/*-
 * SPDX-License-Identifier: BSD-4-Clause
 *
 * Copyright (c) 1990 University of Utah.
 * Copyright (c) 1991 The Regents of the University of California.
 * All rights reserved.
 * Copyright (c) 1993, 1994 John S. Dyson
 * Copyright (c) 1995, David Greenman
 *
 * This code is derived from software contributed to Berkeley by
 * the Systems Programming Group of the University of Utah Computer
 * Science Department.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Page to/from files (vnodes).
 */

/*
 * TODO:
 *      Implement VOP_GETPAGES/PUTPAGES interface for filesystems. Will
 *      greatly re-simplify the vnode_pager.
 */

#include <sys/cdefs.h>
#include "opt_vm.h"

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/sysctl.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/bio.h>
#include <sys/buf.h>
#include <sys/vmmeter.h>
#include <sys/ktr.h>
#include <sys/limits.h>
#include <sys/conf.h>
#include <sys/refcount.h>
#include <sys/rwlock.h>
#include <sys/sf_buf.h>
#include <sys/domainset.h>
#include <sys/user.h>

#include <machine/atomic.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pager.h>
#include <vm/vm_map.h>
#include <vm/vnode_pager.h>
#include <vm/vm_extern.h>
#include <vm/uma.h>

static int vnode_pager_addr(struct vnode *vp, vm_ooffset_t address,
    daddr_t *rtaddress, int *run);
static int vnode_pager_input_smlfs(vm_object_t object, vm_page_t m);
static int vnode_pager_input_old(vm_object_t object, vm_page_t m);
static void vnode_pager_dealloc(vm_object_t);
static int vnode_pager_getpages(vm_object_t, vm_page_t *, int, int *, int *);
static int vnode_pager_getpages_async(vm_object_t, vm_page_t *, int, int *,
    int *, vop_getpages_iodone_t, void *);
static void vnode_pager_putpages(vm_object_t, vm_page_t *, int, int, int *);
static boolean_t vnode_pager_haspage(vm_object_t, vm_pindex_t, int *, int *);
static vm_object_t vnode_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
    vm_ooffset_t, struct ucred *cred);
static int vnode_pager_generic_getpages_done(struct buf *);
static void vnode_pager_generic_getpages_done_async(struct buf *);
static void vnode_pager_update_writecount(vm_object_t, vm_offset_t,
    vm_offset_t);
static void vnode_pager_release_writecount(vm_object_t, vm_offset_t,
    vm_offset_t);
static void vnode_pager_getvp(vm_object_t, struct vnode **, bool *);

const struct pagerops vnodepagerops = {
        .pgo_kvme_type = KVME_TYPE_VNODE,
        .pgo_alloc =    vnode_pager_alloc,
        .pgo_dealloc =  vnode_pager_dealloc,
        .pgo_getpages = vnode_pager_getpages,
        .pgo_getpages_async = vnode_pager_getpages_async,
        .pgo_putpages = vnode_pager_putpages,
        .pgo_haspage =  vnode_pager_haspage,
        .pgo_update_writecount = vnode_pager_update_writecount,
        .pgo_release_writecount = vnode_pager_release_writecount,
        .pgo_set_writeable_dirty = vm_object_set_writeable_dirty_,
        .pgo_mightbedirty = vm_object_mightbedirty_,
        .pgo_getvp = vnode_pager_getvp,
};

static struct domainset *vnode_domainset = NULL;

SYSCTL_PROC(_debug, OID_AUTO, vnode_domainset,
    CTLTYPE_STRING | CTLFLAG_MPSAFE | CTLFLAG_RW, &vnode_domainset, 0,
    sysctl_handle_domainset, "A", "Default vnode NUMA policy");

static int nvnpbufs;
SYSCTL_INT(_vm, OID_AUTO, vnode_pbufs, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
    &nvnpbufs, 0, "number of physical buffers allocated for vnode pager");

static uma_zone_t vnode_pbuf_zone;

static void
vnode_pager_init(void *dummy)
{

#ifdef __LP64__
        nvnpbufs = nswbuf * 2;
#else
        nvnpbufs = nswbuf / 2;
#endif
        TUNABLE_INT_FETCH("vm.vnode_pbufs", &nvnpbufs);
        vnode_pbuf_zone = pbuf_zsecond_create("vnpbuf", nvnpbufs);
}
SYSINIT(vnode_pager, SI_SUB_CPU, SI_ORDER_ANY, vnode_pager_init, NULL);

/* Create the VM system backing object for this vnode */
static int
vnode_create_vobject_any(struct vnode *vp, off_t isize, struct thread *td)
{
        vm_object_t object;
        vm_ooffset_t size;
        bool last;

        object = vp->v_object;
        if (object != NULL)
                return (0);

        if (isize == VNODE_NO_SIZE) {
                if (vn_getsize_locked(vp, &size, td->td_ucred) != 0)
                        return (0);
        } else {
                size = isize;
        }

        object = vnode_pager_alloc(vp, size, 0, 0, td->td_ucred);
        /*
         * Dereference the reference we just created.  This assumes
         * that the object is associated with the vp.  We still have
         * to serialize with vnode_pager_dealloc() for the last
         * potential reference.
         */
        VM_OBJECT_RLOCK(object);
        last = refcount_release(&object->ref_count);
        VM_OBJECT_RUNLOCK(object);
        if (last)
                vrele(vp);

        VNASSERT(vp->v_object != NULL, vp, ("%s: NULL object", __func__));

        return (0);
}

int
vnode_create_vobject(struct vnode *vp, off_t isize, struct thread *td)
{
        VNASSERT(!vn_isdisk(vp), vp, ("%s: disk vnode", __func__));
        VNASSERT(isize == VNODE_NO_SIZE || isize >= 0, vp,
            ("%s: invalid size (%jd)", __func__, (intmax_t)isize));

        if (!vn_canvmio(vp))
                return (0);

        return (vnode_create_vobject_any(vp, isize, td));
}

int
vnode_create_disk_vobject(struct vnode *vp, off_t isize, struct thread *td)
{
        VNASSERT(isize > 0, vp, ("%s: invalid size (%jd)", __func__,
            (intmax_t)isize));

        return (vnode_create_vobject_any(vp, isize, td));
}

void
vnode_destroy_vobject(struct vnode *vp)
{
        struct vm_object *obj;

        obj = vp->v_object;
        if (obj == NULL || obj->handle != vp)
                return;
        ASSERT_VOP_ELOCKED(vp, "vnode_destroy_vobject");
        VM_OBJECT_WLOCK(obj);
        MPASS(obj->type == OBJT_VNODE);
        umtx_shm_object_terminated(obj);
        if (obj->ref_count == 0) {
                KASSERT((obj->flags & OBJ_DEAD) == 0,
                   ("vnode_destroy_vobject: Terminating dead object"));
                vm_object_set_flag(obj, OBJ_DEAD);

                /*
                 * Clean pages and flush buffers.
                 */
                vm_object_page_clean(obj, 0, 0, OBJPC_SYNC);
                VM_OBJECT_WUNLOCK(obj);

                vinvalbuf(vp, V_SAVE, 0, 0);

