include/linux/visorbus.h - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * Copyright (C) 2010 - 2013 UNISYS CORPORATION
  * All rights reserved.
  */

 /*
  *  This header file is to be included by other kernel mode components that
  *  implement a particular kind of visor_device.  Each of these other kernel
  *  mode components is called a visor device driver.  Refer to visortemplate
  *  for a minimal sample visor device driver.
  *
  *  There should be nothing in this file that is private to the visorbus
  *  bus implementation itself.
  */

 #ifndef __VISORBUS_H__
 #define __VISORBUS_H__

 #include <linux/device.h>

 #define VISOR_CHANNEL_SIGNATURE ('L' << 24 | 'N' << 16 | 'C' << 8 | 'E')

 /*
  * enum channel_serverstate
  * @CHANNELSRV_UNINITIALIZED: Channel is in an undefined state.
  * @CHANNELSRV_READY:	      Channel has been initialized by server.
  */
 enum channel_serverstate {
 	CHANNELSRV_UNINITIALIZED = 0,
 	CHANNELSRV_READY = 1
 };

 /*
  * enum channel_clientstate
  * @CHANNELCLI_DETACHED:
  * @CHANNELCLI_DISABLED:  Client can see channel but is NOT allowed to use it
  *			  unless given TBD* explicit request
  *			  (should actually be < DETACHED).
  * @CHANNELCLI_ATTACHING: Legacy EFI client request for EFI server to attach.
  * @CHANNELCLI_ATTACHED:  Idle, but client may want to use channel any time.
  * @CHANNELCLI_BUSY:	  Client either wants to use or is using channel.
  * @CHANNELCLI_OWNED:	  "No worries" state - client can access channel
  *			  anytime.
  */
 enum channel_clientstate {
 	CHANNELCLI_DETACHED = 0,
 	CHANNELCLI_DISABLED = 1,
 	CHANNELCLI_ATTACHING = 2,
 	CHANNELCLI_ATTACHED = 3,
 	CHANNELCLI_BUSY = 4,
 	CHANNELCLI_OWNED = 5
 };

 /*
  * Values for VISOR_CHANNEL_PROTOCOL.Features: This define exists so that
  * a guest can look at the FeatureFlags in the io channel, and configure the
  * driver to use interrupts or not based on this setting. All feature bits for
  * all channels should be defined here. The io channel feature bits are defined
  * below.
  */
 #define VISOR_DRIVER_ENABLES_INTS (0x1ULL << 1)
 #define VISOR_CHANNEL_IS_POLLING (0x1ULL << 3)
 #define VISOR_IOVM_OK_DRIVER_DISABLING_INTS (0x1ULL << 4)
 #define VISOR_DRIVER_DISABLES_INTS (0x1ULL << 5)
 #define VISOR_DRIVER_ENHANCED_RCVBUF_CHECKING (0x1ULL << 6)

