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vfs_bio.c

/*-
 * Copyright (c) 2004 Poul-Henning Kamp
 * 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, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * 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/cdefs.h>
__FBSDID("$FreeBSD: src/sys/kern/vfs_bio.c,v 1.491.2.12 2007/06/11 11:27:04 kib Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/bio.h>
#include <sys/conf.h>
#include <sys/buf.h>
#include <sys/devicestat.h>
#include <sys/eventhandler.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/mutex.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/sysctl.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <geom/geom.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 "opt_directio.h"
#include "opt_swap.h"

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

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

struct      buf_ops buf_ops_bio = {
      .bop_name   =     "buf_ops_bio",
      .bop_write  =     bufwrite,
      .bop_strategy     =     bufstrategy,
      .bop_sync   =     bufsync,
      .bop_bdflush      =     bufbdflush,
};

/*
 * XXX buf is global because kern_shutdown.c and ffs_checkoverlap has
 * carnal knowledge of buffers.  This knowledge should be moved to vfs_bio.c.
 */
struct buf *buf;        /* buffer header pool */

static struct proc *bufdaemonproc;

static int inmem(struct vnode *vp, daddr_t blkno);
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 int vfs_bio_clcheck(struct vnode *vp, int size,
            daddr_t lblkno, daddr_t blkno);
static int flushbufqueues(int flushdeps);
static void buf_daemon(void);
static void bremfreel(struct buf *bp);

int vmiodirenable = TRUE;
SYSCTL_INT(_vfs, OID_AUTO, vmiodirenable, CTLFLAG_RW, &vmiodirenable, 0,
    "Use the VM system for directory writes");
int runningbufspace;
SYSCTL_INT(_vfs, OID_AUTO, runningbufspace, CTLFLAG_RD, &runningbufspace, 0,
    "Amount of presently outstanding async buffer io");
static int bufspace;
SYSCTL_INT(_vfs, OID_AUTO, bufspace, CTLFLAG_RD, &bufspace, 0,
    "KVA memory used for bufs");
static int maxbufspace;
SYSCTL_INT(_vfs, OID_AUTO, maxbufspace, CTLFLAG_RD, &maxbufspace, 0,
    "Maximum allowed value of bufspace (including buf_daemon)");
static int bufmallocspace;
SYSCTL_INT(_vfs, OID_AUTO, bufmallocspace, CTLFLAG_RD, &bufmallocspace, 0,
    "Amount of malloced memory for buffers");
static int maxbufmallocspace;
SYSCTL_INT(_vfs, OID_AUTO, maxmallocbufspace, CTLFLAG_RW, &maxbufmallocspace, 0,
    "Maximum amount of malloced memory for buffers");
static int lobufspace;
SYSCTL_INT(_vfs, OID_AUTO, lobufspace, CTLFLAG_RD, &lobufspace, 0,
    "Minimum amount of buffers we want to have");
int hibufspace;
SYSCTL_INT(_vfs, OID_AUTO, hibufspace, CTLFLAG_RD, &hibufspace, 0,
    "Maximum allowed value of bufspace (excluding buf_daemon)");
static int bufreusecnt;
SYSCTL_INT(_vfs, OID_AUTO, bufreusecnt, CTLFLAG_RW, &bufreusecnt, 0,
    "Number of times we have reused a buffer");
static int buffreekvacnt;
SYSCTL_INT(_vfs, OID_AUTO, buffreekvacnt, CTLFLAG_RW, &buffreekvacnt, 0,
    "Number of times we have freed the KVA space from some buffer");
static int bufdefragcnt;
SYSCTL_INT(_vfs, OID_AUTO, bufdefragcnt, CTLFLAG_RW, &bufdefragcnt, 0,
    "Number of times we have had to repeat buffer allocation to defragment");
static int lorunningspace;
SYSCTL_INT(_vfs, OID_AUTO, lorunningspace, CTLFLAG_RW, &lorunningspace, 0,
    "Minimum preferred space used for in-progress I/O");
static int hirunningspace;
SYSCTL_INT(_vfs, OID_AUTO, hirunningspace, CTLFLAG_RW, &hirunningspace, 0,
    "Maximum amount of space to use for in-progress I/O");
int dirtybufferflushes;
SYSCTL_INT(_vfs, OID_AUTO, dirtybufferflushes, CTLFLAG_RW, &dirtybufferflushes,
    0, "Number of bdwrite to bawrite conversions to limit dirty buffers");
int bdwriteskip;
SYSCTL_INT(_vfs, OID_AUTO, bdwriteskip, CTLFLAG_RW, &bdwriteskip,
    0, "Number of buffers supplied to bdwrite with snapshot deadlock risk");
int altbufferflushes;
SYSCTL_INT(_vfs, OID_AUTO, altbufferflushes, CTLFLAG_RW, &altbufferflushes,
    0, "Number of fsync flushes to limit dirty buffers");
static int recursiveflushes;
SYSCTL_INT(_vfs, OID_AUTO, recursiveflushes, CTLFLAG_RW, &recursiveflushes,
    0, "Number of flushes skipped due to being recursive");
static int numdirtybuffers;
SYSCTL_INT(_vfs, OID_AUTO, numdirtybuffers, CTLFLAG_RD, &numdirtybuffers, 0,
    "Number of buffers that are dirty (has unwritten changes) at the moment");
static int lodirtybuffers;
SYSCTL_INT(_vfs, OID_AUTO, lodirtybuffers, CTLFLAG_RW, &lodirtybuffers, 0,
    "How many buffers we want to have free before bufdaemon can sleep");
static int hidirtybuffers;
SYSCTL_INT(_vfs, OID_AUTO, hidirtybuffers, CTLFLAG_RW, &hidirtybuffers, 0,
    "When the number of dirty buffers is considered severe");
int dirtybufthresh;
SYSCTL_INT(_vfs, OID_AUTO, dirtybufthresh, CTLFLAG_RW, &dirtybufthresh,
    0, "Number of bdwrite to bawrite conversions to clear dirty buffers");
static int numfreebuffers;
SYSCTL_INT(_vfs, OID_AUTO, numfreebuffers, CTLFLAG_RD, &numfreebuffers, 0,
    "Number of free buffers");
static int lofreebuffers;
SYSCTL_INT(_vfs, OID_AUTO, lofreebuffers, CTLFLAG_RW, &lofreebuffers, 0,
   "XXX Unused");
static int hifreebuffers;
SYSCTL_INT(_vfs, OID_AUTO, hifreebuffers, CTLFLAG_RW, &hifreebuffers, 0,
   "XXX Complicatedly unused");
static int getnewbufcalls;
SYSCTL_INT(_vfs, OID_AUTO, getnewbufcalls, CTLFLAG_RW, &getnewbufcalls, 0,
   "Number of calls to getnewbuf");
static int getnewbufrestarts;
SYSCTL_INT(_vfs, OID_AUTO, getnewbufrestarts, CTLFLAG_RW, &getnewbufrestarts, 0,
    "Number of times getnewbuf has had to restart a buffer aquisition");

/*
 * Wakeup point for bufdaemon, as well as indicator of whether it is already
 * active.  Set to 1 when the bufdaemon is already "on" the queue, 0 when it
 * is idling.
 */
static int bd_request;

/*
 * This lock synchronizes access to bd_request.
 */
static struct mtx bdlock;

/*
 * 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;

/*
 * Synchronization (sleep/wakeup) variable for active buffer space requests.
 * Set when wait starts, cleared prior to wakeup().
 * Used in runningbufwakeup() and waitrunningbufspace().
 */
static int runningbufreq;

/*
 * This lock protects the runningbufreq and synchronizes runningbufwakeup and
 * waitrunningbufspace().
 */
static struct mtx rbreqlock;

/* 
 * Synchronization (sleep/wakeup) variable for buffer requests.
 * Can contain the VFS_BIO_NEED flags defined below; setting/clearing is done
 * by and/or.
 * Used in numdirtywakeup(), bufspacewakeup(), bufcountwakeup(), bwillwrite(),
 * getnewbuf(), and getblk().
 */
static int needsbuffer;

/*
 * Lock that protects needsbuffer and the sleeps/wakeups surrounding it.
 */
static struct mtx nblock;

/*
 * Lock that protects against bwait()/bdone()/B_DONE races.
 */

static struct mtx bdonelock;

/*
 * Definitions for the buffer free lists.
 */
#define BUFFER_QUEUES   5     /* number of free buffer queues */

#define QUEUE_NONE      0     /* on no queue */
#define QUEUE_CLEAN     1     /* non-B_DELWRI buffers */
#define QUEUE_DIRTY     2     /* B_DELWRI buffers */
#define QUEUE_EMPTYKVA  3     /* empty buffer headers w/KVA assignment */
#define QUEUE_EMPTY     4     /* empty buffer headers */

/* Queues for free buffers with various properties */
static TAILQ_HEAD(bqueues, buf) bufqueues[BUFFER_QUEUES] = { { 0 } };

/* Lock for the bufqueues */
static struct mtx bqlock;

/*
 * Single global constant for BUF_WMESG, to avoid getting multiple references.
 * buf_wmesg is referred from macros.
 */
const char *buf_wmesg = BUF_WMESG;

#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 */

#ifdef DIRECTIO
extern void ffs_rawread_setup(void);
#endif /* DIRECTIO */
/*
 *    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) {
            mtx_lock(&nblock);
            if (needsbuffer & VFS_BIO_NEED_DIRTYFLUSH) {
                  needsbuffer &= ~VFS_BIO_NEED_DIRTYFLUSH;
                  wakeup(&needsbuffer);
            }
            mtx_unlock(&nblock);
      }
}