                BO_LOCK(&vp->v_bufobj);
                vp->v_bufobj.bo_flag |= BO_DEAD;
                BO_UNLOCK(&vp->v_bufobj);

                VM_OBJECT_WLOCK(obj);
                vm_object_terminate(obj);
        } else {
                /*
                 * Woe to the process that tries to page now :-).
                 */
                vm_pager_deallocate(obj);
                VM_OBJECT_WUNLOCK(obj);
        }
        KASSERT(vp->v_object == NULL, ("vp %p obj %p", vp, vp->v_object));
}

/*
 * Allocate (or lookup) pager for a vnode.
 * Handle is a vnode pointer.
 */
vm_object_t
vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
    vm_ooffset_t offset, struct ucred *cred)
{
        vm_object_t object;
        struct vnode *vp;

        /*
         * Pageout to vnode, no can do yet.
         */
        if (handle == NULL)
                return (NULL);

        vp = (struct vnode *)handle;
        ASSERT_VOP_LOCKED(vp, "vnode_pager_alloc");
        VNPASS(vp->v_usecount > 0, vp);
retry:
        object = vp->v_object;

        if (object == NULL) {
                /*
                 * Add an object of the appropriate size
                 */
                object = vm_object_allocate(OBJT_VNODE,
                    OFF_TO_IDX(round_page(size)));

                object->un_pager.vnp.vnp_size = size;
                object->un_pager.vnp.writemappings = 0;
                object->domain.dr_policy = vnode_domainset;
                object->handle = handle;
                if ((vp->v_vflag & VV_VMSIZEVNLOCK) != 0) {
                        VM_OBJECT_WLOCK(object);
                        vm_object_set_flag(object, OBJ_SIZEVNLOCK);
                        VM_OBJECT_WUNLOCK(object);
                }
                VI_LOCK(vp);
                if (vp->v_object != NULL) {
                        /*
                         * Object has been created while we were allocating.
                         */
                        VI_UNLOCK(vp);
                        VM_OBJECT_WLOCK(object);
                        KASSERT(object->ref_count == 1,
                            ("leaked ref %p %d", object, object->ref_count));
                        object->type = OBJT_DEAD;
                        refcount_init(&object->ref_count, 0);
                        VM_OBJECT_WUNLOCK(object);
                        vm_object_destroy(object);
                        goto retry;
                }
                vp->v_object = object;
                VI_UNLOCK(vp);
                vrefact(vp);
        } else {
                vm_object_reference(object);
#if VM_NRESERVLEVEL > 0
                if ((object->flags & OBJ_COLORED) == 0) {
                        VM_OBJECT_WLOCK(object);
                        vm_object_color(object, 0);
                        VM_OBJECT_WUNLOCK(object);
                }
#endif
        }
        return (object);
}

/*
 *      The object must be locked.
 */
static void
vnode_pager_dealloc(vm_object_t object)
{
        struct vnode *vp;
        int refs;

        vp = object->handle;
        if (vp == NULL)
                panic("vnode_pager_dealloc: pager already dealloced");

        VM_OBJECT_ASSERT_WLOCKED(object);
        vm_object_pip_wait(object, "vnpdea");
        refs = object->ref_count;

        object->handle = NULL;
        object->type = OBJT_DEAD;
        ASSERT_VOP_ELOCKED(vp, "vnode_pager_dealloc");
        if (object->un_pager.vnp.writemappings > 0) {
                object->un_pager.vnp.writemappings = 0;
                VOP_ADD_WRITECOUNT_CHECKED(vp, -1);
                CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
                    __func__, vp, vp->v_writecount);
        }
        vp->v_object = NULL;
        VI_LOCK(vp);

        /*
         * vm_map_entry_set_vnode_text() cannot reach this vnode by
         * following object->handle.  Clear all text references now.
         * This also clears the transient references from
         * kern_execve(), which is fine because dead_vnodeops uses nop
         * for VOP_UNSET_TEXT().
         */
        if (vp->v_writecount < 0)
                vp->v_writecount = 0;
        VI_UNLOCK(vp);
        VM_OBJECT_WUNLOCK(object);
        if (refs > 0)
                vunref(vp);
        VM_OBJECT_WLOCK(object);
}

static boolean_t
vnode_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before,
    int *after)
{
        struct vnode *vp = object->handle;
        daddr_t bn;
        uintptr_t lockstate;
        int err;
        daddr_t reqblock;
        int poff;
        int bsize;
        int pagesperblock, blocksperpage;

        VM_OBJECT_ASSERT_LOCKED(object);
        /*
         * If no vp or vp is doomed or marked transparent to VM, we do not
         * have the page.
         */
        if (vp == NULL || VN_IS_DOOMED(vp))
                return FALSE;
        /*
         * If the offset is beyond end of file we do
         * not have the page.
         */
        if (IDX_TO_OFF(pindex) >= object->un_pager.vnp.vnp_size)
                return FALSE;

        bsize = vp->v_mount->mnt_stat.f_iosize;
        pagesperblock = atop(bsize);
        blocksperpage = 0;
        if (pagesperblock > 0) {
                reqblock = pindex / pagesperblock;
        } else {
                blocksperpage = (PAGE_SIZE / bsize);
                reqblock = pindex * blocksperpage;
        }
        lockstate = VM_OBJECT_DROP(object);
        err = VOP_BMAP(vp, reqblock, NULL, &bn, after, before);
        VM_OBJECT_PICKUP(object, lockstate);
        if (err)
                return TRUE;
        if (bn == -1)
                return FALSE;
        if (pagesperblock > 0) {
                poff = pindex - (reqblock * pagesperblock);
                if (before) {
                        *before *= pagesperblock;
                        *before += poff;
                }
                if (after) {
                        /*
                         * The BMAP vop can report a partial block in the
                         * 'after', but must not report blocks after EOF.
                         * Assert the latter, and truncate 'after' in case
                         * of the former.
                         */
                        KASSERT((reqblock + *after) * pagesperblock <
                            roundup2(object->size, pagesperblock),
                            ("%s: reqblock %jd after %d size %ju", __func__,
                            (intmax_t )reqblock, *after,
                            (uintmax_t )object->size));
                        *after *= pagesperblock;
                        *after += pagesperblock - (poff + 1);
                        if (pindex + *after >= object->size)
                                *after = object->size - 1 - pindex;
                }
        } else {
                if (before) {
                        *before /= blocksperpage;
                }

                if (after) {
                        *after /= blocksperpage;
                }
        }
        return TRUE;
}

/*
 * Internal routine clearing partial-page content
 */
static void
vnode_pager_subpage_purge(struct vm_page *m, int base, int end)
{
        int size;

        KASSERT(end > base && end <= PAGE_SIZE,
            ("%s: start %d end %d", __func__, base, end));
        size = end - base;

        /*
         * Clear out partial-page garbage in case
         * the page has been mapped.
         */
        pmap_zero_page_area(m, base, size);

        /*
         * Update the valid bits to reflect the blocks
         * that have been zeroed.  Some of these valid
         * bits may have already been set.
         */
        vm_page_set_valid_range(m, base, size);

