sys/vm/vnode_pager.c

   1 /*-
   2  * Copyright (c) 1990 University of Utah.
   3  * Copyright (c) 1991 The Regents of the University of California.
   4  * All rights reserved.
   5  * Copyright (c) 1993, 1994 John S. Dyson
   6  * Copyright (c) 1995, David Greenman
   7  *
   8  * This code is derived from software contributed to Berkeley by
   9  * the Systems Programming Group of the University of Utah Computer
  10  * Science Department.
  11  *
  12  * Redistribution and use in source and binary forms, with or without
  13  * modification, are permitted provided that the following conditions
  14  * are met:
  15  * 1. Redistributions of source code must retain the above copyright
  16  *    notice, this list of conditions and the following disclaimer.
  17  * 2. Redistributions in binary form must reproduce the above copyright
  18  *    notice, this list of conditions and the following disclaimer in the
  19  *    documentation and/or other materials provided with the distribution.
  20  * 3. All advertising materials mentioning features or use of this software
  21  *    must display the following acknowledgement:
  22  *      This product includes software developed by the University of
  23  *      California, Berkeley and its contributors.
  24  * 4. Neither the name of the University nor the names of its contributors
  25  *    may be used to endorse or promote products derived from this software
  26  *    without specific prior written permission.
  27  *
  28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  38  * SUCH DAMAGE.
  39  *
  40  *      from: @(#)vnode_pager.c 7.5 (Berkeley) 4/20/91
  41  */
  42
  43 /*
  44  * Page to/from files (vnodes).
  45  */
  46
  47 /*
  48  * TODO:
  49  *      Implement VOP_GETPAGES/PUTPAGES interface for filesystems. Will
  50  *      greatly re-simplify the vnode_pager.
  51  */
  52
  53 #include <sys/cdefs.h>
  54 __FBSDID("$FreeBSD$");
  55
  56 #include <sys/param.h>
  57 #include <sys/systm.h>
  58 #include <sys/proc.h>
  59 #include <sys/vnode.h>
  60 #include <sys/mount.h>
  61 #include <sys/bio.h>
  62 #include <sys/buf.h>
  63 #include <sys/vmmeter.h>
  64 #include <sys/limits.h>
  65 #include <sys/conf.h>
  66 #include <sys/rwlock.h>
  67 #include <sys/sf_buf.h>
  68
  69 #include <machine/atomic.h>
  70
  71 #include <vm/vm.h>
  72 #include <vm/vm_param.h>
  73 #include <vm/vm_object.h>
  74 #include <vm/vm_page.h>
  75 #include <vm/vm_pager.h>
  76 #include <vm/vm_map.h>
  77 #include <vm/vnode_pager.h>
  78 #include <vm/vm_extern.h>
  79
  80 static int vnode_pager_addr(struct vnode *vp, vm_ooffset_t address,
  81     daddr_t *rtaddress, int *run);
  82 static int vnode_pager_input_smlfs(vm_object_t object, vm_page_t m);
  83 static int vnode_pager_input_old(vm_object_t object, vm_page_t m);
  84 static void vnode_pager_dealloc(vm_object_t);
  85 static int vnode_pager_getpages(vm_object_t, vm_page_t *, int, int);
  86 static void vnode_pager_putpages(vm_object_t, vm_page_t *, int, int, int *);
  87 static boolean_t vnode_pager_haspage(vm_object_t, vm_pindex_t, int *, int *);
  88 static vm_object_t vnode_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
  89     vm_ooffset_t, struct ucred *cred);
  90
  91 struct pagerops vnodepagerops = {
  92         .pgo_alloc =    vnode_pager_alloc,
  93         .pgo_dealloc =  vnode_pager_dealloc,
  94         .pgo_getpages = vnode_pager_getpages,
  95         .pgo_putpages = vnode_pager_putpages,
  96         .pgo_haspage =  vnode_pager_haspage,
  97 };
  98
  99 int vnode_pbuf_freecnt;
 100
 101 /* Create the VM system backing object for this vnode */
 102 int
 103 vnode_create_vobject(struct vnode *vp, off_t isize, struct thread *td)
 104 {
 105         vm_object_t object;
 106         vm_ooffset_t size = isize;
 107         struct vattr va;
 108
 109         if (!vn_isdisk(vp, NULL) && vn_canvmio(vp) == FALSE)
 110                 return (0);
 111
 112         while ((object = vp->v_object) != NULL) {
 113                 VM_OBJECT_WLOCK(object);
 114                 if (!(object->flags & OBJ_DEAD)) {
 115                         VM_OBJECT_WUNLOCK(object);
 116                         return (0);
 117                 }
 118                 VOP_UNLOCK(vp, 0);
 119                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
 120                 VM_OBJECT_SLEEP(object, object, PDROP | PVM, "vodead", 0);
 121                 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 122         }
 123
 124         if (size == 0) {
 125                 if (vn_isdisk(vp, NULL)) {
 126                         size = IDX_TO_OFF(INT_MAX);
 127                 } else {
 128                         if (VOP_GETATTR(vp, &va, td->td_ucred))
 129                                 return (0);
 130                         size = va.va_size;
 131                 }
 132         }
 133
 134         object = vnode_pager_alloc(vp, size, 0, 0, td->td_ucred);
 135         /*
 136          * Dereference the reference we just created.  This assumes
 137          * that the object is associated with the vp.
 138          */
 139         VM_OBJECT_WLOCK(object);
 140         object->ref_count--;
 141         VM_OBJECT_WUNLOCK(object);
 142         vrele(vp);
 143
 144         KASSERT(vp->v_object != NULL, ("vnode_create_vobject: NULL object"));
 145
 146         return (0);
 147 }
 148
 149 void
 150 vnode_destroy_vobject(struct vnode *vp)
 151 {
 152         struct vm_object *obj;
 153
 154         obj = vp->v_object;
 155         if (obj == NULL)
 156                 return;
 157         ASSERT_VOP_ELOCKED(vp, "vnode_destroy_vobject");
 158         VM_OBJECT_WLOCK(obj);
 159         if (obj->ref_count == 0) {
 160                 /*
 161                  * don't double-terminate the object
 162                  */
 163                 if ((obj->flags & OBJ_DEAD) == 0)
 164                         vm_object_terminate(obj);
 165                 else
 166                         VM_OBJECT_WUNLOCK(obj);
 167         } else {
 168                 /*
 169                  * Woe to the process that tries to page now :-).
