xref: /src/sys/uvm/uvm_vnode.c

/*	$NetBSD: uvm_vnode.c,v 1.22.2.1.2.5 1999/08/02 23:39:29 thorpej Exp $	*/

/*
 * Copyright (c) 1997 Charles D. Cranor and Washington University.
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.
 * Copyright (c) 1990 University of Utah.
 *
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * the Systems Programming Group of the University of Utah Computer
 * Science Department.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Charles D. Cranor,
 *	Washington University, the University of California, Berkeley and
 *	its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)vnode_pager.c       8.8 (Berkeley) 2/13/94
 * from: Id: uvm_vnode.c,v 1.1.2.26 1998/02/02 20:38:07 chuck Exp
 */

#include "fs_nfs.h"
#include "opt_uvmhist.h"
#include "opt_ddb.h"

/*
 * uvm_vnode.c: the vnode pager.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/malloc.h>
#include <sys/vnode.h>
#include <sys/disklabel.h>
#include <sys/ioctl.h>
#include <sys/fcntl.h>
#include <sys/conf.h>
#include <sys/pool.h>
#include <sys/mount.h>

#include <miscfs/specfs/specdev.h>

#include <vm/vm.h>
#include <vm/vm_page.h>
#include <vm/vm_kern.h>

#include <uvm/uvm.h>
#include <uvm/uvm_vnode.h>

/*
 * private global data structure
 *
 * we keep a list of writeable active vnode-backed VM objects for sync op.
 * we keep a simpleq of vnodes that are currently being sync'd.
 */

LIST_HEAD(uvn_list_struct, uvm_vnode);
static struct uvn_list_struct uvn_wlist;	/* writeable uvns */
static simple_lock_data_t uvn_wl_lock;		/* locks uvn_wlist */

SIMPLEQ_HEAD(uvn_sq_struct, uvm_vnode);
static struct uvn_sq_struct uvn_sync_q;		/* sync'ing uvns */
lock_data_t uvn_sync_lock;			/* locks sync operation */

/*
 * functions
 */

static int		uvn_asyncget __P((struct uvm_object *, vaddr_t,
					    int));
struct uvm_object *	uvn_attach __P((void *, vm_prot_t));
static void		uvn_cluster __P((struct uvm_object *, vaddr_t,
					 vaddr_t *, vaddr_t *));
static void		uvn_detach __P((struct uvm_object *));
static int		uvn_findpage __P((struct uvm_object *, vaddr_t,
					  struct vm_page **, int));
static boolean_t	uvn_flush __P((struct uvm_object *, vaddr_t,
				       vaddr_t, int));
static int		uvn_get __P((struct uvm_object *, vaddr_t,
				     vm_page_t *, int *, int,
				     vm_prot_t, int, int));
static void		uvn_init __P((void));
static int		uvn_put __P((struct uvm_object *, vm_page_t *,
				     int, boolean_t));
static void		uvn_reference __P((struct uvm_object *));
static boolean_t	uvn_releasepg __P((struct vm_page *,
					   struct vm_page **));
static void		uvn_doasyncget __P((struct vm_page **, size_t,
					    daddr_t));

/*
 * master pager structure
 */

struct uvm_pagerops uvm_vnodeops = {
	uvn_init,
	uvn_reference,
	uvn_detach,
	NULL,			/* no specialized fault routine required */
	uvn_flush,
	uvn_get,
	uvn_asyncget,
	uvn_put,
	uvn_cluster,
	uvm_mk_pcluster, /* use generic version of this: see uvm_pager.c */
	uvm_shareprot,	 /* !NULL: allow us in share maps */
	NULL,		 /* AIO-DONE function (not until we have asyncio) */
	uvn_releasepg,
};

/*
 * the ops!
 */

/*
 * uvn_init
 *
 * init pager private data structures.
 */

static void
uvn_init()
{

	LIST_INIT(&uvn_wlist);
	simple_lock_init(&uvn_wl_lock);
	/* note: uvn_sync_q init'd in uvm_vnp_sync() */
	lockinit(&uvn_sync_lock, PVM, "uvnsync", 0, 0);
}

/*
 * uvn_attach
 *
 * attach a vnode structure to a VM object.  if the vnode is already
 * attached, then just bump the reference count by one and return the
 * VM object.   if not already attached, attach and return the new VM obj.
 * the "accessprot" tells the max access the attaching thread wants to
 * our pages.
 *
 * => caller must _not_ already be holding the lock on the uvm_object.
 * => in fact, nothing should be locked so that we can sleep here.
 * => note that uvm_object is first thing in vnode structure, so their
 *    pointers are equiv.
 */

struct uvm_object *
uvn_attach(arg, accessprot)
	void *arg;
	vm_prot_t accessprot;
{
	struct vnode *vp = arg;
	struct uvm_vnode *uvn = &vp->v_uvm;
	struct vattr vattr;
	int result;
	struct partinfo pi;
	off_t used_vnode_size;
	UVMHIST_FUNC("uvn_attach"); UVMHIST_CALLED(maphist);

	UVMHIST_LOG(maphist, "(vn=0x%x)", arg,0,0,0);

	used_vnode_size = (u_quad_t)0;	/* XXX gcc -Wuninitialized */

	/*
	 * first get a lock on the uvn.
	 */
	simple_lock(&uvn->u_obj.vmobjlock);
	while (uvn->u_flags & VXLOCK) {
		uvn->u_flags |= VXWANT;
		UVMHIST_LOG(maphist, "  SLEEPING on blocked vn",0,0,0,0);
		UVM_UNLOCK_AND_WAIT(uvn, &uvn->u_obj.vmobjlock, FALSE,
		    "uvn_attach", 0);
		simple_lock(&uvn->u_obj.vmobjlock);
		UVMHIST_LOG(maphist,"  WOKE UP",0,0,0,0);
	}

	/*
	 * if we're mapping a BLK device, make sure it is a disk.
	 */
	if (vp->v_type == VBLK && bdevsw[major(vp->v_rdev)].d_type != D_DISK) {
		simple_unlock(&uvn->u_obj.vmobjlock);
		UVMHIST_LOG(maphist,"<- done (VBLK not D_DISK!)", 0,0,0,0);
		return(NULL);
	}

	/* check for new writeable uvn */
	if ((accessprot & VM_PROT_WRITE) != 0 &&
	    (uvn->u_flags & VDIRTY) == 0) {
		simple_lock(&uvn_wl_lock);
		LIST_INSERT_HEAD(&uvn_wlist, uvn, u_wlist);
		simple_unlock(&uvn_wl_lock);
		/* we are now on wlist! */
		uvn->u_flags |= VDIRTY;
	}
#ifdef DIAGNOSTIC
	if (vp->v_type != VREG) {
		panic("uvn_attach: vp %p not VREG", vp);
	}
#endif