        /*
         * Round up "base" to the next block boundary so
         * that the dirty bit for a partially zeroed
         * block is not cleared.
         */
        base = roundup2(base, DEV_BSIZE);
        end = rounddown2(end, DEV_BSIZE);

        if (end > base) {
                /*
                 * Clear out partial-page dirty bits.
                 *
                 * note that we do not clear out the
                 * valid bits.  This would prevent
                 * bogus_page replacement from working
                 * properly.
                 */
                vm_page_clear_dirty(m, base, end - base);
        }

}

/*
 * Lets the VM system know about a change in size for a file.
 * We adjust our own internal size and flush any cached pages in
 * the associated object that are affected by the size change.
 *
 * Note: this routine may be invoked as a result of a pager put
 * operation (possibly at object termination time), so we must be careful.
 */
void
vnode_pager_setsize(struct vnode *vp, vm_ooffset_t nsize)
{
        vm_object_t object;
        vm_page_t m;
        vm_pindex_t nobjsize;

        if ((object = vp->v_object) == NULL)
                return;
#ifdef INVARIANTS
        {
                struct mount *mp;

                mp = vp->v_mount;
                if (mp != NULL && (mp->mnt_kern_flag & MNTK_VMSETSIZE_BUG) == 0)
                        assert_vop_elocked(vp,
                            "vnode_pager_setsize and not locked vnode");
        }
#endif
        VM_OBJECT_WLOCK(object);
        if (object->type == OBJT_DEAD) {
                VM_OBJECT_WUNLOCK(object);
                return;
        }
        KASSERT(object->type == OBJT_VNODE,
            ("not vnode-backed object %p", object));
        if (nsize == object->un_pager.vnp.vnp_size) {
                /*
                 * Hasn't changed size
                 */
                VM_OBJECT_WUNLOCK(object);
                return;
        }
        nobjsize = OFF_TO_IDX(nsize + PAGE_MASK);
        if (nsize < object->un_pager.vnp.vnp_size) {
                /*
                 * File has shrunk. Toss any cached pages beyond the new EOF.
                 */
                if (nobjsize < object->size)
                        vm_object_page_remove(object, nobjsize, object->size,
                            0);
                /*
                 * this gets rid of garbage at the end of a page that is now
                 * only partially backed by the vnode.
                 *
                 * XXX for some reason (I don't know yet), if we take a
                 * completely invalid page and mark it partially valid
                 * it can screw up NFS reads, so we don't allow the case.
                 */
                if (!(nsize & PAGE_MASK))
                        goto out;
                m = vm_page_grab(object, OFF_TO_IDX(nsize), VM_ALLOC_NOCREAT);
                if (m == NULL)
                        goto out;
                if (!vm_page_none_valid(m))
                        vnode_pager_subpage_purge(m, (int)nsize & PAGE_MASK,
                            PAGE_SIZE);
                vm_page_xunbusy(m);
        }
out:
#if defined(__powerpc__) && !defined(__powerpc64__)
        object->un_pager.vnp.vnp_size = nsize;
#else
        atomic_store_64(&object->un_pager.vnp.vnp_size, nsize);
#endif
        object->size = nobjsize;
        VM_OBJECT_WUNLOCK(object);
}

/*
 * Lets the VM system know about the purged range for a file. We toss away any
 * cached pages in the associated object that are affected by the purge
 * operation. Partial-page area not aligned to page boundaries will be zeroed
 * and the dirty blocks in DEV_BSIZE unit within a page will not be flushed.
 */
void
vnode_pager_purge_range(struct vnode *vp, vm_ooffset_t start, vm_ooffset_t end)
{
        struct vm_page *m;
        struct vm_object *object;
        vm_pindex_t pi, pistart, piend;
        bool same_page;
        int base, pend;

        ASSERT_VOP_LOCKED(vp, "vnode_pager_purge_range");

        object = vp->v_object;
        pi = start + PAGE_MASK < start ? OBJ_MAX_SIZE :
            OFF_TO_IDX(start + PAGE_MASK);
        pistart = OFF_TO_IDX(start);
        piend = end == 0 ? OBJ_MAX_SIZE : OFF_TO_IDX(end);
        same_page = pistart == piend;
        if ((end != 0 && end <= start) || object == NULL)
                return;

        VM_OBJECT_WLOCK(object);

        if (pi < piend)
                vm_object_page_remove(object, pi, piend, 0);

        if ((start & PAGE_MASK) != 0) {
                base = (int)start & PAGE_MASK;
                pend = same_page ? (int)end & PAGE_MASK : PAGE_SIZE;
                m = vm_page_grab(object, pistart, VM_ALLOC_NOCREAT);
                if (m != NULL) {
                        if (!vm_page_none_valid(m))
                                vnode_pager_subpage_purge(m, base, pend);
                        vm_page_xunbusy(m);
                }
                if (same_page)
                        goto out;
        }
        if ((end & PAGE_MASK) != 0) {
                base = same_page ? (int)start & PAGE_MASK : 0 ;
                pend = (int)end & PAGE_MASK;
                m = vm_page_grab(object, piend, VM_ALLOC_NOCREAT);
                if (m != NULL) {
                        if (!vm_page_none_valid(m))
                                vnode_pager_subpage_purge(m, base, pend);
                        vm_page_xunbusy(m);
                }
        }
out:
        VM_OBJECT_WUNLOCK(object);
}

/*
 * calculate the linear (byte) disk address of specified virtual
 * file address
 */
static int
vnode_pager_addr(struct vnode *vp, vm_ooffset_t address, daddr_t *rtaddress,
    int *run)
{
        int bsize;
        int err;
        daddr_t vblock;
        daddr_t voffset;

        if (VN_IS_DOOMED(vp))
                return -1;

        bsize = vp->v_mount->mnt_stat.f_iosize;
        vblock = address / bsize;
        voffset = address % bsize;

        err = VOP_BMAP(vp, vblock, NULL, rtaddress, run, NULL);
        if (err == 0) {
                if (*rtaddress != -1)
                        *rtaddress += voffset / DEV_BSIZE;
                if (run) {
                        *run += 1;
                        *run *= atop(bsize);
                        *run -= atop(voffset);
                }
        }

        return (err);
}

static void
vnode_pager_input_bdone(struct buf *bp)
{
        runningbufwakeup(bp);
        bdone(bp);
}

/*
 * small block filesystem vnode pager input
 */
static int
vnode_pager_input_smlfs(vm_object_t object, vm_page_t m)
{
        struct vnode *vp;
        struct bufobj *bo;
        struct buf *bp;
        struct sf_buf *sf;
        daddr_t fileaddr;
        vm_offset_t bsize;
        vm_page_bits_t bits;
        int error, i;

        error = 0;
        vp = object->handle;
        if (VN_IS_DOOMED(vp))
                return VM_PAGER_BAD;

        bsize = vp->v_mount->mnt_stat.f_iosize;

        VOP_BMAP(vp, 0, &bo, 0, NULL, NULL);

        sf = sf_buf_alloc(m, 0);

        for (i = 0; i < PAGE_SIZE / bsize; i++) {
                vm_ooffset_t address;

                bits = vm_page_bits(i * bsize, bsize);
                if (m->valid & bits)
                        continue;

                address = IDX_TO_OFF(m->pindex) + i * bsize;
                if (address >= object->un_pager.vnp.vnp_size) {
                        fileaddr = -1;
                } else {
                        error = vnode_pager_addr(vp, address, &fileaddr, NULL);
                        if (error)
                                break;
                }
                if (fileaddr != -1) {
                        bp = uma_zalloc(vnode_pbuf_zone, M_WAITOK);

