The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/vm/vnode_pager.c

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    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: releng/9.2/sys/vm/vnode_pager.c 251897 2013-06-18 05:21:40Z scottl $");
   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/sf_buf.h>
   67 
   68 #include <machine/atomic.h>
   69 
   70 #include <vm/vm.h>
   71 #include <vm/vm_param.h>
   72 #include <vm/vm_object.h>
   73 #include <vm/vm_page.h>
   74 #include <vm/vm_pager.h>
   75 #include <vm/vm_map.h>
   76 #include <vm/vnode_pager.h>
   77 #include <vm/vm_extern.h>
   78 
   79 static int vnode_pager_addr(struct vnode *vp, vm_ooffset_t address,
   80     daddr_t *rtaddress, int *run);
   81 static int vnode_pager_input_smlfs(vm_object_t object, vm_page_t m);
   82 static int vnode_pager_input_old(vm_object_t object, vm_page_t m);
   83 static void vnode_pager_dealloc(vm_object_t);
   84 static int vnode_pager_getpages(vm_object_t, vm_page_t *, int, int);
   85 static void vnode_pager_putpages(vm_object_t, vm_page_t *, int, boolean_t, int *);
   86 static boolean_t vnode_pager_haspage(vm_object_t, vm_pindex_t, int *, int *);
   87 static vm_object_t vnode_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
   88     vm_ooffset_t, struct ucred *cred);
   89 
   90 struct pagerops vnodepagerops = {
   91         .pgo_alloc =    vnode_pager_alloc,
   92         .pgo_dealloc =  vnode_pager_dealloc,
   93         .pgo_getpages = vnode_pager_getpages,
   94         .pgo_putpages = vnode_pager_putpages,
   95         .pgo_haspage =  vnode_pager_haspage,
   96 };
   97 
   98 int vnode_pbuf_freecnt;
   99 
  100 /* Create the VM system backing object for this vnode */
  101 int
  102 vnode_create_vobject(struct vnode *vp, off_t isize, struct thread *td)
  103 {
  104         vm_object_t object;
  105         vm_ooffset_t size = isize;
  106         struct vattr va;
  107 
  108         if (!vn_isdisk(vp, NULL) && vn_canvmio(vp) == FALSE)
  109                 return (0);
  110 
  111         while ((object = vp->v_object) != NULL) {
  112                 VM_OBJECT_LOCK(object);
  113                 if (!(object->flags & OBJ_DEAD)) {
  114                         VM_OBJECT_UNLOCK(object);
  115                         return (0);
  116                 }
  117                 VOP_UNLOCK(vp, 0);
  118                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
  119                 msleep(object, VM_OBJECT_MTX(object), PDROP | PVM, "vodead", 0);
  120                 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
  121         }
  122 
  123         if (size == 0) {
  124                 if (vn_isdisk(vp, NULL)) {
  125                         size = IDX_TO_OFF(INT_MAX);
  126                 } else {
  127                         if (VOP_GETATTR(vp, &va, td->td_ucred))
  128                                 return (0);
  129                         size = va.va_size;
  130                 }
  131         }
  132 
  133         object = vnode_pager_alloc(vp, size, 0, 0, td->td_ucred);
  134         /*
  135          * Dereference the reference we just created.  This assumes
  136          * that the object is associated with the vp.
  137          */
  138         VM_OBJECT_LOCK(object);
  139         object->ref_count--;
  140         VM_OBJECT_UNLOCK(object);
  141         vrele(vp);
  142 
  143         KASSERT(vp->v_object != NULL, ("vnode_create_vobject: NULL object"));
  144 
  145         return (0);
  146 }
  147 
  148 void
  149 vnode_destroy_vobject(struct vnode *vp)
  150 {
  151         struct vm_object *obj;
  152 
  153         obj = vp->v_object;
  154         if (obj == NULL)
  155                 return;
  156         ASSERT_VOP_ELOCKED(vp, "vnode_destroy_vobject");
  157         VM_OBJECT_LOCK(obj);
  158         if (obj->ref_count == 0) {
  159                 /*
  160                  * vclean() may be called twice. The first time
  161                  * removes the primary reference to the object,
  162                  * the second time goes one further and is a
  163                  * special-case to terminate the object.
  164                  *
  165                  * don't double-terminate the object
  166                  */
  167                 if ((obj->flags & OBJ_DEAD) == 0)
  168                         vm_object_terminate(obj);
  169                 else
  170                         VM_OBJECT_UNLOCK(obj);
  171         } else {
  172                 /*
  173                  * Woe to the process that tries to page now :-).
  174                  */
  175                 vm_pager_deallocate(obj);
  176                 VM_OBJECT_UNLOCK(obj);
  177         }
  178         vp->v_object = NULL;
  179 }
  180 
  181 
  182 /*
  183  * Allocate (or lookup) pager for a vnode.
  184  * Handle is a vnode pointer.
  185  *
  186  * MPSAFE
  187  */
  188 vm_object_t
  189 vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
  190     vm_ooffset_t offset, struct ucred *cred)
  191 {
  192         vm_object_t object;
  193         struct vnode *vp;
  194 
  195         /*
  196          * Pageout to vnode, no can do yet.
  197          */
  198         if (handle == NULL)
  199                 return (NULL);
  200 
  201         vp = (struct vnode *) handle;
  202 
  203         /*
  204          * If the object is being terminated, wait for it to
  205          * go away.
  206          */
  207 retry:
  208         while ((object = vp->v_object) != NULL) {
  209                 VM_OBJECT_LOCK(object);
  210                 if ((object->flags & OBJ_DEAD) == 0)
  211                         break;
  212                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
  213                 msleep(object, VM_OBJECT_MTX(object), PDROP | PVM, "vadead", 0);
  214         }
  215 
  216         KASSERT(vp->v_usecount != 0, ("vnode_pager_alloc: no vnode reference"));
  217 
  218         if (object == NULL) {
  219                 /*
  220                  * Add an object of the appropriate size
  221                  */
  222                 object = vm_object_allocate(OBJT_VNODE, OFF_TO_IDX(round_page(size)));
  223 
  224                 object->un_pager.vnp.vnp_size = size;
  225                 object->un_pager.vnp.writemappings = 0;
  226 
  227                 object->handle = handle;
  228                 VI_LOCK(vp);
  229                 if (vp->v_object != NULL) {
  230                         /*
  231                          * Object has been created while we were sleeping
  232                          */
  233                         VI_UNLOCK(vp);
  234                         vm_object_destroy(object);
  235                         goto retry;
  236                 }
  237                 vp->v_object = object;
  238                 VI_UNLOCK(vp);
  239         } else {
  240                 object->ref_count++;
  241                 VM_OBJECT_UNLOCK(object);
  242         }
  243         vref(vp);
  244         return (object);
  245 }
  246 
  247 /*
  248  *      The object must be locked.