/*
 *    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.
       */
      mtx_lock(&nblock);
      if (needsbuffer & VFS_BIO_NEED_BUFSPACE) {
            needsbuffer &= ~VFS_BIO_NEED_BUFSPACE;
            wakeup(&needsbuffer);
      }
      mtx_unlock(&nblock);
}

/*
 * runningbufwakeup() - in-progress I/O accounting.
 *
 */
void
runningbufwakeup(struct buf *bp)
{

      if (bp->b_runningbufspace) {
            atomic_subtract_int(&runningbufspace, bp->b_runningbufspace);
            bp->b_runningbufspace = 0;
            mtx_lock(&rbreqlock);
            if (runningbufreq && runningbufspace <= lorunningspace) {
                  runningbufreq = 0;
                  wakeup(&runningbufreq);
            }
            mtx_unlock(&rbreqlock);
      }
}

/*
 *    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) 
{

      atomic_add_int(&numfreebuffers, 1);
      mtx_lock(&nblock);
      if (needsbuffer) {
            needsbuffer &= ~VFS_BIO_NEED_ANY;
            if (numfreebuffers >= hifreebuffers)
                  needsbuffer &= ~VFS_BIO_NEED_FREE;
            wakeup(&needsbuffer);
      }
      mtx_unlock(&nblock);
}

/*
 *    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.
 */
void
waitrunningbufspace(void)
{

      mtx_lock(&rbreqlock);
      while (runningbufspace > hirunningspace) {
            ++runningbufreq;
            msleep(&runningbufreq, &rbreqlock, PVM, "wdrain", 0);
      }
      mtx_unlock(&rbreqlock);
}


/*
 *    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)
{

      VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
      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;
      }
}

/* Wake up the buffer deamon if necessary */
static __inline
void
bd_wakeup(int dirtybuflevel)
{

      mtx_lock(&bdlock);
      if (bd_request == 0 && numdirtybuffers >= dirtybuflevel) {
            bd_request = 1;
            wakeup(&bd_request);
      }
      mtx_unlock(&bdlock);
}

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

static __inline
void
bd_speedup(void)
{

      bd_wakeup(1);
}

/*
 * Calculating buffer cache scaling values and reserve space for buffer
 * headers.  This is called during low level kernel initialization and
 * may be called more then once.  We CANNOT write to the memory area
 * being reserved at this time.
 */
caddr_t
kern_vfs_bio_buffer_alloc(caddr_t v, long physmem_est)
{

      /*
       * physmem_est is in pages.  Convert it to kilobytes (assumes
       * PAGE_SIZE is >= 1K)
       */
      physmem_est = physmem_est * (PAGE_SIZE / 1024);

      /*
       * The nominal buffer size (and minimum KVA allocation) is BKVASIZE.
       * For the first 64MB of ram nominally allocate sufficient buffers to
       * cover 1/4 of our ram.  Beyond the first 64MB allocate additional
       * buffers to cover 1/20 of our ram over 64MB.  When auto-sizing
       * the buffer cache we limit the eventual kva reservation to
       * maxbcache bytes.
       *
       * factor represents the 1/4 x ram conversion.
       */
      if (nbuf == 0) {
            int factor = 4 * BKVASIZE / 1024;

            nbuf = 50;
            if (physmem_est > 4096)
                  nbuf += min((physmem_est - 4096) / factor,
                      65536 / factor);
            if (physmem_est > 65536)
                  nbuf += (physmem_est - 65536) * 2 / (factor * 5);

            if (maxbcache && nbuf > maxbcache / BKVASIZE)
                  nbuf = maxbcache / BKVASIZE;
      }

#if 0
      /*
       * Do not allow the buffer_map to be more then 1/2 the size of the
       * kernel_map.
       */
      if (nbuf > (kernel_map->max_offset - kernel_map->min_offset) / 
          (BKVASIZE * 2)) {
            nbuf = (kernel_map->max_offset - kernel_map->min_offset) / 
                (BKVASIZE * 2);
            printf("Warning: nbufs capped at %d\n", nbuf);
      }
#endif

      /*
       * swbufs are used as temporary holders for I/O, such as paging I/O.
       * We have no less then 16 and no more then 256.
       */
      nswbuf = max(min(nbuf/4, 256), 16);
#ifdef NSWBUF_MIN
      if (nswbuf < NSWBUF_MIN)
            nswbuf = NSWBUF_MIN;
#endif
#ifdef DIRECTIO
      ffs_rawread_setup();
#endif

      /*
       * Reserve space for the buffer cache buffers
       */
      swbuf = (void *)v;
      v = (caddr_t)(swbuf + nswbuf);
      buf = (void *)v;
      v = (caddr_t)(buf + nbuf);

      return(v);
}

/* Initialize the buffer subsystem.  Called before use of any buffers. */
void
bufinit(void)
{
      struct buf *bp;
      int i;

      mtx_init(&bqlock, "buf queue lock", NULL, MTX_DEF);
      mtx_init(&rbreqlock, "runningbufspace lock", NULL, MTX_DEF);
      mtx_init(&nblock, "needsbuffer lock", NULL, MTX_DEF);
      mtx_init(&bdlock, "buffer daemon lock", NULL, MTX_DEF);
      mtx_init(&bdonelock, "bdone lock", NULL, MTX_DEF);

      /* 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_rcred = NOCRED;
            bp->b_wcred = NOCRED;
            bp->b_qindex = QUEUE_EMPTY;
            bp->b_vflags = 0;
            bp->b_xflags = 0;
            LIST_INIT(&bp->b_dep);
            BUF_LOCKINIT(bp);
            TAILQ_INSERT_TAIL(&bufqueues[QUEUE_EMPTY], bp, b_freelist);
      }

      /*
       * 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;
      dirtybufthresh = hidirtybuffers * 9 / 10;
      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_page = vm_page_alloc(NULL, 0, VM_ALLOC_NOOBJ |
          VM_ALLOC_NORMAL | VM_ALLOC_WIRED);
}

/*
 * bfreekva() - free the kva allocation for a buffer.
 *
 *    Since this call frees up buffer space, we call bufspacewakeup().
 */
static void
bfreekva(struct buf *bp)
{

      if (bp->b_kvasize) {
            atomic_add_int(&buffreekvacnt, 1);
            atomic_subtract_int(&bufspace, bp->b_kvasize);
            vm_map_lock(buffer_map);
            vm_map_delete(buffer_map,
                (vm_offset_t) bp->b_kvabase,
                (vm_offset_t) bp->b_kvabase + bp->b_kvasize
            );
            vm_map_unlock(buffer_map);
            bp->b_kvasize = 0;
            bufspacewakeup();
      }
}

/*
 *    bremfree:
 *
 *    Mark the buffer for removal from the appropriate free list in brelse.
 *    
 */
void
bremfree(struct buf *bp)
{

      CTR3(KTR_BUF, "bremfree(%p) vp %p flags %X", bp, bp->b_vp, bp->b_flags);
      KASSERT(BUF_REFCNT(bp), ("bremfree: buf must be locked."));
      KASSERT((bp->b_flags & B_REMFREE) == 0,
          ("bremfree: buffer %p already marked for delayed removal.", bp));
      KASSERT(bp->b_qindex != QUEUE_NONE,
          ("bremfree: buffer %p not on a queue.", bp));

      bp->b_flags |= B_REMFREE;
      /* Fixup numfreebuffers count.  */
      if ((bp->b_flags & B_INVAL) || (bp->b_flags & B_DELWRI) == 0)
            atomic_subtract_int(&numfreebuffers, 1);
}

/*
 *    bremfreef:
 *
 *    Force an immediate removal from a free list.  Used only in nfs when
 *    it abuses the b_freelist pointer.
 */
void
bremfreef(struct buf *bp)
{
      mtx_lock(&bqlock);
      bremfreel(bp);
      mtx_unlock(&bqlock);
}

/*
 *    bremfreel:
 *
 *    Removes a buffer from the free list, must be called with the
 *    bqlock held.
 */
static void
bremfreel(struct buf *bp)
{
      CTR3(KTR_BUF, "bremfreel(%p) vp %p flags %X",
          bp, bp->b_vp, bp->b_flags);
      KASSERT(BUF_REFCNT(bp), ("bremfreel: buffer %p not locked.", bp));
      KASSERT(bp->b_qindex != QUEUE_NONE,
          ("bremfreel: buffer %p not on a queue.", bp));
      mtx_assert(&bqlock, MA_OWNED);

      TAILQ_REMOVE(&bufqueues[bp->b_qindex], bp, b_freelist);
      bp->b_qindex = QUEUE_NONE;
      /*
       * If this was a delayed bremfree() we only need to remove the buffer
       * from the queue and return the stats are already done.
       */
      if (bp->b_flags & B_REMFREE) {
            bp->b_flags &= ~B_REMFREE;
            return;
      }
      /*
       * Fixup numfreebuffers count.  If the buffer is invalid or not
       * delayed-write, the buffer was free and we must decrement
       * numfreebuffers.
       */
      if ((bp->b_flags & B_INVAL) || (bp->b_flags & B_DELWRI) == 0)
            atomic_subtract_int(&numfreebuffers, 1);
}