 /*
  * struct channel_header - Common Channel Header
  * @signature:	       Signature.
  * @legacy_state:      DEPRECATED - being replaced by.
  * @header_size:       sizeof(struct channel_header).
  * @size:	       Total size of this channel in bytes.
  * @features:	       Flags to modify behavior.
  * @chtype:	       Channel type: data, bus, control, etc..
  * @partition_handle:  ID of guest partition.
  * @handle:	       Device number of this channel in client.
  * @ch_space_offset:   Offset in bytes to channel specific area.
  * @version_id:	       Struct channel_header Version ID.
  * @partition_index:   Index of guest partition.
  * @zone_uuid:	       Guid of Channel's zone.
  * @cli_str_offset:    Offset from channel header to null-terminated
  *		       ClientString (0 if ClientString not present).
  * @cli_state_boot:    CHANNEL_CLIENTSTATE of pre-boot EFI client of this
  *		       channel.
  * @cmd_state_cli:     CHANNEL_COMMANDSTATE (overloaded in Windows drivers, see
  *		       ServerStateUp, ServerStateDown, etc).
  * @cli_state_os:      CHANNEL_CLIENTSTATE of Guest OS client of this channel.
  * @ch_characteristic: CHANNEL_CHARACTERISTIC_<xxx>.
  * @cmd_state_srv:     CHANNEL_COMMANDSTATE (overloaded in Windows drivers, see
  *		       ServerStateUp, ServerStateDown, etc).
  * @srv_state:	       CHANNEL_SERVERSTATE.
  * @cli_error_boot:    Bits to indicate err states for boot clients, so err
  *		       messages can be throttled.
  * @cli_error_os:      Bits to indicate err states for OS clients, so err
  *		       messages can be throttled.
  * @filler:	       Pad out to 128 byte cacheline.
  * @recover_channel:   Please add all new single-byte values below here.
  */
 struct channel_header {
 	u64 signature;
 	u32 legacy_state;
 	/* SrvState, CliStateBoot, and CliStateOS below */
 	u32 header_size;
 	u64 size;
 	u64 features;
 	guid_t chtype;
 	u64 partition_handle;
 	u64 handle;
 	u64 ch_space_offset;
 	u32 version_id;
 	u32 partition_index;
 	guid_t zone_guid;
 	u32 cli_str_offset;
 	u32 cli_state_boot;
 	u32 cmd_state_cli;
 	u32 cli_state_os;
 	u32 ch_characteristic;
 	u32 cmd_state_srv;
 	u32 srv_state;
 	u8 cli_error_boot;
 	u8 cli_error_os;
 	u8 filler[1];
 	u8 recover_channel;
 } __packed;

 #define VISOR_CHANNEL_ENABLE_INTS (0x1ULL << 0)

 /*
  * struct signal_queue_header - Subheader for the Signal Type variation of the
  *                              Common Channel.
  * @version:	      SIGNAL_QUEUE_HEADER Version ID.
  * @chtype:	      Queue type: storage, network.
  * @size:	      Total size of this queue in bytes.
  * @sig_base_offset:  Offset to signal queue area.
  * @features:	      Flags to modify behavior.
  * @num_sent:	      Total # of signals placed in this queue.
  * @num_overflows:    Total # of inserts failed due to full queue.
  * @signal_size:      Total size of a signal for this queue.
  * @max_slots:        Max # of slots in queue, 1 slot is always empty.
  * @max_signals:      Max # of signals in queue (MaxSignalSlots-1).
  * @head:	      Queue head signal #.
  * @num_received:     Total # of signals removed from this queue.
  * @tail:	      Queue tail signal.
  * @reserved1:	      Reserved field.
  * @reserved2:	      Reserved field.
  * @client_queue:
  * @num_irq_received: Total # of Interrupts received. This is incremented by the
  *		      ISR in the guest windows driver.
  * @num_empty:	      Number of times that visor_signal_remove is called and
  *		      returned Empty Status.
  * @errorflags:	      Error bits set during SignalReinit to denote trouble with
  *		      client's fields.
  * @filler:	      Pad out to 64 byte cacheline.
  */
 struct signal_queue_header {
 	/* 1st cache line */
 	u32 version;
 	u32 chtype;
 	u64 size;
 	u64 sig_base_offset;
 	u64 features;
 	u64 num_sent;
 	u64 num_overflows;
 	u32 signal_size;
 	u32 max_slots;
 	u32 max_signals;
 	u32 head;
 	/* 2nd cache line */
 	u64 num_received;
 	u32 tail;
 	u32 reserved1;
 	u64 reserved2;
 	u64 client_queue;
 	u64 num_irq_received;
 	u64 num_empty;
 	u32 errorflags;
 	u8 filler[12];
 } __packed;

 /* VISORCHANNEL Guids */
 /* {414815ed-c58c-11da-95a9-00e08161165f} */
 #define VISOR_VHBA_CHANNEL_GUID \
 	GUID_INIT(0x414815ed, 0xc58c, 0x11da, \
 		  0x95, 0xa9, 0x0, 0xe0, 0x81, 0x61, 0x16, 0x5f)
 #define VISOR_VHBA_CHANNEL_GUID_STR \
 	"414815ed-c58c-11da-95a9-00e08161165f"
 struct visorchipset_state {
 	u32 created:1;
 	u32 attached:1;
 	u32 configured:1;
 	u32 running:1;
 	/* Remaining bits in this 32-bit word are reserved. */
 };

