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

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    1 /*-
    2  * Copyright (c) 2009 Hudson River Trading LLC
    3  * Written by: John H. Baldwin <jhb@FreeBSD.org>
    4  * All rights reserved.
    5  *
    6  * Redistribution and use in source and binary forms, with or without
    7  * modification, are permitted provided that the following conditions
    8  * are met:
    9  * 1. Redistributions of source code must retain the above copyright
   10  *    notice, this list of conditions and the following disclaimer.
   11  * 2. Redistributions in binary form must reproduce the above copyright
   12  *    notice, this list of conditions and the following disclaimer in the
   13  *    documentation and/or other materials provided with the distribution.
   14  *
   15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   16  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   17  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   19  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   21  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   22  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   24  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   25  * SUCH DAMAGE.
   26  */
   27 
   28 #include <sys/cdefs.h>
   29 __FBSDID("$FreeBSD: releng/11.0/sys/vm/sg_pager.c 295330 2016-02-05 19:35:53Z markj $");
   30 
   31 /*
   32  * This pager manages OBJT_SG objects.  These objects are backed by
   33  * a scatter/gather list of physical address ranges.
   34  */
   35 
   36 #include <sys/param.h>
   37 #include <sys/lock.h>
   38 #include <sys/mutex.h>
   39 #include <sys/rwlock.h>
   40 #include <sys/sglist.h>
   41 #include <vm/vm.h>
   42 #include <vm/vm_param.h>
   43 #include <vm/vm_object.h>
   44 #include <vm/vm_page.h>
   45 #include <vm/vm_pager.h>
   46 #include <vm/vm_phys.h>
   47 #include <vm/uma.h>
   48 
   49 static vm_object_t sg_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
   50     vm_ooffset_t, struct ucred *);
   51 static void sg_pager_dealloc(vm_object_t);
   52 static int sg_pager_getpages(vm_object_t, vm_page_t *, int, int *, int *);
   53 static void sg_pager_putpages(vm_object_t, vm_page_t *, int, 
   54                 boolean_t, int *);
   55 static boolean_t sg_pager_haspage(vm_object_t, vm_pindex_t, int *,
   56                 int *);
   57 
   58 struct pagerops sgpagerops = {
   59         .pgo_alloc =    sg_pager_alloc,
   60         .pgo_dealloc =  sg_pager_dealloc,
   61         .pgo_getpages = sg_pager_getpages,
   62         .pgo_putpages = sg_pager_putpages,
   63         .pgo_haspage =  sg_pager_haspage,
   64 };
   65 
   66 static vm_object_t
   67 sg_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
   68     vm_ooffset_t foff, struct ucred *cred)
   69 {
   70         struct sglist *sg;
   71         vm_object_t object;
   72         vm_pindex_t npages, pindex;
   73         int i;
   74 
   75         /*
   76          * Offset should be page aligned.
   77          */
   78         if (foff & PAGE_MASK)
   79                 return (NULL);
   80 
   81         /*
   82          * The scatter/gather list must only include page-aligned
   83          * ranges.
   84          */
   85         npages = 0;
   86         sg = handle;
   87         for (i = 0; i < sg->sg_nseg; i++) {
   88                 if ((sg->sg_segs[i].ss_paddr % PAGE_SIZE) != 0 ||
   89                     (sg->sg_segs[i].ss_len % PAGE_SIZE) != 0)
   90                         return (NULL);
   91                 npages += sg->sg_segs[i].ss_len / PAGE_SIZE;
   92         }
   93 
   94         /*
   95          * The scatter/gather list has a fixed size.  Refuse requests
   96          * to map beyond that.
   97          */
   98         size = round_page(size);
   99         pindex = OFF_TO_IDX(foff + size);
  100         if (pindex > npages)
  101                 return (NULL);
  102 
  103         /*
  104          * Allocate a new object and associate it with the
  105          * scatter/gather list.  It is ok for our purposes to have
  106          * multiple VM objects associated with the same scatter/gather
  107          * list because scatter/gather lists are static.  This is also
  108          * simpler than ensuring a unique object per scatter/gather
  109          * list.