 170                  */
 171                 vm_pager_deallocate(obj);
 172                 VM_OBJECT_WUNLOCK(obj);
 173         }
 174         vp->v_object = NULL;
 175 }
 176
 177
 178 /*
 179  * Allocate (or lookup) pager for a vnode.
 180  * Handle is a vnode pointer.
 181  *
 182  * MPSAFE
 183  */
 184 vm_object_t
 185 vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
 186     vm_ooffset_t offset, struct ucred *cred)
 187 {
 188         vm_object_t object;
 189         struct vnode *vp;
 190
 191         /*
 192          * Pageout to vnode, no can do yet.
 193          */
 194         if (handle == NULL)
 195                 return (NULL);
 196
 197         vp = (struct vnode *) handle;
 198
 199         /*
 200          * If the object is being terminated, wait for it to
 201          * go away.
 202          */
 203 retry:
 204         while ((object = vp->v_object) != NULL) {
 205                 VM_OBJECT_WLOCK(object);
 206                 if ((object->flags & OBJ_DEAD) == 0)
 207                         break;
 208                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
 209                 VM_OBJECT_SLEEP(object, object, PDROP | PVM, "vadead", 0);
 210         }
 211
 212         KASSERT(vp->v_usecount != 0, ("vnode_pager_alloc: no vnode reference"));
 213
 214         if (object == NULL) {
 215                 /*
 216                  * Add an object of the appropriate size
 217                  */
 218                 object = vm_object_allocate(OBJT_VNODE, OFF_TO_IDX(round_page(size)));
 219
 220                 object->un_pager.vnp.vnp_size = size;
 221                 object->un_pager.vnp.writemappings = 0;
 222
 223                 object->handle = handle;
 224                 VI_LOCK(vp);
 225                 if (vp->v_object != NULL) {
 226                         /*
 227                          * Object has been created while we were sleeping
 228                          */
 229                         VI_UNLOCK(vp);
 230                         VM_OBJECT_WLOCK(object);
 231                         KASSERT(object->ref_count == 1,
 232                             ("leaked ref %p %d", object, object->ref_count));
 233                         object->type = OBJT_DEAD;
 234                         object->ref_count = 0;
 235                         VM_OBJECT_WUNLOCK(object);
 236                         vm_object_destroy(object);
 237                         goto retry;
 238                 }
 239                 vp->v_object = object;
 240                 VI_UNLOCK(vp);
 241         } else {
 242                 object->ref_count++;
 243                 VM_OBJECT_WUNLOCK(object);
 244         }
 245         vref(vp);
 246         return (object);
 247 }
 248
 249 /*
 250  *      The object must be locked.
 251  */
 252 static void
 253 vnode_pager_dealloc(object)
 254         vm_object_t object;
 255 {
 256         struct vnode *vp;
 257         int refs;
 258
 259         vp = object->handle;
 260         if (vp == NULL)
 261                 panic("vnode_pager_dealloc: pager already dealloced");
 262
 263         VM_OBJECT_ASSERT_WLOCKED(object);
 264         vm_object_pip_wait(object, "vnpdea");
 265         refs = object->ref_count;
 266
 267         object->handle = NULL;
 268         object->type = OBJT_DEAD;
 269         if (object->flags & OBJ_DISCONNECTWNT) {
 270                 vm_object_clear_flag(object, OBJ_DISCONNECTWNT);
 271                 wakeup(object);
 272         }
 273         ASSERT_VOP_ELOCKED(vp, "vnode_pager_dealloc");
 274         if (object->un_pager.vnp.writemappings > 0) {
 275                 object->un_pager.vnp.writemappings = 0;
 276                 VOP_ADD_WRITECOUNT(vp, -1);
 277                 CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
 278                     __func__, vp, vp->v_writecount);
 279         }
 280         vp->v_object = NULL;
 281         VOP_UNSET_TEXT(vp);
 282         VM_OBJECT_WUNLOCK(object);
 283         while (refs-- > 0)
 284                 vunref(vp);
 285         VM_OBJECT_WLOCK(object);
 286 }
 287
 288 static boolean_t
 289 vnode_pager_haspage(object, pindex, before, after)
 290         vm_object_t object;
 291         vm_pindex_t pindex;
 292         int *before;
 293         int *after;
 294 {
 295         struct vnode *vp = object->handle;
 296         daddr_t bn;
 297         int err;
 298         daddr_t reqblock;
 299         int poff;
 300         int bsize;
 301         int pagesperblock, blocksperpage;
 302
 303         VM_OBJECT_ASSERT_WLOCKED(object);
 304         /*
 305          * If no vp or vp is doomed or marked transparent to VM, we do not
 306          * have the page.
 307          */
 308         if (vp == NULL || vp->v_iflag & VI_DOOMED)
 309                 return FALSE;
 310         /*
 311          * If the offset is beyond end of file we do
 312          * not have the page.
 313          */
 314         if (IDX_TO_OFF(pindex) >= object->un_pager.vnp.vnp_size)
 315                 return FALSE;
 316
 317         bsize = vp->v_mount->mnt_stat.f_iosize;
 318         pagesperblock = bsize / PAGE_SIZE;
 319         blocksperpage = 0;
 320         if (pagesperblock > 0) {
 321                 reqblock = pindex / pagesperblock;
 322         } else {
 323                 blocksperpage = (PAGE_SIZE / bsize);
 324                 reqblock = pindex * blocksperpage;
 325         }
 326         VM_OBJECT_WUNLOCK(object);
 327         err = VOP_BMAP(vp, reqblock, NULL, &bn, after, before);
 328         VM_OBJECT_WLOCK(object);
 329         if (err)
 330                 return TRUE;
 331         if (bn == -1)
 332                 return FALSE;
 333         if (pagesperblock > 0) {
 334                 poff = pindex - (reqblock * pagesperblock);
 335                 if (before) {
 336                         *before *= pagesperblock;
 337                         *before += poff;
 338                 }
 339                 if (after) {
 340                         int numafter;
 341                         *after *= pagesperblock;
 342                         numafter = pagesperblock - (poff + 1);
 343                         if (IDX_TO_OFF(pindex + numafter) >
 344                             object->un_pager.vnp.vnp_size) {
 345                                 numafter =
 346                                     OFF_TO_IDX(object->un_pager.vnp.vnp_size) -
 347                                     pindex;
 348                         }
 349                         *after += numafter;
 350                 }
 351         } else {
 352                 if (before) {
 353                         *before /= blocksperpage;
 354                 }
 355
 356                 if (after) {
 357                         *after /= blocksperpage;
 358                 }
 359         }
 360         return TRUE;
 361 }
 362
 363 /*
 364  * Lets the VM system know about a change in size for a file.