 /**
  * struct visor_device - A device type for things "plugged" into the visorbus
  *                       bus
  * @visorchannel:		Points to the channel that the device is
  *				associated with.
  * @channel_type_guid:		Identifies the channel type to the bus driver.
  * @device:			Device struct meant for use by the bus driver
  *				only.
  * @list_all:			Used by the bus driver to enumerate devices.
  * @timer:		        Timer fired periodically to do interrupt-type
  *				activity.
  * @being_removed:		Indicates that the device is being removed from
  *				the bus. Private bus driver use only.
  * @visordriver_callback_lock:	Used by the bus driver to lock when adding and
  *				removing devices.
  * @pausing:			Indicates that a change towards a paused state.
  *				is in progress. Only modified by the bus driver.
  * @resuming:			Indicates that a change towards a running state
  *				is in progress. Only modified by the bus driver.
  * @chipset_bus_no:		Private field used by the bus driver.
  * @chipset_dev_no:		Private field used the bus driver.
  * @state:			Used to indicate the current state of the
  *				device.
  * @inst:			Unique GUID for this instance of the device.
  * @name:			Name of the device.
  * @pending_msg_hdr:		For private use by bus driver to respond to
  *				hypervisor requests.
  * @vbus_hdr_info:		A pointer to header info. Private use by bus
  *				driver.
  * @partition_guid:		Indicates client partion id. This should be the
  *				same across all visor_devices in the current
  *				guest. Private use by bus driver only.
  */
 struct visor_device {
 	struct visorchannel *visorchannel;
 	guid_t channel_type_guid;
 	/* These fields are for private use by the bus driver only. */
 	struct device device;
 	struct list_head list_all;
 	struct timer_list timer;
 	bool timer_active;
 	bool being_removed;
 	struct mutex visordriver_callback_lock; /* synchronize probe/remove */
 	bool pausing;
 	bool resuming;
 	u32 chipset_bus_no;
 	u32 chipset_dev_no;
 	struct visorchipset_state state;
 	guid_t inst;
 	u8 *name;
 	struct controlvm_message_header *pending_msg_hdr;
 	void *vbus_hdr_info;
 	guid_t partition_guid;
 	struct dentry *debugfs_dir;
 	struct dentry *debugfs_bus_info;
 };

 #define to_visor_device(x) container_of(x, struct visor_device, device)

 typedef void (*visorbus_state_complete_func) (struct visor_device *dev,
 					      int status);

 /*
  * This struct describes a specific visor channel, by providing its GUID, name,
  * and sizes.
  */
 struct visor_channeltype_descriptor {
 	const guid_t guid;
 	const char *name;
 	u64 min_bytes;
 	u32 version;
 };

 /**
  * struct visor_driver - Information provided by each visor driver when it
  *                       registers with the visorbus driver
  * @name:		Name of the visor driver.
  * @owner:		The module owner.
  * @channel_types:	Types of channels handled by this driver, ending with
  *			a zero GUID. Our specialized BUS.match() method knows
  *			about this list, and uses it to determine whether this
  *			driver will in fact handle a new device that it has
  *			detected.
  * @probe:		Called when a new device comes online, by our probe()
  *			function specified by driver.probe() (triggered
  *			ultimately by some call to driver_register(),
  *			bus_add_driver(), or driver_attach()).
  * @remove:		Called when a new device is removed, by our remove()
  *			function specified by driver.remove() (triggered
  *			ultimately by some call to device_release_driver()).
  * @channel_interrupt:	Called periodically, whenever there is a possiblity
  *			that "something interesting" may have happened to the
  *			channel.
  * @pause:		Called to initiate a change of the device's state.  If
  *			the return valu`e is < 0, there was an error and the
  *			state transition will NOT occur.  If the return value
  *			is >= 0, then the state transition was INITIATED
  *			successfully, and complete_func() will be called (or
  *			was just called) with the final status when either the
  *			state transition fails or completes successfully.
  * @resume:		Behaves similar to pause.
  * @driver:		Private reference to the device driver. For use by bus
  *			driver only.
  */
 struct visor_driver {
 	const char *name;
 	struct module *owner;
 	struct visor_channeltype_descriptor *channel_types;
 	int (*probe)(struct visor_device *dev);
 	void (*remove)(struct visor_device *dev);
 	void (*channel_interrupt)(struct visor_device *dev);
 	int (*pause)(struct visor_device *dev,
 		     visorbus_state_complete_func complete_func);
 	int (*resume)(struct visor_device *dev,
 		      visorbus_state_complete_func complete_func);

