FreeBSD/Linux Kernel Cross Reference
sys/dev/nvram/nvram.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2007 Peter Wemm
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     * $FreeBSD$
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/conf.h>
    #include <sys/fcntl.h>
    #include <sys/lock.h>
    #include <sys/proc.h>
    #include <sys/sx.h>
    #include <sys/uio.h>
    #include <sys/module.h>
    
    #include <isa/rtc.h>
    
    /*
     * Linux-style /dev/nvram driver
     *
     * cmos ram starts at bytes 14 through 128, for a total of 114 bytes.
     * The driver exposes byte 14 as file offset 0.
     *
     * Offsets 2 through 31 are checksummed at offset 32, 33.
     * In order to avoid the possibility of making the machine unbootable at the
     * bios level (press F1 to continue!), we refuse to allow writes if we do
     * not see a pre-existing valid checksum.  If the existing sum is invalid,
     * then presumably we do not know how to make a sum that the bios will accept.
     */
    
    #define NVRAM_FIRST     RTC_DIAG        /* 14 */
    #define NVRAM_LAST      128
    
    #define CKSUM_FIRST     2
    #define CKSUM_LAST      31
    #define CKSUM_MSB       32
    #define CKSUM_LSB       33
    
    static d_open_t         nvram_open;
    static d_read_t         nvram_read;
    static d_write_t        nvram_write;
    
    static struct cdev *nvram_dev;
    static struct sx nvram_lock;
    
    static struct cdevsw nvram_cdevsw = {
            .d_version =    D_VERSION,
            .d_open =       nvram_open,
            .d_read =       nvram_read,
            .d_write =      nvram_write,
            .d_name =       "nvram",
    };
    
    static int
    nvram_open(struct cdev *dev __unused, int flags, int fmt __unused,
        struct thread *td)
    {
            int error = 0;
    
            if (flags & FWRITE)
                    error = securelevel_gt(td->td_ucred, 0);
    
            return (error);
    }
    
    static int
    nvram_read(struct cdev *dev, struct uio *uio, int flags)
    {
            int nv_off;
            u_char v;
            int error = 0;
    
            while (uio->uio_resid > 0 && error == 0) {
                   nv_off = uio->uio_offset + NVRAM_FIRST;
                   if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST)
                           return (0);     /* Signal EOF */
                   /* Single byte at a time */
                   v = rtcin(nv_off);
                   error = uiomove(&v, 1, uio);
           }
           return (error);
   
   }
   
   static int
   nvram_write(struct cdev *dev, struct uio *uio, int flags)
   {
           int nv_off;
           u_char v;
           int error = 0;
           int i;
           uint16_t sum;
   
           sx_xlock(&nvram_lock);
   
           /* Assert that we understand the existing checksum first!  */
           sum = rtcin(NVRAM_FIRST + CKSUM_MSB) << 8 |
                 rtcin(NVRAM_FIRST + CKSUM_LSB);
           for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
                   sum -= rtcin(NVRAM_FIRST + i);
           if (sum != 0) {
                   sx_xunlock(&nvram_lock);
                   return (EIO);
           }
           /* Bring in user data and write */
           while (uio->uio_resid > 0 && error == 0) {
                   nv_off = uio->uio_offset + NVRAM_FIRST;
                   if (nv_off < NVRAM_FIRST || nv_off >= NVRAM_LAST) {
                           sx_xunlock(&nvram_lock);
                           return (0);     /* Signal EOF */
                   }
                   /* Single byte at a time */
                   error = uiomove(&v, 1, uio);
                   writertc(nv_off, v);
           }
           /* Recalculate checksum afterwards */
           sum = 0;
           for (i = CKSUM_FIRST; i <= CKSUM_LAST; i++)
                   sum += rtcin(NVRAM_FIRST + i);
           writertc(NVRAM_FIRST + CKSUM_MSB, sum >> 8);
           writertc(NVRAM_FIRST + CKSUM_LSB, sum);
           sx_xunlock(&nvram_lock);
           return (error);
   }
   
   static int
   nvram_modevent(module_t mod __unused, int type, void *data __unused)
   {
           switch (type) {
           case MOD_LOAD:
                   sx_init(&nvram_lock, "nvram");
                   nvram_dev = make_dev(&nvram_cdevsw, 0,
                       UID_ROOT, GID_KMEM, 0640, "nvram");
                   break;
           case MOD_UNLOAD:
           case MOD_SHUTDOWN:
                   destroy_dev(nvram_dev);
                   sx_destroy(&nvram_lock);
                   break;
           default:
                   return (EOPNOTSUPP);
           }
           return (0);
   }
   DEV_MODULE(nvram, nvram_modevent, NULL);

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