The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/uipc_cow.c

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    1 /*--
    2  * Copyright (c) 1997, Duke University
    3  * All rights reserved.
    4  *
    5  * Author:
    6  *         Andrew Gallatin <gallatin@cs.duke.edu>  
    7  *            
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  * 3. The name of Duke University may not be used to endorse or promote 
   17  *    products derived from this software without specific prior written 
   18  *    permission.
   19  * 
   20  * THIS SOFTWARE IS PROVIDED BY DUKE UNIVERSITY ``AS IS'' AND ANY
   21  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   23  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL DUKE UNIVERSITY BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   25  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   26  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITSOR BUSINESS
   27  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
   28  * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
   29  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   30  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  
   31  */
   32 
   33 /*
   34  * This is a set of routines for enabling and disabling copy on write
   35  * protection for data written into sockets.
   36  */
   37 
   38 #include <sys/cdefs.h>
   39 __FBSDID("$FreeBSD: src/sys/kern/uipc_cow.c,v 1.20.2.2 2005/03/09 18:59:20 alc Exp $");
   40 
   41 #include <sys/param.h>
   42 #include <sys/systm.h>
   43 #include <sys/kernel.h>
   44 #include <sys/proc.h>
   45 #include <sys/lock.h>
   46 #include <sys/mutex.h>
   47 #include <sys/mbuf.h>
   48 #include <sys/sf_buf.h>
   49 #include <sys/socketvar.h>
   50 #include <sys/uio.h>
   51 
   52 #include <vm/vm.h>
   53 #include <vm/vm_param.h>
   54 #include <vm/pmap.h>
   55 #include <vm/vm_map.h>
   56 #include <vm/vm_page.h>
   57 #include <vm/vm_object.h>
   58 
   59 
   60 struct netsend_cow_stats {
   61         int attempted;
   62         int fail_not_mapped;
   63         int fail_sf_buf;
   64         int success;
   65         int iodone;
   66 };
   67 
   68 static struct netsend_cow_stats socow_stats;
   69 
   70 static void socow_iodone(void *addr, void *args);
   71 
   72 static void
   73 socow_iodone(void *addr, void *args)
   74 {       
   75         struct sf_buf *sf;
   76         vm_page_t pp;
   77 
   78         sf = args;
   79         pp = sf_buf_page(sf);
   80         sf_buf_free(sf);
   81         /* remove COW mapping  */
   82         vm_page_lock_queues();
   83         vm_page_cowclear(pp);
   84         vm_page_unwire(pp, 0);
   85         /*
   86          * Check for the object going away on us. This can
   87          * happen since we don't hold a reference to it.
   88          * If so, we're responsible for freeing the page.
   89          */
   90         if (pp->wire_count == 0 && pp->object == NULL)
   91                 vm_page_free(pp);
   92         vm_page_unlock_queues();
   93         socow_stats.iodone++;
   94 }
   95 
   96 int
   97 socow_setup(struct mbuf *m0, struct uio *uio)
   98 {
   99         struct sf_buf *sf;
  100         vm_page_t pp;
  101         vm_paddr_t pa;
  102         struct iovec *iov;
  103         struct vmspace *vmspace;
  104         struct vm_map *map;
  105         vm_offset_t uva;
  106         int s;
  107 
  108         vmspace = curproc->p_vmspace;
  109         map = &vmspace->vm_map;
  110         uva = (vm_offset_t) uio->uio_iov->iov_base;
  111 
  112         s = splvm();
  113 
  114        /* 
  115         * verify page is mapped & not already wired for i/o
  116         */
  117         socow_stats.attempted++;
  118         pa=pmap_extract(map->pmap, uva);
  119         if(!pa) {
  120                 socow_stats.fail_not_mapped++;
  121                 splx(s);
  122                 return(0);
  123         }
  124         pp = PHYS_TO_VM_PAGE(pa);
  125 
  126         /* 
  127          * set up COW
  128          */
  129         vm_page_lock_queues();
  130         vm_page_cowsetup(pp);
  131 
  132         /*
  133          * wire the page for I/O
  134          */
  135         vm_page_wire(pp);
  136         vm_page_unlock_queues();
  137 
  138         /*
  139          * Allocate an sf buf
  140          */
  141         sf = sf_buf_alloc(pp, SFB_CATCH);
  142         if (!sf) {
  143                 vm_page_lock_queues();
  144                 vm_page_cowclear(pp);
  145                 vm_page_unwire(pp, 0);
  146                 /*
  147                  * Check for the object going away on us. This can
  148                  * happen since we don't hold a reference to it.
  149                  * If so, we're responsible for freeing the page.
  150                  */
  151                 if (pp->wire_count == 0 && pp->object == NULL)
  152                         vm_page_free(pp);
  153                 vm_page_unlock_queues();
  154                 socow_stats.fail_sf_buf++;
  155                 splx(s);
  156                 return(0);
  157         }
  158         /* 
  159          * attach to mbuf
  160          */
  161         m0->m_data = (caddr_t)sf_buf_kva(sf);
  162         m0->m_len = PAGE_SIZE;
  163         MEXTADD(m0, sf_buf_kva(sf), PAGE_SIZE, socow_iodone, sf, M_RDONLY,
  164             EXT_SFBUF);
  165         socow_stats.success++;
  166 
  167         iov = uio->uio_iov;
  168         iov->iov_base = (char *)iov->iov_base + PAGE_SIZE;
  169         iov->iov_len -= PAGE_SIZE;
  170         uio->uio_resid -= PAGE_SIZE;
  171         uio->uio_offset += PAGE_SIZE;
  172         if (iov->iov_len == 0) {
  173                 uio->uio_iov++;
  174                 uio->uio_iovcnt--;
  175         }
  176 
  177         splx(s);
  178         return(1);
  179 }

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