  249  */
  250 static void
  251 vnode_pager_dealloc(object)
  252         vm_object_t object;
  253 {
  254         struct vnode *vp;
  255         int refs;
  256 
  257         vp = object->handle;
  258         if (vp == NULL)
  259                 panic("vnode_pager_dealloc: pager already dealloced");
  260 
  261         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  262         vm_object_pip_wait(object, "vnpdea");
  263         refs = object->ref_count;
  264 
  265         object->handle = NULL;
  266         object->type = OBJT_DEAD;
  267         if (object->flags & OBJ_DISCONNECTWNT) {
  268                 vm_object_clear_flag(object, OBJ_DISCONNECTWNT);
  269                 wakeup(object);
  270         }
  271         ASSERT_VOP_ELOCKED(vp, "vnode_pager_dealloc");
  272         if (object->un_pager.vnp.writemappings > 0) {
  273                 object->un_pager.vnp.writemappings = 0;
  274                 VOP_ADD_WRITECOUNT(vp, -1);
  275         }
  276         vp->v_object = NULL;
  277         VOP_UNSET_TEXT(vp);
  278         VM_OBJECT_UNLOCK(object);
  279         while (refs-- > 0)
  280                 vunref(vp);
  281         VM_OBJECT_LOCK(object);
  282 }
  283 
  284 static boolean_t
  285 vnode_pager_haspage(object, pindex, before, after)
  286         vm_object_t object;
  287         vm_pindex_t pindex;
  288         int *before;
  289         int *after;
  290 {
  291         struct vnode *vp = object->handle;
  292         daddr_t bn;
  293         int err;
  294         daddr_t reqblock;
  295         int poff;
  296         int bsize;
  297         int pagesperblock, blocksperpage;
  298         int vfslocked;
  299 
  300         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  301         /*
  302          * If no vp or vp is doomed or marked transparent to VM, we do not
  303          * have the page.
  304          */
  305         if (vp == NULL || vp->v_iflag & VI_DOOMED)
  306                 return FALSE;
  307         /*
  308          * If the offset is beyond end of file we do
  309          * not have the page.
  310          */
  311         if (IDX_TO_OFF(pindex) >= object->un_pager.vnp.vnp_size)
  312                 return FALSE;
  313 
  314         bsize = vp->v_mount->mnt_stat.f_iosize;
  315         pagesperblock = bsize / PAGE_SIZE;
  316         blocksperpage = 0;
  317         if (pagesperblock > 0) {
  318                 reqblock = pindex / pagesperblock;
  319         } else {
  320                 blocksperpage = (PAGE_SIZE / bsize);
  321                 reqblock = pindex * blocksperpage;
  322         }
  323         VM_OBJECT_UNLOCK(object);
  324         vfslocked = VFS_LOCK_GIANT(vp->v_mount);
  325         err = VOP_BMAP(vp, reqblock, NULL, &bn, after, before);
  326         VFS_UNLOCK_GIANT(vfslocked);
  327         VM_OBJECT_LOCK(object);
  328         if (err)
  329                 return TRUE;
  330         if (bn == -1)
  331                 return FALSE;
  332         if (pagesperblock > 0) {
  333                 poff = pindex - (reqblock * pagesperblock);
  334                 if (before) {
  335                         *before *= pagesperblock;
  336                         *before += poff;
  337                 }
  338                 if (after) {
  339                         int numafter;
  340                         *after *= pagesperblock;
  341                         numafter = pagesperblock - (poff + 1);
  342                         if (IDX_TO_OFF(pindex + numafter) >
  343                             object->un_pager.vnp.vnp_size) {
  344                                 numafter =
  345                                     OFF_TO_IDX(object->un_pager.vnp.vnp_size) -
  346                                     pindex;
  347                         }
  348                         *after += numafter;
  349                 }
  350         } else {
  351                 if (before) {
  352                         *before /= blocksperpage;
  353                 }
  354 
  355                 if (after) {
  356                         *after /= blocksperpage;
  357                 }
  358         }
  359         return TRUE;
  360 }
  361 
  362 /*
  363  * Lets the VM system know about a change in size for a file.
  364  * We adjust our own internal size and flush any cached pages in
  365  * the associated object that are affected by the size change.
  366  *
  367  * Note: this routine may be invoked as a result of a pager put
  368  * operation (possibly at object termination time), so we must be careful.
  369  */
  370 void
  371 vnode_pager_setsize(vp, nsize)
  372         struct vnode *vp;
  373         vm_ooffset_t nsize;
  374 {
  375         vm_object_t object;
  376         vm_page_t m;
  377         vm_pindex_t nobjsize;
  378 
  379         if ((object = vp->v_object) == NULL)
  380                 return;
  381 /*      ASSERT_VOP_ELOCKED(vp, "vnode_pager_setsize and not locked vnode"); */
  382         VM_OBJECT_LOCK(object);
  383         if (object->type == OBJT_DEAD) {
  384                 VM_OBJECT_UNLOCK(object);
  385                 return;
  386         }
  387         KASSERT(object->type == OBJT_VNODE,
  388             ("not vnode-backed object %p", object));
  389         if (nsize == object->un_pager.vnp.vnp_size) {
  390                 /*
  391                  * Hasn't changed size
  392                  */
  393                 VM_OBJECT_UNLOCK(object);
  394                 return;
  395         }
  396         nobjsize = OFF_TO_IDX(nsize + PAGE_MASK);
  397         if (nsize < object->un_pager.vnp.vnp_size) {
  398                 /*
  399                  * File has shrunk. Toss any cached pages beyond the new EOF.