	/*
	 * set up our idea of the size
	 * if this hasn't been done already.
	 */
	if (uvn->u_size == VSIZENOTSET) {

	uvn->u_flags = VXLOCK;
	simple_unlock(&uvn->u_obj.vmobjlock); /* drop lock in case we sleep */
		/* XXX: curproc? */
	if (vp->v_type == VBLK) {
		/*
		 * We could implement this as a specfs getattr call, but:
		 *
		 *	(1) VOP_GETATTR() would get the file system
		 *	    vnode operation, not the specfs operation.
		 *
		 *	(2) All we want is the size, anyhow.
		 */
		result = (*bdevsw[major(vp->v_rdev)].d_ioctl)(vp->v_rdev,
		    DIOCGPART, (caddr_t)&pi, FREAD, curproc);
		if (result == 0) {
			/* XXX should remember blocksize */
			used_vnode_size = (u_quad_t)pi.disklab->d_secsize *
			    (u_quad_t)pi.part->p_size;
		}
	} else {
		result = VOP_GETATTR(vp, &vattr, curproc->p_ucred, curproc);
		if (result == 0)
			used_vnode_size = vattr.va_size;
	}


	/*
	 * make sure that the newsize fits within a vaddr_t
	 * XXX: need to revise addressing data types
	 */
	if (used_vnode_size > (vaddr_t) -PAGE_SIZE) {
#ifdef DEBUG
		printf("uvn_attach: vn %p size truncated %qx->%x\n", vp,
		    (long long)used_vnode_size, -PAGE_SIZE);
#endif
		used_vnode_size = (vaddr_t) -PAGE_SIZE;
	}

	/* relock object */
	simple_lock(&uvn->u_obj.vmobjlock);

	if (uvn->u_flags & VXWANT)
		wakeup(uvn);
	uvn->u_flags = 0;

	if (result != 0) {
		simple_unlock(&uvn->u_obj.vmobjlock); /* drop lock */
		UVMHIST_LOG(maphist,"<- done (VOP_GETATTR FAILED!)", 0,0,0,0);
		return(NULL);
	}
	uvn->u_size = used_vnode_size;

	}

	/* unlock and return */
	simple_unlock(&uvn->u_obj.vmobjlock);
	UVMHIST_LOG(maphist,"<- done, refcnt=%d", uvn->u_obj.uo_refs,
	    0, 0, 0);
	return (&uvn->u_obj);
}


/*
 * uvn_reference
 *
 * duplicate a reference to a VM object.  Note that the reference
 * count must already be at least one (the passed in reference) so
 * there is no chance of the uvn being killed or locked out here.
 *
 * => caller must call with object unlocked.
 * => caller must be using the same accessprot as was used at attach time
 */


static void
uvn_reference(uobj)
	struct uvm_object *uobj;
{
	UVMHIST_FUNC("uvn_reference"); UVMHIST_CALLED(maphist);

	VREF((struct vnode *)uobj);
}

/*
 * uvn_detach
 *
 * remove a reference to a VM object.
 *
 * => caller must call with object unlocked and map locked.
 * => this starts the detach process, but doesn't have to finish it
 *    (async i/o could still be pending).
 */
static void
uvn_detach(uobj)
	struct uvm_object *uobj;
{
	UVMHIST_FUNC("uvn_detach"); UVMHIST_CALLED(maphist);
	vrele((struct vnode *)uobj);
}

/*
 * uvm_vnp_terminate: external hook to clear out a vnode's VM
 *
 * called in two cases:
 *  [1] when a persisting vnode vm object (i.e. one with a zero reference
 *      count) needs to be freed so that a vnode can be reused.  this
 *      happens under "getnewvnode" in vfs_subr.c.   if the vnode from
 *      the free list is still attached (i.e. not VBAD) then vgone is
 *	called.   as part of the vgone trace this should get called to
 *	free the vm object.   this is the common case.
 *  [2] when a filesystem is being unmounted by force (MNT_FORCE,
 *	"umount -f") the vgone() function is called on active vnodes
 *	on the mounted file systems to kill their data (the vnodes become
 *	"dead" ones [see src/sys/miscfs/deadfs/...]).  that results in a
 *	call here (even if the uvn is still in use -- i.e. has a non-zero
 *	reference count).  this case happens at "umount -f" and during a
 *	"reboot/halt" operation.
 *
 * => the caller must XLOCK and VOP_LOCK the vnode before calling us
 *	[protects us from getting a vnode that is already in the DYING
 *	 state...]
 * => unlike uvn_detach, this function must not return until all the
 *	uvn's pages are disposed of.
 * => in case [2] the uvn is still alive after this call, but all I/O
 *	ops will fail (due to the backing vnode now being "dead").  this
 *	will prob. kill any process using the uvn due to pgo_get failing.
 */

void
uvm_vnp_terminate(vp)
	struct vnode *vp;
{
	struct uvm_vnode *uvn = &vp->v_uvm;
	if (uvn->u_flags & VDIRTY) {
		simple_lock(&uvn_wl_lock);
		LIST_REMOVE(uvn, u_wlist);
		uvn->u_flags &= ~(VDIRTY);
		simple_unlock(&uvn_wl_lock);
	}
}

/*
 * uvn_releasepg: handled a released page in a uvn
 *
 * => "pg" is a PG_BUSY [caller owns it], PG_RELEASED page that we need
 *	to dispose of.
 * => caller must handled PG_WANTED case
 * => called with page's object locked, pageq's unlocked
 * => returns TRUE if page's object is still alive, FALSE if we
 *	killed the page's object.    if we return TRUE, then we
 *	return with the object locked.
 * => if (nextpgp != NULL) => we return pageq.tqe_next here, and return
 *				with the page queues locked [for pagedaemon]
 * => if (nextpgp == NULL) => we return with page queues unlocked [normal case]
 * => we kill the uvn if it is not referenced and we are suppose to
 *	kill it ("relkill").
 */

boolean_t
uvn_releasepg(pg, nextpgp)
	struct vm_page *pg;
	struct vm_page **nextpgp;	/* OUT */
{
	struct uvm_vnode *uvn = (struct uvm_vnode *) pg->uobject;
#ifdef DIAGNOSTIC
	if ((pg->flags & PG_RELEASED) == 0)
		panic("uvn_releasepg: page not released!");
#endif

