include/xen/interface/io/ring.h - maze/linux - Git at Google

 /******************************************************************************
  * ring.h
  *
  * Shared producer-consumer ring macros.
  *
  * Tim Deegan and Andrew Warfield November 2004.
  */

 #ifndef __XEN_PUBLIC_IO_RING_H__
 #define __XEN_PUBLIC_IO_RING_H__

 typedef unsigned int RING_IDX;

 /* Round a 32-bit unsigned constant down to the nearest power of two. */
 #define __RD2(_x)  (((_x) & 0x00000002) ? 0x2		       : ((_x) & 0x1))
 #define __RD4(_x)  (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2    : __RD2(_x))
 #define __RD8(_x)  (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4    : __RD4(_x))
 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8    : __RD8(_x))
 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))

 /*
  * Calculate size of a shared ring, given the total available space for the
  * ring and indexes (_sz), and the name tag of the request/response structure.
  * A ring contains as many entries as will fit, rounded down to the nearest
  * power of two (so we can mask with (size-1) to loop around).
  */
 #define __CONST_RING_SIZE(_s, _sz)				\
 	(__RD32(((_sz) - offsetof(struct _s##_sring, ring)) /	\
 		sizeof(((struct _s##_sring *)0)->ring[0])))

 /*
  * The same for passing in an actual pointer instead of a name tag.
  */
 #define __RING_SIZE(_s, _sz)						\
 	(__RD32(((_sz) - (long)&(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))

 /*
  * Macros to make the correct C datatypes for a new kind of ring.
  *
  * To make a new ring datatype, you need to have two message structures,
  * let's say struct request, and struct response already defined.
  *
  * In a header where you want the ring datatype declared, you then do:
  *
  *     DEFINE_RING_TYPES(mytag, struct request, struct response);
  *
  * These expand out to give you a set of types, as you can see below.
  * The most important of these are:
  *
  *     struct mytag_sring      - The shared ring.
  *     struct mytag_front_ring - The 'front' half of the ring.
  *     struct mytag_back_ring  - The 'back' half of the ring.
  *
  * To initialize a ring in your code you need to know the location and size
  * of the shared memory area (PAGE_SIZE, for instance). To initialise
  * the front half:
  *
  *     struct mytag_front_ring front_ring;
  *     SHARED_RING_INIT((struct mytag_sring *)shared_page);
  *     FRONT_RING_INIT(&front_ring, (struct mytag_sring *)shared_page,
  *		       PAGE_SIZE);
  *
  * Initializing the back follows similarly (note that only the front
  * initializes the shared ring):
  *
  *     struct mytag_back_ring back_ring;
  *     BACK_RING_INIT(&back_ring, (struct mytag_sring *)shared_page,
  *		      PAGE_SIZE);
  */

 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)			\
 									\
 /* Shared ring entry */							\
 union __name##_sring_entry {						\
     __req_t req;							\
     __rsp_t rsp;							\
 };									\
 									\
 /* Shared ring page */							\
 struct __name##_sring {							\
     RING_IDX req_prod, req_event;					\
     RING_IDX rsp_prod, rsp_event;					\
     uint8_t  pad[48];							\
     union __name##_sring_entry ring[1]; /* variable-length */		\
 };									\
 									\
 /* "Front" end's private variables */					\
 struct __name##_front_ring {						\
     RING_IDX req_prod_pvt;						\
     RING_IDX rsp_cons;							\
     unsigned int nr_ents;						\
     struct __name##_sring *sring;					\
 };									\
 									\
 /* "Back" end's private variables */					\
 struct __name##_back_ring {						\
     RING_IDX rsp_prod_pvt;						\
     RING_IDX req_cons;							\
     unsigned int nr_ents;						\
     struct __name##_sring *sring;					\
 };

 /*
  * Macros for manipulating rings.
  *
  * FRONT_RING_whatever works on the "front end" of a ring: here
  * requests are pushed on to the ring and responses taken off it.
  *
  * BACK_RING_whatever works on the "back end" of a ring: here
  * requests are taken off the ring and responses put on.
  *
  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
  * This is OK in 1-for-1 request-response situations where the
  * requestor (front end) never has more than RING_SIZE()-1
  * outstanding requests.
  */

 /* Initialising empty rings */
 #define SHARED_RING_INIT(_s) do {					\
     (_s)->req_prod  = (_s)->rsp_prod  = 0;				\
     (_s)->req_event = (_s)->rsp_event = 1;				\
     memset((_s)->pad, 0, sizeof((_s)->pad));				\
 } while(0)

 #define FRONT_RING_INIT(_r, _s, __size) do {				\
     (_r)->req_prod_pvt = 0;						\
     (_r)->rsp_cons = 0;							\
     (_r)->nr_ents = __RING_SIZE(_s, __size);				\
     (_r)->sring = (_s);							\
 } while (0)