/*
 * Get a buffer with the specified data.  Look in the cache first.  We
 * must clear BIO_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() ).  This is really just a special case of breadn().
 */
int
bread(struct vnode * vp, daddr_t blkno, int size, struct ucred * cred,
    struct buf **bpp)
{

      return (breadn(vp, blkno, size, 0, 0, 0, cred, bpp));
}

/*
 * Operates like bread, but also starts asynchronous I/O on
 * read-ahead blocks.  We must clear BIO_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 ucred * cred, struct buf **bpp)
{
      struct buf *bp, *rabp;
      int i;
      int rv = 0, readwait = 0;

      CTR3(KTR_BUF, "breadn(%p, %jd, %d)", vp, blkno, size);
      *bpp = bp = getblk(vp, blkno, size, 0, 0, 0);

      /* if not found in cache, do some I/O */
      if ((bp->b_flags & B_CACHE) == 0) {
            if (curthread != PCPU_GET(idlethread))
                  curthread->td_proc->p_stats->p_ru.ru_inblock++;
            bp->b_iocmd = BIO_READ;
            bp->b_flags &= ~B_INVAL;
            bp->b_ioflags &= ~BIO_ERROR;
            if (bp->b_rcred == NOCRED && cred != NOCRED)
                  bp->b_rcred = crhold(cred);
            vfs_busy_pages(bp, 0);
            bp->b_iooffset = dbtob(bp->b_blkno);
            bstrategy(bp);
            ++readwait;
      }

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

            if ((rabp->b_flags & B_CACHE) == 0) {
                  if (curthread != PCPU_GET(idlethread))
                        curthread->td_proc->p_stats->p_ru.ru_inblock++;
                  rabp->b_flags |= B_ASYNC;
                  rabp->b_flags &= ~B_INVAL;
                  rabp->b_ioflags &= ~BIO_ERROR;
                  rabp->b_iocmd = BIO_READ;
                  if (rabp->b_rcred == NOCRED && cred != NOCRED)
                        rabp->b_rcred = crhold(cred);
                  vfs_busy_pages(rabp, 0);
                  BUF_KERNPROC(rabp);
                  rabp->b_iooffset = dbtob(rabp->b_blkno);
                  bstrategy(rabp);
            } else {
                  brelse(rabp);
            }
      }

      if (readwait) {
            rv = bufwait(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
bufwrite(struct buf *bp)
{
      int oldflags;
      struct vnode *vp;
      int vp_md;

      CTR3(KTR_BUF, "bufwrite(%p) vp %p flags %X", bp, bp->b_vp, bp->b_flags);
      if (bp->b_flags & B_INVAL) {
            brelse(bp);
            return (0);
      }

      oldflags = bp->b_flags;

      if (BUF_REFCNT(bp) == 0)
            panic("bufwrite: buffer is not busy???");
      KASSERT(!(bp->b_vflags & BV_BKGRDINPROG),
          ("FFS background buffer should not get here %p", bp));

      vp = bp->b_vp;
      if (vp)
            vp_md = vp->v_vflag & VV_MD;
      else
            vp_md = 0;

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

      bp->b_flags &= ~B_DONE;
      bp->b_ioflags &= ~BIO_ERROR;
      bp->b_flags |= B_CACHE;
      bp->b_iocmd = BIO_WRITE;

      bufobj_wref(bp->b_bufobj);
      vfs_busy_pages(bp, 1);

      /*
       * Normal bwrites pipeline writes
       */
      bp->b_runningbufspace = bp->b_bufsize;
      atomic_add_int(&runningbufspace, bp->b_runningbufspace);

      if (curthread != PCPU_GET(idlethread))
            curthread->td_proc->p_stats->p_ru.ru_oublock++;
      if (oldflags & B_ASYNC)
            BUF_KERNPROC(bp);
      bp->b_iooffset = dbtob(bp->b_blkno);
      bstrategy(bp);

      if ((oldflags & B_ASYNC) == 0) {
            int rtval = bufwait(bp);
            brelse(bp);
            return (rtval);
      } else {
            /*
             * don't allow the async write to saturate the I/O
             * system.  We will not deadlock here because
             * we are blocking waiting for I/O that is already in-progress
             * to complete. We do not block here if it is the update
             * or syncer daemon trying to clean up as that can lead
             * to deadlock.
             */
            if ((curthread->td_pflags & TDP_NORUNNINGBUF) == 0 && !vp_md)
                  waitrunningbufspace();
      }

      return (0);
}

void
bufbdflush(struct bufobj *bo, struct buf *bp)
{
      struct buf *nbp;

      if (bo->bo_dirty.bv_cnt > dirtybufthresh + 10) {
            (void) VOP_FSYNC(bp->b_vp, MNT_NOWAIT, curthread);
            altbufferflushes++;
      } else if (bo->bo_dirty.bv_cnt > dirtybufthresh) {
            BO_LOCK(bo);
            /*
             * Try to find a buffer to flush.
             */
            TAILQ_FOREACH(nbp, &bo->bo_dirty.bv_hd, b_bobufs) {
                  if ((nbp->b_vflags & BV_BKGRDINPROG) ||
                      BUF_LOCK(nbp,
                             LK_EXCLUSIVE | LK_NOWAIT, NULL))
                        continue;
                  if (bp == nbp)
                        panic("bdwrite: found ourselves");
                  BO_UNLOCK(bo);
                  /* Don't countdeps with the bo lock held. */
                  if (buf_countdeps(nbp, 0)) {
                        BO_LOCK(bo);
                        BUF_UNLOCK(nbp);
                        continue;
                  }
                  if (nbp->b_flags & B_CLUSTEROK) {
                        vfs_bio_awrite(nbp);
                  } else {
                        bremfree(nbp);
                        bawrite(nbp);
                  }
                  dirtybufferflushes++;
                  break;
            }
            if (nbp == NULL)
                  BO_UNLOCK(bo);
      }
}

/*
 * 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)
{
      struct thread *td = curthread;
      struct vnode *vp;
      struct bufobj *bo;

      CTR3(KTR_BUF, "bdwrite(%p) vp %p flags %X", bp, bp->b_vp, bp->b_flags);
      KASSERT(bp->b_bufobj != NULL, ("No b_bufobj %p", bp));
      KASSERT(BUF_REFCNT(bp) != 0, ("bdwrite: buffer is not busy"));

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

      /*
       * If we have too many dirty buffers, don't create any more.
       * If we are wildly over our limit, then force a complete
       * cleanup. Otherwise, just keep the situation from getting
       * out of control. Note that we have to avoid a recursive
       * disaster and not try to clean up after our own cleanup!
       */
      vp = bp->b_vp;
      bo = bp->b_bufobj;
      if ((td->td_pflags & (TDP_COWINPROGRESS|TDP_INBDFLUSH)) == 0) {
            td->td_pflags |= TDP_INBDFLUSH;
            BO_BDFLUSH(bo, bp);
            td->td_pflags &= ~TDP_INBDFLUSH;
      } else
            recursiveflushes++;

      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 (vp->v_type != VCHR && bp->b_lblkno == bp->b_blkno) {
            VOP_BMAP(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 BIO_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.
 *
 *    The buffer must be on QUEUE_NONE.
 */
void
bdirty(struct buf *bp)
{

      CTR3(KTR_BUF, "bdirty(%p) vp %p flags %X",
          bp, bp->b_vp, bp->b_flags);
      KASSERT(BUF_REFCNT(bp) == 1, ("bdirty: bp %p not locked",bp));
      KASSERT(bp->b_bufobj != NULL, ("No b_bufobj %p", bp));
      KASSERT(bp->b_flags & B_REMFREE || bp->b_qindex == QUEUE_NONE,
          ("bdirty: buffer %p still on queue %d", bp, bp->b_qindex));
      bp->b_flags &= ~(B_RELBUF);
      bp->b_iocmd = BIO_WRITE;

      if ((bp->b_flags & B_DELWRI) == 0) {
            bp->b_flags |= /* XXX B_DONE | */ B_DELWRI;
            reassignbuf(bp);
            atomic_add_int(&numdirtybuffers, 1);
            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.
 *    
 *    The buffer must be on QUEUE_NONE.
 */

void
bundirty(struct buf *bp)
{

      CTR3(KTR_BUF, "bundirty(%p) vp %p flags %X", bp, bp->b_vp, bp->b_flags);
      KASSERT(bp->b_bufobj != NULL, ("No b_bufobj %p", bp));
      KASSERT(bp->b_flags & B_REMFREE || bp->b_qindex == QUEUE_NONE,
          ("bundirty: buffer %p still on queue %d", bp, bp->b_qindex));
      KASSERT(BUF_REFCNT(bp) == 1, ("bundirty: bp %p not locked",bp));

      if (bp->b_flags & B_DELWRI) {
            bp->b_flags &= ~B_DELWRI;
            reassignbuf(bp);
            atomic_subtract_int(&numdirtybuffers, 1);
            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) bwrite(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) {
            mtx_lock(&nblock);
            while (numdirtybuffers >= hidirtybuffers) {
                  bd_wakeup(1);
                  needsbuffer |= VFS_BIO_NEED_DIRTYFLUSH;
                  msleep(&needsbuffer, &nblock,
                      (PRIBIO + 4), "flswai", 0);
            }
            mtx_unlock(&nblock);
      }
}