 365  * We adjust our own internal size and flush any cached pages in
 366  * the associated object that are affected by the size change.
 367  *
 368  * Note: this routine may be invoked as a result of a pager put
 369  * operation (possibly at object termination time), so we must be careful.
 370  */
 371 void
 372 vnode_pager_setsize(vp, nsize)
 373         struct vnode *vp;
 374         vm_ooffset_t nsize;
 375 {
 376         vm_object_t object;
 377         vm_page_t m;
 378         vm_pindex_t nobjsize;
 379
 380         if ((object = vp->v_object) == NULL)
 381                 return;
 382 /*      ASSERT_VOP_ELOCKED(vp, "vnode_pager_setsize and not locked vnode"); */
 383         VM_OBJECT_WLOCK(object);
 384         if (object->type == OBJT_DEAD) {
 385                 VM_OBJECT_WUNLOCK(object);
 386                 return;
 387         }
 388         KASSERT(object->type == OBJT_VNODE,
 389             ("not vnode-backed object %p", object));
 390         if (nsize == object->un_pager.vnp.vnp_size) {
 391                 /*
 392                  * Hasn't changed size
 393                  */
 394                 VM_OBJECT_WUNLOCK(object);
 395                 return;
 396         }
 397         nobjsize = OFF_TO_IDX(nsize + PAGE_MASK);
 398         if (nsize < object->un_pager.vnp.vnp_size) {
 399                 /*
 400                  * File has shrunk. Toss any cached pages beyond the new EOF.
 401                  */
 402                 if (nobjsize < object->size)
 403                         vm_object_page_remove(object, nobjsize, object->size,
 404                             0);
 405                 /*
 406                  * this gets rid of garbage at the end of a page that is now
 407                  * only partially backed by the vnode.
 408                  *
 409                  * XXX for some reason (I don't know yet), if we take a
 410                  * completely invalid page and mark it partially valid
 411                  * it can screw up NFS reads, so we don't allow the case.
 412                  */
 413                 if ((nsize & PAGE_MASK) &&
 414                     (m = vm_page_lookup(object, OFF_TO_IDX(nsize))) != NULL &&
 415                     m->valid != 0) {
 416                         int base = (int)nsize & PAGE_MASK;
 417                         int size = PAGE_SIZE - base;
 418
 419                         /*
 420                          * Clear out partial-page garbage in case
 421                          * the page has been mapped.
 422                          */
 423                         pmap_zero_page_area(m, base, size);
 424
 425                         /*
 426                          * Update the valid bits to reflect the blocks that
 427                          * have been zeroed.  Some of these valid bits may
 428                          * have already been set.
 429                          */
 430                         vm_page_set_valid_range(m, base, size);
 431
 432                         /*
 433                          * Round "base" to the next block boundary so that the
 434                          * dirty bit for a partially zeroed block is not
 435                          * cleared.
 436                          */
 437                         base = roundup2(base, DEV_BSIZE);
 438
 439                         /*
 440                          * Clear out partial-page dirty bits.
 441                          *
 442                          * note that we do not clear out the valid
 443                          * bits.  This would prevent bogus_page
 444                          * replacement from working properly.
 445                          */
 446                         vm_page_clear_dirty(m, base, PAGE_SIZE - base);
 447                 } else if ((nsize & PAGE_MASK) &&
 448                     vm_page_is_cached(object, OFF_TO_IDX(nsize))) {
 449                         vm_page_cache_free(object, OFF_TO_IDX(nsize),
 450                             nobjsize);
 451                 }
 452         }
 453         object->un_pager.vnp.vnp_size = nsize;
 454         object->size = nobjsize;
 455         VM_OBJECT_WUNLOCK(object);
 456 }
 457
 458 /*
 459  * calculate the linear (byte) disk address of specified virtual
 460  * file address
 461  */
 462 static int
 463 vnode_pager_addr(struct vnode *vp, vm_ooffset_t address, daddr_t *rtaddress,
 464     int *run)
 465 {
 466         int bsize;
 467         int err;
 468         daddr_t vblock;
 469         daddr_t voffset;
 470
 471         if (address < 0)
 472                 return -1;
 473
 474         if (vp->v_iflag & VI_DOOMED)
 475                 return -1;
 476
 477         bsize = vp->v_mount->mnt_stat.f_iosize;
 478         vblock = address / bsize;
 479         voffset = address % bsize;
 480
 481         err = VOP_BMAP(vp, vblock, NULL, rtaddress, run, NULL);
 482         if (err == 0) {
 483                 if (*rtaddress != -1)
 484                         *rtaddress += voffset / DEV_BSIZE;
 485                 if (run) {
 486                         *run += 1;
 487                         *run *= bsize/PAGE_SIZE;
 488                         *run -= voffset/PAGE_SIZE;
 489                 }
 490         }
 491
 492         return (err);
 493 }
 494
 495 /*
 496  * small block filesystem vnode pager input
 497  */
 498 static int
 499 vnode_pager_input_smlfs(object, m)
 500         vm_object_t object;
 501         vm_page_t m;
 502 {
 503         struct vnode *vp;
 504         struct bufobj *bo;
 505         struct buf *bp;
 506         struct sf_buf *sf;
 507         daddr_t fileaddr;
 508         vm_offset_t bsize;
 509         vm_page_bits_t bits;
 510         int error, i;
 511
 512         error = 0;
 513         vp = object->handle;
 514         if (vp->v_iflag & VI_DOOMED)
 515                 return VM_PAGER_BAD;
 516
 517         bsize = vp->v_mount->mnt_stat.f_iosize;
 518
