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/******************************************************************************
* ring.h
*
* Shared producer-consumer ring macros.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*
* Tim Deegan and Andrew Warfield November 2004.
*/
#ifndef __XEN_PUBLIC_IO_RING_H__
#define __XEN_PUBLIC_IO_RING_H__
#include "../xen-compat.h"
#if __XEN_INTERFACE_VERSION__ < 0x00030208
#define xen_mb() mb()
#define xen_rmb() rmb()
#define xen_wmb() wmb()
#endif
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))
/*
* The amount of space reserved in the shared ring for accounting information.
*/
#define __RING_HEADER_SIZE(_s) \
((intptr_t)(_s)->ring - (intptr_t)(_s))
/*
* 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 __RING_SIZE(_s, _sz) \
(__RD32(((_sz) - __RING_HEADER_SIZE(_s)) / sizeof((_s)->ring[0])))
/*
* The number of pages needed to support a given number of request/reponse
* entries. The entry count is rounded down to the nearest power of two
* as required by the ring macros.
*/
#define __RING_PAGES(_s, _entries) \
((__RING_HEADER_SIZE(_s) \
+ (__RD32(_entries) * sizeof((_s)->ring[0])) \
+ PAGE_SIZE - 1) / PAGE_SIZE)
/*
* 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 request_t, and response_t already defined.
*
* In a header where you want the ring datatype declared, you then do:
*
* DEFINE_RING_TYPES(mytag, request_t, response_t);
*
* These expand out to give you a set of types, as you can see below.
* The most important of these are:
*
* mytag_sring_t - The shared ring.
* mytag_front_ring_t - The 'front' half of the ring.
* mytag_back_ring_t - 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:
*
* mytag_front_ring_t front_ring;
* SHARED_RING_INIT((mytag_sring_t *)shared_page);
* FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
*
* Initializing the back follows similarly (note that only the front
* initializes the shared ring):
*
* mytag_back_ring_t back_ring;
* BACK_RING_INIT(&back_ring, (mytag_sring_t *)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; \
}; \
\
/* Syntactic sugar */ \
typedef struct __name##_sring __name##_sring_t; \
typedef struct __name##_front_ring __name##_front_ring_t; \
typedef struct __name##_back_ring __name##_back_ring_t
/*
* 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; \
(void)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)
#ifdef __GNUC__
#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; \
})
#else
/* Same as above, but without the nice GCC ({ ... }) syntax. */
#define RING_HAS_UNCONSUMED_REQUESTS(_r) \
((((_r)->sring->req_prod - (_r)->req_cons) < \
(RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \
((_r)->sring->req_prod - (_r)->req_cons) : \
(RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
#endif
/* 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 { \
xen_wmb(); /* back sees requests /before/ updated producer index */ \
(_r)->sring->req_prod = (_r)->req_prod_pvt; \
} while (0)
#define RING_PUSH_RESPONSES(_r) do { \
xen_wmb(); /* front sees resps /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; \
xen_wmb(); /* back sees requests /before/ updated producer index */ \
(_r)->sring->req_prod = __new; \
xen_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; \
xen_wmb(); /* front sees resps /before/ updated producer index */ \
(_r)->sring->rsp_prod = __new; \
xen_mb(); /* front sees new resps /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; \
xen_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; \
xen_mb(); \
(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
} while (0)
#endif /* __XEN_PUBLIC_IO_RING_H__ */
/*
* Local variables:
* mode: C
* c-set-style: "BSD"
* c-basic-offset: 4
* tab-width: 4
* indent-tabs-mode: nil
* End:
*/