 #define BACK_RING_INIT(_r, _s, __size) do {				\
     (_r)->rsp_prod_pvt = 0;						\
     (_r)->req_cons = 0;							\
     (_r)->nr_ents = __RING_SIZE(_s, __size);				\
     (_r)->sring = (_s);							\
 } while (0)

 /* Initialize to existing shared indexes -- for recovery */
 #define FRONT_RING_ATTACH(_r, _s, __size) do {				\
     (_r)->sring = (_s);							\
     (_r)->req_prod_pvt = (_s)->req_prod;				\
     (_r)->rsp_cons = (_s)->rsp_prod;					\
     (_r)->nr_ents = __RING_SIZE(_s, __size);				\
 } while (0)

 #define BACK_RING_ATTACH(_r, _s, __size) do {				\
     (_r)->sring = (_s);							\
     (_r)->rsp_prod_pvt = (_s)->rsp_prod;				\
     (_r)->req_cons = (_s)->req_prod;					\
     (_r)->nr_ents = __RING_SIZE(_s, __size);				\
 } while (0)

 /* How big is this ring? */
 #define RING_SIZE(_r)							\
     ((_r)->nr_ents)

 /* Number of free requests (for use on front side only). */
 #define RING_FREE_REQUESTS(_r)						\
     (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))

 /* Test if there is an empty slot available on the front ring.
  * (This is only meaningful from the front. )
  */
 #define RING_FULL(_r)							\
     (RING_FREE_REQUESTS(_r) == 0)

 /* Test if there are outstanding messages to be processed on a ring. */
 #define RING_HAS_UNCONSUMED_RESPONSES(_r)				\
     ((_r)->sring->rsp_prod - (_r)->rsp_cons)

 #define RING_HAS_UNCONSUMED_REQUESTS(_r)				\
     ({									\
 	unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;	\
 	unsigned int rsp = RING_SIZE(_r) -				\
 			   ((_r)->req_cons - (_r)->rsp_prod_pvt);	\
 	req < rsp ? req : rsp;						\
     })

 /* Direct access to individual ring elements, by index. */
 #define RING_GET_REQUEST(_r, _idx)					\
     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))

 #define RING_GET_RESPONSE(_r, _idx)					\
     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))

 /* Loop termination condition: Would the specified index overflow the ring? */
 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)				\
     (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))

 #define RING_PUSH_REQUESTS(_r) do {					\
     wmb(); /* back sees requests /before/ updated producer index */	\
     (_r)->sring->req_prod = (_r)->req_prod_pvt;				\
 } while (0)

 #define RING_PUSH_RESPONSES(_r) do {					\
     wmb(); /* front sees responses /before/ updated producer index */	\
     (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;				\
 } while (0)

 /*
  * Notification hold-off (req_event and rsp_event):
  *
  * When queueing requests or responses on a shared ring, it may not always be
  * necessary to notify the remote end. For example, if requests are in flight
  * in a backend, the front may be able to queue further requests without
  * notifying the back (if the back checks for new requests when it queues
  * responses).
  *
  * When enqueuing requests or responses:
  *
  *  Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
  *  is a boolean return value. True indicates that the receiver requires an
  *  asynchronous notification.
  *
  * After dequeuing requests or responses (before sleeping the connection):
  *
  *  Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
  *  The second argument is a boolean return value. True indicates that there
  *  are pending messages on the ring (i.e., the connection should not be put
  *  to sleep).
  *
  *  These macros will set the req_event/rsp_event field to trigger a
  *  notification on the very next message that is enqueued. If you want to
  *  create batches of work (i.e., only receive a notification after several
  *  messages have been enqueued) then you will need to create a customised
  *  version of the FINAL_CHECK macro in your own code, which sets the event
  *  field appropriately.
  */

 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {		\
     RING_IDX __old = (_r)->sring->req_prod;				\
     RING_IDX __new = (_r)->req_prod_pvt;				\
     wmb(); /* back sees requests /before/ updated producer index */	\
     (_r)->sring->req_prod = __new;					\
     mb(); /* back sees new requests /before/ we check req_event */	\
     (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <		\
 		 (RING_IDX)(__new - __old));				\
 } while (0)

 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {		\
     RING_IDX __old = (_r)->sring->rsp_prod;				\
     RING_IDX __new = (_r)->rsp_prod_pvt;				\
     wmb(); /* front sees responses /before/ updated producer index */	\
     (_r)->sring->rsp_prod = __new;					\
     mb(); /* front sees new responses /before/ we check rsp_event */	\
     (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <		\
 		 (RING_IDX)(__new - __old));				\
 } while (0)

 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do {		\
     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);			\
     if (_work_to_do) break;						\
     (_r)->sring->req_event = (_r)->req_cons + 1;			\
     mb();								\
     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);			\
 } while (0)

