315 lines
15 KiB
C
315 lines
15 KiB
C
/******************************************************************************
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* ring.h
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*
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* Shared producer-consumer ring macros.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to
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* deal in the Software without restriction, including without limitation the
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* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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* sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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* DEALINGS IN THE SOFTWARE.
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*
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* Tim Deegan and Andrew Warfield November 2004.
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*/
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#ifndef __XEN_PUBLIC_IO_RING_H__
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#define __XEN_PUBLIC_IO_RING_H__
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FILE_LICENCE ( MIT );
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#include "../xen-compat.h"
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#if __XEN_INTERFACE_VERSION__ < 0x00030208
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#define xen_mb() mb()
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#define xen_rmb() rmb()
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#define xen_wmb() wmb()
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#endif
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typedef unsigned int RING_IDX;
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/* Round a 32-bit unsigned constant down to the nearest power of two. */
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#define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1))
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#define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x))
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#define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x))
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#define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x))
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#define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
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/*
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* Calculate size of a shared ring, given the total available space for the
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* ring and indexes (_sz), and the name tag of the request/response structure.
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* A ring contains as many entries as will fit, rounded down to the nearest
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* power of two (so we can mask with (size-1) to loop around).
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*/
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#define __CONST_RING_SIZE(_s, _sz) \
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(__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
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sizeof(((struct _s##_sring *)0)->ring[0])))
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/*
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* The same for passing in an actual pointer instead of a name tag.
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*/
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#define __RING_SIZE(_s, _sz) \
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(__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
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/*
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* Macros to make the correct C datatypes for a new kind of ring.
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*
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* To make a new ring datatype, you need to have two message structures,
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* let's say request_t, and response_t already defined.
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*
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* In a header where you want the ring datatype declared, you then do:
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*
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* DEFINE_RING_TYPES(mytag, request_t, response_t);
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*
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* These expand out to give you a set of types, as you can see below.
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* The most important of these are:
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*
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* mytag_sring_t - The shared ring.
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* mytag_front_ring_t - The 'front' half of the ring.
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* mytag_back_ring_t - The 'back' half of the ring.
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*
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* To initialize a ring in your code you need to know the location and size
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* of the shared memory area (PAGE_SIZE, for instance). To initialise
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* the front half:
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*
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* mytag_front_ring_t front_ring;
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* SHARED_RING_INIT((mytag_sring_t *)shared_page);
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* FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
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*
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* Initializing the back follows similarly (note that only the front
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* initializes the shared ring):
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*
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* mytag_back_ring_t back_ring;
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* BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
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*/
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#define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
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\
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/* Shared ring entry */ \
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union __name##_sring_entry { \
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__req_t req; \
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__rsp_t rsp; \
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}; \
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\
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/* Shared ring page */ \
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struct __name##_sring { \
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RING_IDX req_prod, req_event; \
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RING_IDX rsp_prod, rsp_event; \
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union { \
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struct { \
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uint8_t smartpoll_active; \
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} netif; \
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struct { \
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uint8_t msg; \
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} tapif_user; \
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uint8_t pvt_pad[4]; \
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} private; \
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uint8_t __pad[44]; \
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union __name##_sring_entry ring[1]; /* variable-length */ \
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}; \
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\
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/* "Front" end's private variables */ \
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struct __name##_front_ring { \
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RING_IDX req_prod_pvt; \
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RING_IDX rsp_cons; \
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unsigned int nr_ents; \
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struct __name##_sring *sring; \
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}; \
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\
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/* "Back" end's private variables */ \
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struct __name##_back_ring { \
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RING_IDX rsp_prod_pvt; \
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RING_IDX req_cons; \
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unsigned int nr_ents; \
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struct __name##_sring *sring; \
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}; \
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\
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/* Syntactic sugar */ \
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typedef struct __name##_sring __name##_sring_t; \
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typedef struct __name##_front_ring __name##_front_ring_t; \
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typedef struct __name##_back_ring __name##_back_ring_t
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/*
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* Macros for manipulating rings.
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*
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* FRONT_RING_whatever works on the "front end" of a ring: here
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* requests are pushed on to the ring and responses taken off it.
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*
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* BACK_RING_whatever works on the "back end" of a ring: here
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* requests are taken off the ring and responses put on.
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*
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* N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
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* This is OK in 1-for-1 request-response situations where the
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* requestor (front end) never has more than RING_SIZE()-1
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* outstanding requests.