 	/* These fields are for private use by the bus driver only. */
 	struct device_driver driver;
 };

 #define to_visor_driver(x) (container_of(x, struct visor_driver, driver))

 int visor_check_channel(struct channel_header *ch, struct device *dev,
 			const guid_t *expected_uuid, char *chname,
 			u64 expected_min_bytes,	u32 expected_version,
 			u64 expected_signature);

 int visorbus_register_visor_driver(struct visor_driver *drv);
 void visorbus_unregister_visor_driver(struct visor_driver *drv);
 int visorbus_read_channel(struct visor_device *dev,
 			  unsigned long offset, void *dest,
 			  unsigned long nbytes);
 int visorbus_write_channel(struct visor_device *dev,
 			   unsigned long offset, void *src,
 			   unsigned long nbytes);
 int visorbus_enable_channel_interrupts(struct visor_device *dev);
 void visorbus_disable_channel_interrupts(struct visor_device *dev);

 int visorchannel_signalremove(struct visorchannel *channel, u32 queue,
 			      void *msg);
 int visorchannel_signalinsert(struct visorchannel *channel, u32 queue,
 			      void *msg);
 bool visorchannel_signalempty(struct visorchannel *channel, u32 queue);
 const guid_t *visorchannel_get_guid(struct visorchannel *channel);

 #define BUS_ROOT_DEVICE UINT_MAX
 struct visor_device *visorbus_get_device_by_id(u32 bus_no, u32 dev_no,
 					       struct visor_device *from);
 #endif
	// SPDX-License-Identifier: GPL-2.0+
	/*
	* Copyright (C) 2010 - 2013 UNISYS CORPORATION
	* All rights reserved.
	*/

	/*
	* This header file is to be included by other kernel mode components that
	* implement a particular kind of visor_device. Each of these other kernel
	* mode components is called a visor device driver. Refer to visortemplate
	* for a minimal sample visor device driver.
	*
	* There should be nothing in this file that is private to the visorbus
	* bus implementation itself.
	*/

	#ifndef __VISORBUS_H__
	#define __VISORBUS_H__

	#include <linux/device.h>

	#define VISOR_CHANNEL_SIGNATURE ('L' << 24 \| 'N' << 16 \| 'C' << 8 \| 'E')

	/*
	* enum channel_serverstate
	* @CHANNELSRV_UNINITIALIZED: Channel is in an undefined state.
	* @CHANNELSRV_READY: Channel has been initialized by server.
	*/
	enum channel_serverstate {
	CHANNELSRV_UNINITIALIZED = 0,
	CHANNELSRV_READY = 1
	};

	/*
	* enum channel_clientstate
	* @CHANNELCLI_DETACHED:
	* @CHANNELCLI_DISABLED: Client can see channel but is NOT allowed to use it
	* unless given TBD* explicit request
	* (should actually be < DETACHED).
	* @CHANNELCLI_ATTACHING: Legacy EFI client request for EFI server to attach.
	* @CHANNELCLI_ATTACHED: Idle, but client may want to use channel any time.
	* @CHANNELCLI_BUSY: Client either wants to use or is using channel.
	* @CHANNELCLI_OWNED: "No worries" state - client can access channel
	* anytime.
	*/
	enum channel_clientstate {
	CHANNELCLI_DETACHED = 0,
	CHANNELCLI_DISABLED = 1,
	CHANNELCLI_ATTACHING = 2,
	CHANNELCLI_ATTACHED = 3,
	CHANNELCLI_BUSY = 4,
	CHANNELCLI_OWNED = 5
	};