 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do {		\
     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);			\
     if (_work_to_do) break;						\
     (_r)->sring->rsp_event = (_r)->rsp_cons + 1;			\
     mb();								\
     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);			\
 } while (0)

 #endif /* __XEN_PUBLIC_IO_RING_H__ */
	/******************************************************************************
	* ring.h
	*
	* Shared producer-consumer ring macros.
	*
	* Tim Deegan and Andrew Warfield November 2004.
	*/

	#ifndef __XEN_PUBLIC_IO_RING_H__
	#define __XEN_PUBLIC_IO_RING_H__

	typedef unsigned int RING_IDX;

	/* Round a 32-bit unsigned constant down to the nearest power of two. */
	#define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1))
	#define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x))
	#define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x))
	#define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x))
	#define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))

	/*
	* Calculate size of a shared ring, given the total available space for the
	* ring and indexes (_sz), and the name tag of the request/response structure.
	* A ring contains as many entries as will fit, rounded down to the nearest
	* power of two (so we can mask with (size-1) to loop around).
	*/
	#define __CONST_RING_SIZE(_s, _sz) \
	(__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
	sizeof(((struct _s##_sring *)0)->ring[0])))

	/*
	* The same for passing in an actual pointer instead of a name tag.
	*/
	#define __RING_SIZE(_s, _sz) \
	(__RD32(((_sz) - (long)&(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))

	/*
	* Macros to make the correct C datatypes for a new kind of ring.
	*
	* To make a new ring datatype, you need to have two message structures,
	* let's say struct request, and struct response already defined.
	*
	* In a header where you want the ring datatype declared, you then do:
	*
	* DEFINE_RING_TYPES(mytag, struct request, struct response);
	*
	* These expand out to give you a set of types, as you can see below.
	* The most important of these are:
	*
	* struct mytag_sring - The shared ring.
	* struct mytag_front_ring - The 'front' half of the ring.
	* struct mytag_back_ring - The 'back' half of the ring.
	*
	* To initialize a ring in your code you need to know the location and size
	* of the shared memory area (PAGE_SIZE, for instance). To initialise
	* the front half:
	*
	* struct mytag_front_ring front_ring;
	* SHARED_RING_INIT((struct mytag_sring *)shared_page);
	* FRONT_RING_INIT(&front_ring, (struct mytag_sring *)shared_page,
	* PAGE_SIZE);
	*
	* Initializing the back follows similarly (note that only the front
	* initializes the shared ring):
	*
	* struct mytag_back_ring back_ring;
	* BACK_RING_INIT(&back_ring, (struct mytag_sring *)shared_page,
	* PAGE_SIZE);
	*/

	#define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
	\
	/* Shared ring entry */ \
	union __name##_sring_entry { \
	__req_t req; \
	__rsp_t rsp; \
	}; \
	\
	/* Shared ring page */ \
	struct __name##_sring { \
	RING_IDX req_prod, req_event; \
	RING_IDX rsp_prod, rsp_event; \
	uint8_t pad[48]; \
	union __name##_sring_entry ring[1]; /* variable-length */ \
	}; \
	\
	/* "Front" end's private variables */ \
	struct __name##_front_ring { \
	RING_IDX req_prod_pvt; \
	RING_IDX rsp_cons; \
	unsigned int nr_ents; \
	struct __name##_sring *sring; \
	}; \
	\
	/* "Back" end's private variables */ \
	struct __name##_back_ring { \
	RING_IDX rsp_prod_pvt; \
	RING_IDX req_cons; \
	unsigned int nr_ents; \
	struct __name##_sring *sring; \
	};

	/*
	* Macros for manipulating rings.
	*
	* FRONT_RING_whatever works on the "front end" of a ring: here
	* requests are pushed on to the ring and responses taken off it.
	*
	* BACK_RING_whatever works on the "back end" of a ring: here
	* requests are taken off the ring and responses put on.
	*
	* N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
	* This is OK in 1-for-1 request-response situations where the
	* requestor (front end) never has more than RING_SIZE()-1
	* outstanding requests.
	*/

	/* Initialising empty rings */
	#define SHARED_RING_INIT(_s) do { \
	(_s)->req_prod = (_s)->rsp_prod = 0; \
	(_s)->req_event = (_s)->rsp_event = 1; \
	memset((_s)->pad, 0, sizeof((_s)->pad)); \
	} while(0)

	#define FRONT_RING_INIT(_r, _s, __size) do { \
	(_r)->req_prod_pvt = 0; \
	(_r)->rsp_cons = 0; \
	(_r)->nr_ents = __RING_SIZE(_s, __size); \
	(_r)->sring = (_s); \
	} while (0)

