text: /*-
   * Copyright (c) 2000 Mark R. V. Murray & Jeroen C. van Gelderen
   * 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
   *    in this position and unchanged.
   * 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 AUTHORS ``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 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.
   *
   */
  
  #include <sys/cdefs.h>
  __FBSDID("$FreeBSD: src/sys/dev/null/null.c,v 1.23 2003/11/01 09:31:54 markm Exp $");
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/conf.h>
  #include <sys/uio.h>
  #include <sys/kernel.h>
  #include <sys/malloc.h>
  #include <sys/module.h>
  #include <sys/disk.h>
  #include <sys/bus.h>
  #include <machine/bus.h>
  
  /* For use with destroy_dev(9). */
  static dev_t null_dev;
  static dev_t zero_dev;
  
  static d_write_t null_write;
  static d_ioctl_t null_ioctl;
  static d_read_t zero_read;
  
  #define CDEV_MAJOR	2
  #define NULL_MINOR	2
  #define ZERO_MINOR	12
  
  static struct cdevsw null_cdevsw = {
  	.d_read =	(d_read_t *)nullop,
  	.d_write =	null_write,
  	.d_ioctl =	null_ioctl,
  	.d_name =	"null",
  	.d_maj =	CDEV_MAJOR,
  	.d_flags =	D_NOGIANT,
  };
  
  static struct cdevsw zero_cdevsw = {
  	.d_read =	zero_read,
  	.d_write =	null_write,
  	.d_name =	"zero",
  	.d_maj =	CDEV_MAJOR,
  	.d_flags =	D_MMAP_ANON | D_NOGIANT,
  };
  
  static void *zbuf;
  
  /* ARGSUSED */
  static int
  null_write(dev_t dev __unused, struct uio *uio, int flags __unused)
  {
  	uio->uio_resid = 0;
  	return 0;
  }
  
  /* ARGSUSED */
  static int
  null_ioctl(dev_t dev __unused, u_long cmd, caddr_t data __unused,
      int flags __unused, struct thread *td)
  {
  	int error;
  
  	if (cmd != DIOCSKERNELDUMP)
  		return (ENOIOCTL);
  	error = suser(td);
  	if (error)
  		return (error);
  	return (set_dumper(NULL));
  }
  
  /* ARGSUSED */
  static int
  zero_read(dev_t dev __unused, struct uio *uio, int flags __unused)
  {
  	int c;
  	int error = 0;
  
  	while (uio->uio_resid > 0 && error == 0) {
  		c = uio->uio_resid < PAGE_SIZE ? uio->uio_resid : PAGE_SIZE;
  		error = uiomove(zbuf, c, uio);
  	}
  	return error;
  }
  
  /* ARGSUSED */
  static int
  null_modevent(module_t mod __unused, int type, void *data __unused)
  {
  	switch(type) {
  	case MOD_LOAD:
  		if (bootverbose)
  			printf("null: <null device, zero device>\n");
  		zbuf = (void *)malloc(PAGE_SIZE, M_TEMP, M_WAITOK | M_ZERO);
  		zero_dev = make_dev(&zero_cdevsw, ZERO_MINOR, UID_ROOT,
  			GID_WHEEL, 0666, "zero");
  		null_dev = make_dev(&null_cdevsw, NULL_MINOR, UID_ROOT,
  			GID_WHEEL, 0666, "null");
  		return 0;
  
  	case MOD_UNLOAD:
  		destroy_dev(null_dev);
  		destroy_dev(zero_dev);
  		free(zbuf, M_TEMP);
  		return 0;
  
  	case MOD_SHUTDOWN:
  		return 0;
  
  	default:
  		return EOPNOTSUPP;
  	}
  }
  
  DEV_MODULE(null, null_modevent, NULL);
  