	/*
	* Values for VISOR_CHANNEL_PROTOCOL.Features: This define exists so that
	* a guest can look at the FeatureFlags in the io channel, and configure the
	* driver to use interrupts or not based on this setting. All feature bits for
	* all channels should be defined here. The io channel feature bits are defined
	* below.
	*/
	#define VISOR_DRIVER_ENABLES_INTS (0x1ULL << 1)
	#define VISOR_CHANNEL_IS_POLLING (0x1ULL << 3)
	#define VISOR_IOVM_OK_DRIVER_DISABLING_INTS (0x1ULL << 4)
	#define VISOR_DRIVER_DISABLES_INTS (0x1ULL << 5)
	#define VISOR_DRIVER_ENHANCED_RCVBUF_CHECKING (0x1ULL << 6)

	/*
	* struct channel_header - Common Channel Header
	* @signature: Signature.
	* @legacy_state: DEPRECATED - being replaced by.
	* @header_size: sizeof(struct channel_header).
	* @size: Total size of this channel in bytes.
	* @features: Flags to modify behavior.
	* @chtype: Channel type: data, bus, control, etc..
	* @partition_handle: ID of guest partition.
	* @handle: Device number of this channel in client.
	* @ch_space_offset: Offset in bytes to channel specific area.
	* @version_id: Struct channel_header Version ID.
	* @partition_index: Index of guest partition.
	* @zone_uuid: Guid of Channel's zone.
	* @cli_str_offset: Offset from channel header to null-terminated
	* ClientString (0 if ClientString not present).
	* @cli_state_boot: CHANNEL_CLIENTSTATE of pre-boot EFI client of this
	* channel.
	* @cmd_state_cli: CHANNEL_COMMANDSTATE (overloaded in Windows drivers, see
	* ServerStateUp, ServerStateDown, etc).
	* @cli_state_os: CHANNEL_CLIENTSTATE of Guest OS client of this channel.
	* @ch_characteristic: CHANNEL_CHARACTERISTIC_<xxx>.
	* @cmd_state_srv: CHANNEL_COMMANDSTATE (overloaded in Windows drivers, see
	* ServerStateUp, ServerStateDown, etc).
	* @srv_state: CHANNEL_SERVERSTATE.
	* @cli_error_boot: Bits to indicate err states for boot clients, so err
	* messages can be throttled.
	* @cli_error_os: Bits to indicate err states for OS clients, so err
	* messages can be throttled.
	* @filler: Pad out to 128 byte cacheline.
	* @recover_channel: Please add all new single-byte values below here.
	*/
	struct channel_header {
	u64 signature;
	u32 legacy_state;
	/* SrvState, CliStateBoot, and CliStateOS below */
	u32 header_size;
	u64 size;
	u64 features;
	guid_t chtype;
	u64 partition_handle;
	u64 handle;
	u64 ch_space_offset;
	u32 version_id;
	u32 partition_index;
	guid_t zone_guid;
	u32 cli_str_offset;
	u32 cli_state_boot;
	u32 cmd_state_cli;
	u32 cli_state_os;
	u32 ch_characteristic;
	u32 cmd_state_srv;
	u32 srv_state;
	u8 cli_error_boot;
	u8 cli_error_os;
	u8 filler[1];
	u8 recover_channel;
	} __packed;

	#define VISOR_CHANNEL_ENABLE_INTS (0x1ULL << 0)

