->b_bufsize == 0) &&
				(mbsize <= PAGE_SIZE/2)) {

				bp->b_data = malloc(mbsize, M_BIOBUF, M_WAITOK);
				bp->b_bufsize = mbsize;
				bp->b_bcount = size;
				bp->b_flags |= B_MALLOC;
				bufmallocspace += mbsize;
				return 1;
			}
#endif
			origbuf = NULL;
			origbufsize = 0;
#if !defined(NO_B_MALLOC)
			/*
			 * If the buffer is growing on its other-than-first allocation,
			 * then we revert to the page-allocation scheme.
			 */
			if (bp->b_flags & B_MALLOC) {
				origbuf = bp->b_data;
				origbufsize = bp->b_bufsize;
				bp->b_data = bp->b_kvabase;
				if (bp->b_bufsize) {
					bufmallocspace -= bp->b_bufsize;
					bufspacewakeup();
					bp->b_bufsize = 0;
				}
				bp->b_flags &= ~B_MALLOC;
				newbsize = round_page(newbsize);
			}
#endif
			vm_hold_load_pages(
			    bp,
			    (vm_offset_t) bp->b_data + bp->b_bufsize,
			    (vm_offset_t) bp->b_data + newbsize);
#if !defined(NO_B_MALLOC)
			if (origbuf) {
				bcopy(origbuf, bp->b_data, origbufsize);
				free(origbuf, M_BIOBUF);
			}
#endif
		}
	} else {
		vm_page_t m;
		int desiredpages;

		newbsize = (size + DEV_BSIZE - 1) & ~(DEV_BSIZE - 1);
		desiredpages = (size == 0) ? 0 :
			num_pages((bp->b_offset & PAGE_MASK) + newbsize);

#if !defined(NO_B_MALLOC)
		if (bp->b_flags & B_MALLOC)
			panic("allocbuf: VMIO buffer can't be malloced");
#endif
		/*
		 * Set B_CACHE initially if buffer is 0 length or will become
		 * 0-length.
		 */
		if (size == 0 || bp->b_bufsize == 0)
			bp->b_flags |= B_CACHE;

		if (newbsize < bp->b_bufsize) {
			/*
			 * DEV_BSIZE aligned new buffer size is less then the
			 * DEV_BSIZE aligned existing buffer size.  Figure out
			 * if we have to remove any pages.
			 */
			if (desiredpages < bp->b_npages) {
				for (i = desiredpages; i < bp->b_npages; i++) {
					/*
					 * the page is not freed here -- it
					 * is the responsibility of 
					 * vnode_pager_setsize
					 */
					m = bp->b_pages[i];
					KASSERT(m != bogus_page,
					    ("allocbuf: bogus page found"));
					while (vm_page_sleep_busy(m, TRUE, "biodep"))
						;

					bp->b_pages[i] = NULL;
					vm_page_unwire(m, 0);
				}
				pmap_qremove((vm_offset_t) trunc_page((vm_offset_t)bp->b_data) +
				    (desiredpages << PAGE_SHIFT), (bp->b_npages - desiredpages));
				bp->b_npages = desiredpages;
			}
		} else if (size > bp->b_bcount) {
			/*
			 * We are growing the buffer, possibly in a 
			 * byte-granular fashion.
			 */
			struct vnode *vp;
			vm_object_t obj;
			vm_offset_t toff;
			vm_offset_t tinc;
			int s;

			/*
			 * Step 1, bring in the VM pages from the object, 
			 * allocating them if necessary.  We must clear
			 * B_CACHE if these pages are not valid for the 
			 * range covered by the buffer.
			 *
			 * spl protection is required to protect against
			 * interrupts unbusying and freeing pages between
			 * our vm_page_lookup() and our busycheck/wiring
			 * call.
			 */
			vp = bp->b_vp;
			VOP_GETVOBJECT(vp, &obj);

			s = splbio();
			while (bp->b_npages < desiredpages) {
				vm_page_t m;
				vm_pindex_t pi;

				pi = OFF_TO_IDX(bp->b_offset) + bp->b_npages;
				if ((m = vm_page_lookup(obj, pi)) == NULL) {
					/*
					 * note: must allocate system pages
					 * since blocking here could intefere
					 * with paging I/O, no matter which
					 * process we are.
					 */
					m = vm_page_alloc(obj, pi, VM_ALLOC_NORMAL | VM_ALLOC_SYSTEM);
					if (m == NULL) {
						VM_WAIT;
						vm_pageout_deficit += desiredpages - bp->b_npages;
					} else {
						vm_page_wire(m);
						vm_page_wakeup(m);
						bp->b_flags &= ~B_CACHE;
						bp->b_pages[bp->b_npages] = m;
						++bp->b_npages;
					}
					continue;
				}