	/*
	 * dispose of the page [caller handles PG_WANTED]
	 */
	pmap_page_protect(PMAP_PGARG(pg), VM_PROT_NONE);
	uvm_lock_pageq();
	if (nextpgp)
		*nextpgp = pg->pageq.tqe_next;	/* next page for daemon */
	uvm_pagefree(pg);
	if (!nextpgp)
		uvm_unlock_pageq();

#if 1
	/* XXX I'm sure we need to do something here. */
	uvn = uvn;
#else
	/*
	 * now see if we need to kill the object
	 */
	if (uvn->u_flags & UVM_VNODE_RELKILL) {
		if (uvn->u_obj.uo_refs)
			panic("uvn_releasepg: kill flag set on referenced "
			    "object!");
		if (uvn->u_obj.uo_npages == 0) {
			if (uvn->u_flags & VDIRTY) {
				simple_lock(&uvn_wl_lock);
				LIST_REMOVE(uvn, u_wlist);
				simple_unlock(&uvn_wl_lock);
			}
#ifdef DIAGNOSTIC
			if (uvn->u_obj.memq.tqh_first)
	panic("uvn_releasepg: pages in object with npages == 0");
#endif
			if (uvn->u_flags & VXWANT)
				/* still holding object lock */
				wakeup(uvn);

			uvn->u_flags = 0;		/* DEAD! */
			simple_unlock(&uvn->u_obj.vmobjlock);
			return (FALSE);
		}
	}
#endif
	return (TRUE);
}

/*
 * NOTE: currently we have to use VOP_READ/VOP_WRITE because they go
 * through the buffer cache and allow I/O in any size.  These VOPs use
 * synchronous i/o.  [vs. VOP_STRATEGY which can be async, but doesn't
 * go through the buffer cache or allow I/O sizes larger than a
 * block].  we will eventually want to change this.
 *
 * issues to consider:
 *   uvm provides the uvm_aiodesc structure for async i/o management.
 * there are two tailq's in the uvm. structure... one for pending async
 * i/o and one for "done" async i/o.   to do an async i/o one puts
 * an aiodesc on the "pending" list (protected by splbio()), starts the
 * i/o and returns VM_PAGER_PEND.    when the i/o is done, we expect
 * some sort of "i/o done" function to be called (at splbio(), interrupt
 * time).   this function should remove the aiodesc from the pending list
 * and place it on the "done" list and wakeup the daemon.   the daemon
 * will run at normal spl() and will remove all items from the "done"
 * list and call the "aiodone" hook for each done request (see uvm_pager.c).
 * [in the old vm code, this was done by calling the "put" routine with
 * null arguments which made the code harder to read and understand because
 * you had one function ("put") doing two things.]
 *
 * so the current pager needs:
 *   int uvn_aiodone(struct uvm_aiodesc *)
 *
 * => return KERN_SUCCESS (aio finished, free it).  otherwise requeue for
 *	later collection.
 * => called with pageq's locked by the daemon.
 *
 * general outline:
 * - "try" to lock object.   if fail, just return (will try again later)
 * - drop "u_nio" (this req is done!)
 * - if (object->iosync && u_naio == 0) { wakeup &uvn->u_naio }
 * - get "page" structures (atop?).
 * - handle "wanted" pages
 * - handle "released" pages [using pgo_releasepg]
 *   >>> pgo_releasepg may kill the object
 * dont forget to look at "object" wanted flag in all cases.
 */


/*
 * uvn_flush: flush pages out of a uvm object.
 *
 * => object should be locked by caller.   we may _unlock_ the object
 *	if (and only if) we need to clean a page (PGO_CLEANIT).
 *	we return with the object locked.
 * => if PGO_CLEANIT is set, we may block (due to I/O).   thus, a caller
 *	might want to unlock higher level resources (e.g. vm_map)
 *	before calling flush.
 * => if PGO_CLEANIT is not set, then we will neither unlock the object
 *	or block.
 * => if PGO_ALLPAGE is set, then all pages in the object are valid targets
 *	for flushing.
 * => NOTE: we rely on the fact that the object's memq is a TAILQ and
 *	that new pages are inserted on the tail end of the list.   thus,
 *	we can make a complete pass through the object in one go by starting
 *	at the head and working towards the tail (new pages are put in
 *	front of us).
 * => NOTE: we are allowed to lock the page queues, so the caller
 *	must not be holding the lock on them [e.g. pagedaemon had
 *	better not call us with the queues locked]
 * => we return TRUE unless we encountered some sort of I/O error
 *
 * comment on "cleaning" object and PG_BUSY pages:
 *	this routine is holding the lock on the object.   the only time
 *	that it can run into a PG_BUSY page that it does not own is if
 *	some other process has started I/O on the page (e.g. either
 *	a pagein, or a pageout).    if the PG_BUSY page is being paged
 *	in, then it can not be dirty (!PG_CLEAN) because no one has
 *	had a chance to modify it yet.    if the PG_BUSY page is being
 *	paged out then it means that someone else has already started
 *	cleaning the page for us (how nice!).    in this case, if we
 *	have syncio specified, then after we make our pass through the
 *	object we need to wait for the other PG_BUSY pages to clear
 *	off (i.e. we need to do an iosync).   also note that once a
 *	page is PG_BUSY it must stay in its object until it is un-busyed.
 *
 * note on page traversal:
 *	we can traverse the pages in an object either by going down the
 *	linked list in "uobj->memq", or we can go over the address range
 *	by page doing hash table lookups for each address.    depending
 *	on how many pages are in the object it may be cheaper to do one
 *	or the other.   we set "by_list" to true if we are using memq.
 *	if the cost of a hash lookup was equal to the cost of the list
 *	traversal we could compare the number of pages in the start->stop
 *	range to the total number of pages in the object.   however, it
 *	seems that a hash table lookup is more expensive than the linked
 *	list traversal, so we multiply the number of pages in the
 *	start->stop range by a penalty which we define below.
 */

