#ifndef _LINUX_LGUEST_LAUNCHER
  #define _LINUX_LGUEST_LAUNCHER
  /* Everything the "lguest" userspace program needs to know. */
  #include <linux/types.h>
  
  /*D:010
   * Drivers
   *
   * The Guest needs devices to do anything useful.  Since we don't let it touch
   * real devices (think of the damage it could do!) we provide virtual devices.
   * We could emulate a PCI bus with various devices on it, but that is a fairly
   * complex burden for the Host and suboptimal for the Guest, so we have our own
   * simple lguest bus and we use "virtio" drivers.  These drivers need a set of
   * routines from us which will actually do the virtual I/O, but they handle all
   * the net/block/console stuff themselves.  This means that if we want to add
   * a new device, we simply need to write a new virtio driver and create support
   * for it in the Launcher: this code won't need to change.
   *
   * Virtio devices are also used by kvm, so we can simply reuse their optimized
   * device drivers.  And one day when everyone uses virtio, my plan will be
   * complete.  Bwahahahah!
   *
   * Devices are described by a simplified ID, a status byte, and some "config"
   * bytes which describe this device's configuration.  This is placed by the
   * Launcher just above the top of physical memory:
   */
  struct lguest_device_desc {
  	/* The device type: console, network, disk etc.  Type 0 terminates. */
  	__u8 type;
  	/* The number of virtqueues (first in config array) */
  	__u8 num_vq;
  	/*
  	 * The number of bytes of feature bits.  Multiply by 2: one for host
  	 * features and one for Guest acknowledgements.
  	 */
  	__u8 feature_len;
  	/* The number of bytes of the config array after virtqueues. */
  	__u8 config_len;
  	/* A status byte, written by the Guest. */
  	__u8 status;
  	__u8 config[0];
  };
  
  /*D:135
   * This is how we expect the device configuration field for a virtqueue
   * to be laid out in config space.
   */
  struct lguest_vqconfig {
  	/* The number of entries in the virtio_ring */
  	__u16 num;
  	/* The interrupt we get when something happens. */
  	__u16 irq;
  	/* The page number of the virtio ring for this device. */
  	__u32 pfn;
  };
  /*:*/
  
  /* Write command first word is a request. */
  enum lguest_req
  {
  	LHREQ_INITIALIZE, /* + base, pfnlimit, start */
  	LHREQ_GETDMA, /* No longer used */
  	LHREQ_IRQ, /* + irq */
  	LHREQ_BREAK, /* No longer used */
  	LHREQ_EVENTFD, /* + address, fd. */
  };
  
  /*
   * The alignment to use between consumer and producer parts of vring.
   * x86 pagesize for historical reasons.
   */
  #define LGUEST_VRING_ALIGN	4096
  #endif /* _LINUX_LGUEST_LAUNCHER */