				/*
				 * We found a page.  If we have to sleep on it,
				 * retry because it might have gotten freed out
				 * from under us.
				 *
				 * We can only test PG_BUSY here.  Blocking on
				 * m->busy might lead to a deadlock:
				 *
				 *  vm_fault->getpages->cluster_read->allocbuf
				 *
				 */

				if (vm_page_sleep_busy(m, FALSE, "pgtblk"))
					continue;

				/*
				 * We have a good page.  Should we wakeup the
				 * page daemon?
				 */
				if ((curthread != pagethread) &&
				    ((m->queue - m->pc) == PQ_CACHE) &&
				    ((vmstats.v_free_count + vmstats.v_cache_count) <
					(vmstats.v_free_min + vmstats.v_cache_min))) {
					pagedaemon_wakeup();
				}
				vm_page_flag_clear(m, PG_ZERO);
				vm_page_wire(m);
				bp->b_pages[bp->b_npages] = m;
				++bp->b_npages;
			}
			splx(s);

			/*
			 * Step 2.  We've loaded the pages into the buffer,
			 * we have to figure out if we can still have B_CACHE
			 * set.  Note that B_CACHE is set according to the
			 * byte-granular range ( bcount and size ), new the
			 * aligned range ( newbsize ).
			 *
			 * The VM test is against m->valid, which is DEV_BSIZE
			 * aligned.  Needless to say, the validity of the data
			 * needs to also be DEV_BSIZE aligned.  Note that this
			 * fails with NFS if the server or some other client
			 * extends the file's EOF.  If our buffer is resized, 
			 * B_CACHE may remain set! XXX
			 */

			toff = bp->b_bcount;
			tinc = PAGE_SIZE - ((bp->b_offset + toff) & PAGE_MASK);

			while ((bp->b_flags & B_CACHE) && toff < size) {
				vm_pindex_t pi;

				if (tinc > (size - toff))
					tinc = size - toff;

				pi = ((bp->b_offset & PAGE_MASK) + toff) >> 
				    PAGE_SHIFT;

				vfs_buf_test_cache(
				    bp, 
				    bp->b_offset,
				    toff, 
				    tinc, 
				    bp->b_pages[pi]
				);
				toff += tinc;
				tinc = PAGE_SIZE;
			}

			/*
			 * Step 3, fixup the KVM pmap.  Remember that
			 * bp->b_data is relative to bp->b_offset, but 
			 * bp->b_offset may be offset into the first page.
			 */

			bp->b_data = (caddr_t)
			    trunc_page((vm_offset_t)bp->b_data);
			pmap_qenter(
			    (vm_offset_t)bp->b_data,
			    bp->b_pages, 
			    bp->b_npages
			);
			bp->b_data = (caddr_t)((vm_offset_t)bp->b_data | 
			    (vm_offset_t)(bp->b_offset & PAGE_MASK));
		}
	}
	if (newbsize < bp->b_bufsize)
		bufspacewakeup();
	bp->b_bufsize = newbsize;	/* actual buffer allocation	*/
	bp->b_bcount = size;		/* requested buffer size	*/
	return 1;
}