/*
 * 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)
{
      CTR3(KTR_BUF, "brelse(%p) vp %p flags %X",
          bp, bp->b_vp, bp->b_flags);
      KASSERT(!(bp->b_flags & (B_CLUSTER|B_PAGING)),
          ("brelse: inappropriate B_PAGING or B_CLUSTER bp %p", bp));

      if (bp->b_iocmd == BIO_WRITE &&
          (bp->b_ioflags & BIO_ERROR) &&
          !(bp->b_flags & B_INVAL)) {
            /*
             * Failed write, redirty.  Must clear BIO_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_ioflags &= ~BIO_ERROR;
            bdirty(bp);
      } else if ((bp->b_flags & (B_NOCACHE | B_INVAL)) ||
          (bp->b_ioflags & BIO_ERROR) || (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)
                  buf_deallocate(bp);
            if (bp->b_flags & B_DELWRI) {
                  atomic_subtract_int(&numdirtybuffers, 1);
                  numdirtywakeup(lodirtybuffers);
            }
            bp->b_flags &= ~(B_DELWRI | B_CACHE);
            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()) {
            /*
             * XXX This lock may not be necessary since BKGRDINPROG
             * cannot be set while we hold the buf lock, it can only be
             * cleared if it is already pending.
             */
            if (bp->b_vp) {
                  BO_LOCK(bp->b_bufobj);
                  if (!(bp->b_vflags & BV_BKGRDINPROG))
                        bp->b_flags |= B_RELBUF;
                  BO_UNLOCK(bp->b_bufobj);
            } else
                  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 BIO_ERROR or B_NOCACHE is set, pages in the VM object will be
       * invalidated.  BIO_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_mount != NULL &&
             (bp->b_vp->v_mount->mnt_vfc->vfc_flags & VFCF_NETWORK) != 0 &&
             !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;

            obj = bp->b_bufobj->bo_object;

            /*
             * 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;
            VM_OBJECT_LOCK(obj);
            for (i = 0; i < bp->b_npages; i++) {
                  int had_bogus = 0;

                  m = bp->b_pages[i];

                  /*
                   * If we hit a bogus page, fixup *all* the bogus pages
                   * now.
                   */
                  if (m == bogus_page) {
                        poff = OFF_TO_IDX(bp->b_offset);
                        had_bogus = 1;

                        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\n");
                                    }
                                    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];
                  }
                  if ((bp->b_flags & B_NOCACHE) ||
                      (bp->b_ioflags & BIO_ERROR)) {
                        int poffset = foff & PAGE_MASK;
                        int presid = resid > (PAGE_SIZE - poffset) ?
                              (PAGE_SIZE - poffset) : resid;

                        KASSERT(presid >= 0, ("brelse: extra page"));
                        vm_page_lock_queues();
                        vm_page_set_invalid(m, poffset, presid);
                        vm_page_unlock_queues();
                        if (had_bogus)
                              printf("avoided corruption bug in bogus_page/brelse code\n");
                  }
                  resid -= PAGE_SIZE - (foff & PAGE_MASK);
                  foff = (foff + PAGE_SIZE) & ~(off_t)PAGE_MASK;
            }
            VM_OBJECT_UNLOCK(obj);
            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);
            }

      } else if ((bp->b_flags & (B_INVAL | B_RELBUF)) != 0) {
            if (bp->b_bufsize != 0)
                  allocbuf(bp, 0);
            if (bp->b_vp != NULL)
                  brelvp(bp);
      }
                  
      if (BUF_REFCNT(bp) > 1) {
            /* do not release to free list */
            BUF_UNLOCK(bp);
            return;
      }

      /* enqueue */
      mtx_lock(&bqlock);
      /* Handle delayed bremfree() processing. */
      if (bp->b_flags & B_REMFREE)
            bremfreel(bp);
      if (bp->b_qindex != QUEUE_NONE)
            panic("brelse: free buffer onto another queue???");

      /* buffers with no memory */
      if (bp->b_bufsize == 0) {
            bp->b_flags |= B_INVAL;
            bp->b_xflags &= ~(BX_BKGRDWRITE | BX_ALTDATA);
            if (bp->b_vflags & BV_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);
      /* buffers with junk contents */
      } else if (bp->b_flags & (B_INVAL | B_NOCACHE | B_RELBUF) ||
          (bp->b_ioflags & BIO_ERROR)) {
            bp->b_flags |= B_INVAL;
            bp->b_xflags &= ~(BX_BKGRDWRITE | BX_ALTDATA);
            if (bp->b_vflags & BV_BKGRDINPROG)
                  panic("losing buffer 2");
            bp->b_qindex = QUEUE_CLEAN;
            TAILQ_INSERT_HEAD(&bufqueues[QUEUE_CLEAN], bp, b_freelist);
      /* remaining buffers */
      } else {
            if (bp->b_flags & B_DELWRI)
                  bp->b_qindex = QUEUE_DIRTY;
            else
                  bp->b_qindex = QUEUE_CLEAN;
            if (bp->b_flags & B_AGE)
                  TAILQ_INSERT_HEAD(&bufqueues[bp->b_qindex], bp, b_freelist);
            else
                  TAILQ_INSERT_TAIL(&bufqueues[bp->b_qindex], bp, b_freelist);
      }
      mtx_unlock(&bqlock);

      /*
       * If B_INVAL and B_DELWRI is set, clear B_DELWRI.  We have already
       * placed the buffer on the correct queue.  We must also disassociate
       * the device and vnode for a B_INVAL buffer so gbincore() doesn't
       * find it.
       */
      if (bp->b_flags & B_INVAL) {
            if (bp->b_flags & B_DELWRI)
                  bundirty(bp);
            if (bp->b_vp)
                  brelvp(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_DELWRI))
            bufcountwakeup();

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

      bp->b_flags &= ~(B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF | B_DIRECT);
      if ((bp->b_flags & B_DELWRI) == 0 && (bp->b_xflags & BX_VNDIRTY))
            panic("brelse: not dirty");
      /* unlock */
      BUF_UNLOCK(bp);
}

/*
 * 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)
{
      CTR3(KTR_BUF, "bqrelse(%p) vp %p flags %X", bp, bp->b_vp, bp->b_flags);
      KASSERT(!(bp->b_flags & (B_CLUSTER|B_PAGING)),
          ("bqrelse: inappropriate B_PAGING or B_CLUSTER bp %p", bp));

      if (BUF_REFCNT(bp) > 1) {
            /* do not release to free list */
            BUF_UNLOCK(bp);
            return;
      }
      mtx_lock(&bqlock);
      /* Handle delayed bremfree() processing. */
      if (bp->b_flags & B_REMFREE)
            bremfreel(bp);
      if (bp->b_qindex != QUEUE_NONE)
            panic("bqrelse: free buffer onto another queue???");
      /* buffers with stale but valid contents */
      if (bp->b_flags & B_DELWRI) {
            bp->b_qindex = QUEUE_DIRTY;
            TAILQ_INSERT_TAIL(&bufqueues[QUEUE_DIRTY], bp, b_freelist);
      } else {
            /*
             * XXX This lock may not be necessary since BKGRDINPROG
             * cannot be set while we hold the buf lock, it can only be
             * cleared if it is already pending.
             */
            BO_LOCK(bp->b_bufobj);
            if (!vm_page_count_severe() || bp->b_vflags & BV_BKGRDINPROG) {
                  BO_UNLOCK(bp->b_bufobj);
                  bp->b_qindex = QUEUE_CLEAN;
                  TAILQ_INSERT_TAIL(&bufqueues[QUEUE_CLEAN], bp,
                      b_freelist);
            } else {
                  /*
                   * 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*.
                   */
                  BO_UNLOCK(bp->b_bufobj);
                  mtx_unlock(&bqlock);
                  brelse(bp);
                  return;
            }
      }
      mtx_unlock(&bqlock);

      if ((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();

      bp->b_flags &= ~(B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF);
      if ((bp->b_flags & B_DELWRI) == 0 && (bp->b_xflags & BX_VNDIRTY))
            panic("bqrelse: not dirty");
      /* unlock */
      BUF_UNLOCK(bp);
}

/* Give pages used by the bp back to the VM system (where possible) */
static void
vfs_vmio_release(struct buf *bp)
{
      int i;
      vm_page_t m;

      VM_OBJECT_LOCK(bp->b_bufobj->bo_object);
      vm_page_lock_queues();
      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) {
                  /*
                   * 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) {
                        pmap_remove_all(m);
                        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);
                  }
            }
      }
      vm_page_unlock_queues();
      VM_OBJECT_UNLOCK(bp->b_bufobj->bo_object);
      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 at a particular lbn is available for a clustered
 * write.
 */
static int
vfs_bio_clcheck(struct vnode *vp, int size, daddr_t lblkno, daddr_t blkno)
{
      struct buf *bpa;
      int match;

      match = 0;

      /* If the buf isn't in core skip it */
      if ((bpa = gbincore(&vp->v_bufobj, lblkno)) == NULL)
            return (0);

      /* If the buf is busy we don't want to wait for it */
      if (BUF_LOCK(bpa, LK_EXCLUSIVE | LK_NOWAIT, NULL) != 0)
            return (0);

      /* Only cluster with valid clusterable delayed write buffers */
      if ((bpa->b_flags & (B_DELWRI | B_CLUSTEROK | B_INVAL)) !=
          (B_DELWRI | B_CLUSTEROK))
            goto done;

      if (bpa->b_bufsize != size)
            goto done;

      /*
       * Check to see if it is in the expected place on disk and that the
       * block has been mapped.
       */
      if ((bpa->b_blkno != bpa->b_lblkno) && (bpa->b_blkno == blkno))
            match = 1;
done:
      BUF_UNLOCK(bpa);
      return (match);
}

/*
 *    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 ncl;
      int nwritten;
      int size;
      int maxcl;

      /*
       * 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;