                        /* build a minimal buffer header */
                        bp->b_iocmd = BIO_READ;
                        bp->b_iodone = vnode_pager_input_bdone;
                        KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
                        KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
                        bp->b_rcred = crhold(curthread->td_ucred);
                        bp->b_wcred = crhold(curthread->td_ucred);
                        bp->b_data = (caddr_t)sf_buf_kva(sf) + i * bsize;
                        bp->b_blkno = fileaddr;
                        pbgetbo(bo, bp);
                        bp->b_vp = vp;
                        bp->b_bcount = bsize;
                        bp->b_bufsize = bsize;
                        (void)runningbufclaim(bp, bp->b_bufsize);

                        /* do the input */
                        bp->b_iooffset = dbtob(bp->b_blkno);
                        bstrategy(bp);

                        bwait(bp, PVM, "vnsrd");

                        if ((bp->b_ioflags & BIO_ERROR) != 0) {
                                KASSERT(bp->b_error != 0,
                                    ("%s: buf error but b_error == 0\n", __func__));
                                error = bp->b_error;
                        }

                        /*
                         * free the buffer header back to the swap buffer pool
                         */
                        bp->b_vp = NULL;
                        pbrelbo(bp);
                        uma_zfree(vnode_pbuf_zone, bp);
                        if (error)
                                break;
                } else
                        bzero((caddr_t)sf_buf_kva(sf) + i * bsize, bsize);
                KASSERT((m->dirty & bits) == 0,
                    ("vnode_pager_input_smlfs: page %p is dirty", m));
                vm_page_bits_set(m, &m->valid, bits);
        }
        sf_buf_free(sf);
        if (error) {
                return VM_PAGER_ERROR;
        }
        return VM_PAGER_OK;
}

/*
 * old style vnode pager input routine
 */
static int
vnode_pager_input_old(vm_object_t object, vm_page_t m)
{
        struct uio auio;
        struct iovec aiov;
        int error;
        int size;
        struct sf_buf *sf;
        struct vnode *vp;

        VM_OBJECT_ASSERT_WLOCKED(object);
        error = 0;

        /*
         * Return failure if beyond current EOF
         */
        if (IDX_TO_OFF(m->pindex) >= object->un_pager.vnp.vnp_size) {
                return VM_PAGER_BAD;
        } else {
                size = PAGE_SIZE;
                if (IDX_TO_OFF(m->pindex) + size > object->un_pager.vnp.vnp_size)
                        size = object->un_pager.vnp.vnp_size - IDX_TO_OFF(m->pindex);
                vp = object->handle;
                VM_OBJECT_WUNLOCK(object);

                /*
                 * Allocate a kernel virtual address and initialize so that
                 * we can use VOP_READ/WRITE routines.
                 */
                sf = sf_buf_alloc(m, 0);

                aiov.iov_base = (caddr_t)sf_buf_kva(sf);
                aiov.iov_len = size;
                auio.uio_iov = &aiov;
                auio.uio_iovcnt = 1;
                auio.uio_offset = IDX_TO_OFF(m->pindex);
                auio.uio_segflg = UIO_SYSSPACE;
                auio.uio_rw = UIO_READ;
                auio.uio_resid = size;
                auio.uio_td = curthread;

                error = VOP_READ(vp, &auio, 0, curthread->td_ucred);
                if (!error) {
                        int count = size - auio.uio_resid;

                        if (count == 0)
                                error = EINVAL;
                        else if (count != PAGE_SIZE)
                                bzero((caddr_t)sf_buf_kva(sf) + count,
                                    PAGE_SIZE - count);
                }
                sf_buf_free(sf);

                VM_OBJECT_WLOCK(object);
        }
        KASSERT(m->dirty == 0, ("vnode_pager_input_old: page %p is dirty", m));
        if (!error)
                vm_page_valid(m);
        return error ? VM_PAGER_ERROR : VM_PAGER_OK;
}

/*
 * generic vnode pager input routine
 */

/*
 * Local media VFS's that do not implement their own VOP_GETPAGES
 * should have their VOP_GETPAGES call to vnode_pager_generic_getpages()
 * to implement the previous behaviour.
 *
 * All other FS's should use the bypass to get to the local media
 * backing vp's VOP_GETPAGES.
 */
static int
vnode_pager_getpages(vm_object_t object, vm_page_t *m, int count, int *rbehind,
    int *rahead)
{
        struct vnode *vp;
        int rtval;

        /* Handle is stable with paging in progress. */
        vp = object->handle;
        rtval = VOP_GETPAGES(vp, m, count, rbehind, rahead);
        KASSERT(rtval != EOPNOTSUPP,
            ("vnode_pager: FS getpages not implemented\n"));
        return rtval;
}

static int
vnode_pager_getpages_async(vm_object_t object, vm_page_t *m, int count,
    int *rbehind, int *rahead, vop_getpages_iodone_t iodone, void *arg)
{
        struct vnode *vp;
        int rtval;

        vp = object->handle;
        rtval = VOP_GETPAGES_ASYNC(vp, m, count, rbehind, rahead, iodone, arg);
        KASSERT(rtval != EOPNOTSUPP,
            ("vnode_pager: FS getpages_async not implemented\n"));
        return (rtval);
}

/*
 * The implementation of VOP_GETPAGES() and VOP_GETPAGES_ASYNC() for
 * local filesystems, where partially valid pages can only occur at
 * the end of file.
 */
int
vnode_pager_local_getpages(struct vop_getpages_args *ap)
{

        return (vnode_pager_generic_getpages(ap->a_vp, ap->a_m, ap->a_count,
            ap->a_rbehind, ap->a_rahead, NULL, NULL));
}

int
vnode_pager_local_getpages_async(struct vop_getpages_async_args *ap)
{
        int error;

        error = vnode_pager_generic_getpages(ap->a_vp, ap->a_m, ap->a_count,
            ap->a_rbehind, ap->a_rahead, ap->a_iodone, ap->a_arg);
        if (error != 0 && ap->a_iodone != NULL)
                ap->a_iodone(ap->a_arg, ap->a_m, ap->a_count, error);
        return (error);
}

/*
 * This is now called from local media FS's to operate against their
 * own vnodes if they fail to implement VOP_GETPAGES.
 */
int
vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int count,
    int *a_rbehind, int *a_rahead, vop_getpages_iodone_t iodone, void *arg)
{
        vm_object_t object;
        struct bufobj *bo;
        struct buf *bp;
        off_t foff;
#ifdef INVARIANTS
        off_t blkno0;
#endif
        int bsize, pagesperblock;
        int error, before, after, rbehind, rahead, poff, i;
        int bytecount, secmask;

        KASSERT(!VN_ISDEV(vp), ("%s does not support devices", __func__));

        if (VN_IS_DOOMED(vp))
                return (VM_PAGER_BAD);

        object = vp->v_object;
        foff = IDX_TO_OFF(m[0]->pindex);
        bsize = vp->v_mount->mnt_stat.f_iosize;
        pagesperblock = atop(bsize);