/*
 *	biowait:
 *
 *	Wait for buffer I/O completion, returning error status.  The buffer
 *	is left locked and B_DONE on return.  B_EINTR is converted into a EINTR
 *	error and cleared.
 */
int
biowait(struct buf * bp)
{
	int s;

	s = splbio();
	while ((bp->b_flags & B_DONE) == 0) {
#if defined(NO_SCHEDULE_MODS)
		tsleep(bp, 0, "biowait", 0);
#else
		if (bp->b_flags & B_READ)
			tsleep(bp, 0, "biord", 0);
		else
			tsleep(bp, 0, "biowr", 0);
#endif
	}
	splx(s);
	if (bp->b_flags & B_EINTR) {
		bp->b_flags &= ~B_EINTR;
		return (EINTR);
	}
	if (bp->b_flags & B_ERROR) {
		return (bp->b_error ? bp->b_error : EIO);
	} else {
		return (0);
	}
}

/*
 *	biodone:
 *
 *	Finish I/O on a buffer, optionally calling a completion function.
 *	This is usually called from an interrupt so process blocking is
 *	not allowed.
 *
 *	biodone is also responsible for setting B_CACHE in a B_VMIO bp.
 *	In a non-VMIO bp, B_CACHE will be set on the next getblk() 
 *	assuming B_INVAL is clear.
 *
 *	For the VMIO case, we set B_CACHE if the op was a read and no
 *	read error occured, or if the op was a write.  B_CACHE is never
 *	set if the buffer is invalid or otherwise uncacheable.
 *
 *	biodone does not mess with B_INVAL, allowing the I/O routine or the
 *	initiator to leave B_INVAL set to brelse the buffer out of existance
 *	in the biodone routine.
 *
 *	b_dev is required to be reinitialized prior to the top level strategy
 *	call in a device stack.  To avoid improper reuse, biodone() sets
 *	b_dev to NODEV.
 */
void
biodone(struct buf * bp)
{
	int s, error;

	s = splbio();

	KASSERT(BUF_REFCNT(bp) > 0, ("biodone: bp %p not busy %d", bp, BUF_REFCNT(bp)));
	KASSERT(!(bp->b_flags & B_DONE), ("biodone: bp %p already done", bp));

	bp->b_flags |= B_DONE;
	bp->b_dev = NODEV;
	runningbufwakeup(bp);

	if (bp->b_flags & B_FREEBUF) {
		brelse(bp);
		splx(s);
		return;
	}

	if ((bp->b_flags & B_READ) == 0) {
		vwakeup(bp);
	}

	/* call optional completion function if requested */
	if (bp->b_flags & B_CALL) {
		bp->b_flags &= ~B_CALL;
		(*bp->b_iodone) (bp);
		splx(s);
		return;
	}
	if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_complete)
		(*bioops.io_complete)(bp);

	if (bp->b_flags & B_VMIO) {
		int i;
		vm_ooffset_t foff;
		vm_page_t m;
		vm_object_t obj;
		int iosize;
		struct vnode *vp = bp->b_vp;

		error = VOP_GETVOBJECT(vp, &obj);

#if defined(VFS_BIO_DEBUG)
		if (vp->v_holdcnt == 0) {
			panic("biodone: zero vnode hold count");
		}

		if (error) {
			panic("biodone: missing VM object");
		}

		if ((vp->v_flag & VOBJBUF) == 0) {
			panic("biodone: vnode is not setup for merged cache");
		}
#endif

		foff = bp->b_offset;
		KASSERT(bp->b_offset != NOOFFSET,
		    ("biodone: no buffer offset"));

		if (error) {
			panic("biodone: no object");
		}
#if defined(VFS_BIO_DEBUG)
		if (obj->paging_in_progress < bp->b_npages) {
			printf("biodone: paging in progress(%d) < bp->b_npages(%d)\n",
			    obj->paging_in_progress, bp->b_npages);
		}
#endif

		/*
		 * Set B_CACHE if the op was a normal read and no error
		 * occured.  B_CACHE is set for writes in the b*write()
		 * routines.
		 */
		iosize = bp->b_bcount - bp->b_resid;
		if ((bp->b_flags & (B_READ|B_FREEBUF|B_INVAL|B_NOCACHE|B_ERROR)) == B_READ) {
			bp->b_flags |= B_CACHE;
		}

		for (i = 0; i < bp->b_npages; i++) {
			int bogusflag = 0;
			int resid;

			resid = ((foff + PAGE_SIZE) & ~(off_t)PAGE_MASK) - foff;
			if (resid > iosize)
				resid = iosize;