            VI_LOCK(vp);
            for (i = 1; i < maxcl; i++)
                  if (vfs_bio_clcheck(vp, size, lblkno + i,
                      bp->b_blkno + ((i * size) >> DEV_BSHIFT)) == 0)
                        break;

            for (j = 1; i + j <= maxcl && j <= lblkno; j++) 
                  if (vfs_bio_clcheck(vp, size, lblkno - j,
                      bp->b_blkno - ((j * size) >> DEV_BSHIFT)) == 0)
                        break;

            VI_UNLOCK(vp);
            --j;
            ncl = i + j;
            /*
             * this is a possible cluster write
             */
            if (ncl != 1) {
                  BUF_UNLOCK(bp);
                  nwritten = cluster_wbuild(vp, size, lblkno - j, ncl);
                  return nwritten;
            }
      }
      bremfree(bp);
      bp->b_flags |= B_ASYNC;
      /*
       * default (old) behavior, writing out only one block
       *
       * XXX returns b_bufsize instead of b_bcount for nwritten?
       */
      nwritten = bp->b_bufsize;
      (void) bwrite(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.
       */

      atomic_add_int(&getnewbufcalls, 1);
      atomic_subtract_int(&getnewbufrestarts, 1);
restart:
      atomic_add_int(&getnewbufrestarts, 1);

      /*
       * 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.
       */
      mtx_lock(&bqlock);
      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;
                        /* FALLTHROUGH */
                  case QUEUE_EMPTYKVA:
                        nqindex = QUEUE_CLEAN;
                        if ((nbp = TAILQ_FIRST(&bufqueues[QUEUE_CLEAN])))
                              break;
                        /* FALLTHROUGH */
                  case QUEUE_CLEAN:
                        /*
                         * nbp is NULL. 
                         */
                        break;
                  }
            }
            /*
             * 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, NULL) != 0)
                  continue;
            if (bp->b_vp) {
                  BO_LOCK(bp->b_bufobj);
                  if (bp->b_vflags & BV_BKGRDINPROG) {
                        BO_UNLOCK(bp->b_bufobj);
                        BUF_UNLOCK(bp);
                        continue;
                  }
                  BO_UNLOCK(bp->b_bufobj);
            }
            CTR6(KTR_BUF,
                "getnewbuf(%p) vp %p flags %X kvasize %d bufsize %d "
                "queue %d (recycling)", bp, bp->b_vp, bp->b_flags,
                bp->b_kvasize, bp->b_bufsize, qindex);

            /*
             * 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));

            bremfreel(bp);
            mtx_unlock(&bqlock);

            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 (bp->b_rcred != NOCRED) {
                  crfree(bp->b_rcred);
                  bp->b_rcred = NOCRED;
            }
            if (bp->b_wcred != NOCRED) {
                  crfree(bp->b_wcred);
                  bp->b_wcred = NOCRED;
            }
            if (LIST_FIRST(&bp->b_dep) != NULL)
                  buf_deallocate(bp);
            if (bp->b_vflags & BV_BKGRDINPROG)
                  panic("losing buffer 3");
            KASSERT(bp->b_vp == NULL,
                ("bp: %p still has vnode %p.  qindex: %d",
                bp, bp->b_vp, qindex));
            KASSERT((bp->b_xflags & (BX_VNCLEAN|BX_VNDIRTY)) == 0,
               ("bp: %p still on a buffer list. xflags %X",
                bp, bp->b_xflags));

            if (bp->b_bufsize)
                  allocbuf(bp, 0);

            bp->b_flags = 0;
            bp->b_ioflags = 0;
            bp->b_xflags = 0;
            bp->b_vflags = 0;
            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;
            bp->b_bufobj = NULL;

            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;
            }

            /*
             * Notify any waiters for the buffer lock about
             * identity change by freeing the buffer.
             */
            if (qindex == QUEUE_CLEAN && BUF_LOCKWAITERS(bp) > 0) {
                  bp->b_flags |= B_INVAL;
                  bfreekva(bp);
                  brelse(bp);
                  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;
            }
            mtx_lock(&nblock);
            needsbuffer |= flags;
            mtx_unlock(&nblock);
            mtx_unlock(&bqlock);

            bd_speedup();     /* heeeelp */

            mtx_lock(&nblock);
            while (needsbuffer & flags) {
                  if (msleep(&needsbuffer, &nblock,
                      (PRIBIO + 4) | slpflag, waitmsg, slptimeo)) {
                        mtx_unlock(&nblock);
                        return (NULL);
                  }
            }
            mtx_unlock(&nblock);
      } 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;

                  bfreekva(bp);

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

                        bp->b_kvabase = (caddr_t) addr;
                        bp->b_kvasize = maxsize;
                        atomic_add_int(&bufspace, bp->b_kvasize);
                        atomic_add_int(&bufreusecnt, 1);
                  }
                  vm_map_unlock(buffer_map);
            }
            bp->b_saveaddr = bp->b_kvabase;
            bp->b_data = bp->b_saveaddr;
      }
      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 kproc_desc buf_kp = {
      "bufdaemon",
      buf_daemon,
      &bufdaemonproc
};
SYSINIT(bufdaemon, SI_SUB_KTHREAD_BUF, SI_ORDER_FIRST, kproc_start, &buf_kp)

static void
buf_daemon()
{
      mtx_lock(&Giant);

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

      /*
       * This process is allowed to take the buffer cache to the limit
       */
      curthread->td_pflags |= TDP_NORUNNINGBUF;
      mtx_lock(&bdlock);
      for (;;) {
            bd_request = 0;
            mtx_unlock(&bdlock);

            kthread_suspend_check(bufdaemonproc);

            /*
             * 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) == 0) {
                        /*
                         * Could not find any buffers without rollback
                         * dependencies, so just write the first one
                         * in the hopes of eventually making progress.
                         */
                        flushbufqueues(1);
                        break;
                  }
                  uio_yield();
            }

            /*
             * Only clear bd_request if we have reached our low water
             * mark.  The buf_daemon normally waits 1 second 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.
             */
            mtx_lock(&bdlock);
            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;
                  msleep(&bd_request, &bdlock, PVM, "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)
                   */
                  msleep(&bd_request, &bdlock, PVM, "qsleep", hz / 10);
            }
      }
}

/*
 *    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 flushwithdeps = 0;
SYSCTL_INT(_vfs, OID_AUTO, flushwithdeps, CTLFLAG_RW, &flushwithdeps,
    0, "Number of buffers flushed with dependecies that require rollbacks");

static int
flushbufqueues(int flushdeps)
{
      struct thread *td = curthread;
      struct buf sentinel;
      struct vnode *vp;
      struct mount *mp;
      struct buf *bp;
      int hasdeps;
      int flushed;
      int target;

      target = numdirtybuffers - lodirtybuffers;
      if (flushdeps && target > 2)
            target /= 2;
      flushed = 0;
      bp = NULL;
      mtx_lock(&bqlock);
      TAILQ_INSERT_TAIL(&bufqueues[QUEUE_DIRTY], &sentinel, b_freelist);
      while (flushed != target) {
            bp = TAILQ_FIRST(&bufqueues[QUEUE_DIRTY]);
            if (bp == &sentinel)
                  break;
            TAILQ_REMOVE(&bufqueues[QUEUE_DIRTY], bp, b_freelist);
            TAILQ_INSERT_TAIL(&bufqueues[QUEUE_DIRTY], bp, b_freelist);

            if (BUF_LOCK(bp, LK_EXCLUSIVE | LK_NOWAIT, NULL) != 0)
                  continue;
            BO_LOCK(bp->b_bufobj);
            if ((bp->b_vflags & BV_BKGRDINPROG) != 0 ||
                (bp->b_flags & B_DELWRI) == 0) {
                  BO_UNLOCK(bp->b_bufobj);
                  BUF_UNLOCK(bp);
                  continue;
            }
            BO_UNLOCK(bp->b_bufobj);
            if (bp->b_flags & B_INVAL) {
                  bremfreel(bp);
                  mtx_unlock(&bqlock);
                  brelse(bp);
                  flushed++;
                  numdirtywakeup((lodirtybuffers + hidirtybuffers) / 2);
                  mtx_lock(&bqlock);
                  continue;
            }

            if (LIST_FIRST(&bp->b_dep) != NULL && buf_countdeps(bp, 0)) {
                  if (flushdeps == 0) {
                        BUF_UNLOCK(bp);
                        continue;
                  }
                  hasdeps = 1;
            } else
                  hasdeps = 0;
            /*
             * We must hold the lock on a vnode before writing
             * one of its buffers. Otherwise we may confuse, or
             * in the case of a snapshot vnode, deadlock the
             * system.
             *
             * The lock order here is the reverse of the normal
             * of vnode followed by buf lock.  This is ok because
             * the NOWAIT will prevent deadlock.
             */
            vp = bp->b_vp;
            if (vn_start_write(vp, &mp, V_NOWAIT) != 0) {
                  BUF_UNLOCK(bp);
                  continue;
            }
            if (vn_lock(vp, LK_EXCLUSIVE | LK_NOWAIT, td) == 0) {
                  mtx_unlock(&bqlock);
                  CTR3(KTR_BUF, "flushbufqueue(%p) vp %p flags %X",
                      bp, bp->b_vp, bp->b_flags);
                  vfs_bio_awrite(bp);
                  vn_finished_write(mp);
                  VOP_UNLOCK(vp, 0, td);
                  flushwithdeps += hasdeps;
                  flushed++;
                  waitrunningbufspace();
                  numdirtywakeup((lodirtybuffers + hidirtybuffers) / 2);
                  mtx_lock(&bqlock);
                  continue;
            }
            vn_finished_write(mp);
            BUF_UNLOCK(bp);
      }
      TAILQ_REMOVE(&bufqueues[QUEUE_DIRTY], &sentinel, b_freelist);
      mtx_unlock(&bqlock);
      return (flushed);
}