#define UVN_HASH_PENALTY 4	/* XXX: a guess */

static boolean_t
uvn_flush(uobj, start, stop, flags)
	struct uvm_object *uobj;
	vaddr_t start, stop;
	int flags;
{
	struct uvm_vnode *uvn = (struct uvm_vnode *) uobj;
	struct vnode *vp = (struct vnode *)uobj;
	struct vm_page *pp, *ppnext, *ptmp;
	struct vm_page *pps[MAXBSIZE >> PAGE_SHIFT], **ppsp;
	int s;
	int npages, result, lcv;
	boolean_t retval, need_iosync, by_list, needs_clean;
	vaddr_t curoff;
	u_short pp_version;
	UVMHIST_FUNC("uvn_flush"); UVMHIST_CALLED(maphist);

	if (uvn->u_size == VSIZENOTSET) {
#ifdef DEBUG
		void vp_name(void *);

		printf("uvn_flush: size not set vp %p\n", uvn);
		if ((flags & PGO_ALLPAGES) == 0)
			printf("... and PGO_ALLPAGES not set: "
			       "start 0x%lx end 0x%lx flags 0x%x\n",
			       start, stop, flags);
		vprint("uvn_flush VSIZENOTSET", vp);
		vp_name(uvn);
#endif
		flags |= PGO_ALLPAGES;
	}

	curoff = 0;	/* XXX: shut up gcc */
	/*
	 * get init vals and determine how we are going to traverse object
	 */

	need_iosync = FALSE;
	retval = TRUE;		/* return value */
	if (flags & PGO_ALLPAGES) {
		start = 0;
		stop = -1;
		by_list = TRUE;		/* always go by the list */
	} else {
		start = trunc_page(start);
		stop = round_page(stop);
		if (stop > round_page(uvn->u_size)) {
			printf("uvn_flush: oor vp %p start 0x%x stop 0x%x "
			       "size 0x%x\n", uvn, (int)start, (int)stop,
			       (int)round_page(uvn->u_size));
		}

		by_list = (uobj->uo_npages <=
		    ((stop - start) >> PAGE_SHIFT) * UVN_HASH_PENALTY);
	}

	UVMHIST_LOG(maphist,
	    " flush start=0x%x, stop=0x%x, by_list=%d, flags=0x%x",
	    start, stop, by_list, flags);

	/*
	 * PG_CLEANCHK: this bit is used by the pgo_mk_pcluster function as
	 * a _hint_ as to how up to date the PG_CLEAN bit is.   if the hint
	 * is wrong it will only prevent us from clustering... it won't break
	 * anything.   we clear all PG_CLEANCHK bits here, and pgo_mk_pcluster
	 * will set them as it syncs PG_CLEAN.   This is only an issue if we
	 * are looking at non-inactive pages (because inactive page's PG_CLEAN
	 * bit is always up to date since there are no mappings).
	 * [borrowed PG_CLEANCHK idea from FreeBSD VM]
	 */

	if ((flags & PGO_CLEANIT) != 0 &&
	    uobj->pgops->pgo_mk_pcluster != NULL) {
		if (by_list) {
			for (pp = TAILQ_FIRST(&uobj->memq);
			     pp != NULL ;
			     pp = TAILQ_NEXT(pp, listq)) {
				if (pp->offset < start ||
				    (pp->offset >= stop && stop != -1))
					continue;
				pp->flags &= ~PG_CLEANCHK;
			}

		} else {   /* by hash */
			for (curoff = start ; curoff < stop;
			    curoff += PAGE_SIZE) {
				pp = uvm_pagelookup(uobj, curoff);
				if (pp)
					pp->flags &= ~PG_CLEANCHK;
			}
		}
	}

	/*
	 * now do it.   note: we must update ppnext in body of loop or we
	 * will get stuck.  we need to use ppnext because we may free "pp"
	 * before doing the next loop.
	 */

	if (by_list) {
		pp = TAILQ_FIRST(&uobj->memq);
	} else {
		curoff = start;
		pp = uvm_pagelookup(uobj, curoff);
	}

	ppnext = NULL;	/* XXX: shut up gcc */
	ppsp = NULL;		/* XXX: shut up gcc */
	uvm_lock_pageq();	/* page queues locked */

	/* locked: both page queues and uobj */
	for ( ; (by_list && pp != NULL) ||
	  (!by_list && curoff < stop) ; pp = ppnext) {

		if (by_list) {

			/*
			 * range check
			 */

			if (pp->offset < start || pp->offset >= stop) {
				ppnext = TAILQ_NEXT(pp, listq);
				continue;
			}

		} else {

			/*
			 * null check
			 */

			curoff += PAGE_SIZE;
			if (pp == NULL) {
				if (curoff < stop)
					ppnext = uvm_pagelookup(uobj, curoff);
				continue;
			}

		}

		/*
		 * handle case where we do not need to clean page (either
		 * because we are not clean or because page is not dirty or
		 * is busy):
		 *
		 * NOTE: we are allowed to deactivate a non-wired active
		 * PG_BUSY page, but once a PG_BUSY page is on the inactive
		 * queue it must stay put until it is !PG_BUSY (so as not to
		 * confuse pagedaemon).
		 */

		if ((flags & PGO_CLEANIT) == 0 || (pp->flags & PG_BUSY) != 0) {
			needs_clean = FALSE;
			if ((pp->flags & PG_BUSY) != 0 &&
			    (flags & (PGO_CLEANIT|PGO_SYNCIO)) ==
			             (PGO_CLEANIT|PGO_SYNCIO))
				need_iosync = TRUE;
		} else {
			/*
			 * freeing: nuke all mappings so we can sync
			 * PG_CLEAN bit with no race
			 */
			if ((pp->flags & PG_CLEAN) != 0 &&
			    (flags & PGO_FREE) != 0 &&
			    (pp->pqflags & PQ_ACTIVE) != 0)
				pmap_page_protect(PMAP_PGARG(pp), VM_PROT_NONE);
			if ((pp->flags & PG_CLEAN) != 0 &&
			    pmap_is_modified(PMAP_PGARG(pp)))
				pp->flags &= ~(PG_CLEAN);
			pp->flags |= PG_CLEANCHK;	/* update "hint" */

			needs_clean = ((pp->flags & PG_CLEAN) == 0);
		}

		/*
		 * if we don't need a clean... load ppnext and dispose of pp
		 */
		if (!needs_clean) {
			/* load ppnext */
			if (by_list)
				ppnext = pp->listq.tqe_next;
			else {
				if (curoff < stop)
					ppnext = uvm_pagelookup(uobj, curoff);
			}

			/* now dispose of pp */
			if (flags & PGO_DEACTIVATE) {
				if ((pp->pqflags & PQ_INACTIVE) == 0 &&
				    pp->wire_count == 0) {
					pmap_page_protect(PMAP_PGARG(pp),
					    VM_PROT_NONE);
					uvm_pagedeactivate(pp);
				}