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*/
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/* Initialising empty rings */
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#define SHARED_RING_INIT(_s) do { \
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(_s)->req_prod = (_s)->rsp_prod = 0; \
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(_s)->req_event = (_s)->rsp_event = 1; \
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(void)memset((_s)->private.pvt_pad, 0, sizeof((_s)->private.pvt_pad)); \
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(void)memset((_s)->__pad, 0, sizeof((_s)->__pad)); \
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} while(0)
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#define FRONT_RING_INIT(_r, _s, __size) do { \
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(_r)->req_prod_pvt = 0; \
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(_r)->rsp_cons = 0; \
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(_r)->nr_ents = __RING_SIZE(_s, __size); \
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(_r)->sring = (_s); \
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} while (0)
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#define BACK_RING_INIT(_r, _s, __size) do { \
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(_r)->rsp_prod_pvt = 0; \
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(_r)->req_cons = 0; \
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(_r)->nr_ents = __RING_SIZE(_s, __size); \
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(_r)->sring = (_s); \
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} while (0)
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/* How big is this ring? */
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#define RING_SIZE(_r) \
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((_r)->nr_ents)
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/* Number of free requests (for use on front side only). */
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#define RING_FREE_REQUESTS(_r) \
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(RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
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/* Test if there is an empty slot available on the front ring.
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* (This is only meaningful from the front. )
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*/
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#define RING_FULL(_r) \
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(RING_FREE_REQUESTS(_r) == 0)
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/* Test if there are outstanding messages to be processed on a ring. */
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#define RING_HAS_UNCONSUMED_RESPONSES(_r) \
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((_r)->sring->rsp_prod - (_r)->rsp_cons)
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#ifdef __GNUC__
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#define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \
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unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
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unsigned int rsp = RING_SIZE(_r) - \
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((_r)->req_cons - (_r)->rsp_prod_pvt); \
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req < rsp ? req : rsp; \
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})
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#else
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/* Same as above, but without the nice GCC ({ ... }) syntax. */
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#define RING_HAS_UNCONSUMED_REQUESTS(_r) \
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((((_r)->sring->req_prod - (_r)->req_cons) < \
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(RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \
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((_r)->sring->req_prod - (_r)->req_cons) : \
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(RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
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#endif
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/* Direct access to individual ring elements, by index. */
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#define RING_GET_REQUEST(_r, _idx) \
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(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
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#define RING_GET_RESPONSE(_r, _idx) \
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(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
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/* Loop termination condition: Would the specified index overflow the ring? */
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#define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
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(((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
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/* Ill-behaved frontend determination: Can there be this many requests? */
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#define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \
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(((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
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#define RING_PUSH_REQUESTS(_r) do { \
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xen_wmb(); /* back sees requests /before/ updated producer index */ \
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(_r)->sring->req_prod = (_r)->req_prod_pvt; \
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} while (0)
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#define RING_PUSH_RESPONSES(_r) do { \
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xen_wmb(); /* front sees resps /before/ updated producer index */ \
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(_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
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} while (0)
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/*
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* Notification hold-off (req_event and rsp_event):
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*
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* When queueing requests or responses on a shared ring, it may not always be
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* necessary to notify the remote end. For example, if requests are in flight
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* in a backend, the front may be able to queue further requests without
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* notifying the back (if the back checks for new requests when it queues
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* responses).
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*
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* When enqueuing requests or responses:
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*
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* Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
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* is a boolean return value. True indicates that the receiver requires an
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* asynchronous notification.
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*
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* After dequeuing requests or responses (before sleeping the connection):
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*
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* Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
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* The second argument is a boolean return value. True indicates that there
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* are pending messages on the ring (i.e., the connection should not be put
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* to sleep).
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*
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* These macros will set the req_event/rsp_event field to trigger a
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* notification on the very next message that is enqueued. If you want to
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* create batches of work (i.e., only receive a notification after several
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* messages have been enqueued) then you will need to create a customised
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* version of the FINAL_CHECK macro in your own code, which sets the event
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* field appropriately.
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*/
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#define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
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RING_IDX __old = (_r)->sring->req_prod; \
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RING_IDX __new = (_r)->req_prod_pvt; \
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xen_wmb(); /* back sees requests /before/ updated producer index */ \
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(_r)->sring->req_prod = __new; \
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xen_mb(); /* back sees new requests /before/ we check req_event */ \
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(_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
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(RING_IDX)(__new - __old)); \
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} while (0)
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#define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
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RING_IDX __old = (_r)->sring->rsp_prod; \
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RING_IDX __new = (_r)->rsp_prod_pvt; \
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xen_wmb(); /* front sees resps /before/ updated producer index */ \
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(_r)->sring->rsp_prod = __new; \
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xen_mb(); /* front sees new resps /before/ we check rsp_event */ \
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(_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
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(RING_IDX)(__new - __old)); \
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} while (0)
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#define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
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(_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
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if (_work_to_do) break; \
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(_r)->sring->req_event = (_r)->req_cons + 1; \
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xen_mb(); \
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(_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
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} while (0)
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#define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
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(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
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if (_work_to_do) break; \
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(_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
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xen_mb(); \
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(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
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} while (0)
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#endif /* __XEN_PUBLIC_IO_RING_H__ */
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/*
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* Local variables:
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* mode: C
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* c-file-style: "BSD"
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* c-basic-offset: 4
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* tab-width: 4
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* indent-tabs-mode: nil
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* End:
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*/
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