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

      BO_LOCK(bo);
      bp = gbincore(bo, blkno);
      BO_UNLOCK(bo);
      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.
 */

static 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;

      ASSERT_VOP_LOCKED(vp, "inmem");

      if (incore(&vp->v_bufobj, blkno))
            return 1;
      if (vp->v_mount == NULL)
            return 0;
      obj = vp->v_object;
      if (obj == NULL)
            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;

      VM_OBJECT_LOCK(obj);
      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)
                  goto notinmem;
            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)
                  goto notinmem;
      }
      VM_OBJECT_UNLOCK(obj);
      return 1;

notinmem:
      VM_OBJECT_UNLOCK(obj);
      return (0);
}

/*
 *    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;
      VM_OBJECT_LOCK(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;

            vm_page_lock_queues();
            /*
             * 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_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);

            vm_page_unlock_queues();
            /*
             * 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;
            }
      }
      VM_OBJECT_UNLOCK(object);
}

/*
 *    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 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 BIO_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,
    int flags)
{
      struct buf *bp;
      struct bufobj *bo;
      int error;

      CTR3(KTR_BUF, "getblk(%p, %ld, %d)", vp, (long)blkno, size);
      ASSERT_VOP_LOCKED(vp, "getblk");
      if (size > MAXBSIZE)
            panic("getblk: size(%d) > MAXBSIZE(%d)\n", size, MAXBSIZE);

      bo = &vp->v_bufobj;
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 if 0 sections (clean this up after its proven)
         */
      if (numfreebuffers == 0) {
            if (curthread == PCPU_GET(idlethread))
                  return NULL;
            mtx_lock(&nblock);
            needsbuffer |= VFS_BIO_NEED_ANY;
            mtx_unlock(&nblock);
      }

      VI_LOCK(vp);
      bp = gbincore(bo, blkno);
      if (bp != NULL) {
            int lockflags;
            /*
             * Buffer is in-core.  If the buffer is not busy, it must
             * be on a queue.
             */
            lockflags = LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK;

            if (flags & GB_LOCK_NOWAIT)
                  lockflags |= LK_NOWAIT;

            error = BUF_TIMELOCK(bp, lockflags,
                VI_MTX(vp), "getblk", slpflag, slptimeo);

            /*
             * If we slept and got the lock we have to restart in case
             * the buffer changed identities.
             */
            if (error == ENOLCK)
                  goto loop;
            /* We timed out or were interrupted. */
            else if (error)
                  return (NULL);

            /*
             * The buffer is locked.  B_CACHE is cleared if the buffer is 
             * invalid.  Otherwise, 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;
                              bwrite(bp);
                        } else {
                              if (LIST_FIRST(&bp->b_dep) == NULL) {
                                    bp->b_flags |= B_RELBUF;
                                    brelse(bp);
                              } else {
                                    bp->b_flags |= B_NOCACHE;
                                    bwrite(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;
                  bwrite(bp);
                  goto loop;
            }
            bp->b_flags &= ~B_DONE;
      } else {
            int bsize, maxsize, vmio;
            off_t offset;

            /*
             * 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).
             */
            VI_UNLOCK(vp);
            /*
             * If the user does not want us to create the buffer, bail out
             * here.
             */
            if (flags & GB_NOCREAT)
                  return NULL;
            bsize = bo->bo_bsize;
            offset = blkno * bsize;
            vmio = vp->v_object != NULL;
            maxsize = vmio ? size + (offset & PAGE_MASK) : size;
            maxsize = imax(maxsize, bsize);

            bp = getnewbuf(slpflag, slptimeo, size, maxsize);
            if (bp == NULL) {
                  if (slpflag || slptimeo)
                        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.
             *
             * Note: this must occur before we associate the buffer
             * with the vp especially considering limitations in
             * the splay tree implementation when dealing with duplicate
             * lblkno's.
             */
            BO_LOCK(bo);
            if (gbincore(bo, blkno)) {
                  BO_UNLOCK(bo);
                  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);
            BO_UNLOCK(bo);

            /*
             * 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: VMIO on vnode type %d\n",
                              vp->v_type);
#endif
                  KASSERT(vp->v_object == bp->b_bufobj->bo_object,
                      ("ARGH! different b_bufobj->bo_object %p %p %p\n",
                      bp, vp->v_object, bp->b_bufobj->bo_object));
            } else {
                  bp->b_flags &= ~B_VMIO;
                  KASSERT(bp->b_bufobj->bo_object == NULL,
                      ("ARGH! has b_bufobj->bo_object %p %p\n",
                      bp, bp->b_bufobj->bo_object));
            }

            allocbuf(bp, size);
            bp->b_flags &= ~B_DONE;
      }
      CTR4(KTR_BUF, "getblk(%p, %ld, %d) = %p", vp, (long)blkno, size, bp);
      KASSERT(BUF_REFCNT(bp) == 1, ("getblk: bp %p not locked",bp));
      KASSERT(bp->b_bufobj == bo,
          ("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
      return (bp);
}

/*
 * Get an empty, disassociated buffer of given size.  The buffer is initially
 * set to B_INVAL.
 */
struct buf *
geteblk(int size)
{
      struct buf *bp;
      int maxsize;

      maxsize = (size + BKVAMASK) & ~BKVAMASK;
      while ((bp = getnewbuf(0, 0, size, maxsize)) == 0)
            continue;
      allocbuf(bp, size);
      bp->b_flags |= B_INVAL; /* b_dep cleared by getnewbuf() */
      KASSERT(BUF_REFCNT(bp) == 1, ("geteblk: bp %p not locked",bp));
      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.
 */

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 (bp->b_flags & B_MALLOC)
                  newbsize = mbsize;
            else
                  newbsize = round_page(size);

            if (newbsize < bp->b_bufsize) {
                  /*
                   * 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) {
                                    atomic_subtract_int(
                                        &bufmallocspace,
                                        bp->b_bufsize);
                                    bufspacewakeup();
                                    bp->b_bufsize = 0;
                              }
                              bp->b_saveaddr = bp->b_kvabase;
                              bp->b_data = bp->b_saveaddr;
                              bp->b_bcount = 0;
                              bp->b_flags &= ~B_MALLOC;
                        }
                        return 1;
                  }           
                  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) {
                  /*
                   * We only use malloced memory on the first allocation.
                   * and revert to page-allocated memory when the buffer
                   * grows.
                   */
                  /*
                   * There is a potential smp race here that could lead
                   * to bufmallocspace slightly passing the max.  It
                   * is probably extremely rare and not worth worrying
                   * over.
                   */
                  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;
                        atomic_add_int(&bufmallocspace, mbsize);
                        return 1;
                  }
                  origbuf = NULL;
                  origbufsize = 0;
                  /*
                   * 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) {
                              atomic_subtract_int(&bufmallocspace,
                                  bp->b_bufsize);
                              bufspacewakeup();
                              bp->b_bufsize = 0;
                        }
                        bp->b_flags &= ~B_MALLOC;
                        newbsize = round_page(newbsize);
                  }
                  vm_hold_load_pages(
                      bp,
                      (vm_offset_t) bp->b_data + bp->b_bufsize,
                      (vm_offset_t) bp->b_data + newbsize);
                  if (origbuf) {
                        bcopy(origbuf, bp->b_data, origbufsize);
                        free(origbuf, M_BIOBUF);
                  }
            }
      } else {
            int desiredpages;

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

            if (bp->b_flags & B_MALLOC)
                  panic("allocbuf: VMIO buffer can't be malloced");
            /*
             * 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) {
                        vm_page_t m;

                        VM_OBJECT_LOCK(bp->b_bufobj->bo_object);
                        vm_page_lock_queues();
                        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_if_busy(m, TRUE, "biodep"))
                                    vm_page_lock_queues();

                              bp->b_pages[i] = NULL;
                              vm_page_unwire(m, 0);
                        }
                        vm_page_unlock_queues();
                        VM_OBJECT_UNLOCK(bp->b_bufobj->bo_object);
                        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;

                  /*
                   * 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.
                   */

                  vp = bp->b_vp;
                  obj = bp->b_bufobj->bo_object;

                  VM_OBJECT_LOCK(obj);
                  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_NOBUSY | VM_ALLOC_SYSTEM |
                                  VM_ALLOC_WIRED);
                              if (m == NULL) {
                                    atomic_add_int(&vm_pageout_deficit,
                                        desiredpages - bp->b_npages);
                                    VM_OBJECT_UNLOCK(obj);
                                    VM_WAIT;
                                    VM_OBJECT_LOCK(obj);
                              } else {
                                    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
                         *
                         */
                        vm_page_lock_queues();
                        if (vm_page_sleep_if_busy(m, FALSE, "pgtblk"))
                              continue;

                        /*
                         * We have a good page.  Should we wakeup the
                         * page daemon?
                         */
                        if ((curproc != pageproc) &&
                            ((m->queue - m->pc) == PQ_CACHE) &&
                            ((cnt.v_free_count + cnt.v_cache_count) <
                              (cnt.v_free_min + cnt.v_cache_min))) {
                              pagedaemon_wakeup();
                        }
                        vm_page_wire(m);
                        vm_page_unlock_queues();
                        bp->b_pages[bp->b_npages] = m;
                        ++bp->b_npages;
                  }