  110          */
  111         object = vm_object_allocate(OBJT_SG, npages);
  112         object->handle = sglist_hold(sg);
  113         TAILQ_INIT(&object->un_pager.sgp.sgp_pglist);
  114         return (object);
  115 }
  116 
  117 static void
  118 sg_pager_dealloc(vm_object_t object)
  119 {
  120         struct sglist *sg;
  121         vm_page_t m;
  122 
  123         /*
  124          * Free up our fake pages.
  125          */
  126         while ((m = TAILQ_FIRST(&object->un_pager.sgp.sgp_pglist)) != 0) {
  127                 TAILQ_REMOVE(&object->un_pager.sgp.sgp_pglist, m, plinks.q);
  128                 vm_page_putfake(m);
  129         }
  130         
  131         sg = object->handle;
  132         sglist_free(sg);
  133         object->handle = NULL;
  134         object->type = OBJT_DEAD;
  135 }
  136 
  137 static int
  138 sg_pager_getpages(vm_object_t object, vm_page_t *m, int count, int *rbehind,
  139     int *rahead)
  140 {
  141         struct sglist *sg;
  142         vm_page_t m_paddr, page;
  143         vm_pindex_t offset;
  144         vm_paddr_t paddr;
  145         vm_memattr_t memattr;
  146         size_t space;
  147         int i;
  148 
  149         /* Since our haspage reports zero after/before, the count is 1. */
  150         KASSERT(count == 1, ("%s: count %d", __func__, count));
  151         VM_OBJECT_ASSERT_WLOCKED(object);
  152         sg = object->handle;
  153         memattr = object->memattr;
  154         VM_OBJECT_WUNLOCK(object);
  155         offset = m[0]->pindex;
  156 
  157         /*
  158          * Lookup the physical address of the requested page.  An initial
  159          * value of '1' instead of '' is used so we can assert that the
  160          * page is found since '' can be a valid page-aligned physical
  161          * address.
  162          */
  163         space = 0;
  164         paddr = 1;
  165         for (i = 0; i < sg->sg_nseg; i++) {
  166                 if (space + sg->sg_segs[i].ss_len <= (offset * PAGE_SIZE)) {
  167                         space += sg->sg_segs[i].ss_len;
  168                         continue;
  169                 }
  170                 paddr = sg->sg_segs[i].ss_paddr + offset * PAGE_SIZE - space;
  171                 break;
  172         }
  173         KASSERT(paddr != 1, ("invalid SG page index"));
  174 
  175         /* If "paddr" is a real page, perform a sanity check on "memattr". */
  176         if ((m_paddr = vm_phys_paddr_to_vm_page(paddr)) != NULL &&
  177             pmap_page_get_memattr(m_paddr) != memattr) {
  178                 memattr = pmap_page_get_memattr(m_paddr);
  179                 printf(
  180             "WARNING: A device driver has set \"memattr\" inconsistently.\n");
  181         }
  182 
  183         /* Return a fake page for the requested page. */
  184         KASSERT(!(m[0]->flags & PG_FICTITIOUS),
  185             ("backing page for SG is fake"));
  186 
  187         /* Construct a new fake page. */
  188         page = vm_page_getfake(paddr, memattr);
  189         VM_OBJECT_WLOCK(object);
  190         TAILQ_INSERT_TAIL(&object->un_pager.sgp.sgp_pglist, page, plinks.q);
  191         vm_page_replace_checked(page, object, offset, m[0]);
  192         vm_page_lock(m[0]);
  193         vm_page_free(m[0]);
  194         vm_page_unlock(m[0]);
  195         m[0] = page;
  196         page->valid = VM_PAGE_BITS_ALL;
  197 
  198         if (rbehind)
  199                 *rbehind = 0;
  200         if (rahead)
  201                 *rahead = 0;
  202 
  203         return (VM_PAGER_OK);
  204 }
  205 
  206 static void
  207 sg_pager_putpages(vm_object_t object, vm_page_t *m, int count,
  208     boolean_t sync, int *rtvals)
  209 {
  210 
  211         panic("sg_pager_putpage called");
  212 }
  213 
  214 static boolean_t
  215 sg_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before,
  216     int *after)
  217 {
  218 
  219         if (before != NULL)
  220                 *before = 0;
  221         if (after != NULL)
  222                 *after = 0;
  223         return (TRUE);
  224 }

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