  400                  */
  401                 if (nobjsize < object->size)
  402                         vm_object_page_remove(object, nobjsize, object->size,
  403                             0);
  404                 /*
  405                  * this gets rid of garbage at the end of a page that is now
  406                  * only partially backed by the vnode.
  407                  *
  408                  * XXX for some reason (I don't know yet), if we take a
  409                  * completely invalid page and mark it partially valid
  410                  * it can screw up NFS reads, so we don't allow the case.
  411                  */
  412                 if ((nsize & PAGE_MASK) &&
  413                     (m = vm_page_lookup(object, OFF_TO_IDX(nsize))) != NULL &&
  414                     m->valid != 0) {
  415                         int base = (int)nsize & PAGE_MASK;
  416                         int size = PAGE_SIZE - base;
  417 
  418                         /*
  419                          * Clear out partial-page garbage in case
  420                          * the page has been mapped.
  421                          */
  422                         pmap_zero_page_area(m, base, size);
  423 
  424                         /*
  425                          * Update the valid bits to reflect the blocks that
  426                          * have been zeroed.  Some of these valid bits may
  427                          * have already been set.
  428                          */
  429                         vm_page_set_valid(m, base, size);
  430 
  431                         /*
  432                          * Round "base" to the next block boundary so that the
  433                          * dirty bit for a partially zeroed block is not
  434                          * cleared.
  435                          */
  436                         base = roundup2(base, DEV_BSIZE);
  437 
  438                         /*
  439                          * Clear out partial-page dirty bits.
  440                          *
  441                          * note that we do not clear out the valid
  442                          * bits.  This would prevent bogus_page
  443                          * replacement from working properly.
  444                          */
  445                         vm_page_clear_dirty(m, base, PAGE_SIZE - base);
  446                 } else if ((nsize & PAGE_MASK) &&
  447                     __predict_false(object->cache != NULL)) {
  448                         vm_page_cache_free(object, OFF_TO_IDX(nsize),
  449                             nobjsize);
  450                 }
  451         }
  452         object->un_pager.vnp.vnp_size = nsize;
  453         object->size = nobjsize;
  454         VM_OBJECT_UNLOCK(object);
  455 }
  456 
  457 /*
  458  * calculate the linear (byte) disk address of specified virtual
  459  * file address
  460  */
  461 static int
  462 vnode_pager_addr(struct vnode *vp, vm_ooffset_t address, daddr_t *rtaddress,
  463     int *run)
  464 {
  465         int bsize;
  466         int err;
  467         daddr_t vblock;
  468         daddr_t voffset;
  469 
  470         if (address < 0)
  471                 return -1;
  472 
  473         if (vp->v_iflag & VI_DOOMED)
  474                 return -1;
  475 
  476         bsize = vp->v_mount->mnt_stat.f_iosize;
  477         vblock = address / bsize;
  478         voffset = address % bsize;
  479 
  480         err = VOP_BMAP(vp, vblock, NULL, rtaddress, run, NULL);
  481         if (err == 0) {
  482                 if (*rtaddress != -1)
  483                         *rtaddress += voffset / DEV_BSIZE;
  484                 if (run) {
  485                         *run += 1;
  486                         *run *= bsize/PAGE_SIZE;
  487                         *run -= voffset/PAGE_SIZE;
  488                 }
  489         }
  490 
  491         return (err);
  492 }
  493 
  494 /*
  495  * small block filesystem vnode pager input
  496  */
  497 static int
  498 vnode_pager_input_smlfs(object, m)
  499         vm_object_t object;
  500         vm_page_t m;
  501 {
  502         struct vnode *vp;
  503         struct bufobj *bo;
  504         struct buf *bp;
  505         struct sf_buf *sf;
  506         daddr_t fileaddr;
  507         vm_offset_t bsize;
  508         vm_page_bits_t bits;
  509         int error, i;
  510 
  511         error = 0;
  512         vp = object->handle;
  513         if (vp->v_iflag & VI_DOOMED)
  514                 return VM_PAGER_BAD;
  515 
  516         bsize = vp->v_mount->mnt_stat.f_iosize;
  517 
  518         VOP_BMAP(vp, 0, &bo, 0, NULL, NULL);
  519 
  520         sf = sf_buf_alloc(m, 0);
  521 
  522         for (i = 0; i < PAGE_SIZE / bsize; i++) {
  523                 vm_ooffset_t address;
  524 
  525                 bits = vm_page_bits(i * bsize, bsize);
  526                 if (m->valid & bits)
  527                         continue;
  528 
  529                 address = IDX_TO_OFF(m->pindex) + i * bsize;
  530                 if (address >= object->un_pager.vnp.vnp_size) {
  531                         fileaddr = -1;
  532                 } else {
  533                         error = vnode_pager_addr(vp, address, &fileaddr, NULL);
  534                         if (error)
  535                                 break;
  536                 }
  537                 if (fileaddr != -1) {
  538                         bp = getpbuf(&vnode_pbuf_freecnt);
  539 
  540                         /* build a minimal buffer header */
  541                         bp->b_iocmd = BIO_READ;
  542                         bp->b_iodone = bdone;
  543                         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
  544                         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
  545                         bp->b_rcred = crhold(curthread->td_ucred);
  546                         bp->b_wcred = crhold(curthread->td_ucred);
  547                         bp->b_data = (caddr_t)sf_buf_kva(sf) + i * bsize;
  548                         bp->b_blkno = fileaddr;
  549                         pbgetbo(bo, bp);
  550                         bp->b_vp = vp;
  551                         bp->b_bcount = bsize;
  552                         bp->b_bufsize = bsize;
  553                         bp->b_runningbufspace = bp->b_bufsize;
  554                         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