			/*
			 * cleanup bogus pages, restoring the originals.  Since
			 * the originals should still be wired, we don't have
			 * to worry about interrupt/freeing races destroying
			 * the VM object association.
			 */
			m = bp->b_pages[i];
			if (m == bogus_page) {
				bogusflag = 1;
				m = vm_page_lookup(obj, OFF_TO_IDX(foff));
				if (m == NULL)
					panic("biodone: page disappeared");
				bp->b_pages[i] = m;
				pmap_qenter(trunc_page((vm_offset_t)bp->b_data), bp->b_pages, bp->b_npages);
			}
#if defined(VFS_BIO_DEBUG)
			if (OFF_TO_IDX(foff) != m->pindex) {
				printf(
"biodone: foff(%lu)/m->pindex(%d) mismatch\n",
				    (unsigned long)foff, m->pindex);
			}
#endif

			/*
			 * In the write case, the valid and clean bits are
			 * already changed correctly ( see bdwrite() ), so we 
			 * only need to do this here in the read case.
			 */
			if ((bp->b_flags & B_READ) && !bogusflag && resid > 0) {
				vfs_page_set_valid(bp, foff, i, m);
			}
			vm_page_flag_clear(m, PG_ZERO);

			/*
			 * when debugging new filesystems or buffer I/O methods, this
			 * is the most common error that pops up.  if you see this, you
			 * have not set the page busy flag correctly!!!
			 */
			if (m->busy == 0) {
				printf("biodone: page busy < 0, "
				    "pindex: %d, foff: 0x(%x,%x), "
				    "resid: %d, index: %d\n",
				    (int) m->pindex, (int)(foff >> 32),
						(int) foff & 0xffffffff, resid, i);
				if (!vn_isdisk(vp, NULL))
					printf(" iosize: %ld, lblkno: %d, flags: 0x%lx, npages: %d\n",
					    bp->b_vp->v_mount->mnt_stat.f_iosize,
					    (int) bp->b_lblkno,
					    bp->b_flags, bp->b_npages);
				else
					printf(" VDEV, lblkno: %d, flags: 0x%lx, npages: %d\n",
					    (int) bp->b_lblkno,
					    bp->b_flags, bp->b_npages);
				printf(" valid: 0x%x, dirty: 0x%x, wired: %d\n",
				    m->valid, m->dirty, m->wire_count);
				panic("biodone: page busy < 0");
			}
			vm_page_io_finish(m);
			vm_object_pip_subtract(obj, 1);
			foff = (foff + PAGE_SIZE) & ~(off_t)PAGE_MASK;
			iosize -= resid;
		}
		if (obj)
			vm_object_pip_wakeupn(obj, 0);
	}

	/*
	 * For asynchronous completions, release the buffer now. The brelse
	 * will do a wakeup there if necessary - so no need to do a wakeup
	 * here in the async case. The sync case always needs to do a wakeup.
	 */

	if (bp->b_flags & B_ASYNC) {
		if ((bp->b_flags & (B_NOCACHE | B_INVAL | B_ERROR | B_RELBUF)) != 0)
			brelse(bp);
		else
			bqrelse(bp);
	} else {
		wakeup(bp);
	}
	splx(s);
}

/*
 * This routine is called in lieu of iodone in the case of
 * incomplete I/O.  This keeps the busy status for pages
 * consistant.
 */
void
vfs_unbusy_pages(struct buf * bp)
{
	int i;

	runningbufwakeup(bp);
	if (bp->b_flags & B_VMIO) {
		struct vnode *vp = bp->b_vp;
		vm_object_t obj;

		VOP_GETVOBJECT(vp, &obj);

		for (i = 0; i < bp->b_npages; i++) {
			vm_page_t m = bp->b_pages[i];

