text: /*-
   * Copyright (c) 2011 Google, Inc.
   * 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.
   *
   * $FreeBSD$
   */
  
  /*
   * Device descriptor for partitioned disks. To use, set the
   * d_slice and d_partition variables as follows:
   *
   * Whole disk access:
   *
   * 	d_slice = -1
   * 	d_partition = -1
   *
   * Whole MBR slice:
   *
   * 	d_slice = MBR slice number (typically 1..4)
   * 	d_partition = -1
   *
   * BSD disklabel partition within an MBR slice:
   *
   * 	d_slice = MBR slice number (typically 1..4)
   * 	d_partition = disklabel partition (typically 0..19)
   *
   * BSD disklabel partition on the true dedicated disk:
   *
   * 	d_slice = -1
   * 	d_partition = disklabel partition (typically 0..19)
   *
   * GPT partition:
   *
   * 	d_slice = GPT partition number (typically 1..N)
   * 	d_partition = 255
   *
   * For both MBR and GPT, to automatically find the 'best' slice or partition,
   * set d_slice to zero. This uses the partition type to decide which partition
   * to use according to the following list of preferences:
   *
   * 	FreeBSD (active)
   * 	FreeBSD (inactive)
   * 	Linux (active)
   * 	Linux (inactive)
   * 	DOS/Windows (active)
   * 	DOS/Windows (inactive)
   *
   * Active MBR slices (marked as bootable) are preferred over inactive. GPT
   * doesn't have the concept of active/inactive partitions. In both MBR and GPT,
   * if there are multiple slices/partitions of a given type, the first one
   * is chosen.
   *
   * The low-level disk device will typically call disk_open() from its open
   * method to interpret the disk partition tables according to the rules above.
   * This will initialize d_offset to the block offset of the start of the
   * selected partition - this offset should be added to the offset passed to
   * the device's strategy method.
   */
  
  struct disk_devdesc
  {
  	struct devsw	*d_dev;
  	int		d_type;
  	int		d_unit;
  	void		*d_opendata;
  	int		d_slice;
  	int		d_partition;
  	off_t		d_offset;
  };
  
  enum disk_ioctl {
  	IOCTL_GET_BLOCKS,
  	IOCTL_GET_BLOCK_SIZE
  };
  
  /*
   * Parse disk metadata and initialise dev->d_offset.
   */
  extern int disk_open(struct disk_devdesc *dev, off_t mediasize,
      u_int sectorsize, u_int flags);
  #define	DISK_F_NOCACHE	0x0001		/* Do not use metadata caching */
  extern int disk_close(struct disk_devdesc *dev);
  extern void disk_cleanup(const struct devsw *d_dev);
  extern int disk_ioctl(struct disk_devdesc *dev, u_long cmd, void *buf);
  extern int disk_read(struct disk_devdesc *dev, void *buf, off_t offset,
      u_int blocks);
  extern int disk_write(struct disk_devdesc *dev, void *buf, off_t offset,
      u_int blocks);
  extern int ptblread(void *d, void *buf, size_t blocks, off_t offset);
  
  /*
   * Print information about slices on a disk.
   */
  extern int disk_print(struct disk_devdesc *dev, char *prefix, int verbose);
  extern char* disk_fmtdev(struct disk_devdesc *dev);
  extern int disk_parsedev(struct disk_devdesc *dev, const char *devspec,
      const char **path);
  
  