        KASSERT(foff < object->un_pager.vnp.vnp_size,
            ("%s: page %p offset beyond vp %p size", __func__, m[0], vp));
        KASSERT(count <= atop(maxphys),
            ("%s: requested %d pages", __func__, count));

        /*
         * The last page has valid blocks.  Invalid part can only
         * exist at the end of file, and the page is made fully valid
         * by zeroing in vm_pager_get_pages().
         */
        if (!vm_page_none_valid(m[count - 1]) && --count == 0) {
                if (iodone != NULL)
                        iodone(arg, m, 1, 0);
                return (VM_PAGER_OK);
        }

        bp = uma_zalloc(vnode_pbuf_zone, M_WAITOK);
        MPASS((bp->b_flags & B_MAXPHYS) != 0);

        /*
         * Get the underlying device blocks for the file with VOP_BMAP().
         * If the file system doesn't support VOP_BMAP, use old way of
         * getting pages via VOP_READ.
         */
        error = VOP_BMAP(vp, foff / bsize, &bo, &bp->b_blkno, &after, &before);
        if (error == EOPNOTSUPP) {
                uma_zfree(vnode_pbuf_zone, bp);
                VM_OBJECT_WLOCK(object);
                for (i = 0; i < count; i++) {
                        VM_CNT_INC(v_vnodein);
                        VM_CNT_INC(v_vnodepgsin);
                        error = vnode_pager_input_old(object, m[i]);
                        if (error)
                                break;
                }
                VM_OBJECT_WUNLOCK(object);
                return (error);
        } else if (error != 0) {
                uma_zfree(vnode_pbuf_zone, bp);
                return (VM_PAGER_ERROR);
        }

        /*
         * If the file system supports BMAP, but blocksize is smaller
         * than a page size, then use special small filesystem code.
         */
        if (pagesperblock == 0) {
                uma_zfree(vnode_pbuf_zone, bp);
                for (i = 0; i < count; i++) {
                        VM_CNT_INC(v_vnodein);
                        VM_CNT_INC(v_vnodepgsin);
                        error = vnode_pager_input_smlfs(object, m[i]);
                        if (error)
                                break;
                }
                return (error);
        }

        /*
         * A sparse file can be encountered only for a single page request,
         * which may not be preceded by call to vm_pager_haspage().
         */
        if (bp->b_blkno == -1) {
                KASSERT(count == 1,
                    ("%s: array[%d] request to a sparse file %p", __func__,
                    count, vp));
                uma_zfree(vnode_pbuf_zone, bp);
                pmap_zero_page(m[0]);
                KASSERT(m[0]->dirty == 0, ("%s: page %p is dirty",
                    __func__, m[0]));
                vm_page_valid(m[0]);
                return (VM_PAGER_OK);
        }

#ifdef INVARIANTS
        blkno0 = bp->b_blkno;
#endif
        bp->b_blkno += (foff % bsize) / DEV_BSIZE;

        /* Recalculate blocks available after/before to pages. */
        poff = atop(foff % bsize);
        before *= pagesperblock;
        before += poff;
        after *= pagesperblock;
        after += pagesperblock - (poff + 1);
        if (m[0]->pindex + after >= object->size)
                after = object->size - 1 - m[0]->pindex;
        KASSERT(count <= after + 1, ("%s: %d pages asked, can do only %d",
            __func__, count, after + 1));
        after -= count - 1;

        /* Trim requested rbehind/rahead to possible values. */   
        rbehind = a_rbehind ? *a_rbehind : 0;
        rahead = a_rahead ? *a_rahead : 0;
        rbehind = min(rbehind, before);
        rahead = min(rahead, after);

        /*
         * Check that total amount of pages fit into buf.  Trim rbehind and
         * rahead evenly if not.
         */
        if (rbehind + rahead + count > atop(maxphys)) {
                int trim, sum;

                trim = rbehind + rahead + count - atop(maxphys) + 1;
                sum = rbehind + rahead;
                if (rbehind == before) {
                        /* Roundup rbehind trim to block size. */
                        rbehind -= roundup(trim * rbehind / sum, pagesperblock);
                        if (rbehind < 0)
                                rbehind = 0;
                } else
                        rbehind -= trim * rbehind / sum;
                rahead -= trim * rahead / sum;
        }
        KASSERT(rbehind + rahead + count <= atop(maxphys),
            ("%s: behind %d ahead %d count %d maxphys %lu", __func__,
            rbehind, rahead, count, maxphys));

        /*
         * Fill in the bp->b_pages[] array with requested and optional   
         * read behind or read ahead pages.  Read behind pages are looked
         * up in a backward direction, down to a first cached page.  Same
         * for read ahead pages, but there is no need to shift the array
         * in case of encountering a cached page.
         */
        if (rbehind != 0 || rahead != 0) {
                VM_OBJECT_WLOCK(object);
                vm_object_prepare_buf_pages(object, bp->b_pages, count,
                    &rbehind, &rahead, m);
                VM_OBJECT_WUNLOCK(object);
        } else {
                for (int j = 0; j < count; j++)
                        bp->b_pages[j] = m[j];
        }
        bp->b_blkno -= IDX_TO_OFF(rbehind) / DEV_BSIZE;
        bp->b_pgbefore = rbehind;
        bp->b_pgafter = rahead;
        bp->b_npages = rbehind + count + rahead;

        /* Report back actual behind/ahead read. */
        if (a_rbehind)
                *a_rbehind = bp->b_pgbefore;
        if (a_rahead)
                *a_rahead = bp->b_pgafter;

#ifdef INVARIANTS
        KASSERT(bp->b_npages <= atop(maxphys),
            ("%s: buf %p overflowed", __func__, bp));
        for (int j = 1, prev = 0; j < bp->b_npages; j++) {
                if (bp->b_pages[j] == bogus_page)
                        continue;
                KASSERT(bp->b_pages[j]->pindex - bp->b_pages[prev]->pindex ==
                    j - prev, ("%s: pages array not consecutive, bp %p",
                     __func__, bp));
                prev = j;
        }
#endif

        /*
         * Recalculate first offset and bytecount with regards to read behind.
         * Truncate bytecount to vnode real size and round up physical size
         * for real devices.
         */
        foff = IDX_TO_OFF(bp->b_pages[0]->pindex);
        bytecount = ptoa(bp->b_npages);
        if ((foff + bytecount) > object->un_pager.vnp.vnp_size)
                bytecount = object->un_pager.vnp.vnp_size - foff;
        secmask = bo->bo_bsize - 1;
        KASSERT(secmask < PAGE_SIZE && secmask > 0,
            ("%s: sector size %d too large", __func__, secmask + 1));
        bytecount = (bytecount + secmask) & ~secmask;

        /*
         * And map the pages to be read into the kva, if the filesystem
         * requires mapped buffers.
         */
        if ((vp->v_mount->mnt_kern_flag & MNTK_UNMAPPED_BUFS) != 0 &&
            unmapped_buf_allowed) {
                bp->b_data = unmapped_buf;
                bp->b_offset = 0;
        } else {
                bp->b_data = bp->b_kvabase;
                pmap_qenter((vm_offset_t)bp->b_data, bp->b_pages, bp->b_npages);
        }