 519         VOP_BMAP(vp, 0, &bo, 0, NULL, NULL);
 520
 521         sf = sf_buf_alloc(m, 0);
 522
 523         for (i = 0; i < PAGE_SIZE / bsize; i++) {
 524                 vm_ooffset_t address;
 525
 526                 bits = vm_page_bits(i * bsize, bsize);
 527                 if (m->valid & bits)
 528                         continue;
 529
 530                 address = IDX_TO_OFF(m->pindex) + i * bsize;
 531                 if (address >= object->un_pager.vnp.vnp_size) {
 532                         fileaddr = -1;
 533                 } else {
 534                         error = vnode_pager_addr(vp, address, &fileaddr, NULL);
 535                         if (error)
 536                                 break;
 537                 }
 538                 if (fileaddr != -1) {
 539                         bp = getpbuf(&vnode_pbuf_freecnt);
 540
 541                         /* build a minimal buffer header */
 542                         bp->b_iocmd = BIO_READ;
 543                         bp->b_iodone = bdone;
 544                         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 545                         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 546                         bp->b_rcred = crhold(curthread->td_ucred);
 547                         bp->b_wcred = crhold(curthread->td_ucred);
 548                         bp->b_data = (caddr_t)sf_buf_kva(sf) + i * bsize;
 549                         bp->b_blkno = fileaddr;
 550                         pbgetbo(bo, bp);
 551                         bp->b_vp = vp;
 552                         bp->b_bcount = bsize;
 553                         bp->b_bufsize = bsize;
 554                         bp->b_runningbufspace = bp->b_bufsize;
 555                         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 556
 557                         /* do the input */
 558                         bp->b_iooffset = dbtob(bp->b_blkno);
 559                         bstrategy(bp);
 560
 561                         bwait(bp, PVM, "vnsrd");
 562
 563                         if ((bp->b_ioflags & BIO_ERROR) != 0)
 564                                 error = EIO;
 565
 566                         /*
 567                          * free the buffer header back to the swap buffer pool
 568                          */
 569                         bp->b_vp = NULL;
 570                         pbrelbo(bp);
 571                         relpbuf(bp, &vnode_pbuf_freecnt);
 572                         if (error)
 573                                 break;
 574                 } else
 575                         bzero((caddr_t)sf_buf_kva(sf) + i * bsize, bsize);
 576                 KASSERT((m->dirty & bits) == 0,
 577                     ("vnode_pager_input_smlfs: page %p is dirty", m));
 578                 VM_OBJECT_WLOCK(object);
 579                 m->valid |= bits;
 580                 VM_OBJECT_WUNLOCK(object);
 581         }
 582         sf_buf_free(sf);
 583         if (error) {
 584                 return VM_PAGER_ERROR;
 585         }
 586         return VM_PAGER_OK;
 587 }
 588
 589 /*
 590  * old style vnode pager input routine
 591  */
 592 static int
 593 vnode_pager_input_old(object, m)
 594         vm_object_t object;
 595         vm_page_t m;
 596 {
 597         struct uio auio;
 598         struct iovec aiov;
 599         int error;
 600         int size;
 601         struct sf_buf *sf;
 602         struct vnode *vp;
 603
 604         VM_OBJECT_ASSERT_WLOCKED(object);
 605         error = 0;
 606
 607         /*
 608          * Return failure if beyond current EOF
 609          */
 610         if (IDX_TO_OFF(m->pindex) >= object->un_pager.vnp.vnp_size) {
 611                 return VM_PAGER_BAD;
 612         } else {
 613                 size = PAGE_SIZE;
 614                 if (IDX_TO_OFF(m->pindex) + size > object->un_pager.vnp.vnp_size)
 615                         size = object->un_pager.vnp.vnp_size - IDX_TO_OFF(m->pindex);
 616                 vp = object->handle;
 617                 VM_OBJECT_WUNLOCK(object);
 618
 619                 /*
 620                  * Allocate a kernel virtual address and initialize so that
 621                  * we can use VOP_READ/WRITE routines.
 622                  */
 623                 sf = sf_buf_alloc(m, 0);
 624
 625                 aiov.iov_base = (caddr_t)sf_buf_kva(sf);
 626                 aiov.iov_len = size;
 627                 auio.uio_iov = &aiov;
 628                 auio.uio_iovcnt = 1;
 629                 auio.uio_offset = IDX_TO_OFF(m->pindex);
 630                 auio.uio_segflg = UIO_SYSSPACE;
 631                 auio.uio_rw = UIO_READ;
 632                 auio.uio_resid = size;
 633                 auio.uio_td = curthread;
 634
 635                 error = VOP_READ(vp, &auio, 0, curthread->td_ucred);
 636                 if (!error) {
 637                         int count = size - auio.uio_resid;
 638
 639                         if (count == 0)
 640                                 error = EINVAL;
 641                         else if (count != PAGE_SIZE)
 642                                 bzero((caddr_t)sf_buf_kva(sf) + count,
 643                                     PAGE_SIZE - count);
 644                 }
 645                 sf_buf_free(sf);
 646
 647                 VM_OBJECT_WLOCK(object);
 648         }
 649         KASSERT(m->dirty == 0, ("vnode_pager_input_old: page %p is dirty", m));
 650         if (!error)
 651                 m->valid = VM_PAGE_BITS_ALL;
 652         return error ? VM_PAGER_ERROR : VM_PAGER_OK;
 653 }
 654
 655 /*
 656  * generic vnode pager input routine
 657  */
 658
 659 /*
 660  * Local media VFS's that do not implement their own VOP_GETPAGES
 661  * should have their VOP_GETPAGES call to vnode_pager_generic_getpages()
 662  * to implement the previous behaviour.
 663  *
 664  * All other FS's should use the bypass to get to the local media
 665  * backing vp's VOP_GETPAGES.