                  /*
                   * 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;
                  }
                  VM_OBJECT_UNLOCK(obj);

                  /*
                   * 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;
}

void
biodone(struct bio *bp)
{
      void (*done)(struct bio *);

      mtx_lock(&bdonelock);
      bp->bio_flags |= BIO_DONE;
      done = bp->bio_done;
      if (done == NULL)
            wakeup(bp);
      mtx_unlock(&bdonelock);
      if (done != NULL)
            done(bp);
}

/*
 * Wait for a BIO to finish.
 *
 * XXX: resort to a timeout for now.  The optimal locking (if any) for this
 * case is not yet clear.
 */
int
biowait(struct bio *bp, const char *wchan)
{

      mtx_lock(&bdonelock);
      while ((bp->bio_flags & BIO_DONE) == 0)
            msleep(bp, &bdonelock, PRIBIO, wchan, hz / 10);
      mtx_unlock(&bdonelock);
      if (bp->bio_error != 0)
            return (bp->bio_error);
      if (!(bp->bio_flags & BIO_ERROR))
            return (0);
      return (EIO);
}

void
biofinish(struct bio *bp, struct devstat *stat, int error)
{
      
      if (error) {
            bp->bio_error = error;
            bp->bio_flags |= BIO_ERROR;
      }
      if (stat != NULL)
            devstat_end_transaction_bio(stat, bp);
      biodone(bp);
}

/*
 *    bufwait:
 *
 *    Wait for buffer I/O completion, returning error status.  The buffer
 *    is left locked and B_DONE on return.  B_EINTR is converted into an EINTR
 *    error and cleared.
 */
int
bufwait(struct buf *bp)
{
      if (bp->b_iocmd == BIO_READ)
            bwait(bp, PRIBIO, "biord");
      else
            bwait(bp, PRIBIO, "biowr");
      if (bp->b_flags & B_EINTR) {
            bp->b_flags &= ~B_EINTR;
            return (EINTR);
      }
      if (bp->b_ioflags & BIO_ERROR) {
            return (bp->b_error ? bp->b_error : EIO);
      } else {
            return (0);
      }
}

 /*
  * Call back function from struct bio back up to struct buf.
  */
static void
bufdonebio(struct bio *bip)
{
      struct buf *bp;

      bp = bip->bio_caller2;
      bp->b_resid = bp->b_bcount - bip->bio_completed;
      bp->b_resid = bip->bio_resid; /* XXX: remove */
      bp->b_ioflags = bip->bio_flags;
      bp->b_error = bip->bio_error;
      if (bp->b_error)
            bp->b_ioflags |= BIO_ERROR;
      bufdone(bp);
      g_destroy_bio(bip);
}

void
dev_strategy(struct cdev *dev, struct buf *bp)
{
      struct cdevsw *csw;
      struct bio *bip;

      if ((!bp->b_iocmd) || (bp->b_iocmd & (bp->b_iocmd - 1)))
            panic("b_iocmd botch");
      for (;;) {
            bip = g_new_bio();
            if (bip != NULL)
                  break;
            /* Try again later */
            tsleep(&bp, PRIBIO, "dev_strat", hz/10);
      }
      bip->bio_cmd = bp->b_iocmd;
      bip->bio_offset = bp->b_iooffset;
      bip->bio_length = bp->b_bcount;
      bip->bio_bcount = bp->b_bcount;     /* XXX: remove */
      bip->bio_data = bp->b_data;
      bip->bio_done = bufdonebio;
      bip->bio_caller2 = bp;
      bip->bio_dev = dev;
      KASSERT(dev->si_refcount > 0,
          ("dev_strategy on un-referenced struct cdev *(%s)",
          devtoname(dev)));
      csw = dev_refthread(dev);
      if (csw == NULL) {
            g_destroy_bio(bip);
            bp->b_error = ENXIO;
            bp->b_ioflags = BIO_ERROR;
            bufdone(bp);
            return;
      }
      (*csw->d_strategy)(bip);
      dev_relthread(dev);
}

/*
 *    bufdone:
 *
 *    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.
 */
void
bufdone(struct buf *bp)
{
      struct bufobj *dropobj;
      void    (*biodone)(struct buf *);


      CTR3(KTR_BUF, "bufdone(%p) vp %p flags %X", bp, bp->b_vp, bp->b_flags);
      dropobj = NULL;

      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));

      runningbufwakeup(bp);
      if (bp->b_iocmd == BIO_WRITE)
            dropobj = bp->b_bufobj;
      /* call optional completion function if requested */
      if (bp->b_iodone != NULL) {
            biodone = bp->b_iodone;
            bp->b_iodone = NULL;
            (*biodone) (bp);
            if (dropobj)
                  bufobj_wdrop(dropobj);
            return;
      }
      if (LIST_FIRST(&bp->b_dep) != NULL)
            buf_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;

            obj = bp->b_bufobj->bo_object;

#if defined(VFS_BIO_DEBUG)
            mp_fixme("usecount and vflag accessed without locks.");
            if (vp->v_usecount == 0) {
                  panic("biodone: zero vnode ref count");
            }

            KASSERT(vp->v_object != NULL,
                  ("biodone: vnode %p has no vm_object", vp));
#endif

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

            VM_OBJECT_LOCK(obj);
#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_iocmd == BIO_READ &&
                !(bp->b_flags & (B_INVAL|B_NOCACHE)) &&
                !(bp->b_ioflags & BIO_ERROR)) {
                  bp->b_flags |= B_CACHE;
            }
            vm_page_lock_queues();
            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
                   */
                  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(%jd)/m->pindex(%ju) mismatch\n",
                            (intmax_t)foff, (uintmax_t)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_iocmd == BIO_READ) && !bogusflag && resid > 0) {
                        vfs_page_set_valid(bp, foff, i, m);
                  }

                  /*
                   * 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: %jd, lblkno: %jd, flags: 0x%x, npages: %d\n",
                                  (intmax_t)bp->b_vp->v_mount->mnt_stat.f_iosize,
                                  (intmax_t) bp->b_lblkno,
                                  bp->b_flags, bp->b_npages);
                        else
                              printf(" VDEV, lblkno: %jd, flags: 0x%x, npages: %d\n",
                                  (intmax_t) bp->b_lblkno,
                                  bp->b_flags, bp->b_npages);
                        printf(" valid: 0x%lx, dirty: 0x%lx, wired: %d\n",
                            (u_long)m->valid, (u_long)m->dirty,
                            m->wire_count);
                        panic("biodone: page busy < 0\n");
                  }
                  vm_page_io_finish(m);
                  vm_object_pip_subtract(obj, 1);
                  foff = (foff + PAGE_SIZE) & ~(off_t)PAGE_MASK;
                  iosize -= resid;
            }
            vm_page_unlock_queues();
            vm_object_pip_wakeupn(obj, 0);
            VM_OBJECT_UNLOCK(obj);
      }

      /*
       * 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_RELBUF)) || (bp->b_ioflags & BIO_ERROR))
                  brelse(bp);
            else
                  bqrelse(bp);
      } else
            bdone(bp);
      if (dropobj)
            bufobj_wdrop(dropobj);
}

/*
 * 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;
      vm_object_t obj;
      vm_page_t m;

      runningbufwakeup(bp);
      if (!(bp->b_flags & B_VMIO))
            return;

      obj = bp->b_bufobj->bo_object;
      VM_OBJECT_LOCK(obj);
      vm_page_lock_queues();
      for (i = 0; i < bp->b_npages; i++) {
            m = bp->b_pages[i];
            if (m == bogus_page) {
                  m = vm_page_lookup(obj, OFF_TO_IDX(bp->b_offset) + i);
                  if (!m)
                        panic("vfs_unbusy_pages: page missing\n");
                  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_io_finish(m);
      }
      vm_page_unlock_queues();
      vm_object_pip_wakeupn(obj, 0);
      VM_OBJECT_UNLOCK(obj);
}

/*
 * 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;

      mtx_assert(&vm_page_queue_mtx, MA_OWNED);
      /*
       * 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 BIO_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;
      vm_object_t obj;
      vm_ooffset_t foff;
      vm_page_t m;

      if (!(bp->b_flags & B_VMIO))
            return;

      obj = bp->b_bufobj->bo_object;
      foff = bp->b_offset;
      KASSERT(bp->b_offset != NOOFFSET,
          ("vfs_busy_pages: no buffer offset"));
      vfs_setdirty(bp);
      VM_OBJECT_LOCK(obj);
retry:
      vm_page_lock_queues();
      for (i = 0; i < bp->b_npages; i++) {
            m = bp->b_pages[i];

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

            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.
             */
            pmap_remove_all(m);
            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;
      }
      vm_page_unlock_queues();
      VM_OBJECT_UNLOCK(obj);
      if (bogus)
            pmap_qenter(trunc_page((vm_offset_t)bp->b_data),
                bp->b_pages, bp->b_npages);
}

/*
 * 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;
      vm_ooffset_t foff, noff, eoff;
      vm_page_t m;

      if (!(bp->b_flags & B_VMIO))
            return;

      foff = bp->b_offset;
      KASSERT(bp->b_offset != NOOFFSET,
          ("vfs_clean_pages: no buffer offset"));
      VM_OBJECT_LOCK(bp->b_bufobj->bo_object);
      vm_page_lock_queues();
      for (i = 0; i < bp->b_npages; i++) {
            m = bp->b_pages[i];
            noff = (foff + PAGE_SIZE) & ~(off_t)PAGE_MASK;
            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;
      }
      vm_page_unlock_queues();
      VM_OBJECT_UNLOCK(bp->b_bufobj->bo_object);
}