        /* Build a minimal buffer header. */
        bp->b_iocmd = BIO_READ;
        KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
        KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
        bp->b_rcred = crhold(curthread->td_ucred);
        bp->b_wcred = crhold(curthread->td_ucred);
        pbgetbo(bo, bp);
        bp->b_vp = vp;
        bp->b_bcount = bp->b_bufsize = bytecount;
        bp->b_iooffset = dbtob(bp->b_blkno);
        KASSERT(IDX_TO_OFF(m[0]->pindex - bp->b_pages[0]->pindex) ==
            (blkno0 - bp->b_blkno) * DEV_BSIZE +
            IDX_TO_OFF(m[0]->pindex) % bsize,
            ("wrong offsets bsize %d m[0] %ju b_pages[0] %ju "
            "blkno0 %ju b_blkno %ju", bsize,
            (uintmax_t)m[0]->pindex, (uintmax_t)bp->b_pages[0]->pindex,
            (uintmax_t)blkno0, (uintmax_t)bp->b_blkno));

        (void)runningbufclaim(bp, bp->b_bufsize);

        VM_CNT_INC(v_vnodein);
        VM_CNT_ADD(v_vnodepgsin, bp->b_npages);

        if (iodone != NULL) { /* async */
                bp->b_pgiodone = iodone;
                bp->b_caller1 = arg;
                bp->b_iodone = vnode_pager_generic_getpages_done_async;
                bp->b_flags |= B_ASYNC;
                BUF_KERNPROC(bp);
                bstrategy(bp);
                return (VM_PAGER_OK);
        } else {
                bp->b_iodone = bdone;
                bstrategy(bp);
                bwait(bp, PVM, "vnread");
                error = vnode_pager_generic_getpages_done(bp);
                for (i = 0; i < bp->b_npages; i++)
                        bp->b_pages[i] = NULL;
                bp->b_vp = NULL;
                pbrelbo(bp);
                uma_zfree(vnode_pbuf_zone, bp);
                return (error != 0 ? VM_PAGER_ERROR : VM_PAGER_OK);
        }
}

static void
vnode_pager_generic_getpages_done_async(struct buf *bp)
{
        int error;

        error = vnode_pager_generic_getpages_done(bp);
        /* Run the iodone upon the requested range. */
        bp->b_pgiodone(bp->b_caller1, bp->b_pages + bp->b_pgbefore,
            bp->b_npages - bp->b_pgbefore - bp->b_pgafter, error);
        for (int i = 0; i < bp->b_npages; i++)
                bp->b_pages[i] = NULL;
        bp->b_vp = NULL;
        pbrelbo(bp);
        uma_zfree(vnode_pbuf_zone, bp);
}

static int
vnode_pager_generic_getpages_done(struct buf *bp)
{
        vm_object_t object;
        off_t tfoff, nextoff;
        int i, error;

        KASSERT((bp->b_ioflags & BIO_ERROR) == 0 || bp->b_error != 0,
            ("%s: buf error but b_error == 0\n", __func__));
        error = (bp->b_ioflags & BIO_ERROR) != 0 ? bp->b_error : 0;
        object = bp->b_vp->v_object;

        runningbufwakeup(bp);

        if (error == 0 && bp->b_bcount != ptoa(bp->b_npages)) {
                if (!buf_mapped(bp)) {
                        bp->b_data = bp->b_kvabase;
                        pmap_qenter((vm_offset_t)bp->b_data, bp->b_pages,
                            bp->b_npages);
                }
                bzero(bp->b_data + bp->b_bcount,
                    ptoa(bp->b_npages) - bp->b_bcount);
        }
        if (buf_mapped(bp)) {
                pmap_qremove((vm_offset_t)bp->b_data, bp->b_npages);
                bp->b_data = unmapped_buf;
        }

        /*
         * If the read failed, we must free any read ahead/behind pages here.
         * The requested pages are freed by the caller (for sync requests)
         * or by the bp->b_pgiodone callback (for async requests).
         */
        if (error != 0) {
                VM_OBJECT_WLOCK(object);
                for (i = 0; i < bp->b_pgbefore; i++)
                        vm_page_free_invalid(bp->b_pages[i]);
                for (i = bp->b_npages - bp->b_pgafter; i < bp->b_npages; i++)
                        vm_page_free_invalid(bp->b_pages[i]);
                VM_OBJECT_WUNLOCK(object);
                return (error);
        }

        /* Read lock to protect size. */
        VM_OBJECT_RLOCK(object);
        for (i = 0, tfoff = IDX_TO_OFF(bp->b_pages[0]->pindex);
            i < bp->b_npages; i++, tfoff = nextoff) {
                vm_page_t mt;

                nextoff = tfoff + PAGE_SIZE;
                mt = bp->b_pages[i];
                if (mt == bogus_page)
                        continue;

                if (nextoff <= object->un_pager.vnp.vnp_size) {
                        /*
                         * Read filled up entire page.
                         */
                        vm_page_valid(mt);
                        KASSERT(mt->dirty == 0,
                            ("%s: page %p is dirty", __func__, mt));
                        KASSERT(!pmap_page_is_mapped(mt),
                            ("%s: page %p is mapped", __func__, mt));
                } else {
                        /*
                         * Read did not fill up entire page.
                         *
                         * Currently we do not set the entire page valid,
                         * we just try to clear the piece that we couldn't
                         * read.
                         */
                        vm_page_set_valid_range(mt, 0,
                            object->un_pager.vnp.vnp_size - tfoff);
                        KASSERT((mt->dirty & vm_page_bits(0,
                            object->un_pager.vnp.vnp_size - tfoff)) == 0,
                            ("%s: page %p is dirty", __func__, mt));
                }

                if (i < bp->b_pgbefore || i >= bp->b_npages - bp->b_pgafter)
                        vm_page_readahead_finish(mt);
        }
        VM_OBJECT_RUNLOCK(object);

        return (error);
}

/*
 * EOPNOTSUPP is no longer legal.  For local media VFS's that do not
 * implement their own VOP_PUTPAGES, their VOP_PUTPAGES should call to
 * vnode_pager_generic_putpages() to implement the previous behaviour.
 *
 * All other FS's should use the bypass to get to the local media
 * backing vp's VOP_PUTPAGES.
 */
static void
vnode_pager_putpages(vm_object_t object, vm_page_t *m, int count,
    int flags, int *rtvals)
{
        int rtval __diagused;
        struct vnode *vp;
        int bytes = ptoa(count);

        /*
         * Force synchronous operation if we are extremely low on memory
         * to prevent a low-memory deadlock.  VOP operations often need to
         * allocate more memory to initiate the I/O ( i.e. do a BMAP
         * operation ).  The swap pager handles the case by limiting the amount
         * of asynchronous I/O, but that sort of solution doesn't scale well
         * for the vnode pager without a lot of work.
         *
         * Also, the backing vnode's iodone routine may not wake the pageout
         * daemon up.  This should be probably be addressed XXX.
         */

        if (vm_page_count_min())
                flags |= VM_PAGER_PUT_SYNC;