  555 
  556                         /* do the input */
  557                         bp->b_iooffset = dbtob(bp->b_blkno);
  558                         bstrategy(bp);
  559 
  560                         bwait(bp, PVM, "vnsrd");
  561 
  562                         if ((bp->b_ioflags & BIO_ERROR) != 0)
  563                                 error = EIO;
  564 
  565                         /*
  566                          * free the buffer header back to the swap buffer pool
  567                          */
  568                         bp->b_vp = NULL;
  569                         pbrelbo(bp);
  570                         relpbuf(bp, &vnode_pbuf_freecnt);
  571                         if (error)
  572                                 break;
  573                 } else
  574                         bzero((caddr_t)sf_buf_kva(sf) + i * bsize, bsize);
  575                 KASSERT((m->dirty & bits) == 0,
  576                     ("vnode_pager_input_smlfs: page %p is dirty", m));
  577                 VM_OBJECT_LOCK(object);
  578                 m->valid |= bits;
  579                 VM_OBJECT_UNLOCK(object);
  580         }
  581         sf_buf_free(sf);
  582         if (error) {
  583                 return VM_PAGER_ERROR;
  584         }
  585         return VM_PAGER_OK;
  586 }
  587 
  588 /*
  589  * old style vnode pager input routine
  590  */
  591 static int
  592 vnode_pager_input_old(object, m)
  593         vm_object_t object;
  594         vm_page_t m;
  595 {
  596         struct uio auio;
  597         struct iovec aiov;
  598         int error;
  599         int size;
  600         struct sf_buf *sf;
  601         struct vnode *vp;
  602 
  603         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  604         error = 0;
  605 
  606         /*
  607          * Return failure if beyond current EOF
  608          */
  609         if (IDX_TO_OFF(m->pindex) >= object->un_pager.vnp.vnp_size) {
  610                 return VM_PAGER_BAD;
  611         } else {
  612                 size = PAGE_SIZE;
  613                 if (IDX_TO_OFF(m->pindex) + size > object->un_pager.vnp.vnp_size)
  614                         size = object->un_pager.vnp.vnp_size - IDX_TO_OFF(m->pindex);
  615                 vp = object->handle;
  616                 VM_OBJECT_UNLOCK(object);
  617 
  618                 /*
  619                  * Allocate a kernel virtual address and initialize so that
  620                  * we can use VOP_READ/WRITE routines.
  621                  */
  622                 sf = sf_buf_alloc(m, 0);
  623 
  624                 aiov.iov_base = (caddr_t)sf_buf_kva(sf);
  625                 aiov.iov_len = size;
  626                 auio.uio_iov = &aiov;
  627                 auio.uio_iovcnt = 1;
  628                 auio.uio_offset = IDX_TO_OFF(m->pindex);
  629                 auio.uio_segflg = UIO_SYSSPACE;
  630                 auio.uio_rw = UIO_READ;
  631                 auio.uio_resid = size;
  632                 auio.uio_td = curthread;
  633 
  634                 error = VOP_READ(vp, &auio, 0, curthread->td_ucred);
  635                 if (!error) {
  636                         int count = size - auio.uio_resid;
  637 
  638                         if (count == 0)
  639                                 error = EINVAL;
  640                         else if (count != PAGE_SIZE)
  641                                 bzero((caddr_t)sf_buf_kva(sf) + count,
  642                                     PAGE_SIZE - count);
  643                 }
  644                 sf_buf_free(sf);
  645 
  646                 VM_OBJECT_LOCK(object);
  647         }
  648         KASSERT(m->dirty == 0, ("vnode_pager_input_old: page %p is dirty", m));
  649         if (!error)
  650                 m->valid = VM_PAGE_BITS_ALL;
  651         return error ? VM_PAGER_ERROR : VM_PAGER_OK;
  652 }
  653 
  654 /*
  655  * generic vnode pager input routine
  656  */
  657 
  658 /*
  659  * Local media VFS's that do not implement their own VOP_GETPAGES
  660  * should have their VOP_GETPAGES call to vnode_pager_generic_getpages()
  661  * to implement the previous behaviour.
  662  *
  663  * All other FS's should use the bypass to get to the local media
  664  * backing vp's VOP_GETPAGES.
  665  */
  666 static int
  667 vnode_pager_getpages(object, m, count, reqpage)
  668         vm_object_t object;
  669         vm_page_t *m;
  670         int count;
  671         int reqpage;
  672 {
  673         int rtval;
  674         struct vnode *vp;
  675         int bytes = count * PAGE_SIZE;
  676         int vfslocked;
  677 
  678         vp = object->handle;
  679         VM_OBJECT_UNLOCK(object);
  680         vfslocked = VFS_LOCK_GIANT(vp->v_mount);
  681         rtval = VOP_GETPAGES(vp, m, bytes, reqpage, 0);
  682         KASSERT(rtval != EOPNOTSUPP,
  683             ("vnode_pager: FS getpages not implemented\n"));
  684         VFS_UNLOCK_GIANT(vfslocked);
  685         VM_OBJECT_LOCK(object);
  686         return rtval;
  687 }
  688 
  689 /*
  690  * This is now called from local media FS's to operate against their
  691  * own vnodes if they fail to implement VOP_GETPAGES.
  692  */
  693 int
  694 vnode_pager_generic_getpages(vp, m, bytecount, reqpage)
  695         struct vnode *vp;
  696         vm_page_t *m;
  697         int bytecount;
  698         int reqpage;
  699 {
  700         vm_object_t object;
  701         vm_offset_t kva;
  702         off_t foff, tfoff, nextoff;
  703         int i, j, size, bsize, first;
  704         daddr_t firstaddr, reqblock;
  705         struct bufobj *bo;
  706         int runpg;
  707         int runend;
  708         struct buf *bp;
  709         struct mount *mp;
  710         int count;
  711         int error;
  712 
  713         object = vp->v_object;
  714         count = bytecount / PAGE_SIZE;
  715 
  716         KASSERT(vp->v_type != VCHR && vp->v_type != VBLK,
  717             ("vnode_pager_generic_getpages does not support devices"));
  718         if (vp->v_iflag & VI_DOOMED)
  719                 return VM_PAGER_BAD;
  720 
  721         bsize = vp->v_mount->mnt_stat.f_iosize;
  722 
  723         /* get the UNDERLYING device for the file with VOP_BMAP() */
  724 
  725         /*
  726          * originally, we did not check for an error return value -- assuming
  727          * an fs always has a bmap entry point -- that assumption is wrong!!!