			/*
			 * When restoring bogus changes the original pages
			 * should still be wired, so we are in no danger of
			 * losing the object association and do not need
			 * spl protection particularly.
			 */
			if (m == bogus_page) {
				m = vm_page_lookup(obj, OFF_TO_IDX(bp->b_offset) + i);
				if (!m) {
					panic("vfs_unbusy_pages: page missing");
				}
				bp->b_pages[i] = m;
				pmap_qenter(trunc_page((vm_offset_t)bp->b_data), bp->b_pages, bp->b_npages);
			}
			vm_object_pip_subtract(obj, 1);
			vm_page_flag_clear(m, PG_ZERO);
			vm_page_io_finish(m);
		}
		vm_object_pip_wakeupn(obj, 0);
	}
}

/*
 * vfs_page_set_valid:
 *
 *	Set the valid bits in a page based on the supplied offset.   The
 *	range is restricted to the buffer's size.
 *
 *	This routine is typically called after a read completes.
 */
static void
vfs_page_set_valid(struct buf *bp, vm_ooffset_t off, int pageno, vm_page_t m)
{
	vm_ooffset_t soff, eoff;

	/*
	 * Start and end offsets in buffer.  eoff - soff may not cross a
	 * page boundry or cross the end of the buffer.  The end of the
	 * buffer, in this case, is our file EOF, not the allocation size
	 * of the buffer.
	 */
	soff = off;
	eoff = (off + PAGE_SIZE) & ~(off_t)PAGE_MASK;
	if (eoff > bp->b_offset + bp->b_bcount)
		eoff = bp->b_offset + bp->b_bcount;

	/*
	 * Set valid range.  This is typically the entire buffer and thus the
	 * entire page.
	 */
	if (eoff > soff) {
		vm_page_set_validclean(
		    m,
		   (vm_offset_t) (soff & PAGE_MASK),
		   (vm_offset_t) (eoff - soff)
		);
	}
}

/*
 * This routine is called before a device strategy routine.
 * It is used to tell the VM system that paging I/O is in
 * progress, and treat the pages associated with the buffer
 * almost as being PG_BUSY.  Also the object paging_in_progress
 * flag is handled to make sure that the object doesn't become
 * inconsistant.
 *
 * Since I/O has not been initiated yet, certain buffer flags
 * such as B_ERROR or B_INVAL may be in an inconsistant state
 * and should be ignored.
 */
void
vfs_busy_pages(struct buf * bp, int clear_modify)
{
	int i, bogus;

	if (bp->b_flags & B_VMIO) {
		struct vnode *vp = bp->b_vp;
		vm_object_t obj;
		vm_ooffset_t foff;

		VOP_GETVOBJECT(vp, &obj);
		foff = bp->b_offset;
		KASSERT(bp->b_offset != NOOFFSET,
		    ("vfs_busy_pages: no buffer offset"));
		vfs_setdirty(bp);

retry:
		for (i = 0; i < bp->b_npages; i++) {
			vm_page_t m = bp->b_pages[i];
			if (vm_page_sleep_busy(m, FALSE, "vbpage"))
				goto retry;
		}

		bogus = 0;
		for (i = 0; i < bp->b_npages; i++) {
			vm_page_t m = bp->b_pages[i];

			vm_page_flag_clear(m, PG_ZERO);
			if ((bp->b_flags & B_CLUSTER) == 0) {
				vm_object_pip_add(obj, 1);
				vm_page_io_start(m);
			}

			/*
			 * When readying a buffer for a read ( i.e
			 * clear_modify == 0 ), it is important to do
			 * bogus_page replacement for valid pages in 
			 * partially instantiated buffers.  Partially 
			 * instantiated buffers can, in turn, occur when
			 * reconstituting a buffer from its VM backing store
			 * base.  We only have to do this if B_CACHE is
			 * clear ( which causes the I/O to occur in the
			 * first place ).  The replacement prevents the read
			 * I/O from overwriting potentially dirty VM-backed
			 * pages.  XXX bogus page replacement is, uh, bogus.
			 * It may not work properly with small-block devices.
			 * We need to find a better way.
			 */

			vm_page_protect(m, VM_PROT_NONE);
			if (clear_modify)
				vfs_page_set_valid(bp, foff, i, m);
			else if (m->valid == VM_PAGE_BITS_ALL &&
				(bp->b_flags & B_CACHE) == 0) {
				bp->b_pages[i] = bogus_page;
				bogus++;
			}
			foff = (foff + PAGE_SIZE) & ~(off_t)PAGE_MASK;
		}
		if (bogus)
			pmap_qenter(trunc_page((vm_offset_t)bp->b_data), bp->b_pages, bp->b_npages);
	}