        /*
         * Call device-specific putpages function
         */
        vp = object->handle;
        VM_OBJECT_WUNLOCK(object);
        rtval = VOP_PUTPAGES(vp, m, bytes, flags, rtvals);
        KASSERT(rtval != EOPNOTSUPP, 
            ("vnode_pager: stale FS putpages\n"));
        VM_OBJECT_WLOCK(object);
}

static int
vn_off2bidx(vm_ooffset_t offset)
{

        return ((offset & PAGE_MASK) / DEV_BSIZE);
}

static bool
vn_dirty_blk(vm_page_t m, vm_ooffset_t offset)
{

        KASSERT(IDX_TO_OFF(m->pindex) <= offset &&
            offset < IDX_TO_OFF(m->pindex + 1),
            ("page %p pidx %ju offset %ju", m, (uintmax_t)m->pindex,
            (uintmax_t)offset));
        return ((m->dirty & ((vm_page_bits_t)1 << vn_off2bidx(offset))) != 0);
}

/*
 * This is now called from local media FS's to operate against their
 * own vnodes if they fail to implement VOP_PUTPAGES.
 *
 * This is typically called indirectly via the pageout daemon and
 * clustering has already typically occurred, so in general we ask the
 * underlying filesystem to write the data out asynchronously rather
 * then delayed.
 */
int
vnode_pager_generic_putpages(struct vnode *vp, vm_page_t *ma, int bytecount,
    int flags, int *rtvals)
{
        vm_object_t object;
        vm_page_t m;
        vm_ooffset_t max_offset, next_offset, poffset, prev_offset;
        struct uio auio;
        struct iovec aiov;
        off_t prev_resid, wrsz;
        int count, error, i, maxsize, ncount, pgoff, ppscheck;
        bool in_hole;
        static struct timeval lastfail;
        static int curfail;

        object = vp->v_object;
        count = atop(bytecount);

        for (i = 0; i < count; i++)
                rtvals[i] = VM_PAGER_ERROR;

        if ((int64_t)ma[0]->pindex < 0) {
                printf("vnode_pager_generic_putpages: "
                    "attempt to write meta-data 0x%jx(%lx)\n",
                    (uintmax_t)ma[0]->pindex, (u_long)ma[0]->dirty);
                rtvals[0] = VM_PAGER_BAD;
                return (VM_PAGER_BAD);
        }

        maxsize = ptoa(count);
        ncount = count;

        poffset = IDX_TO_OFF(ma[0]->pindex);

        /*
         * If the page-aligned write is larger then the actual file we
         * have to invalidate pages occurring beyond the file EOF.  However,
         * there is an edge case where a file may not be page-aligned where
         * the last page is partially invalid.  In this case the filesystem
         * may not properly clear the dirty bits for the entire page (which
         * could be VM_PAGE_BITS_ALL due to the page having been mmap()d).
         * With the page busied we are free to fix up the dirty bits here.
         *
         * We do not under any circumstances truncate the valid bits, as
         * this will screw up bogus page replacement.
         */
        VM_OBJECT_RLOCK(object);
        if (maxsize + poffset > object->un_pager.vnp.vnp_size) {
                if (object->un_pager.vnp.vnp_size > poffset) {
                        maxsize = object->un_pager.vnp.vnp_size - poffset;
                        ncount = btoc(maxsize);
                        if ((pgoff = (int)maxsize & PAGE_MASK) != 0) {
                                pgoff = roundup2(pgoff, DEV_BSIZE);

                                /*
                                 * If the page is busy and the following
                                 * conditions hold, then the page's dirty
                                 * field cannot be concurrently changed by a
                                 * pmap operation.
                                 */
                                m = ma[ncount - 1];
                                vm_page_assert_sbusied(m);
                                KASSERT(!pmap_page_is_write_mapped(m),
                ("vnode_pager_generic_putpages: page %p is not read-only", m));
                                MPASS(m->dirty != 0);
                                vm_page_clear_dirty(m, pgoff, PAGE_SIZE -
                                    pgoff);
                        }
                } else {
                        maxsize = 0;
                        ncount = 0;
                }
                for (i = ncount; i < count; i++)
                        rtvals[i] = VM_PAGER_BAD;
        }
        VM_OBJECT_RUNLOCK(object);

        auio.uio_iov = &aiov;
        auio.uio_segflg = UIO_NOCOPY;
        auio.uio_rw = UIO_WRITE;
        auio.uio_td = NULL;
        max_offset = roundup2(poffset + maxsize, DEV_BSIZE);

        for (prev_offset = poffset; prev_offset < max_offset;) {
                /* Skip clean blocks. */
                for (in_hole = true; in_hole && prev_offset < max_offset;) {
                        m = ma[OFF_TO_IDX(prev_offset - poffset)];
                        for (i = vn_off2bidx(prev_offset);
                            i < sizeof(vm_page_bits_t) * NBBY &&
                            prev_offset < max_offset; i++) {
                                if (vn_dirty_blk(m, prev_offset)) {
                                        in_hole = false;
                                        break;
                                }
                                prev_offset += DEV_BSIZE;
                        }
                }
                if (in_hole)
                        goto write_done;

                /* Find longest run of dirty blocks. */
                for (next_offset = prev_offset; next_offset < max_offset;) {
                        m = ma[OFF_TO_IDX(next_offset - poffset)];
                        for (i = vn_off2bidx(next_offset);
                            i < sizeof(vm_page_bits_t) * NBBY &&
                            next_offset < max_offset; i++) {
                                if (!vn_dirty_blk(m, next_offset))
                                        goto start_write;
                                next_offset += DEV_BSIZE;
                        }
                }
start_write:
                if (next_offset > poffset + maxsize)
                        next_offset = poffset + maxsize;
                if (prev_offset == next_offset)
                        goto write_done;

                /*
                 * Getting here requires finding a dirty block in the
                 * 'skip clean blocks' loop.
                 */

                aiov.iov_base = NULL;
                auio.uio_iovcnt = 1;
                auio.uio_offset = prev_offset;
                prev_resid = auio.uio_resid = aiov.iov_len = next_offset -
                    prev_offset;
                error = VOP_WRITE(vp, &auio,
                    vnode_pager_putpages_ioflags(flags), curthread->td_ucred);

                wrsz = prev_resid - auio.uio_resid;
                if (wrsz == 0) {
                        if (ppsratecheck(&lastfail, &curfail, 1) != 0) {
                                vn_printf(vp, "vnode_pager_putpages: "
                                    "zero-length write at %ju resid %zd\n",
                                    auio.uio_offset, auio.uio_resid);
                        }
                        break;
                }