  728          */
  729         foff = IDX_TO_OFF(m[reqpage]->pindex);
  730 
  731         /*
  732          * if we can't bmap, use old VOP code
  733          */
  734         error = VOP_BMAP(vp, foff / bsize, &bo, &reqblock, NULL, NULL);
  735         if (error == EOPNOTSUPP) {
  736                 VM_OBJECT_LOCK(object);
  737                 
  738                 for (i = 0; i < count; i++)
  739                         if (i != reqpage) {
  740                                 vm_page_lock(m[i]);
  741                                 vm_page_free(m[i]);
  742                                 vm_page_unlock(m[i]);
  743                         }
  744                 PCPU_INC(cnt.v_vnodein);
  745                 PCPU_INC(cnt.v_vnodepgsin);
  746                 error = vnode_pager_input_old(object, m[reqpage]);
  747                 VM_OBJECT_UNLOCK(object);
  748                 return (error);
  749         } else if (error != 0) {
  750                 VM_OBJECT_LOCK(object);
  751                 for (i = 0; i < count; i++)
  752                         if (i != reqpage) {
  753                                 vm_page_lock(m[i]);
  754                                 vm_page_free(m[i]);
  755                                 vm_page_unlock(m[i]);
  756                         }
  757                 VM_OBJECT_UNLOCK(object);
  758                 return (VM_PAGER_ERROR);
  759 
  760                 /*
  761                  * if the blocksize is smaller than a page size, then use
  762                  * special small filesystem code.  NFS sometimes has a small
  763                  * blocksize, but it can handle large reads itself.
  764                  */
  765         } else if ((PAGE_SIZE / bsize) > 1 &&
  766             (vp->v_mount->mnt_stat.f_type != nfs_mount_type)) {
  767                 VM_OBJECT_LOCK(object);
  768                 for (i = 0; i < count; i++)
  769                         if (i != reqpage) {
  770                                 vm_page_lock(m[i]);
  771                                 vm_page_free(m[i]);
  772                                 vm_page_unlock(m[i]);
  773                         }
  774                 VM_OBJECT_UNLOCK(object);
  775                 PCPU_INC(cnt.v_vnodein);
  776                 PCPU_INC(cnt.v_vnodepgsin);
  777                 return vnode_pager_input_smlfs(object, m[reqpage]);
  778         }
  779 
  780         /*
  781          * If we have a completely valid page available to us, we can
  782          * clean up and return.  Otherwise we have to re-read the
  783          * media.
  784          */
  785         VM_OBJECT_LOCK(object);
  786         if (m[reqpage]->valid == VM_PAGE_BITS_ALL) {
  787                 for (i = 0; i < count; i++)
  788                         if (i != reqpage) {
  789                                 vm_page_lock(m[i]);
  790                                 vm_page_free(m[i]);
  791                                 vm_page_unlock(m[i]);
  792                         }
  793                 VM_OBJECT_UNLOCK(object);
  794                 return VM_PAGER_OK;
  795         } else if (reqblock == -1) {
  796                 pmap_zero_page(m[reqpage]);
  797                 KASSERT(m[reqpage]->dirty == 0,
  798                     ("vnode_pager_generic_getpages: page %p is dirty", m));
  799                 m[reqpage]->valid = VM_PAGE_BITS_ALL;
  800                 for (i = 0; i < count; i++)
  801                         if (i != reqpage) {
  802                                 vm_page_lock(m[i]);
  803                                 vm_page_free(m[i]);
  804                                 vm_page_unlock(m[i]);
  805                         }
  806                 VM_OBJECT_UNLOCK(object);
  807                 return (VM_PAGER_OK);
  808         }
  809         m[reqpage]->valid = 0;
  810         VM_OBJECT_UNLOCK(object);
  811 
  812         /*
  813          * here on direct device I/O
  814          */
  815         firstaddr = -1;
  816 
  817         /*
  818          * calculate the run that includes the required page
  819          */
  820         for (first = 0, i = 0; i < count; i = runend) {
  821                 if (vnode_pager_addr(vp, IDX_TO_OFF(m[i]->pindex), &firstaddr,
  822                     &runpg) != 0) {
  823                         VM_OBJECT_LOCK(object);
  824                         for (; i < count; i++)
  825                                 if (i != reqpage) {
  826                                         vm_page_lock(m[i]);
  827                                         vm_page_free(m[i]);
  828                                         vm_page_unlock(m[i]);
  829                                 }
  830                         VM_OBJECT_UNLOCK(object);
  831                         return (VM_PAGER_ERROR);
  832                 }
  833                 if (firstaddr == -1) {
  834                         VM_OBJECT_LOCK(object);
  835                         if (i == reqpage && foff < object->un_pager.vnp.vnp_size) {
  836                                 panic("vnode_pager_getpages: unexpected missing page: firstaddr: %jd, foff: 0x%jx%08jx, vnp_size: 0x%jx%08jx",
  837                                     (intmax_t)firstaddr, (uintmax_t)(foff >> 32),
  838                                     (uintmax_t)foff,
  839                                     (uintmax_t)
  840                                     (object->un_pager.vnp.vnp_size >> 32),
  841                                     (uintmax_t)object->un_pager.vnp.vnp_size);
  842                         }
  843                         vm_page_lock(m[i]);
  844                         vm_page_free(m[i]);
  845                         vm_page_unlock(m[i]);
  846                         VM_OBJECT_UNLOCK(object);
  847                         runend = i + 1;
  848                         first = runend;
  849                         continue;
  850                 }
  851                 runend = i + runpg;
  852                 if (runend <= reqpage) {
  853                         VM_OBJECT_LOCK(object);
  854                         for (j = i; j < runend; j++) {
  855                                 vm_page_lock(m[j]);
  856                                 vm_page_free(m[j]);
  857                                 vm_page_unlock(m[j]);
  858                         }
  859                         VM_OBJECT_UNLOCK(object);
  860                 } else {
  861                         if (runpg < (count - first)) {
  862                                 VM_OBJECT_LOCK(object);
  863                                 for (i = first + runpg; i < count; i++) {
  864                                         vm_page_lock(m[i]);
  865                                         vm_page_free(m[i]);
  866                                         vm_page_unlock(m[i]);
  867                                 }
  868                                 VM_OBJECT_UNLOCK(object);
  869                                 count = first + runpg;
  870                         }
  871                         break;
  872                 }
  873                 first = runend;
  874         }
  875 
  876         /*
  877          * the first and last page have been calculated now, move input pages
  878          * to be zero based...