	/*
	 * This is the easiest place to put the process accounting for the I/O
	 * for now.
	 */
	{
		struct proc *p;

		if ((p = curthread->td_proc) != NULL) {
			if (bp->b_flags & B_READ)
				p->p_stats->p_ru.ru_inblock++;
			else
				p->p_stats->p_ru.ru_oublock++;
		}
	}
}

/*
 * Tell the VM system that the pages associated with this buffer
 * are clean.  This is used for delayed writes where the data is
 * going to go to disk eventually without additional VM intevention.
 *
 * Note that while we only really need to clean through to b_bcount, we
 * just go ahead and clean through to b_bufsize.
 */
static void
vfs_clean_pages(struct buf * bp)
{
	int i;

	if (bp->b_flags & B_VMIO) {
		vm_ooffset_t foff;

		foff = bp->b_offset;
		KASSERT(bp->b_offset != NOOFFSET,
		    ("vfs_clean_pages: no buffer offset"));
		for (i = 0; i < bp->b_npages; i++) {
			vm_page_t m = bp->b_pages[i];
			vm_ooffset_t noff = (foff + PAGE_SIZE) & ~(off_t)PAGE_MASK;
			vm_ooffset_t eoff = noff;

			if (eoff > bp->b_offset + bp->b_bufsize)
				eoff = bp->b_offset + bp->b_bufsize;
			vfs_page_set_valid(bp, foff, i, m);
			/* vm_page_clear_dirty(m, foff & PAGE_MASK, eoff - foff); */
			foff = noff;
		}
	}
}

/*
 *	vfs_bio_set_validclean:
 *
 *	Set the range within the buffer to valid and clean.  The range is 
 *	relative to the beginning of the buffer, b_offset.  Note that b_offset
 *	itself may be offset from the beginning of the first page.
 */

void   
vfs_bio_set_validclean(struct buf *bp, int base, int size)
{
	if (bp->b_flags & B_VMIO) {
		int i;
		int n;

		/*
		 * Fixup base to be relative to beginning of first page.
		 * Set initial n to be the maximum number of bytes in the
		 * first page that can be validated.
		 */

		base += (bp->b_offset & PAGE_MASK);
		n = PAGE_SIZE - (base & PAGE_MASK);

		for (i = base / PAGE_SIZE; size > 0 && i < bp->b_npages; ++i) {
			vm_page_t m = bp->b_pages[i];

			if (n > size)
				n = size;

			vm_page_set_validclean(m, base & PAGE_MASK, n);
			base += n;
			size -= n;
			n = PAGE_SIZE;
		}
	}
}

/*
 *	vfs_bio_clrbuf:
 *
 *	clear a buffer.  This routine essentially fakes an I/O, so we need
 *	to clear B_ERROR and B_INVAL.
 *
 *	Note that while we only theoretically need to clear through b_bcount,
 *	we go ahead and clear through b_bufsize.
 */