	/*
	* struct signal_queue_header - Subheader for the Signal Type variation of the
	* Common Channel.
	* @version: SIGNAL_QUEUE_HEADER Version ID.
	* @chtype: Queue type: storage, network.
	* @size: Total size of this queue in bytes.
	* @sig_base_offset: Offset to signal queue area.
	* @features: Flags to modify behavior.
	* @num_sent: Total # of signals placed in this queue.
	* @num_overflows: Total # of inserts failed due to full queue.
	* @signal_size: Total size of a signal for this queue.
	* @max_slots: Max # of slots in queue, 1 slot is always empty.
	* @max_signals: Max # of signals in queue (MaxSignalSlots-1).
	* @head: Queue head signal #.
	* @num_received: Total # of signals removed from this queue.
	* @tail: Queue tail signal.
	* @reserved1: Reserved field.
	* @reserved2: Reserved field.
	* @client_queue:
	* @num_irq_received: Total # of Interrupts received. This is incremented by the
	* ISR in the guest windows driver.
	* @num_empty: Number of times that visor_signal_remove is called and
	* returned Empty Status.
	* @errorflags: Error bits set during SignalReinit to denote trouble with
	* client's fields.
	* @filler: Pad out to 64 byte cacheline.
	*/
	struct signal_queue_header {
	/* 1st cache line */
	u32 version;
	u32 chtype;
	u64 size;
	u64 sig_base_offset;
	u64 features;
	u64 num_sent;
	u64 num_overflows;
	u32 signal_size;
	u32 max_slots;
	u32 max_signals;
	u32 head;
	/* 2nd cache line */
	u64 num_received;
	u32 tail;
	u32 reserved1;
	u64 reserved2;
	u64 client_queue;
	u64 num_irq_received;
	u64 num_empty;
	u32 errorflags;
	u8 filler[12];
	} __packed;

	/* VISORCHANNEL Guids */
	/* {414815ed-c58c-11da-95a9-00e08161165f} */
	#define VISOR_VHBA_CHANNEL_GUID \
	GUID_INIT(0x414815ed, 0xc58c, 0x11da, \
	0x95, 0xa9, 0x0, 0xe0, 0x81, 0x61, 0x16, 0x5f)
	#define VISOR_VHBA_CHANNEL_GUID_STR \
	"414815ed-c58c-11da-95a9-00e08161165f"
	struct visorchipset_state {
	u32 created:1;
	u32 attached:1;
	u32 configured:1;
	u32 running:1;
	/* Remaining bits in this 32-bit word are reserved. */
	};

	/**
	* struct visor_device - A device type for things "plugged" into the visorbus
	* bus
	* @visorchannel: Points to the channel that the device is
	* associated with.
	* @channel_type_guid: Identifies the channel type to the bus driver.
	* @device: Device struct meant for use by the bus driver
	* only.
	* @list_all: Used by the bus driver to enumerate devices.
	* @timer: Timer fired periodically to do interrupt-type
	* activity.
	* @being_removed: Indicates that the device is being removed from
	* the bus. Private bus driver use only.
	* @visordriver_callback_lock: Used by the bus driver to lock when adding and
	* removing devices.
	* @pausing: Indicates that a change towards a paused state.
	* is in progress. Only modified by the bus driver.
	* @resuming: Indicates that a change towards a running state
	* is in progress. Only modified by the bus driver.
	* @chipset_bus_no: Private field used by the bus driver.
	* @chipset_dev_no: Private field used the bus driver.
	* @state: Used to indicate the current state of the
	* device.
	* @inst: Unique GUID for this instance of the device.
	* @name: Name of the device.
	* @pending_msg_hdr: For private use by bus driver to respond to
	* hypervisor requests.
	* @vbus_hdr_info: A pointer to header info. Private use by bus
	* driver.
	* @partition_guid: Indicates client partion id. This should be the
	* same across all visor_devices in the current
	* guest. Private use by bus driver only.
	*/
	struct visor_device {
	struct visorchannel *visorchannel;
	guid_t channel_type_guid;
	/* These fields are for private use by the bus driver only. */
	struct device device;
	struct list_head list_all;
	struct timer_list timer;
	bool timer_active;
	bool being_removed;
	struct mutex visordriver_callback_lock; /* synchronize probe/remove */
	bool pausing;
	bool resuming;
	u32 chipset_bus_no;
	u32 chipset_dev_no;
	struct visorchipset_state state;
	guid_t inst;
	u8 *name;
	struct controlvm_message_header *pending_msg_hdr;
	void *vbus_hdr_info;
	guid_t partition_guid;
	struct dentry *debugfs_dir;
	struct dentry *debugfs_bus_info;
	};