			} else if (flags & PGO_FREE) {
				if (pp->flags & PG_BUSY) {
					/* release busy pages */
					pp->flags |= PG_RELEASED;
				} else {
					pmap_page_protect(PMAP_PGARG(pp),
					    VM_PROT_NONE);
					/* removed page from object */
					uvm_pagefree(pp);
				}
			}
			/* ppnext is valid so we can continue... */
			continue;
		}

		/*
		 * pp points to a page in the locked object that we are
		 * working on.  if it is !PG_CLEAN,!PG_BUSY and we asked
		 * for cleaning (PGO_CLEANIT).  we clean it now.
		 *
		 * let uvm_pager_put attempted a clustered page out.
		 * note: locked: uobj and page queues.
		 */

		pp->flags |= PG_BUSY;	/* we 'own' page now */
		UVM_PAGE_OWN(pp, "uvn_flush");
		pmap_page_protect(PMAP_PGARG(pp), VM_PROT_READ);
		pp_version = pp->version;
ReTry:
		ppsp = pps;
		npages = sizeof(pps) / sizeof(struct vm_page *);

		/* locked: page queues, uobj */
		result = uvm_pager_put(uobj, pp, &ppsp, &npages,
				       flags | PGO_DOACTCLUST, start, stop);
		/* unlocked: page queues, uobj */

		/*
		 * at this point nothing is locked.   if we did an async I/O
		 * it is remotely possible for the async i/o to complete and
		 * the page "pp" be freed or what not before we get a chance
		 * to relock the object.   in order to detect this, we have
		 * saved the version number of the page in "pp_version".
		 */

		/* relock! */
		simple_lock(&uobj->vmobjlock);
		uvm_lock_pageq();

		/*
		 * VM_PAGER_AGAIN: given the structure of this pager, this
		 * can only happen when  we are doing async I/O and can't
		 * map the pages into kernel memory (pager_map) due to lack
		 * of vm space.   if this happens we drop back to sync I/O.
		 */

		if (result == VM_PAGER_AGAIN) {
			/*
			 * it is unlikely, but page could have been released
			 * while we had the object lock dropped.   we ignore
			 * this now and retry the I/O.  we will detect and
			 * handle the released page after the syncio I/O
			 * completes.
			 */
#ifdef DIAGNOSTIC
			if (flags & PGO_SYNCIO)
	panic("uvn_flush: PGO_SYNCIO return 'try again' error (impossible)");
#endif
			flags |= PGO_SYNCIO;
			goto ReTry;
		}

		/*
		 * the cleaning operation is now done.   finish up.  note that
		 * on error (!OK, !PEND) uvm_pager_put drops the cluster for us.
		 * if success (OK, PEND) then uvm_pager_put returns the cluster
		 * to us in ppsp/npages.
		 */

		/*
		 * for pending async i/o if we are not deactivating/freeing
		 * we can move on to the next page.
		 */

		if (result == VM_PAGER_PEND) {

			if ((flags & (PGO_DEACTIVATE|PGO_FREE)) == 0) {
				/*
				 * no per-page ops: refresh ppnext and continue
				 */
				if (by_list) {
					if (pp->version == pp_version)
						ppnext = pp->listq.tqe_next;
					else
						/* reset */
						ppnext = uobj->memq.tqh_first;
				} else {
					if (curoff < stop)
						ppnext = uvm_pagelookup(uobj,
						    curoff);
				}
				continue;
			}

			/* need to do anything here? */
		}

		/*
		 * need to look at each page of the I/O operation.  we defer
		 * processing "pp" until the last trip through this "for" loop
		 * so that we can load "ppnext" for the main loop after we
		 * play with the cluster pages [thus the "npages + 1" in the
		 * loop below].
		 */

		for (lcv = 0 ; lcv < npages + 1 ; lcv++) {

			/*
			 * handle ppnext for outside loop, and saving pp
			 * until the end.
			 */
			if (lcv < npages) {
				if (ppsp[lcv] == pp)
					continue; /* skip pp until the end */
				ptmp = ppsp[lcv];
			} else {
				ptmp = pp;

				/* set up next page for outer loop */
				if (by_list) {
					if (pp->version == pp_version)
						ppnext = pp->listq.tqe_next;
					else
						/* reset */
						ppnext = uobj->memq.tqh_first;
				} else {
					if (curoff < stop)
					ppnext = uvm_pagelookup(uobj, curoff);
				}
			}

			/*
			 * verify the page didn't get moved while obj was
			 * unlocked
			 */
			if (result == VM_PAGER_PEND && ptmp->uobject != uobj)
				continue;

			/*
			 * unbusy the page if I/O is done.   note that for
			 * pending I/O it is possible that the I/O op
			 * finished before we relocked the object (in
			 * which case the page is no longer busy).
			 */

			if (result != VM_PAGER_PEND) {
				if (ptmp->flags & PG_WANTED)
					/* still holding object lock */
					wakeup(ptmp);

				ptmp->flags &= ~(PG_WANTED|PG_BUSY);
				UVM_PAGE_OWN(ptmp, NULL);
				if (ptmp->flags & PG_RELEASED) {

					/* pgo_releasepg wants this */
					uvm_unlock_pageq();
					if (!uvn_releasepg(ptmp, NULL))
						return (TRUE);

					uvm_lock_pageq();	/* relock */
					continue;		/* next page */

				} else {
					ptmp->flags |= (PG_CLEAN|PG_CLEANCHK);
					if ((flags & PGO_FREE) == 0)
						pmap_clear_modify(
						    PMAP_PGARG(ptmp));
				}
			}

			/*
			 * dispose of page
			 */

			if (flags & PGO_DEACTIVATE) {
				if ((pp->pqflags & PQ_INACTIVE) == 0 &&
				    pp->wire_count == 0) {
					pmap_page_protect(PMAP_PGARG(ptmp),
					    VM_PROT_NONE);
					uvm_pagedeactivate(ptmp);
				}

			} else if (flags & PGO_FREE) {
				if (result == VM_PAGER_PEND) {
					if ((ptmp->flags & PG_BUSY) != 0)
						/* signal for i/o done */
						ptmp->flags |= PG_RELEASED;
				} else {
					if (result != VM_PAGER_OK) {
						printf("uvn_flush: obj=%p, "
						   "offset=0x%lx.  error %d\n",
						    pp->uobject, pp->offset,
						    result);
						printf("uvn_flush: WARNING: "
						    "changes to page may be "
						    "lost!\n");
						retval = FALSE;
					}
					pmap_page_protect(PMAP_PGARG(ptmp),
					    VM_PROT_NONE);
					uvm_pagefree(ptmp);
				}
			}