  879          */
  880         if (first != 0) {
  881                 m += first;
  882                 count -= first;
  883                 reqpage -= first;
  884         }
  885 
  886         /*
  887          * calculate the file virtual address for the transfer
  888          */
  889         foff = IDX_TO_OFF(m[0]->pindex);
  890 
  891         /*
  892          * calculate the size of the transfer
  893          */
  894         size = count * PAGE_SIZE;
  895         KASSERT(count > 0, ("zero count"));
  896         if ((foff + size) > object->un_pager.vnp.vnp_size)
  897                 size = object->un_pager.vnp.vnp_size - foff;
  898         KASSERT(size > 0, ("zero size"));
  899 
  900         /*
  901          * round up physical size for real devices.
  902          */
  903         if (1) {
  904                 int secmask = bo->bo_bsize - 1;
  905                 KASSERT(secmask < PAGE_SIZE && secmask > 0,
  906                     ("vnode_pager_generic_getpages: sector size %d too large",
  907                     secmask + 1));
  908                 size = (size + secmask) & ~secmask;
  909         }
  910 
  911         bp = getpbuf(&vnode_pbuf_freecnt);
  912         kva = (vm_offset_t)bp->b_data;
  913 
  914         /*
  915          * and map the pages to be read into the kva, if the filesystem
  916          * requires mapped buffers.
  917          */
  918         mp = vp->v_mount;
  919         if (mp != NULL && (mp->mnt_kern_flag & MNTK_UNMAPPED_BUFS) != 0 &&
  920             unmapped_buf_allowed) {
  921                 bp->b_data = unmapped_buf;
  922                 bp->b_kvabase = unmapped_buf;
  923                 bp->b_offset = 0;
  924                 bp->b_flags |= B_UNMAPPED;
  925                 bp->b_npages = count;
  926                 for (i = 0; i < count; i++)
  927                         bp->b_pages[i] = m[i];
  928         } else
  929                 pmap_qenter(kva, m, count);
  930 
  931         /* build a minimal buffer header */
  932         bp->b_iocmd = BIO_READ;
  933         bp->b_iodone = bdone;
  934         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
  935         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
  936         bp->b_rcred = crhold(curthread->td_ucred);
  937         bp->b_wcred = crhold(curthread->td_ucred);
  938         bp->b_blkno = firstaddr;
  939         pbgetbo(bo, bp);
  940         bp->b_vp = vp;
  941         bp->b_bcount = size;
  942         bp->b_bufsize = size;
  943         bp->b_runningbufspace = bp->b_bufsize;
  944         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
  945 
  946         PCPU_INC(cnt.v_vnodein);
  947         PCPU_ADD(cnt.v_vnodepgsin, count);
  948 
  949         /* do the input */
  950         bp->b_iooffset = dbtob(bp->b_blkno);
  951         bstrategy(bp);
  952 
  953         bwait(bp, PVM, "vnread");
  954 
  955         if ((bp->b_ioflags & BIO_ERROR) != 0)
  956                 error = EIO;
  957 
  958         if (error == 0 && size != count * PAGE_SIZE) {
  959                 if ((bp->b_flags & B_UNMAPPED) != 0) {
  960                         bp->b_flags &= ~B_UNMAPPED;
  961                         pmap_qenter(kva, m, count);
  962                 }
  963                 bzero((caddr_t)kva + size, PAGE_SIZE * count - size);
  964         }
  965         if ((bp->b_flags & B_UNMAPPED) == 0)
  966                 pmap_qremove(kva, count);
  967         if (mp != NULL && (mp->mnt_kern_flag & MNTK_UNMAPPED_BUFS) != 0) {
  968                 bp->b_data = (caddr_t)kva;
  969                 bp->b_kvabase = (caddr_t)kva;
  970                 bp->b_flags &= ~B_UNMAPPED;
  971                 for (i = 0; i < count; i++)
  972                         bp->b_pages[i] = NULL;
  973         }
  974 
  975         /*
  976          * free the buffer header back to the swap buffer pool
  977          */
  978         bp->b_vp = NULL;
  979         pbrelbo(bp);
  980         relpbuf(bp, &vnode_pbuf_freecnt);
  981 
  982         VM_OBJECT_LOCK(object);
  983         for (i = 0, tfoff = foff; i < count; i++, tfoff = nextoff) {
  984                 vm_page_t mt;
  985 
  986                 nextoff = tfoff + PAGE_SIZE;
  987                 mt = m[i];
  988 
  989                 if (nextoff <= object->un_pager.vnp.vnp_size) {
  990                         /*
  991                          * Read filled up entire page.
  992                          */
  993                         mt->valid = VM_PAGE_BITS_ALL;
  994                         KASSERT(mt->dirty == 0,
  995                             ("vnode_pager_generic_getpages: page %p is dirty",
  996                             mt));
  997                         KASSERT(!pmap_page_is_mapped(mt),
  998                             ("vnode_pager_generic_getpages: page %p is mapped",
  999                             mt));
 1000                 } else {
 1001                         /*
 1002                          * Read did not fill up entire page.
 1003                          *
 1004                          * Currently we do not set the entire page valid,
 1005                          * we just try to clear the piece that we couldn't
 1006                          * read.
 1007                          */
 1008                         vm_page_set_valid(mt, 0,
 1009                             object->un_pager.vnp.vnp_size - tfoff);
 1010                         KASSERT((mt->dirty & vm_page_bits(0,
 1011                             object->un_pager.vnp.vnp_size - tfoff)) == 0,
 1012                             ("vnode_pager_generic_getpages: page %p is dirty",
 1013                             mt));
 1014                 }
 1015                 
 1016                 if (i != reqpage)
 1017                         vm_page_readahead_finish(mt);
 1018         }
 1019         VM_OBJECT_UNLOCK(object);
 1020         if (error) {
 1021                 printf("vnode_pager_getpages: I/O read error\n");
 1022         }
 1023         return (error ? VM_PAGER_ERROR : VM_PAGER_OK);
 1024 }
 1025 
 1026 /*
 1027  * EOPNOTSUPP is no longer legal.  For local media VFS's that do not
 1028  * implement their own VOP_PUTPAGES, their VOP_PUTPAGES should call to
 1029  * vnode_pager_generic_putpages() to implement the previous behaviour.