/*
 *    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)
{
      int i, n;
      vm_page_t m;

      if (!(bp->b_flags & B_VMIO))
            return;
      /*
       * 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);

      VM_OBJECT_LOCK(bp->b_bufobj->bo_object);
      vm_page_lock_queues();
      for (i = base / PAGE_SIZE; size > 0 && i < bp->b_npages; ++i) {
            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;
      }
      vm_page_unlock_queues();
      VM_OBJECT_UNLOCK(bp->b_bufobj->bo_object);
}

/*
 *    vfs_bio_clrbuf:
 *
 *    clear a buffer.  This routine essentially fakes an I/O, so we need
 *    to clear BIO_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, j, mask = 0;
      caddr_t sa, ea;

      if ((bp->b_flags & (B_VMIO | B_MALLOC)) != B_VMIO) {
            clrbuf(bp);
            return;
      }

      bp->b_flags &= ~B_INVAL;
      bp->b_ioflags &= ~BIO_ERROR;
      VM_OBJECT_LOCK(bp->b_bufobj->bo_object);
      if ((bp->b_npages == 1) && (bp->b_bufsize < PAGE_SIZE) &&
          (bp->b_offset & PAGE_MASK) == 0) {
            if (bp->b_pages[0] == bogus_page)
                  goto unlock;
            mask = (1 << (bp->b_bufsize / DEV_BSIZE)) - 1;
            VM_OBJECT_LOCK_ASSERT(bp->b_pages[0]->object, MA_OWNED);
            if ((bp->b_pages[0]->valid & mask) == mask)
                  goto unlock;
            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;
                  goto unlock;
            }
      }
      ea = sa = bp->b_data;
      for(i = 0; i < bp->b_npages; i++, sa = ea) {
            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);
            if (bp->b_pages[i] == bogus_page)
                  continue;
            j = ((vm_offset_t)sa & PAGE_MASK) / DEV_BSIZE;
            mask = ((1 << ((ea - sa) / DEV_BSIZE)) - 1) << j;
            VM_OBJECT_LOCK_ASSERT(bp->b_pages[i]->object, MA_OWNED);
            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;
      }
unlock:
      VM_OBJECT_UNLOCK(bp->b_bufobj->bo_object);
      bp->b_resid = 0;
}

/*
 * vm_hold_load_pages and vm_hold_free_pages get pages into
 * a buffers address space.  The pages are anonymous and are
 * not associated with a file object.
 */
static 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;

      VM_OBJECT_LOCK(kernel_object);
      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_NOBUSY | VM_ALLOC_SYSTEM | VM_ALLOC_WIRED);
            if (!p) {
                  atomic_add_int(&vm_pageout_deficit,
                      (to - pg) >> PAGE_SHIFT);
                  VM_OBJECT_UNLOCK(kernel_object);
                  VM_WAIT;
                  VM_OBJECT_LOCK(kernel_object);
                  goto tryagain;
            }
            p->valid = VM_PAGE_BITS_ALL;
            pmap_qenter(pg, &p, 1);
            bp->b_pages[index] = p;
      }
      VM_OBJECT_UNLOCK(kernel_object);
      bp->b_npages = index;
}

/* Return pages associated with this buf to the vm system */
static 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;

      VM_OBJECT_LOCK(kernel_object);
      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: %jd, lblkno: %jd\n",
                            (intmax_t)bp->b_blkno,
                            (intmax_t)bp->b_lblkno);
                  }
                  bp->b_pages[index] = NULL;
                  pmap_qremove(pg, 1);
                  vm_page_lock_queues();
                  vm_page_unwire(p, 0);
                  vm_page_free(p);
                  vm_page_unlock_queues();
            }
      }
      VM_OBJECT_UNLOCK(kernel_object);
      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.
 *
 * Note that even if the caller determines that the address space should
 * be valid, a race or a smaller-file mapped into a larger space may
 * actually cause vmapbuf() to fail, so all callers of vmapbuf() MUST
 * check the return value.
 */
int
vmapbuf(struct buf *bp)
{
      caddr_t addr, kva;
      vm_prot_t prot;
      int pidx, i;
      struct vm_page *m;
      struct pmap *pmap = &curproc->p_vmspace->vm_pmap;

      if (bp->b_bufsize < 0)
            return (-1);
      prot = VM_PROT_READ;
      if (bp->b_iocmd == BIO_READ)
            prot |= VM_PROT_WRITE;  /* Less backwards than it looks */
      for (addr = (caddr_t)trunc_page((vm_offset_t)bp->b_data), pidx = 0;
           addr < bp->b_data + bp->b_bufsize;
           addr += PAGE_SIZE, pidx++) {
            /*
             * Do the vm_fault if needed; do the copy-on-write thing
             * when reading stuff off device into memory.
             *
             * NOTE! Must use pmap_extract() because addr may be in
             * the userland address space, and kextract is only guarenteed
             * to work for the kernland address space (see: sparc64 port).
             */
retry:
            if (vm_fault_quick(addr >= bp->b_data ? addr : bp->b_data,
                prot) < 0) {
                  vm_page_lock_queues();
                  for (i = 0; i < pidx; ++i) {
                        vm_page_unhold(bp->b_pages[i]);
                        bp->b_pages[i] = NULL;
                  }
                  vm_page_unlock_queues();
                  return(-1);
            }
            m = pmap_extract_and_hold(pmap, (vm_offset_t)addr, prot);
            if (m == NULL)
                  goto retry;
            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(struct buf *bp)
{
      int pidx;
      int npages;

      npages = bp->b_npages;
      pmap_qremove(trunc_page((vm_offset_t)bp->b_data), npages);
      vm_page_lock_queues();
      for (pidx = 0; pidx < npages; pidx++)
            vm_page_unhold(bp->b_pages[pidx]);
      vm_page_unlock_queues();

      bp->b_data = bp->b_saveaddr;
}

void
bdone(struct buf *bp)
{

      mtx_lock(&bdonelock);
      bp->b_flags |= B_DONE;
      wakeup(bp);
      mtx_unlock(&bdonelock);
}

void
bwait(struct buf *bp, u_char pri, const char *wchan)
{

      mtx_lock(&bdonelock);
      while ((bp->b_flags & B_DONE) == 0)
            msleep(bp, &bdonelock, pri, wchan, 0);
      mtx_unlock(&bdonelock);
}

int
bufsync(struct bufobj *bo, int waitfor, struct thread *td)
{

      return (VOP_FSYNC(bo->__bo_vnode, waitfor, td));
}

void
bufstrategy(struct bufobj *bo, struct buf *bp)
{
      int i = 0;
      struct vnode *vp;

      vp = bp->b_vp;
      KASSERT(vp == bo->bo_private, ("Inconsistent vnode bufstrategy"));
      KASSERT(vp->v_type != VCHR && vp->v_type != VBLK,
          ("Wrong vnode in bufstrategy(bp=%p, vp=%p)", bp, vp));
      i = VOP_STRATEGY(vp, bp);
      KASSERT(i == 0, ("VOP_STRATEGY failed bp=%p vp=%p", bp, bp->b_vp));
}

void
bufobj_wrefl(struct bufobj *bo)
{

      KASSERT(bo != NULL, ("NULL bo in bufobj_wref"));
      ASSERT_BO_LOCKED(bo);
      bo->bo_numoutput++;
}

void
bufobj_wref(struct bufobj *bo)
{

      KASSERT(bo != NULL, ("NULL bo in bufobj_wref"));
      BO_LOCK(bo);
      bo->bo_numoutput++;
      BO_UNLOCK(bo);
}

void
bufobj_wdrop(struct bufobj *bo)
{

      KASSERT(bo != NULL, ("NULL bo in bufobj_wdrop"));
      BO_LOCK(bo);
      KASSERT(bo->bo_numoutput > 0, ("bufobj_wdrop non-positive count"));
      if ((--bo->bo_numoutput == 0) && (bo->bo_flag & BO_WWAIT)) {
            bo->bo_flag &= ~BO_WWAIT;
            wakeup(&bo->bo_numoutput);
      }
      BO_UNLOCK(bo);
}

int
bufobj_wwait(struct bufobj *bo, int slpflag, int timeo)
{
      int error;

      KASSERT(bo != NULL, ("NULL bo in bufobj_wwait"));
      ASSERT_BO_LOCKED(bo);
      error = 0;
      while (bo->bo_numoutput) {
            bo->bo_flag |= BO_WWAIT;
            error = msleep(&bo->bo_numoutput, BO_MTX(bo),
                slpflag | (PRIBIO + 1), "bo_wwait", timeo);
            if (error)
                  break;
      }
      return (error);
}

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

/* DDB command to show buffer data */
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("buf at %p\n", bp);
      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\n"
          "b_bufobj = (%p), b_data = %p, b_blkno = %jd\n",
          bp->b_error, bp->b_bufsize, bp->b_bcount, bp->b_resid,
          bp->b_bufobj, bp->b_data, (intmax_t)bp->b_blkno);
      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");
      }
      lockmgr_printinfo(&bp->b_lock);
}

DB_SHOW_COMMAND(lockedbufs, lockedbufs)
{
      struct buf *bp;
      int i;

      for (i = 0; i < nbuf; i++) {
            bp = &buf[i];
            if (lockcount(&bp->b_lock)) {
                  db_show_buffer((uintptr_t)bp, 1, 0, NULL);
                  db_printf("\n");
            }
      }
}
#endif /* DDB */

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