		}		/* end of "lcv" for loop */

	}		/* end of "pp" for loop */

	/*
	 * done with pagequeues: unlock
	 */
	uvm_unlock_pageq();

	/*
	 * now wait for all I/O if required.
	 */
	if (need_iosync) {
		UVMHIST_LOG(maphist,"  <<DOING IOSYNC>>",0,0,0,0);

		/*
		 * XXX this doesn't use the new two-flag scheme,
		 * but to use that, all i/o initiators will have to change.
		 */

		s = splbio();
		while (vp->v_numoutput != 0) {
			UVMHIST_LOG(ubchist, "waiting for vp %p num %d",
				    vp, vp->v_numoutput,0,0);

			vp->v_flag |= VBWAIT;
			UVM_UNLOCK_AND_WAIT(&vp->v_numoutput,
					    &uvn->u_obj.vmobjlock,
					    FALSE, "uvn_flush",0);
			simple_lock(&uvn->u_obj.vmobjlock);
		}
		splx(s);
	}

	/* return, with object locked! */
	UVMHIST_LOG(maphist,"<- done (retval=0x%x)",retval,0,0,0);
	return(retval);
}

/*
 * uvn_cluster
 *
 * we are about to do I/O in an object at offset.   this function is called
 * to establish a range of offsets around "offset" in which we can cluster
 * I/O.
 *
 * - currently doesn't matter if obj locked or not.
 */

static void
uvn_cluster(uobj, offset, loffset, hoffset)
	struct uvm_object *uobj;
	vaddr_t offset;
	vaddr_t *loffset, *hoffset; /* OUT */
{
	struct uvm_vnode *uvn = (struct uvm_vnode *)uobj;

	*loffset = offset;
	*hoffset = min(offset + MAXBSIZE, round_page(uvn->u_size));
}

/*
 * uvn_put: flush page data to backing store.
 *
 * => object must be locked!   we will _unlock_ it before starting I/O.
 * => flags: PGO_SYNCIO -- use sync. I/O
 * => note: caller must set PG_CLEAN and pmap_clear_modify (if needed)
 */

static int
uvn_put(uobj, pps, npages, flags)
	struct uvm_object *uobj;
	struct vm_page **pps;
	int npages, flags;
{
	struct vnode *vp = (struct vnode *)uobj;
	int error, sync;

	sync = (flags & PGO_SYNCIO) ? 1 : 0;

	simple_unlock(&uobj->vmobjlock);
	error = VOP_PUTPAGES(vp, pps, npages, sync, NULL);

	return uvm_errno2vmerror(error);
}


/*
 * uvn_get: get pages (synchronously) from backing store
 *
 * => prefer map unlocked (not required)
 * => object must be locked!  we will _unlock_ it before starting any I/O.
 * => flags: PGO_ALLPAGES: get all of the pages
 *           PGO_LOCKED: fault data structures are locked
 * => NOTE: offset is the offset of pps[0], _NOT_ pps[centeridx]
 * => NOTE: caller must check for released pages!!
 */

static int
uvn_get(uobj, offset, pps, npagesp, centeridx, access_type, advice, flags)
	struct uvm_object *uobj;
	vaddr_t offset;
	struct vm_page **pps;		/* IN/OUT */
	int *npagesp;			/* IN (OUT if PGO_LOCKED) */
	int centeridx;
	vm_prot_t access_type;
	int advice, flags;
{
	struct vnode *vp = (struct vnode *)uobj;
	int error;
	UVMHIST_FUNC("uvn_get"); UVMHIST_CALLED(ubchist);
	UVMHIST_LOG(ubchist, "vp %p off 0x%x", vp, (int)offset, 0,0);

	error = VOP_GETPAGES(vp, offset, pps, npagesp, centeridx,
			     access_type, advice, flags);
	return uvm_errno2vmerror(error);
}

/*
 * uvn_findpages:
 * return the page for the uobj and offset requested, allocating if needed.
 * => uobj must be locked.
 * => returned page will be BUSY.
 */

void
uvn_findpages(uobj, offset, npagesp, pps, flags)
	struct uvm_object *uobj;
	vaddr_t offset;
	int *npagesp;
	struct vm_page **pps;
	int flags;
{
	int i, rv, npages;

	rv = 0;
	npages = *npagesp;
	for (i = 0; i < npages; i++, offset += PAGE_SIZE) {
		rv += uvn_findpage(uobj, offset, &pps[i], flags);
	}
	*npagesp = rv;
}


static int
uvn_findpage(uobj, offset, pps, flags)
	struct uvm_object *uobj;
	vaddr_t offset;
	struct vm_page **pps;
	int flags;
{
	struct vm_page *ptmp;
	UVMHIST_FUNC("uvn_findpage"); UVMHIST_CALLED(ubchist);
	UVMHIST_LOG(ubchist, "vp %p off 0x%lx", uobj, offset,0,0);

	if (*pps != NULL) {
		UVMHIST_LOG(ubchist, "dontcare", 0,0,0,0);
		return 0;
	}
	for (;;) {
		/* look for an existing page */
		ptmp = uvm_pagelookup(uobj, offset);

		/* nope?   allocate one now */
		if (ptmp == NULL) {
			if (flags & UFP_NOALLOC) {
				UVMHIST_LOG(ubchist, "noalloc", 0,0,0,0);
				return 0;
			}
			ptmp = uvm_pagealloc(uobj, offset, NULL, 0);
			if (ptmp == NULL) {
				if (flags & UFP_NOWAIT) {
					UVMHIST_LOG(ubchist, "nowait",0,0,0,0);
					return 0;
				}
				simple_unlock(&uobj->vmobjlock);
				uvm_wait("uvn_fp1");
				simple_lock(&uobj->vmobjlock);
				continue;
			}
			UVMHIST_LOG(ubchist, "alloced",0,0,0,0);
			break;
		} else if (flags & UFP_NOCACHE) {
			UVMHIST_LOG(ubchist, "nocache",0,0,0,0);
			return 0;
		}

		/* page is there, see if we need to wait on it */
		if ((ptmp->flags & (PG_BUSY|PG_RELEASED)) != 0) {
			if (flags & UFP_NOWAIT) {
				UVMHIST_LOG(ubchist, "nowait",0,0,0,0);
				return 0;
			}
			ptmp->flags |= PG_WANTED;
			UVM_UNLOCK_AND_WAIT(ptmp, &uobj->vmobjlock, 0,
					    "uvn_fp2",0);
			simple_lock(&uobj->vmobjlock);
			continue;
		}