	#define BACK_RING_INIT(_r, _s, __size) do { \
	(_r)->rsp_prod_pvt = 0; \
	(_r)->req_cons = 0; \
	(_r)->nr_ents = __RING_SIZE(_s, __size); \
	(_r)->sring = (_s); \
	} while (0)

	/* Initialize to existing shared indexes -- for recovery */
	#define FRONT_RING_ATTACH(_r, _s, __size) do { \
	(_r)->sring = (_s); \
	(_r)->req_prod_pvt = (_s)->req_prod; \
	(_r)->rsp_cons = (_s)->rsp_prod; \
	(_r)->nr_ents = __RING_SIZE(_s, __size); \
	} while (0)

	#define BACK_RING_ATTACH(_r, _s, __size) do { \
	(_r)->sring = (_s); \
	(_r)->rsp_prod_pvt = (_s)->rsp_prod; \
	(_r)->req_cons = (_s)->req_prod; \
	(_r)->nr_ents = __RING_SIZE(_s, __size); \
	} while (0)

	/* How big is this ring? */
	#define RING_SIZE(_r) \
	((_r)->nr_ents)

	/* Number of free requests (for use on front side only). */
	#define RING_FREE_REQUESTS(_r) \
	(RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))

	/* Test if there is an empty slot available on the front ring.
	* (This is only meaningful from the front. )
	*/
	#define RING_FULL(_r) \
	(RING_FREE_REQUESTS(_r) == 0)

	/* Test if there are outstanding messages to be processed on a ring. */
	#define RING_HAS_UNCONSUMED_RESPONSES(_r) \
	((_r)->sring->rsp_prod - (_r)->rsp_cons)

	#define RING_HAS_UNCONSUMED_REQUESTS(_r) \
	({ \
	unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
	unsigned int rsp = RING_SIZE(_r) - \
	((_r)->req_cons - (_r)->rsp_prod_pvt); \
	req < rsp ? req : rsp; \
	})

	/* Direct access to individual ring elements, by index. */
	#define RING_GET_REQUEST(_r, _idx) \
	(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))

	#define RING_GET_RESPONSE(_r, _idx) \
	(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))

	/* Loop termination condition: Would the specified index overflow the ring? */
	#define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
	(((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))

	#define RING_PUSH_REQUESTS(_r) do { \
	wmb(); /* back sees requests /before/ updated producer index */ \
	(_r)->sring->req_prod = (_r)->req_prod_pvt; \
	} while (0)

	#define RING_PUSH_RESPONSES(_r) do { \
	wmb(); /* front sees responses /before/ updated producer index */ \
	(_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
	} while (0)

	/*
	* Notification hold-off (req_event and rsp_event):
	*
	* When queueing requests or responses on a shared ring, it may not always be
	* necessary to notify the remote end. For example, if requests are in flight
	* in a backend, the front may be able to queue further requests without
	* notifying the back (if the back checks for new requests when it queues
	* responses).
	*
	* When enqueuing requests or responses:
	*
	* Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
	* is a boolean return value. True indicates that the receiver requires an
	* asynchronous notification.
	*
	* After dequeuing requests or responses (before sleeping the connection):
	*
	* Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
	* The second argument is a boolean return value. True indicates that there
	* are pending messages on the ring (i.e., the connection should not be put
	* to sleep).
	*
	* These macros will set the req_event/rsp_event field to trigger a
	* notification on the very next message that is enqueued. If you want to
	* create batches of work (i.e., only receive a notification after several
	* messages have been enqueued) then you will need to create a customised
	* version of the FINAL_CHECK macro in your own code, which sets the event
	* field appropriately.
	*/

	#define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
	RING_IDX __old = (_r)->sring->req_prod; \
	RING_IDX __new = (_r)->req_prod_pvt; \
	wmb(); /* back sees requests /before/ updated producer index */ \
	(_r)->sring->req_prod = __new; \
	mb(); /* back sees new requests /before/ we check req_event */ \
	(_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
	(RING_IDX)(__new - __old)); \
	} while (0)

	#define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
	RING_IDX __old = (_r)->sring->rsp_prod; \
	RING_IDX __new = (_r)->rsp_prod_pvt; \
	wmb(); /* front sees responses /before/ updated producer index */ \
	(_r)->sring->rsp_prod = __new; \
	mb(); /* front sees new responses /before/ we check rsp_event */ \
	(_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
	(RING_IDX)(__new - __old)); \
	} while (0)

	#define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
	(_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
	if (_work_to_do) break; \
	(_r)->sring->req_event = (_r)->req_cons + 1; \
	mb(); \
	(_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
	} while (0)

	#define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
	(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
	if (_work_to_do) break; \
	(_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
	mb(); \
	(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
	} while (0)

	#endif /* __XEN_PUBLIC_IO_RING_H__ */