 666  */
 667 static int
 668 vnode_pager_getpages(object, m, count, reqpage)
 669         vm_object_t object;
 670         vm_page_t *m;
 671         int count;
 672         int reqpage;
 673 {
 674         int rtval;
 675         struct vnode *vp;
 676         int bytes = count * PAGE_SIZE;
 677
 678         vp = object->handle;
 679         VM_OBJECT_WUNLOCK(object);
 680         rtval = VOP_GETPAGES(vp, m, bytes, reqpage, 0);
 681         KASSERT(rtval != EOPNOTSUPP,
 682             ("vnode_pager: FS getpages not implemented\n"));
 683         VM_OBJECT_WLOCK(object);
 684         return rtval;
 685 }
 686
 687 /*
 688  * This is now called from local media FS's to operate against their
 689  * own vnodes if they fail to implement VOP_GETPAGES.
 690  */
 691 int
 692 vnode_pager_generic_getpages(vp, m, bytecount, reqpage)
 693         struct vnode *vp;
 694         vm_page_t *m;
 695         int bytecount;
 696         int reqpage;
 697 {
 698         vm_object_t object;
 699         struct bufobj *bo;
 700         struct buf *bp;
 701         struct mount *mp;
 702         vm_offset_t kva;
 703         daddr_t firstaddr, reqblock;
 704         off_t foff, nextoff, tfoff, pib;
 705         int pbefore, pafter, i, size, bsize, first, last;
 706         int count, error, before, after, secmask;
 707
 708         KASSERT(vp->v_type != VCHR && vp->v_type != VBLK,
 709             ("vnode_pager_generic_getpages does not support devices"));
 710         if (vp->v_iflag & VI_DOOMED)
 711                 return (VM_PAGER_BAD);
 712
 713         object = vp->v_object;
 714         count = bytecount / PAGE_SIZE;
 715         bsize = vp->v_mount->mnt_stat.f_iosize;
 716
 717         /* get the UNDERLYING device for the file with VOP_BMAP() */
 718
 719         /*
 720          * originally, we did not check for an error return value -- assuming
 721          * an fs always has a bmap entry point -- that assumption is wrong!!!
 722          */
 723         foff = IDX_TO_OFF(m[reqpage]->pindex);
 724
 725         /*
 726          * if we can't bmap, use old VOP code
 727          */
 728         error = VOP_BMAP(vp, IDX_TO_OFF(m[reqpage]->pindex) / bsize, &bo,
 729             &reqblock, &after, &before);
 730         if (error == EOPNOTSUPP) {
 731                 VM_OBJECT_WLOCK(object);
 732
 733                 for (i = 0; i < count; i++)
 734                         if (i != reqpage) {
 735                                 vm_page_lock(m[i]);
 736                                 vm_page_free(m[i]);
 737                                 vm_page_unlock(m[i]);
 738                         }
 739                 PCPU_INC(cnt.v_vnodein);
 740                 PCPU_INC(cnt.v_vnodepgsin);
 741                 error = vnode_pager_input_old(object, m[reqpage]);
 742                 VM_OBJECT_WUNLOCK(object);
 743                 return (error);
 744         } else if (error != 0) {
 745                 VM_OBJECT_WLOCK(object);
 746                 for (i = 0; i < count; i++)
 747                         if (i != reqpage) {
 748                                 vm_page_lock(m[i]);
 749                                 vm_page_free(m[i]);
 750                                 vm_page_unlock(m[i]);
 751                         }
 752                 VM_OBJECT_WUNLOCK(object);
 753                 return (VM_PAGER_ERROR);
 754
 755                 /*
 756                  * if the blocksize is smaller than a page size, then use
 757                  * special small filesystem code.  NFS sometimes has a small
 758                  * blocksize, but it can handle large reads itself.
 759                  */
 760         } else if ((PAGE_SIZE / bsize) > 1 &&
 761             (vp->v_mount->mnt_stat.f_type != nfs_mount_type)) {
 762                 VM_OBJECT_WLOCK(object);
 763                 for (i = 0; i < count; i++)
 764                         if (i != reqpage) {
 765                                 vm_page_lock(m[i]);
 766                                 vm_page_free(m[i]);
 767                                 vm_page_unlock(m[i]);
 768                         }
 769                 VM_OBJECT_WUNLOCK(object);
 770                 PCPU_INC(cnt.v_vnodein);
 771                 PCPU_INC(cnt.v_vnodepgsin);
 772                 return (vnode_pager_input_smlfs(object, m[reqpage]));
 773         }
 774
 775         /*
 776          * If we have a completely valid page available to us, we can
 777          * clean up and return.  Otherwise we have to re-read the
 778          * media.
 779          */
 780         VM_OBJECT_WLOCK(object);
 781         if (m[reqpage]->valid == VM_PAGE_BITS_ALL) {
 782                 for (i = 0; i < count; i++)
 783                         if (i != reqpage) {
 784                                 vm_page_lock(m[i]);
 785                                 vm_page_free(m[i]);
 786                                 vm_page_unlock(m[i]);
 787                         }
 788                 VM_OBJECT_WUNLOCK(object);
 789                 return VM_PAGER_OK;
 790         } else if (reqblock == -1) {
 791                 pmap_zero_page(m[reqpage]);
 792                 KASSERT(m[reqpage]->dirty == 0,
 793                     ("vnode_pager_generic_getpages: page %p is dirty", m));
 794                 m[reqpage]->valid = VM_PAGE_BITS_ALL;
 795                 for (i = 0; i < count; i++)
 796                         if (i != reqpage) {
 797                                 vm_page_lock(m[i]);
 798                                 vm_page_free(m[i]);
 799                                 vm_page_unlock(m[i]);
 800                         }
 801                 VM_OBJECT_WUNLOCK(object);
 802                 return (VM_PAGER_OK);
 803         }
 804         m[reqpage]->valid = 0;
 805         VM_OBJECT_WUNLOCK(object);
 806
 807         pib = IDX_TO_OFF(m[reqpage]->pindex) % bsize;
 808         pbefore = ((daddr_t)before * bsize + pib) / PAGE_SIZE;
 809         pafter = ((daddr_t)(after + 1) * bsize - pib) / PAGE_SIZE - 1;
 810         first = reqpage < pbefore ? 0 : reqpage - pbefore;
 811         last = reqpage + pafter >= count ? count - 1 : reqpage + pafter;
 812         if (first > 0 || last + 1 < count) {
 813                 VM_OBJECT_WLOCK(object);
 814                 for (i = 0; i < first; i++) {
 815                         vm_page_lock(m[i]);
 816                         vm_page_free(m[i]);
 817                         vm_page_unlock(m[i]);
 818                 }
 819                 for (i = last + 1; i < count; i++) {
 820                         vm_page_lock(m[i]);
 821                         vm_page_free(m[i]);
 822                         vm_page_unlock(m[i]);
 823                 }
 824                 VM_OBJECT_WUNLOCK(object);
 825         }
 826
 827         /*
 828          * here on direct device I/O
 829          */
 830         firstaddr = reqblock;
 831         firstaddr += pib / DEV_BSIZE;
 832         firstaddr -= IDX_TO_OFF(reqpage - first) / DEV_BSIZE;
 833
 834         /*
 835          * The first and last page have been calculated now, move
 836          * input pages to be zero based, and adjust the count.