		/* skip PG_RDONLY pages if requested */
		if ((flags & UFP_NORDONLY) && (ptmp->flags & PG_RDONLY)) {
			UVMHIST_LOG(ubchist, "nordonly",0,0,0,0);
			return 0;
		}
		/* BUSY the page and we're done. */
		ptmp->flags |= PG_BUSY;
		UVM_PAGE_OWN(ptmp, "uvn_findpage");
		UVMHIST_LOG(ubchist, "found",0,0,0,0);
		break;
	}
	*pps = ptmp;
	return 1;
}

/*
 * uvn_asyncget: start async I/O to bring pages into ram
 *
 * => caller must lock object(???XXX: see if this is best)
 * => could be called from uvn_get or a madvise() fault-ahead.
 * => if it fails, it doesn't matter.
 */

static int
uvn_asyncget(uobj, offset, npages)
	struct uvm_object *uobj;
	vaddr_t offset;
	int npages;
{

	/*
	 * XXXCDC: we can't do async I/O yet
	 */
	printf("uvn_asyncget called\n");
	return (KERN_SUCCESS);
}

/*
 * uvm_vnp_setsize: grow or shrink a vnode uvn
 *
 * grow   => just update size value
 * shrink => toss un-needed pages
 *
 * => we assume that the caller has a reference of some sort to the
 *	vnode in question so that it will not be yanked out from under
 *	us.
 *
 * called from:
 *  => truncate fns (ext2fs_truncate, ffs_truncate, detrunc[msdos])
 *  => "write" fns (ext2fs_write, WRITE [ufs/ufs], msdosfs_write, nfs_write)
 *  => ffs_balloc [XXX: why? doesn't WRITE handle?]
 *  => NFS: nfs_loadattrcache, nfs_getattrcache, nfs_setattr
 *  => union fs: union_newsize
 */

void
uvm_vnp_setsize(vp, newsize)
	struct vnode *vp;
	u_quad_t newsize;
{
	struct uvm_vnode *uvn = &vp->v_uvm;

	/*
	 * lock uvn and check for valid object, and if valid: do it!
	 */
	simple_lock(&uvn->u_obj.vmobjlock);

	/*
	 * make sure that the newsize fits within a vaddr_t
	 * XXX: need to revise addressing data types
	 */

	if (newsize > (vaddr_t) -PAGE_SIZE) {
#ifdef DEBUG
		printf("uvm_vnp_setsize: vn %p size truncated "
		       "%qx->%lx\n", vp, (long long)newsize,
		       (vaddr_t)-PAGE_SIZE);
#endif
		newsize = (vaddr_t)-PAGE_SIZE;
	}

	/*
	 * now check if the size has changed: if we shrink we had better
	 * toss some pages...
	 */

	if (uvn->u_size > newsize && uvn->u_size != VSIZENOTSET) {
		(void) uvn_flush(&uvn->u_obj, (vaddr_t)newsize,
				 uvn->u_size, PGO_FREE);
	}
	uvn->u_size = (vaddr_t)newsize;
	simple_unlock(&uvn->u_obj.vmobjlock);
}

/*
 * uvm_vnp_sync: flush all dirty VM pages back to their backing vnodes.
 *
 * => called from sys_sync with no VM structures locked
 * => only one process can do a sync at a time (because the uvn
 *    structure only has one queue for sync'ing).  we ensure this
 *    by holding the uvn_sync_lock while the sync is in progress.
 *    other processes attempting a sync will sleep on this lock
 *    until we are done.
 */

void
uvm_vnp_sync(mp)
	struct mount *mp;
{
	struct uvm_vnode *uvn;
	struct vnode *vp;
	boolean_t got_lock;

	/*
	 * step 1: ensure we are only ones using the uvn_sync_q by locking
	 * our lock...
	 */
	lockmgr(&uvn_sync_lock, LK_EXCLUSIVE, (void *)0);

	/*
	 * step 2: build up a simpleq of uvns of interest based on the
	 * write list.   we gain a reference to uvns of interest.  must
	 * be careful about locking uvn's since we will be holding uvn_wl_lock
	 * in the body of the loop.
	 */
	SIMPLEQ_INIT(&uvn_sync_q);
	simple_lock(&uvn_wl_lock);
	for (uvn = LIST_FIRST(&uvn_wlist); uvn != NULL;
	     uvn = LIST_NEXT(uvn, u_wlist)) {

		vp = (struct vnode *) uvn;
		if (mp && vp->v_mount != mp)
			continue;

		/* attempt to gain reference */
		while ((got_lock = simple_lock_try(&uvn->u_obj.vmobjlock)) ==
		    						FALSE &&
				(uvn->u_flags & VXLOCK) == 0)
			/* spin */ ;

		/*
		 * we will exit the loop if either if the following are true:
		 *  - we got the lock [always true if NCPU == 1]
		 *  - we failed to get the lock but noticed the vnode was
		 * 	"blocked" -- in this case the vnode must be a dying
		 *	vnode, and since dying vnodes are in the process of
		 *	being flushed out, we can safely skip this one
		 *
		 * we want to skip over the vnode if we did not get the lock,
		 * or if the vnode is already dying (due to the above logic).
		 *
		 * note that uvn must already be valid because we found it on
		 * the wlist (this also means it can't be ALOCK'd).
		 */
		if (!got_lock || (uvn->u_flags & VXLOCK) != 0) {
			if (got_lock)
				simple_unlock(&uvn->u_obj.vmobjlock);
			continue;		/* skip it */
		}

		vget(vp, LK_INTERLOCK);

		/*
		 * got it!
		 */
		SIMPLEQ_INSERT_HEAD(&uvn_sync_q, uvn, u_syncq);
	}
	simple_unlock(&uvn_wl_lock);

	/*
	 * step 3: we now have a list of uvn's that may need cleaning.
	 * we are holding the uvn_sync_lock, but have dropped the uvn_wl_lock
	 * (so we can now safely lock uvn's again).
	 */

	for (uvn = uvn_sync_q.sqh_first ; uvn ; uvn = uvn->u_syncq.sqe_next) {
		simple_lock(&uvn->u_obj.vmobjlock);
		uvn_flush(&uvn->u_obj, 0, 0,
			  PGO_CLEANIT|PGO_ALLPAGES|PGO_DOACTCLUST);