 1030  *
 1031  * All other FS's should use the bypass to get to the local media
 1032  * backing vp's VOP_PUTPAGES.
 1033  */
 1034 static void
 1035 vnode_pager_putpages(object, m, count, sync, rtvals)
 1036         vm_object_t object;
 1037         vm_page_t *m;
 1038         int count;
 1039         boolean_t sync;
 1040         int *rtvals;
 1041 {
 1042         int rtval;
 1043         struct vnode *vp;
 1044         int bytes = count * PAGE_SIZE;
 1045 
 1046         /*
 1047          * Force synchronous operation if we are extremely low on memory
 1048          * to prevent a low-memory deadlock.  VOP operations often need to
 1049          * allocate more memory to initiate the I/O ( i.e. do a BMAP 
 1050          * operation ).  The swapper handles the case by limiting the amount
 1051          * of asynchronous I/O, but that sort of solution doesn't scale well
 1052          * for the vnode pager without a lot of work.
 1053          *
 1054          * Also, the backing vnode's iodone routine may not wake the pageout
 1055          * daemon up.  This should be probably be addressed XXX.
 1056          */
 1057 
 1058         if ((cnt.v_free_count + cnt.v_cache_count) < cnt.v_pageout_free_min)
 1059                 sync |= OBJPC_SYNC;
 1060 
 1061         /*
 1062          * Call device-specific putpages function
 1063          */
 1064         vp = object->handle;
 1065         VM_OBJECT_UNLOCK(object);
 1066         rtval = VOP_PUTPAGES(vp, m, bytes, sync, rtvals, 0);
 1067         KASSERT(rtval != EOPNOTSUPP, 
 1068             ("vnode_pager: stale FS putpages\n"));
 1069         VM_OBJECT_LOCK(object);
 1070 }
 1071 
 1072 
 1073 /*
 1074  * This is now called from local media FS's to operate against their
 1075  * own vnodes if they fail to implement VOP_PUTPAGES.
 1076  *
 1077  * This is typically called indirectly via the pageout daemon and
 1078  * clustering has already typically occured, so in general we ask the
 1079  * underlying filesystem to write the data out asynchronously rather
 1080  * then delayed.
 1081  */
 1082 int
 1083 vnode_pager_generic_putpages(struct vnode *vp, vm_page_t *ma, int bytecount,
 1084     int flags, int *rtvals)
 1085 {
 1086         int i;
 1087         vm_object_t object;
 1088         vm_page_t m;
 1089         int count;
 1090 
 1091         int maxsize, ncount;
 1092         vm_ooffset_t poffset;
 1093         struct uio auio;
 1094         struct iovec aiov;
 1095         int error;
 1096         int ioflags;
 1097         int ppscheck = 0;
 1098         static struct timeval lastfail;
 1099         static int curfail;
 1100 
 1101         object = vp->v_object;
 1102         count = bytecount / PAGE_SIZE;
 1103 
 1104         for (i = 0; i < count; i++)
 1105                 rtvals[i] = VM_PAGER_ERROR;
 1106 
 1107         if ((int64_t)ma[0]->pindex < 0) {
 1108                 printf("vnode_pager_putpages: attempt to write meta-data!!! -- 0x%lx(%lx)\n",
 1109                     (long)ma[0]->pindex, (u_long)ma[0]->dirty);
 1110                 rtvals[0] = VM_PAGER_BAD;
 1111                 return VM_PAGER_BAD;
 1112         }
 1113 
 1114         maxsize = count * PAGE_SIZE;
 1115         ncount = count;
 1116 
 1117         poffset = IDX_TO_OFF(ma[0]->pindex);
 1118 
 1119         /*
 1120          * If the page-aligned write is larger then the actual file we
 1121          * have to invalidate pages occuring beyond the file EOF.  However,
 1122          * there is an edge case where a file may not be page-aligned where
 1123          * the last page is partially invalid.  In this case the filesystem
 1124          * may not properly clear the dirty bits for the entire page (which
 1125          * could be VM_PAGE_BITS_ALL due to the page having been mmap()d).
 1126          * With the page locked we are free to fix-up the dirty bits here.
 1127          *
 1128          * We do not under any circumstances truncate the valid bits, as
 1129          * this will screw up bogus page replacement.
 1130          */
 1131         VM_OBJECT_LOCK(object);
 1132         if (maxsize + poffset > object->un_pager.vnp.vnp_size) {
 1133                 if (object->un_pager.vnp.vnp_size > poffset) {
 1134                         int pgoff;
 1135 
 1136                         maxsize = object->un_pager.vnp.vnp_size - poffset;
 1137                         ncount = btoc(maxsize);
 1138                         if ((pgoff = (int)maxsize & PAGE_MASK) != 0) {
 1139                                 /*
 1140                                  * If the object is locked and the following
 1141                                  * conditions hold, then the page's dirty
 1142                                  * field cannot be concurrently changed by a
 1143                                  * pmap operation.
 1144                                  */
 1145                                 m = ma[ncount - 1];
 1146                                 KASSERT(m->busy > 0,
 1147                 ("vnode_pager_generic_putpages: page %p is not busy", m));
 1148                                 KASSERT(!pmap_page_is_write_mapped(m),
 1149                 ("vnode_pager_generic_putpages: page %p is not read-only", m));
 1150                                 vm_page_clear_dirty(m, pgoff, PAGE_SIZE -
 1151                                     pgoff);
 1152                         }
 1153                 } else {
 1154                         maxsize = 0;
 1155                         ncount = 0;
 1156                 }
 1157                 if (ncount < count) {
 1158                         for (i = ncount; i < count; i++) {
 1159                                 rtvals[i] = VM_PAGER_BAD;
 1160                         }
 1161                 }
 1162         }
 1163         VM_OBJECT_UNLOCK(object);
 1164 
 1165         /*
 1166          * pageouts are already clustered, use IO_ASYNC t o force a bawrite()
 1167          * rather then a bdwrite() to prevent paging I/O from saturating 
 1168          * the buffer cache.  Dummy-up the sequential heuristic to cause
 1169          * large ranges to cluster.  If neither IO_SYNC or IO_ASYNC is set,
 1170          * the system decides how to cluster.
