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/dev/nvram/nvram.c

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    1 /*-
    2  * Copyright (c) 2007 Peter Wemm
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  *
   26  * $FreeBSD$
   27  */
   28 
   29 #include <sys/param.h>
   30 #include <sys/systm.h>
   31 #include <sys/kernel.h>
   32 #include <sys/conf.h>
   33 #include <sys/fcntl.h>
   34 #include <sys/lock.h>
   35 #include <sys/proc.h>
   36 #include <sys/sx.h>
   37 #include <sys/uio.h>
   38 #include <sys/module.h>
   39 
   40 #include <machine/clock.h>
   41 #include <isa/rtc.h>
   42 
   43 /*
   44  * Linux-style /dev/nvram driver
   45  *
   46  * cmos ram starts at bytes 14 through 128, for a total of 114 bytes.
   47  * The driver exposes byte 14 as file offset 0.
   48  *
   49  * Offsets 2 through 31 are checksummed at offset 32, 33.
   50  * In order to avoid the possibility of making the machine unbootable at the
   51  * bios level (press F1 to continue!), we refuse to allow writes if we do
   52  * not see a pre-existing valid checksum.  If the existing sum is invalid,
   53  * then presumably we do not know how to make a sum that the bios will accept.
   54  */
   55 
   56 #define NVRAM_FIRST     RTC_DIAG        /* 14 */
   57 #define NVRAM_LAST      128
   58 
   59 #define CKSUM_FIRST     2
   60 #define CKSUM_LAST      31
   61 #define CKSUM_MSB       32
   62 #define CKSUM_LSB       33
   63 
   64 static d_open_t         nvram_open;
   65 static d_read_t         nvram_read;
   66 static d_write_t        nvram_write;
   67 
   68 static struct cdev *nvram_dev;
   69 static struct sx nvram_lock;
   70 
   71 static struct cdevsw nvram_cdevsw = {
   72         .d_version =    D_VERSION,
   73         .d_open =       nvram_open,
   74         .d_read =       nvram_read,
   75         .d_write =      nvram_write,
   76         .d_name =       "nvram",
   77 };
   78 
   79 static int
   80 nvram_open(struct cdev *dev __unused, int flags, int fmt __unused,
   81     struct thread *td)
   82 {
   83         int error = 0;
   84 
   85         if (flags & FWRITE)
   86                 error = securelevel_gt(td->td_ucred, 0);
   87 
   88         return (error);
   89 }
   90 
   91 static int
   92 nvram_read(struct cdev *dev, struct uio *uio, int flags)
   93 {
   94         int nv_off;
   95         u_char v;
   96         int error = 0;
   97 
   98         while (uio->uio_resid > 0 && error == 0) {
   99                 nv_off = uio->uio_offset + NVRAM_FIRST;
  100                 if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST)
  101                         return (0);     /* Signal EOF */
  102                 /* Single byte at a time */
  103                 v = rtcin(nv_off);
  104                 error = uiomove(&v, 1, uio);
  105         }
  106         return (error);
  107 
  108 }
  109 
  110 static int
  111 nvram_write(struct cdev *dev, struct uio *uio, int flags)
  112 {
  113         int nv_off;
  114         u_char v;
  115         int error = 0;
  116         int i;
  117         uint16_t sum;
  118 
  119         sx_xlock(&nvram_lock);
  120 
  121         /* Assert that we understand the existing checksum first!  */
  122         sum = rtcin(NVRAM_FIRST + CKSUM_MSB) << 8 |
  123               rtcin(NVRAM_FIRST + CKSUM_LSB);
  124         for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
  125                 sum -= rtcin(NVRAM_FIRST + i);
  126         if (sum != 0) {
  127                 sx_xunlock(&nvram_lock);
  128                 return (EIO);
  129         }
  130         /* Bring in user data and write */
  131         while (uio->uio_resid > 0 && error == 0) {
  132                 nv_off = uio->uio_offset + NVRAM_FIRST;
  133                 if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST) {
  134                         sx_xunlock(&nvram_lock);
  135                         return (0);     /* Signal EOF */
  136                 }
  137                 /* Single byte at a time */
  138                 error = uiomove(&v, 1, uio);
  139                 writertc(nv_off, v);
  140         }
  141         /* Recalculate checksum afterwards */
  142         sum = 0;
  143         for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
  144                 sum += rtcin(NVRAM_FIRST + i);
  145         writertc(NVRAM_FIRST + CKSUM_MSB, sum >> 8);
  146         writertc(NVRAM_FIRST + CKSUM_LSB, sum);
  147         sx_xunlock(&nvram_lock);
  148         return (error);
  149 }
  150 
  151 static int
  152 nvram_modevent(module_t mod __unused, int type, void *data __unused)
  153 {
  154         switch (type) {
  155         case MOD_LOAD:
  156                 sx_init(&nvram_lock, "nvram");
  157                 nvram_dev = make_dev(&nvram_cdevsw, 0,
  158                     UID_ROOT, GID_KMEM, 0640, "nvram");
  159                 break;
  160         case MOD_UNLOAD:
  161         case MOD_SHUTDOWN:
  162                 destroy_dev(nvram_dev);
  163                 sx_destroy(&nvram_lock);
  164                 break;
  165         default:
  166                 return (EOPNOTSUPP);
  167         }
  168         return (0);
  169 }
  170 DEV_MODULE(nvram, nvram_modevent, NULL);

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