 837          */
 838         m += first;
 839         reqpage -= first;
 840         count = last - first + 1;
 841
 842         /*
 843          * calculate the file virtual address for the transfer
 844          */
 845         foff = IDX_TO_OFF(m[0]->pindex);
 846
 847         /*
 848          * calculate the size of the transfer
 849          */
 850         size = count * PAGE_SIZE;
 851         KASSERT(count > 0, ("zero count"));
 852         if ((foff + size) > object->un_pager.vnp.vnp_size)
 853                 size = object->un_pager.vnp.vnp_size - foff;
 854         KASSERT(size > 0, ("zero size"));
 855
 856         /*
 857          * round up physical size for real devices.
 858          */
 859         secmask = bo->bo_bsize - 1;
 860         KASSERT(secmask < PAGE_SIZE && secmask > 0,
 861             ("vnode_pager_generic_getpages: sector size %d too large",
 862             secmask + 1));
 863         size = (size + secmask) & ~secmask;
 864
 865         bp = getpbuf(&vnode_pbuf_freecnt);
 866         kva = (vm_offset_t)bp->b_data;
 867
 868         /*
 869          * and map the pages to be read into the kva, if the filesystem
 870          * requires mapped buffers.
 871          */
 872         mp = vp->v_mount;
 873         if (mp != NULL && (mp->mnt_kern_flag & MNTK_UNMAPPED_BUFS) != 0 &&
 874             unmapped_buf_allowed) {
 875                 bp->b_data = unmapped_buf;
 876                 bp->b_kvabase = unmapped_buf;
 877                 bp->b_offset = 0;
 878                 bp->b_flags |= B_UNMAPPED;
 879                 bp->b_npages = count;
 880                 for (i = 0; i < count; i++)
 881                         bp->b_pages[i] = m[i];
 882         } else
 883                 pmap_qenter(kva, m, count);
 884
 885         /* build a minimal buffer header */
 886         bp->b_iocmd = BIO_READ;
 887         bp->b_iodone = bdone;
 888         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 889         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 890         bp->b_rcred = crhold(curthread->td_ucred);
 891         bp->b_wcred = crhold(curthread->td_ucred);
 892         bp->b_blkno = firstaddr;
 893         pbgetbo(bo, bp);
 894         bp->b_vp = vp;
 895         bp->b_bcount = size;
 896         bp->b_bufsize = size;
 897         bp->b_runningbufspace = bp->b_bufsize;
 898         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 899
 900         PCPU_INC(cnt.v_vnodein);
 901         PCPU_ADD(cnt.v_vnodepgsin, count);
 902
 903         /* do the input */
 904         bp->b_iooffset = dbtob(bp->b_blkno);
 905         bstrategy(bp);
 906
 907         bwait(bp, PVM, "vnread");
 908
 909         if ((bp->b_ioflags & BIO_ERROR) != 0)
 910                 error = EIO;
 911
 912         if (error == 0 && size != count * PAGE_SIZE) {
 913                 if ((bp->b_flags & B_UNMAPPED) != 0) {
 914                         bp->b_flags &= ~B_UNMAPPED;
 915                         pmap_qenter(kva, m, count);
 916                 }
 917                 bzero((caddr_t)kva + size, PAGE_SIZE * count - size);
 918         }
 919         if ((bp->b_flags & B_UNMAPPED) == 0)
 920                 pmap_qremove(kva, count);
 921         if (mp != NULL && (mp->mnt_kern_flag & MNTK_UNMAPPED_BUFS) != 0) {
 922                 bp->b_data = (caddr_t)kva;
 923                 bp->b_kvabase = (caddr_t)kva;
 924                 bp->b_flags &= ~B_UNMAPPED;
 925                 for (i = 0; i < count; i++)
 926                         bp->b_pages[i] = NULL;
 927         }
 928
 929         /*
 930          * free the buffer header back to the swap buffer pool
 931          */
 932         bp->b_vp = NULL;
 933         pbrelbo(bp);
 934         relpbuf(bp, &vnode_pbuf_freecnt);
 935
 936         VM_OBJECT_WLOCK(object);
 937         for (i = 0, tfoff = foff; i < count; i++, tfoff = nextoff) {
 938                 vm_page_t mt;
 939
 940                 nextoff = tfoff + PAGE_SIZE;
 941                 mt = m[i];
 942
 943                 if (nextoff <= object->un_pager.vnp.vnp_size) {
 944                         /*
 945                          * Read filled up entire page.
 946                          */
 947                         mt->valid = VM_PAGE_BITS_ALL;
 948                         KASSERT(mt->dirty == 0,
 949                             ("vnode_pager_generic_getpages: page %p is dirty",
 950                             mt));
 951                         KASSERT(!pmap_page_is_mapped(mt),
 952                             ("vnode_pager_generic_getpages: page %p is mapped",
 953                             mt));
 954                 } else {
 955                         /*
 956                          * Read did not fill up entire page.
 957                          *
 958                          * Currently we do not set the entire page valid,
 959                          * we just try to clear the piece that we couldn't
 960                          * read.