 1171          */
 1172         ioflags = IO_VMIO;
 1173         if (flags & (VM_PAGER_PUT_SYNC | VM_PAGER_PUT_INVAL))
 1174                 ioflags |= IO_SYNC;
 1175         else if ((flags & VM_PAGER_CLUSTER_OK) == 0)
 1176                 ioflags |= IO_ASYNC;
 1177         ioflags |= (flags & VM_PAGER_PUT_INVAL) ? IO_INVAL: 0;
 1178         ioflags |= IO_SEQMAX << IO_SEQSHIFT;
 1179 
 1180         aiov.iov_base = (caddr_t) 0;
 1181         aiov.iov_len = maxsize;
 1182         auio.uio_iov = &aiov;
 1183         auio.uio_iovcnt = 1;
 1184         auio.uio_offset = poffset;
 1185         auio.uio_segflg = UIO_NOCOPY;
 1186         auio.uio_rw = UIO_WRITE;
 1187         auio.uio_resid = maxsize;
 1188         auio.uio_td = (struct thread *) 0;
 1189         error = VOP_WRITE(vp, &auio, ioflags, curthread->td_ucred);
 1190         PCPU_INC(cnt.v_vnodeout);
 1191         PCPU_ADD(cnt.v_vnodepgsout, ncount);
 1192 
 1193         if (error) {
 1194                 if ((ppscheck = ppsratecheck(&lastfail, &curfail, 1)))
 1195                         printf("vnode_pager_putpages: I/O error %d\n", error);
 1196         }
 1197         if (auio.uio_resid) {
 1198                 if (ppscheck || ppsratecheck(&lastfail, &curfail, 1))
 1199                         printf("vnode_pager_putpages: residual I/O %zd at %lu\n",
 1200                             auio.uio_resid, (u_long)ma[0]->pindex);
 1201         }
 1202         for (i = 0; i < ncount; i++) {
 1203                 rtvals[i] = VM_PAGER_OK;
 1204         }
 1205         return rtvals[0];
 1206 }
 1207 
 1208 void
 1209 vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written)
 1210 {
 1211         vm_object_t obj;
 1212         int i, pos;
 1213 
 1214         if (written == 0)
 1215                 return;
 1216         obj = ma[0]->object;
 1217         VM_OBJECT_LOCK(obj);
 1218         for (i = 0, pos = 0; pos < written; i++, pos += PAGE_SIZE) {
 1219                 if (pos < trunc_page(written)) {
 1220                         rtvals[i] = VM_PAGER_OK;
 1221                         vm_page_undirty(ma[i]);
 1222                 } else {
 1223                         /* Partially written page. */
 1224                         rtvals[i] = VM_PAGER_AGAIN;
 1225                         vm_page_clear_dirty(ma[i], 0, written & PAGE_MASK);
 1226                 }
 1227         }
 1228         VM_OBJECT_UNLOCK(obj);
 1229 }
 1230 
 1231 void
 1232 vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
 1233     vm_offset_t end)
 1234 {
 1235         struct vnode *vp;
 1236         vm_ooffset_t old_wm;
 1237 
 1238         VM_OBJECT_LOCK(object);
 1239         if (object->type != OBJT_VNODE) {
 1240                 VM_OBJECT_UNLOCK(object);
 1241                 return;
 1242         }
 1243         old_wm = object->un_pager.vnp.writemappings;
 1244         object->un_pager.vnp.writemappings += (vm_ooffset_t)end - start;
 1245         vp = object->handle;
 1246         if (old_wm == 0 && object->un_pager.vnp.writemappings != 0) {
 1247                 ASSERT_VOP_ELOCKED(vp, "v_writecount inc");
 1248                 VOP_ADD_WRITECOUNT(vp, 1);
 1249         } else if (old_wm != 0 && object->un_pager.vnp.writemappings == 0) {
 1250                 ASSERT_VOP_ELOCKED(vp, "v_writecount dec");
 1251                 VOP_ADD_WRITECOUNT(vp, -1);
 1252         }
 1253         VM_OBJECT_UNLOCK(object);
 1254 }
 1255 
 1256 void
 1257 vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
 1258     vm_offset_t end)
 1259 {
 1260         struct vnode *vp;
 1261         struct mount *mp;
 1262         vm_offset_t inc;
 1263         int vfslocked;
 1264 
 1265         VM_OBJECT_LOCK(object);
 1266 
 1267         /*
 1268          * First, recheck the object type to account for the race when
 1269          * the vnode is reclaimed.
 1270          */
 1271         if (object->type != OBJT_VNODE) {
 1272                 VM_OBJECT_UNLOCK(object);
 1273                 return;
 1274         }
 1275 
 1276         /*
 1277          * Optimize for the case when writemappings is not going to
 1278          * zero.
 1279          */
 1280         inc = end - start;
 1281         if (object->un_pager.vnp.writemappings != inc) {
 1282                 object->un_pager.vnp.writemappings -= inc;
 1283                 VM_OBJECT_UNLOCK(object);
 1284                 return;
 1285         }
 1286 
 1287         vp = object->handle;
 1288         vhold(vp);
 1289         VM_OBJECT_UNLOCK(object);
 1290         vfslocked = VFS_LOCK_GIANT(vp->v_mount);
 1291         mp = NULL;
 1292         vn_start_write(vp, &mp, V_WAIT);
 1293         vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 1294 
 1295         /*
 1296          * Decrement the object's writemappings, by swapping the start
 1297          * and end arguments for vnode_pager_update_writecount().  If
 1298          * there was not a race with vnode reclaimation, then the
 1299          * vnode's v_writecount is decremented.
 1300          */
 1301         vnode_pager_update_writecount(object, end, start);
 1302         VOP_UNLOCK(vp, 0);
 1303         vdrop(vp);
 1304         if (mp != NULL)
 1305                 vn_finished_write(mp);
 1306         VFS_UNLOCK_GIANT(vfslocked);
 1307 }

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