void
vfs_bio_clrbuf(struct buf *bp)
{
	int i, mask = 0;
	caddr_t sa, ea;
	if ((bp->b_flags & (B_VMIO | B_MALLOC)) == B_VMIO) {
		bp->b_flags &= ~(B_INVAL|B_ERROR);
		if ((bp->b_npages == 1) && (bp->b_bufsize < PAGE_SIZE) &&
		    (bp->b_offset & PAGE_MASK) == 0) {
			mask = (1 << (bp->b_bufsize / DEV_BSIZE)) - 1;
			if ((bp->b_pages[0]->valid & mask) == mask) {
				bp->b_resid = 0;
				return;
			}
			if (((bp->b_pages[0]->flags & PG_ZERO) == 0) &&
			    ((bp->b_pages[0]->valid & mask) == 0)) {
				bzero(bp->b_data, bp->b_bufsize);
				bp->b_pages[0]->valid |= mask;
				bp->b_resid = 0;
				return;
			}
		}
		ea = sa = bp->b_data;
		for(i=0;i<bp->b_npages;i++,sa=ea) {
			int j = ((vm_offset_t)sa & PAGE_MASK) / DEV_BSIZE;
			ea = (caddr_t)trunc_page((vm_offset_t)sa + PAGE_SIZE);
			ea = (caddr_t)(vm_offset_t)ulmin(
			    (u_long)(vm_offset_t)ea,
			    (u_long)(vm_offset_t)bp->b_data + bp->b_bufsize);
			mask = ((1 << ((ea - sa) / DEV_BSIZE)) - 1) << j;
			if ((bp->b_pages[i]->valid & mask) == mask)
				continue;
			if ((bp->b_pages[i]->valid & mask) == 0) {
				if ((bp->b_pages[i]->flags & PG_ZERO) == 0) {
					bzero(sa, ea - sa);
				}
			} else {
				for (; sa < ea; sa += DEV_BSIZE, j++) {
					if (((bp->b_pages[i]->flags & PG_ZERO) == 0) &&
						(bp->b_pages[i]->valid & (1<<j)) == 0)
						bzero(sa, DEV_BSIZE);
				}
			}
			bp->b_pages[i]->valid |= mask;
			vm_page_flag_clear(bp->b_pages[i], PG_ZERO);
		}
		bp->b_resid = 0;
	} else {
		clrbuf(bp);
	}
}

/*
 * vm_hold_load_pages and vm_hold_unload pages get pages into
 * a buffers address space.  The pages are anonymous and are
 * not associated with a file object.
 */
void
vm_hold_load_pages(struct buf * bp, vm_offset_t from, vm_offset_t to)
{
	vm_offset_t pg;
	vm_page_t p;
	int index;

	to = round_page(to);
	from = round_page(from);
	index = (from - trunc_page((vm_offset_t)bp->b_data)) >> PAGE_SHIFT;

	for (pg = from; pg < to; pg += PAGE_SIZE, index++) {

tryagain:

		/*
		 * note: must allocate system pages since blocking here
		 * could intefere with paging I/O, no matter which
		 * process we are.
		 */
		p = vm_page_alloc(kernel_object,
			((pg - VM_MIN_KERNEL_ADDRESS) >> PAGE_SHIFT),
			VM_ALLOC_NORMAL | VM_ALLOC_SYSTEM);
		if (!p) {
			vm_pageout_deficit += (to - from) >> PAGE_SHIFT;
			VM_WAIT;
			goto tryagain;
		}
		vm_page_wire(p);
		p->valid = VM_PAGE_BITS_ALL;
		vm_page_flag_clear(p, PG_ZERO);
		pmap_kenter(pg, VM_PAGE_TO_PHYS(p));
		bp->b_pages[index] = p;
		vm_page_wakeup(p);
	}
	bp->b_npages = index;
}

void
vm_hold_free_pages(struct buf * bp, vm_offset_t from, vm_offset_t to)
{
	vm_offset_t pg;
	vm_page_t p;
	int index, newnpages;

	from = round_page(from);
	to = round_page(to);
	newnpages = index = (from - trunc_page((vm_offset_t)bp->b_data)) >> PAGE_SHIFT;

	for (pg = from; pg < to; pg += PAGE_SIZE, index++) {
		p = bp->b_pages[index];
		if (p && (index < bp->b_npages)) {
			if (p->busy) {
				printf("vm_hold_free_pages: blkno: %d, lblkno: %d\n",
					bp->b_blkno, bp->b_lblkno);
			}
			bp->b_pages[index] = NULL;
			pmap_kremove(pg);
			vm_page_busy(p);
			vm_page_unwire(p, 0);
			vm_page_free(p);
		}
	}
	bp->b_npages = newnpages;
}