 961                          */
 962                         vm_page_set_valid_range(mt, 0,
 963                             object->un_pager.vnp.vnp_size - tfoff);
 964                         KASSERT((mt->dirty & vm_page_bits(0,
 965                             object->un_pager.vnp.vnp_size - tfoff)) == 0,
 966                             ("vnode_pager_generic_getpages: page %p is dirty",
 967                             mt));
 968                 }
 969
 970                 if (i != reqpage)
 971                         vm_page_readahead_finish(mt);
 972         }
 973         VM_OBJECT_WUNLOCK(object);
 974         if (error) {
 975                 printf("vnode_pager_getpages: I/O read error\n");
 976         }
 977         return (error ? VM_PAGER_ERROR : VM_PAGER_OK);
 978 }
 979
 980 /*
 981  * EOPNOTSUPP is no longer legal.  For local media VFS's that do not
 982  * implement their own VOP_PUTPAGES, their VOP_PUTPAGES should call to
 983  * vnode_pager_generic_putpages() to implement the previous behaviour.
 984  *
 985  * All other FS's should use the bypass to get to the local media
 986  * backing vp's VOP_PUTPAGES.
 987  */
 988 static void
 989 vnode_pager_putpages(vm_object_t object, vm_page_t *m, int count,
 990     int flags, int *rtvals)
 991 {
 992         int rtval;
 993         struct vnode *vp;
 994         int bytes = count * PAGE_SIZE;
 995
 996         /*
 997          * Force synchronous operation if we are extremely low on memory
 998          * to prevent a low-memory deadlock.  VOP operations often need to
 999          * allocate more memory to initiate the I/O ( i.e. do a BMAP
1000          * operation ).  The swapper handles the case by limiting the amount
1001          * of asynchronous I/O, but that sort of solution doesn't scale well
1002          * for the vnode pager without a lot of work.
1003          *
1004          * Also, the backing vnode's iodone routine may not wake the pageout
1005          * daemon up.  This should be probably be addressed XXX.
1006          */
1007
1008         if (cnt.v_free_count + cnt.v_cache_count < cnt.v_pageout_free_min)
1009                 flags |= VM_PAGER_PUT_SYNC;
1010
1011         /*
1012          * Call device-specific putpages function
1013          */
1014         vp = object->handle;
1015         VM_OBJECT_WUNLOCK(object);
1016         rtval = VOP_PUTPAGES(vp, m, bytes, flags, rtvals, 0);
1017         KASSERT(rtval != EOPNOTSUPP,
1018             ("vnode_pager: stale FS putpages\n"));
1019         VM_OBJECT_WLOCK(object);
1020 }
1021
1022
1023 /*
1024  * This is now called from local media FS's to operate against their
1025  * own vnodes if they fail to implement VOP_PUTPAGES.
1026  *
1027  * This is typically called indirectly via the pageout daemon and
1028  * clustering has already typically occured, so in general we ask the
1029  * underlying filesystem to write the data out asynchronously rather
1030  * then delayed.
1031  */
1032 int
1033 vnode_pager_generic_putpages(struct vnode *vp, vm_page_t *ma, int bytecount,
1034     int flags, int *rtvals)
1035 {
1036         int i;
1037         vm_object_t object;
1038         vm_page_t m;
1039         int count;
1040
1041         int maxsize, ncount;
1042         vm_ooffset_t poffset;
1043         struct uio auio;
1044         struct iovec aiov;
1045         int error;
1046         int ioflags;
1047         int ppscheck = 0;
1048         static struct timeval lastfail;
1049         static int curfail;
1050
1051         object = vp->v_object;
1052         count = bytecount / PAGE_SIZE;
1053
1054         for (i = 0; i < count; i++)
1055                 rtvals[i] = VM_PAGER_ERROR;
1056
1057         if ((int64_t)ma[0]->pindex < 0) {
1058                 printf("vnode_pager_putpages: attempt to write meta-data!!! -- 0x%lx(%lx)\n",
1059                     (long)ma[0]->pindex, (u_long)ma[0]->dirty);
1060                 rtvals[0] = VM_PAGER_BAD;
1061                 return VM_PAGER_BAD;
1062         }
1063
1064         maxsize = count * PAGE_SIZE;
1065         ncount = count;
1066
1067         poffset = IDX_TO_OFF(ma[0]->pindex);
1068
1069         /*
1070          * If the page-aligned write is larger then the actual file we
1071          * have to invalidate pages occuring beyond the file EOF.  However,
1072          * there is an edge case where a file may not be page-aligned where
1073          * the last page is partially invalid.  In this case the filesystem
1074          * may not properly clear the dirty bits for the entire page (which
1075          * could be VM_PAGE_BITS_ALL due to the page having been mmap()d).
1076          * With the page locked we are free to fix-up the dirty bits here.
1077          *
1078          * We do not under any circumstances truncate the valid bits, as
1079          * this will screw up bogus page replacement.
1080          */
1081         VM_OBJECT_WLOCK(object);
1082         if (maxsize + poffset > object->un_pager.vnp.vnp_size) {
1083                 if (object->un_pager.vnp.vnp_size > poffset) {
1084                         int pgoff;
1085
1086                         maxsize = object->un_pager.vnp.vnp_size - poffset;
1087                         ncount = btoc(maxsize);
1088                         if ((pgoff = (int)maxsize & PAGE_MASK) != 0) {
1089                                 /*
1090                                  * If the object is locked and the following
1091                                  * conditions hold, then the page's dirty
1092                                  * field cannot be concurrently changed by a
1093                                  * pmap operation.