		/*
		 * if we have the only reference and we just cleaned the uvn,
		 * then we can pull it out of the VDIRTY state
		 * thus allowing us to avoid thinking about flushing it again
		 * on later sync ops.
		 */
		if (uvn->u_obj.uo_refs == 1 && (uvn->u_flags & VDIRTY)) {
			simple_lock(&uvn_wl_lock);
			LIST_REMOVE(uvn, u_wlist);
			uvn->u_flags &= ~VDIRTY;
			simple_unlock(&uvn_wl_lock);
		}

		simple_unlock(&uvn->u_obj.vmobjlock);

		/* now drop our reference to the uvn */
		uvn_detach(&uvn->u_obj);
	}

	/*
	 * done!  release sync lock
	 */
	lockmgr(&uvn_sync_lock, LK_RELEASE, (void *)0);
}


/*
 * uvm_vnp_zerorange:  set a range of bytes in a file to zero.
 */

void
uvm_vnp_zerorange(vp, off, len)
	struct vnode *vp;
	off_t off;
	size_t len;
{
        void *win;

        /*
         * XXX invent kzero() and use it
         */

        while (len) {
                vsize_t bytelen = len;

                win = ubc_alloc(&vp->v_uvm.u_obj, off, &bytelen, UBC_WRITE);
                memset(win, 0, bytelen);
                ubc_release(win, 0);

                off += bytelen;
                len -= bytelen;
        }
}

/*
 * uvn_doasyncget: start one readahead i/o.
 */

static void
uvn_doasyncget(pgs, bytes, blkno)
	struct vm_page **pgs;
	size_t bytes;
	daddr_t blkno;
{
	struct buf *bp;
	struct vnode *vp = (struct vnode *)pgs[0]->uobject;
	int pages = roundup(bytes, PAGE_SIZE) >> PAGE_SHIFT;
	int s;
	UVMHIST_FUNC("uvn_doasyncget"); UVMHIST_CALLED(ubchist);

	UVMHIST_LOG(ubchist, "vp %p offset 0x%x bytes 0x%x blkno 0x%x",
		    vp, (int)pgs[0]->offset, (int)bytes, (int)blkno);

	s = splbio();
	bp = pool_get(&bufpool, PR_WAITOK);
	splx(s);
	bp->b_data = (void *)uvm_pagermapin(pgs, pages, M_WAITOK);
	bp->b_flags = B_BUSY|B_READ|B_CALL|B_ASYNC;
	bp->b_iodone = uvm_aio_biodone;
	bp->b_lblkno = 0;
	bp->b_blkno = blkno;
	bp->b_bufsize = pages << PAGE_SHIFT;
	bp->b_bcount = bytes;
	bp->b_vp = vp;
	UVMHIST_LOG(ubchist, "bp %p", bp, 0,0,0);

	VOP_STRATEGY(bp);
}

#define MAXRAPAGES 16

/*
 * asynchronously create pages for a vnode and read their data.
 */

void
uvm_vnp_asyncget(vp, off, len)
	struct vnode *vp;
	off_t off;
	size_t len;
{
	off_t filesize = vp->v_uvm.u_size;
	struct vm_page *pgs[MAXRAPAGES];
	struct uvm_object *uobj = &vp->v_uvm.u_obj;
	daddr_t lbn, blkno;
	int bshift = vp->v_mount->mnt_fs_bshift;
	int dev_bshift = vp->v_mount->mnt_dev_bshift;
	int i, npages, npgs, startidx, run, bytes, startpage, endpage;
	int count;
	UVMHIST_FUNC("uvn_asyncget"); UVMHIST_CALLED(ubchist);

	if (off != trunc_page(off)) {
		panic("off 0x%x not page-aligned", (int)off);
	}

	UVMHIST_LOG(ubchist, "asyncget off 0x%x len 0x%x",
		    (int)off, (int)len,0,0);

	count = round_page(len) >> PAGE_SHIFT;
	while (count > 0) {
		if (off >= filesize) {
			return;
		}

		lbn = off >> bshift;
		if (VOP_BMAP(vp, lbn, NULL, &blkno, &run) != 0) {
			return;
		}

		UVMHIST_LOG(ubchist, "bmap lbn 0x%x bn 0x%x",
			    (int)lbn, (int)blkno,0,0);

		/* don't do readahead past file holes... */
		if (blkno == (daddr_t)-1) {
			return;
		}

		startpage = off >> PAGE_SHIFT;
		endpage = min(roundup(off + 1 + (run << bshift), 1 << bshift),
			      round_page(filesize)) >> PAGE_SHIFT;
		npages = min(endpage - startpage, min(count, MAXRAPAGES));

		UVMHIST_LOG(ubchist, "off 0x%x run 0x%x "
			    "startpage %d endpage %d",
			    (int)off, run, startpage, endpage);
		UVMHIST_LOG(ubchist, "runend 0x%x fileend 0x%x sum 0x%x",
			    (int)roundup(off + 1 + (run << bshift),
					 (1 << bshift)),
			    (int)round_page(filesize),
			    (int)(off + 1 + (run << bshift)), 0);

		if (npages == 0) {
			return;
		}

		memset(pgs, 0, npages * sizeof(pgs[0]));

		simple_lock(&uobj->vmobjlock);
		npgs = npages;
		uvn_findpages(uobj, off, &npgs, pgs, UFP_NOWAIT | UFP_NOCACHE);
		simple_unlock(&uobj->vmobjlock);

		blkno += (off - (lbn << bshift)) >> dev_bshift;

		/*
		 * activate any pages we just allocated.
		 */

		for (i = 0; i < npages; i++) {
			if (pgs[i] == NULL) {
				continue;
			}
			uvm_pageactivate(pgs[i]);
		}

		/*
		 * start i/os on the pages.
		 */

		for (i = 0; i < npages; i++) {
			for (startidx = i; i < npages; i++) {
				if (pgs[i] == NULL) {
					break;
				}
			}
			if (i > startidx) {
				bytes = min((i - startidx) << PAGE_SHIFT,
					    filesize - pgs[startidx]->offset);
				bytes = roundup(bytes, 1 << dev_bshift);

				UVMHIST_LOG(ubchist, "bytes i %d startidx %d "
					    "filesize 0x%x pgoff 0x%x",
					    i, startidx, (int)filesize,
					    (int)pgs[startidx]->offset);

				uvn_doasyncget(&pgs[startidx], bytes,
					       blkno + startidx *
					       (PAGE_SIZE >> dev_bshift));
			}
		}

		off += npages << PAGE_SHIFT;
		count -= npages;

		/* XXX for now, don't loop */
		return;
	}
}