                /* Adjust the starting offset for next iteration. */
                prev_offset += wrsz;
                MPASS(auio.uio_offset == prev_offset);

                ppscheck = 0;
                if (error != 0 && (ppscheck = ppsratecheck(&lastfail,
                    &curfail, 1)) != 0)
                        vn_printf(vp, "vnode_pager_putpages: I/O error %d\n",
                            error);
                if (auio.uio_resid != 0 && (ppscheck != 0 ||
                    ppsratecheck(&lastfail, &curfail, 1) != 0))
                        vn_printf(vp, "vnode_pager_putpages: residual I/O %zd "
                            "at %ju\n", auio.uio_resid,
                            (uintmax_t)ma[0]->pindex);
                if (error != 0 || auio.uio_resid != 0)
                        break;
        }
write_done:
        /* Mark completely processed pages. */
        for (i = 0; i < OFF_TO_IDX(prev_offset - poffset); i++)
                rtvals[i] = VM_PAGER_OK;
        /* Mark partial EOF page. */
        if (prev_offset == poffset + maxsize && (prev_offset & PAGE_MASK) != 0)
                rtvals[i++] = VM_PAGER_OK;
        /* Unwritten pages in range, free bonus if the page is clean. */
        for (; i < ncount; i++)
                rtvals[i] = ma[i]->dirty == 0 ? VM_PAGER_OK : VM_PAGER_ERROR;
        VM_CNT_ADD(v_vnodepgsout, i);
        VM_CNT_INC(v_vnodeout);
        return (rtvals[0]);
}

int
vnode_pager_putpages_ioflags(int pager_flags)
{
        int ioflags;

        /*
         * Pageouts are already clustered, use IO_ASYNC to force a
         * bawrite() rather then a bdwrite() to prevent paging I/O
         * from saturating the buffer cache.  Dummy-up the sequential
         * heuristic to cause large ranges to cluster.  If neither
         * IO_SYNC or IO_ASYNC is set, the system decides how to
         * cluster.
         */
        ioflags = IO_VMIO;
        if ((pager_flags & (VM_PAGER_PUT_SYNC | VM_PAGER_PUT_INVAL)) != 0)
                ioflags |= IO_SYNC;
        else if ((pager_flags & VM_PAGER_CLUSTER_OK) == 0)
                ioflags |= IO_ASYNC;
        ioflags |= (pager_flags & VM_PAGER_PUT_INVAL) != 0 ? IO_INVAL: 0;
        ioflags |= (pager_flags & VM_PAGER_PUT_NOREUSE) != 0 ? IO_NOREUSE : 0;
        ioflags |= IO_SEQMAX << IO_SEQSHIFT;
        return (ioflags);
}

/*
 * vnode_pager_undirty_pages().
 *
 * A helper to mark pages as clean after pageout that was possibly
 * done with a short write.  The lpos argument specifies the page run
 * length in bytes, and the written argument specifies how many bytes
 * were actually written.  eof is the offset past the last valid byte
 * in the vnode using the absolute file position of the first byte in
 * the run as the base from which it is computed.
 */
void
vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written, off_t eof,
    int lpos)
{
        int i, npages, pos;

        /* Process pages up to round_page(written) */
        pos = written & PAGE_MASK;
        npages = atop(written);
        for (i = 0; i < npages; i++) {
                rtvals[i] = VM_PAGER_OK;
                vm_page_undirty(ma[i]);
        }
        if (pos != 0) {
                /* Partially written page. */
                rtvals[i] = VM_PAGER_AGAIN;
                vm_page_clear_dirty(ma[i], 0, pos);
        }

        /* Process pages from trunc_page(eof) to round_page(lpos) */
        pos = eof & PAGE_MASK;
        i = atop(eof);
        npages = atop(lpos);
        if (i < npages && pos != 0) {
                /*
                 * The page contains the last valid byte in the
                 * vnode, mark the rest of the page as clean,
                 * potentially making the whole page clean.
                 */
                pos = roundup2(pos, DEV_BSIZE);
                vm_page_clear_dirty(ma[i], pos, PAGE_SIZE - pos);

                /*
                 * If the page was cleaned, report the pageout on it
                 * as successful.  msync() no longer needs to write
                 * out the page, endlessly creating write requests
                 * and dirty buffers.
                 */
                if (ma[i]->dirty == 0)
                        rtvals[i] = VM_PAGER_OK;
                i++;
        }
        for (; i < npages; i++) {
                /* vm_pageout_flush() clears dirty */
                rtvals[i] = VM_PAGER_BAD;
        }
}

static void
vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
    vm_offset_t end)
{
        struct vnode *vp;
        vm_ooffset_t old_wm;

        VM_OBJECT_WLOCK(object);
        if (object->type != OBJT_VNODE) {
                VM_OBJECT_WUNLOCK(object);
                return;
        }
        old_wm = object->un_pager.vnp.writemappings;
        object->un_pager.vnp.writemappings += (vm_ooffset_t)end - start;
        vp = object->handle;
        if (old_wm == 0 && object->un_pager.vnp.writemappings != 0) {
                ASSERT_VOP_LOCKED(vp, "v_writecount inc");
                VOP_ADD_WRITECOUNT_CHECKED(vp, 1);
                CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d",
                    __func__, vp, vp->v_writecount);
        } else if (old_wm != 0 && object->un_pager.vnp.writemappings == 0) {
                ASSERT_VOP_LOCKED(vp, "v_writecount dec");
                VOP_ADD_WRITECOUNT_CHECKED(vp, -1);
                CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
                    __func__, vp, vp->v_writecount);
        }
        VM_OBJECT_WUNLOCK(object);
}

static void
vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
    vm_offset_t end)
{
        struct vnode *vp;
        struct mount *mp;
        vm_offset_t inc;

        VM_OBJECT_WLOCK(object);

        /*
         * First, recheck the object type to account for the race when
         * the vnode is reclaimed.
         */
        if (object->type != OBJT_VNODE) {
                VM_OBJECT_WUNLOCK(object);
                return;
        }

        /*
         * Optimize for the case when writemappings is not going to
         * zero.
         */
        inc = end - start;
        if (object->un_pager.vnp.writemappings != inc) {
                object->un_pager.vnp.writemappings -= inc;
                VM_OBJECT_WUNLOCK(object);
                return;
        }

        vp = object->handle;
        vhold(vp);
        VM_OBJECT_WUNLOCK(object);
        mp = NULL;
        vn_start_write(vp, &mp, V_WAIT);
        vn_lock(vp, LK_SHARED | LK_RETRY);

        /*
         * Decrement the object's writemappings, by swapping the start
         * and end arguments for vnode_pager_update_writecount().  If
         * there was not a race with vnode reclaimation, then the
         * vnode's v_writecount is decremented.
         */
        vnode_pager_update_writecount(object, end, start);
        VOP_UNLOCK(vp);
        vdrop(vp);
        if (mp != NULL)
                vn_finished_write(mp);
}

static void
vnode_pager_getvp(vm_object_t object, struct vnode **vpp, bool *vp_heldp)
{
        *vpp = object->handle;
}

static void
vnode_pager_clean1(struct vnode *vp, int sync_flags)
{
        struct vm_object *obj;

        ASSERT_VOP_LOCKED(vp, "needs lock for writes");
        obj = vp->v_object;
        if (obj == NULL)
                return;

        VM_OBJECT_WLOCK(obj);
        vm_object_page_clean(obj, 0, 0, sync_flags);
        VM_OBJECT_WUNLOCK(obj);
}

void
vnode_pager_clean_sync(struct vnode *vp)
{
        vnode_pager_clean1(vp, OBJPC_SYNC);
}

void
vnode_pager_clean_async(struct vnode *vp)
{
        vnode_pager_clean1(vp, 0);
}