1094                                  */
1095                                 m = ma[ncount - 1];
1096                                 vm_page_assert_sbusied(m);
1097                                 KASSERT(!pmap_page_is_write_mapped(m),
1098                 ("vnode_pager_generic_putpages: page %p is not read-only", m));
1099                                 vm_page_clear_dirty(m, pgoff, PAGE_SIZE -
1100                                     pgoff);
1101                         }
1102                 } else {
1103                         maxsize = 0;
1104                         ncount = 0;
1105                 }
1106                 if (ncount < count) {
1107                         for (i = ncount; i < count; i++) {
1108                                 rtvals[i] = VM_PAGER_BAD;
1109                         }
1110                 }
1111         }
1112         VM_OBJECT_WUNLOCK(object);
1113
1114         /*
1115          * pageouts are already clustered, use IO_ASYNC to force a bawrite()
1116          * rather then a bdwrite() to prevent paging I/O from saturating
1117          * the buffer cache.  Dummy-up the sequential heuristic to cause
1118          * large ranges to cluster.  If neither IO_SYNC or IO_ASYNC is set,
1119          * the system decides how to cluster.
1120          */
1121         ioflags = IO_VMIO;
1122         if (flags & (VM_PAGER_PUT_SYNC | VM_PAGER_PUT_INVAL))
1123                 ioflags |= IO_SYNC;
1124         else if ((flags & VM_PAGER_CLUSTER_OK) == 0)
1125                 ioflags |= IO_ASYNC;
1126         ioflags |= (flags & VM_PAGER_PUT_INVAL) ? IO_INVAL: 0;
1127         ioflags |= IO_SEQMAX << IO_SEQSHIFT;
1128
1129         aiov.iov_base = (caddr_t) 0;
1130         aiov.iov_len = maxsize;
1131         auio.uio_iov = &aiov;
1132         auio.uio_iovcnt = 1;
1133         auio.uio_offset = poffset;
1134         auio.uio_segflg = UIO_NOCOPY;
1135         auio.uio_rw = UIO_WRITE;
1136         auio.uio_resid = maxsize;
1137         auio.uio_td = (struct thread *) 0;
1138         error = VOP_WRITE(vp, &auio, ioflags, curthread->td_ucred);
1139         PCPU_INC(cnt.v_vnodeout);
1140         PCPU_ADD(cnt.v_vnodepgsout, ncount);
1141
1142         if (error) {
1143                 if ((ppscheck = ppsratecheck(&lastfail, &curfail, 1)))
1144                         printf("vnode_pager_putpages: I/O error %d\n", error);
1145         }
1146         if (auio.uio_resid) {
1147                 if (ppscheck || ppsratecheck(&lastfail, &curfail, 1))
1148                         printf("vnode_pager_putpages: residual I/O %zd at %lu\n",
1149                             auio.uio_resid, (u_long)ma[0]->pindex);
1150         }
1151         for (i = 0; i < ncount; i++) {
1152                 rtvals[i] = VM_PAGER_OK;
1153         }
1154         return rtvals[0];
1155 }
1156
1157 void
1158 vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written)
1159 {
1160         vm_object_t obj;
1161         int i, pos;
1162
1163         if (written == 0)
1164                 return;
1165         obj = ma[0]->object;
1166         VM_OBJECT_WLOCK(obj);
1167         for (i = 0, pos = 0; pos < written; i++, pos += PAGE_SIZE) {
1168                 if (pos < trunc_page(written)) {
1169                         rtvals[i] = VM_PAGER_OK;
1170                         vm_page_undirty(ma[i]);
1171                 } else {
1172                         /* Partially written page. */
1173                         rtvals[i] = VM_PAGER_AGAIN;
1174                         vm_page_clear_dirty(ma[i], 0, written & PAGE_MASK);
1175                 }
1176         }
1177         VM_OBJECT_WUNLOCK(obj);
1178 }
1179
1180 void
1181 vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
1182     vm_offset_t end)
1183 {
1184         struct vnode *vp;
1185         vm_ooffset_t old_wm;
1186
1187         VM_OBJECT_WLOCK(object);
1188         if (object->type != OBJT_VNODE) {
1189                 VM_OBJECT_WUNLOCK(object);
1190                 return;
1191         }
1192         old_wm = object->un_pager.vnp.writemappings;
1193         object->un_pager.vnp.writemappings += (vm_ooffset_t)end - start;
1194         vp = object->handle;
1195         if (old_wm == 0 && object->un_pager.vnp.writemappings != 0) {
1196                 ASSERT_VOP_ELOCKED(vp, "v_writecount inc");
1197                 VOP_ADD_WRITECOUNT(vp, 1);
1198                 CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d",
1199                     __func__, vp, vp->v_writecount);
1200         } else if (old_wm != 0 && object->un_pager.vnp.writemappings == 0) {
1201                 ASSERT_VOP_ELOCKED(vp, "v_writecount dec");
1202                 VOP_ADD_WRITECOUNT(vp, -1);
1203                 CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
1204                     __func__, vp, vp->v_writecount);
1205         }
1206         VM_OBJECT_WUNLOCK(object);
1207 }
1208
1209 void
1210 vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
1211     vm_offset_t end)
1212 {
1213         struct vnode *vp;
1214         struct mount *mp;
1215         vm_offset_t inc;
1216
1217         VM_OBJECT_WLOCK(object);
1218
1219         /*
1220          * First, recheck the object type to account for the race when
1221          * the vnode is reclaimed.
1222          */
1223         if (object->type != OBJT_VNODE) {
1224                 VM_OBJECT_WUNLOCK(object);
1225                 return;
1226         }
1227
1228         /*
1229          * Optimize for the case when writemappings is not going to
1230          * zero.
1231          */
1232         inc = end - start;
1233         if (object->un_pager.vnp.writemappings != inc) {
1234                 object->un_pager.vnp.writemappings -= inc;
1235                 VM_OBJECT_WUNLOCK(object);
1236                 return;
1237         }
1238
1239         vp = object->handle;
1240         vhold(vp);
1241         VM_OBJECT_WUNLOCK(object);
1242         mp = NULL;
1243         vn_start_write(vp, &mp, V_WAIT);
1244         vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
1245
1246         /*
1247          * Decrement the object's writemappings, by swapping the start
1248          * and end arguments for vnode_pager_update_writecount().  If
1249          * there was not a race with vnode reclaimation, then the
1250          * vnode's v_writecount is decremented.
1251          */
1252         vnode_pager_update_writecount(object, end, start);
1253         VOP_UNLOCK(vp, 0);
1254         vdrop(vp);
1255         if (mp != NULL)
1256                 vn_finished_write(mp);
1257 }