#ifndef _LINUX_VIRTIO_BLK_H
  #define _LINUX_VIRTIO_BLK_H

  /* This header is BSD licensed so anyone can use the definitions to implement
   * compatible drivers/servers. */

  #include <linux/types.h>

  #include <linux/virtio_ids.h>

  #include <linux/virtio_config.h>

  /* Feature bits */

  #define VIRTIO_BLK_F_BARRIER	0	/* Does host support barriers? */
  #define VIRTIO_BLK_F_SIZE_MAX	1	/* Indicates maximum segment size */
  #define VIRTIO_BLK_F_SEG_MAX	2	/* Indicates maximum # of segments */

  #define VIRTIO_BLK_F_GEOMETRY	4	/* Legacy geometry available  */

  #define VIRTIO_BLK_F_RO		5	/* Disk is read-only */

  #define VIRTIO_BLK_F_BLK_SIZE	6	/* Block size of disk is available*/

  #define VIRTIO_BLK_F_SCSI	7	/* Supports scsi command passthru */

  #define VIRTIO_BLK_F_FLUSH	9	/* Cache flush command support */

  #define VIRTIO_BLK_F_TOPOLOGY	10	/* Topology information is available */

  #define VIRTIO_BLK_ID_BYTES	20	/* ID string length */

  struct virtio_blk_config {

  	/* The capacity (in 512-byte sectors). */

  	__u64 capacity;

  	/* The maximum segment size (if VIRTIO_BLK_F_SIZE_MAX) */

  	__u32 size_max;

  	/* The maximum number of segments (if VIRTIO_BLK_F_SEG_MAX) */

  	__u32 seg_max;

  	/* geometry the device (if VIRTIO_BLK_F_GEOMETRY) */
  	struct virtio_blk_geometry {

  		__u16 cylinders;

  		__u8 heads;
  		__u8 sectors;
  	} geometry;

  	/* block size of device (if VIRTIO_BLK_F_BLK_SIZE) */
  	__u32 blk_size;

  
  	/* the next 4 entries are guarded by VIRTIO_BLK_F_TOPOLOGY  */
  	/* exponent for physical block per logical block. */
  	__u8 physical_block_exp;
  	/* alignment offset in logical blocks. */
  	__u8 alignment_offset;
  	/* minimum I/O size without performance penalty in logical blocks. */
  	__u16 min_io_size;
  	/* optimal sustained I/O size in logical blocks. */
  	__u32 opt_io_size;

  } __attribute__((packed));

  /*
   * Command types
   *
   * Usage is a bit tricky as some bits are used as flags and some are not.
   *
   * Rules:
   *   VIRTIO_BLK_T_OUT may be combined with VIRTIO_BLK_T_SCSI_CMD or
   *   VIRTIO_BLK_T_BARRIER.  VIRTIO_BLK_T_FLUSH is a command of its own
   *   and may not be combined with any of the other flags.
   */

  /* These two define direction. */
  #define VIRTIO_BLK_T_IN		0
  #define VIRTIO_BLK_T_OUT	1
  
  /* This bit says it's a scsi command, not an actual read or write. */
  #define VIRTIO_BLK_T_SCSI_CMD	2

  /* Cache flush command */
  #define VIRTIO_BLK_T_FLUSH	4

  /* Get device ID command */
  #define VIRTIO_BLK_T_GET_ID    8

  /* Barrier before this op. */
  #define VIRTIO_BLK_T_BARRIER	0x80000000
  
  /* This is the first element of the read scatter-gather list. */

  struct virtio_blk_outhdr {

  	/* VIRTIO_BLK_T* */
  	__u32 type;
  	/* io priority. */
  	__u32 ioprio;
  	/* Sector (ie. 512 byte offset) */
  	__u64 sector;

  };

  struct virtio_scsi_inhdr {
  	__u32 errors;
  	__u32 data_len;
  	__u32 sense_len;
  	__u32 residual;
  };

  /* And this is the final byte of the write scatter-gather list. */

  #define VIRTIO_BLK_S_OK		0
  #define VIRTIO_BLK_S_IOERR	1
  #define VIRTIO_BLK_S_UNSUPP	2

  #endif /* _LINUX_VIRTIO_BLK_H */