/*
 * Map an IO request into kernel virtual address space.
 *
 * All requests are (re)mapped into kernel VA space.
 * Notice that we use b_bufsize for the size of the buffer
 * to be mapped.  b_bcount might be modified by the driver.
 */
int
vmapbuf(struct buf *bp)
{
	caddr_t addr, v, kva;
	vm_paddr_t pa;
	int pidx;
	int i;
	struct vm_page *m;

	if ((bp->b_flags & B_PHYS) == 0)
		panic("vmapbuf");
	if (bp->b_bufsize < 0)
		return (-1);
	for (v = bp->b_saveaddr,
		     addr = (caddr_t)trunc_page((vm_offset_t)bp->b_data),
		     pidx = 0;
	     addr < bp->b_data + bp->b_bufsize;
	     addr += PAGE_SIZE, v += PAGE_SIZE, pidx++) {
		/*
		 * Do the vm_fault if needed; do the copy-on-write thing
		 * when reading stuff off device into memory.
		 */
retry:
		i = vm_fault_quick((addr >= bp->b_data) ? addr : bp->b_data,
			(bp->b_flags&B_READ)?(VM_PROT_READ|VM_PROT_WRITE):VM_PROT_READ);
		if (i < 0) {
			for (i = 0; i < pidx; ++i) {
			    vm_page_unhold(bp->b_pages[i]);
			    bp->b_pages[i] = NULL;
			}
			return(-1);
		}

		/*
		 * WARNING!  If sparc support is MFCd in the future this will
		 * have to be changed from pmap_kextract() to pmap_extract()
		 * ala -current.
		 */
#ifdef __sparc64__
#error "If MFCing sparc support use pmap_extract"
#endif
		pa = pmap_kextract((vm_offset_t)addr);
		if (pa == 0) {
			printf("vmapbuf: warning, race against user address during I/O");
			goto retry;
		}
		m = PHYS_TO_VM_PAGE(pa);
		vm_page_hold(m);
		bp->b_pages[pidx] = m;
	}
	if (pidx > btoc(MAXPHYS))
		panic("vmapbuf: mapped more than MAXPHYS");
	pmap_qenter((vm_offset_t)bp->b_saveaddr, bp->b_pages, pidx);
	
	kva = bp->b_saveaddr;
	bp->b_npages = pidx;
	bp->b_saveaddr = bp->b_data;
	bp->b_data = kva + (((vm_offset_t) bp->b_data) & PAGE_MASK);
	return(0);
}

/*
 * Free the io map PTEs associated with this IO operation.
 * We also invalidate the TLB entries and restore the original b_addr.
 */
void
vunmapbuf(bp)
	struct buf *bp;
{
	int pidx;
	int npages;
	vm_page_t *m;

	if ((bp->b_flags & B_PHYS) == 0)
		panic("vunmapbuf");

	npages = bp->b_npages;
	pmap_qremove(trunc_page((vm_offset_t)bp->b_data),
		     npages);
	m = bp->b_pages;
	for (pidx = 0; pidx < npages; pidx++)
		vm_page_unhold(*m++);

	bp->b_data = bp->b_saveaddr;
}

#include "opt_ddb.h"
#ifdef DDB
#include <ddb/ddb.h>

DB_SHOW_COMMAND(buffer, db_show_buffer)
{
	/* get args */
	struct buf *bp = (struct buf *)addr;

	if (!have_addr) {
		db_printf("usage: show buffer <addr>\n");
		return;
	}

	db_printf("b_flags = 0x%b\n", (u_int)bp->b_flags, PRINT_BUF_FLAGS);
	db_printf("b_error = %d, b_bufsize = %ld, b_bcount = %ld, "
		  "b_resid = %ld\nb_dev = (%d,%d), b_data = %p, "
		  "b_blkno = %d, b_pblkno = %d\n",
		  bp->b_error, bp->b_bufsize, bp->b_bcount, bp->b_resid,
		  major(bp->b_dev), minor(bp->b_dev),
		  bp->b_data, bp->b_blkno, bp->b_pblkno);
	if (bp->b_npages) {
		int i;
		db_printf("b_npages = %d, pages(OBJ, IDX, PA): ", bp->b_npages);
		for (i = 0; i < bp->b_npages; i++) {
			vm_page_t m;
			m = bp->b_pages[i];
			db_printf("(%p, 0x%lx, 0x%lx)", (void *)m->object,
			    (u_long)m->pindex, (u_long)VM_PAGE_TO_PHYS(m));
			if ((i + 1) < bp->b_npages)
				db_printf(",");
		}
		db_printf("\n");
	}
}
#endif /* DDB */