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("$FreeBSD$");
   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_extern.h>
   54 #include <vm/vm_param.h>
   55 #include <vm/pmap.h>
   56 #include <vm/vm_map.h>
   57 #include <vm/vm_page.h>
   58 #include <vm/vm_object.h>
   59 
   60 
   61 struct netsend_cow_stats {
   62         int attempted;
   63         int fail_not_mapped;
   64         int fail_sf_buf;
   65         int success;
   66         int iodone;
   67 };
   68 
   69 static struct netsend_cow_stats socow_stats;
   70 
   71 static void socow_iodone(void *addr, void *args);
   72 
   73 static void
   74 socow_iodone(void *addr, void *args)
   75 {       
   76         struct sf_buf *sf;
   77         vm_page_t pp;
   78 
   79         sf = args;
   80         pp = sf_buf_page(sf);
   81         sf_buf_free(sf);
   82         /* remove COW mapping  */
   83         vm_page_lock_queues();
   84         vm_page_cowclear(pp);
   85         vm_page_unwire(pp, 0);
   86         /*
   87          * Check for the object going away on us. This can
   88          * happen since we don't hold a reference to it.
   89          * If so, we're responsible for freeing the page.
   90          */
   91         if (pp->wire_count == 0 && pp->object == NULL)
   92                 vm_page_free(pp);
   93         vm_page_unlock_queues();
   94         socow_stats.iodone++;
   95 }
   96 
   97 int
   98 socow_setup(struct mbuf *m0, struct uio *uio)
   99 {
  100         struct sf_buf *sf;
  101         vm_page_t pp;
  102         struct iovec *iov;
  103         struct vmspace *vmspace;
  104         struct vm_map *map;
  105         vm_offset_t offset, uva;
  106 
  107         socow_stats.attempted++;
  108         vmspace = curproc->p_vmspace;
  109         map = &vmspace->vm_map;
  110         uva = (vm_offset_t) uio->uio_iov->iov_base;
  111         offset = uva & PAGE_MASK;
  112 
  113         /*
  114          * Verify that access to the given address is allowed from user-space.
  115          */
  116         if (vm_fault_quick((caddr_t)uva, VM_PROT_READ) < 0)
  117                 return (0);
  118 
  119        /* 
  120         * verify page is mapped & not already wired for i/o
  121         */
  122         pp = pmap_extract_and_hold(map->pmap, uva, VM_PROT_READ);
  123         if (pp == NULL) {
  124                 socow_stats.fail_not_mapped++;
  125                 return(0);
  126         }
  127 
  128         /* 
  129          * set up COW
  130          */
  131         vm_page_lock_queues();
  132         vm_page_cowsetup(pp);
  133 
  134         /*
  135          * wire the page for I/O
  136          */
  137         vm_page_wire(pp);
  138         vm_page_unhold(pp);
  139         vm_page_unlock_queues();
  140 
  141         /*
  142          * Allocate an sf buf
  143          */
  144         sf = sf_buf_alloc(pp, SFB_CATCH);
  145         if (!sf) {
  146                 vm_page_lock_queues();
  147                 vm_page_cowclear(pp);
  148                 vm_page_unwire(pp, 0);
  149                 /*
  150                  * Check for the object going away on us. This can
  151                  * happen since we don't hold a reference to it.
  152                  * If so, we're responsible for freeing the page.
  153                  */
  154                 if (pp->wire_count == 0 && pp->object == NULL)
  155                         vm_page_free(pp);
  156                 vm_page_unlock_queues();
  157                 socow_stats.fail_sf_buf++;
  158                 return(0);
  159         }
  160         /* 
  161          * attach to mbuf
  162          */
  163         MEXTADD(m0, sf_buf_kva(sf), PAGE_SIZE, socow_iodone, sf, M_RDONLY,
  164             EXT_SFBUF);
  165         m0->m_len = PAGE_SIZE - offset;
  166         m0->m_data = (caddr_t)sf_buf_kva(sf) + offset;
  167         socow_stats.success++;
  168 
  169         iov = uio->uio_iov;
  170         iov->iov_base = (char *)iov->iov_base + m0->m_len;
  171         iov->iov_len -= m0->m_len;
  172         uio->uio_resid -= m0->m_len;
  173         uio->uio_offset += m0->m_len;
  174         if (iov->iov_len == 0) {
  175                 uio->uio_iov++;
  176                 uio->uio_iovcnt--;
  177         }
  178 
  179         return(m0->m_len);
  180 }

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