	#define to_visor_device(x) container_of(x, struct visor_device, device)

	typedef void (visorbus_state_complete_func) (struct visor_device dev,
	int status);

	/*
	* This struct describes a specific visor channel, by providing its GUID, name,
	* and sizes.
	*/
	struct visor_channeltype_descriptor {
	const guid_t guid;
	const char *name;
	u64 min_bytes;
	u32 version;
	};

	/**
	* struct visor_driver - Information provided by each visor driver when it
	* registers with the visorbus driver
	* @name: Name of the visor driver.
	* @owner: The module owner.
	* @channel_types: Types of channels handled by this driver, ending with
	* a zero GUID. Our specialized BUS.match() method knows
	* about this list, and uses it to determine whether this
	* driver will in fact handle a new device that it has
	* detected.
	* @probe: Called when a new device comes online, by our probe()
	* function specified by driver.probe() (triggered
	* ultimately by some call to driver_register(),
	* bus_add_driver(), or driver_attach()).
	* @remove: Called when a new device is removed, by our remove()
	* function specified by driver.remove() (triggered
	* ultimately by some call to device_release_driver()).
	* @channel_interrupt: Called periodically, whenever there is a possiblity
	* that "something interesting" may have happened to the
	* channel.
	* @pause: Called to initiate a change of the device's state. If
	* the return valu`e is < 0, there was an error and the
	* state transition will NOT occur. If the return value
	* is >= 0, then the state transition was INITIATED
	* successfully, and complete_func() will be called (or
	* was just called) with the final status when either the
	* state transition fails or completes successfully.
	* @resume: Behaves similar to pause.
	* @driver: Private reference to the device driver. For use by bus
	* driver only.
	*/
	struct visor_driver {
	const char *name;
	struct module *owner;
	struct visor_channeltype_descriptor *channel_types;
	int (probe)(struct visor_device dev);
	void (remove)(struct visor_device dev);
	void (channel_interrupt)(struct visor_device dev);
	int (pause)(struct visor_device dev,
	visorbus_state_complete_func complete_func);
	int (resume)(struct visor_device dev,
	visorbus_state_complete_func complete_func);

	/* These fields are for private use by the bus driver only. */
	struct device_driver driver;
	};

	#define to_visor_driver(x) (container_of(x, struct visor_driver, driver))

	int visor_check_channel(struct channel_header ch, struct device dev,
	const guid_t expected_uuid, char chname,
	u64 expected_min_bytes, u32 expected_version,
	u64 expected_signature);

	int visorbus_register_visor_driver(struct visor_driver *drv);
	void visorbus_unregister_visor_driver(struct visor_driver *drv);
	int visorbus_read_channel(struct visor_device *dev,
	unsigned long offset, void *dest,
	unsigned long nbytes);
	int visorbus_write_channel(struct visor_device *dev,
	unsigned long offset, void *src,
	unsigned long nbytes);
	int visorbus_enable_channel_interrupts(struct visor_device *dev);
	void visorbus_disable_channel_interrupts(struct visor_device *dev);

	int visorchannel_signalremove(struct visorchannel *channel, u32 queue,
	void *msg);
	int visorchannel_signalinsert(struct visorchannel *channel, u32 queue,
	void *msg);
	bool visorchannel_signalempty(struct visorchannel *channel, u32 queue);
	const guid_t visorchannel_get_guid(struct visorchannel channel);

	#define BUS_ROOT_DEVICE UINT_MAX
	struct visor_device *visorbus_get_device_by_id(u32 bus_no, u32 dev_no,
	struct visor_device *from);
	#endif