ring.h revision 181624
1/****************************************************************************** 2 * ring.h 3 * 4 * Shared producer-consumer ring macros. 5 * 6 * Permission is hereby granted, free of charge, to any person obtaining a copy 7 * of this software and associated documentation files (the "Software"), to 8 * deal in the Software without restriction, including without limitation the 9 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or 10 * sell copies of the Software, and to permit persons to whom the Software is 11 * furnished to do so, subject to the following conditions: 12 * 13 * The above copyright notice and this permission notice shall be included in 14 * all copies or substantial portions of the Software. 15 * 16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 19 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 21 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 22 * DEALINGS IN THE SOFTWARE. 23 * 24 * Tim Deegan and Andrew Warfield November 2004. 25 */ 26 27#ifndef __XEN_PUBLIC_IO_RING_H__ 28#define __XEN_PUBLIC_IO_RING_H__ 29 30typedef unsigned int RING_IDX; 31 32/* Round a 32-bit unsigned constant down to the nearest power of two. */ 33#define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1)) 34#define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x)) 35#define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x)) 36#define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x)) 37#define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x)) 38 39/* 40 * Calculate size of a shared ring, given the total available space for the 41 * ring and indexes (_sz), and the name tag of the request/response structure. 42 * A ring contains as many entries as will fit, rounded down to the nearest 43 * power of two (so we can mask with (size-1) to loop around). 44 */ 45#define __RING_SIZE(_s, _sz) \ 46 (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0]))) 47 48/* 49 * Macros to make the correct C datatypes for a new kind of ring. 50 * 51 * To make a new ring datatype, you need to have two message structures, 52 * let's say request_t, and response_t already defined. 53 * 54 * In a header where you want the ring datatype declared, you then do: 55 * 56 * DEFINE_RING_TYPES(mytag, request_t, response_t); 57 * 58 * These expand out to give you a set of types, as you can see below. 59 * The most important of these are: 60 * 61 * mytag_sring_t - The shared ring. 62 * mytag_front_ring_t - The 'front' half of the ring. 63 * mytag_back_ring_t - The 'back' half of the ring. 64 * 65 * To initialize a ring in your code you need to know the location and size 66 * of the shared memory area (PAGE_SIZE, for instance). To initialise 67 * the front half: 68 * 69 * mytag_front_ring_t front_ring; 70 * SHARED_RING_INIT((mytag_sring_t *)shared_page); 71 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 72 * 73 * Initializing the back follows similarly (note that only the front 74 * initializes the shared ring): 75 * 76 * mytag_back_ring_t back_ring; 77 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 78 */ 79 80#define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ 81 \ 82/* Shared ring entry */ \ 83union __name##_sring_entry { \ 84 __req_t req; \ 85 __rsp_t rsp; \ 86}; \ 87 \ 88/* Shared ring page */ \ 89struct __name##_sring { \ 90 RING_IDX req_prod, req_event; \ 91 RING_IDX rsp_prod, rsp_event; \ 92 uint8_t pad[48]; \ 93 union __name##_sring_entry ring[1]; /* variable-length */ \ 94}; \ 95 \ 96/* "Front" end's private variables */ \ 97struct __name##_front_ring { \ 98 RING_IDX req_prod_pvt; \ 99 RING_IDX rsp_cons; \ 100 unsigned int nr_ents; \ 101 struct __name##_sring *sring; \ 102}; \ 103 \ 104/* "Back" end's private variables */ \ 105struct __name##_back_ring { \ 106 RING_IDX rsp_prod_pvt; \ 107 RING_IDX req_cons; \ 108 unsigned int nr_ents; \ 109 struct __name##_sring *sring; \ 110}; \ 111 \ 112/* Syntactic sugar */ \ 113typedef struct __name##_sring __name##_sring_t; \ 114typedef struct __name##_front_ring __name##_front_ring_t; \ 115typedef struct __name##_back_ring __name##_back_ring_t 116 117/* 118 * Macros for manipulating rings. 119 * 120 * FRONT_RING_whatever works on the "front end" of a ring: here 121 * requests are pushed on to the ring and responses taken off it. 122 * 123 * BACK_RING_whatever works on the "back end" of a ring: here 124 * requests are taken off the ring and responses put on. 125 * 126 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. 127 * This is OK in 1-for-1 request-response situations where the 128 * requestor (front end) never has more than RING_SIZE()-1 129 * outstanding requests. 130 */ 131 132/* Initialising empty rings */ 133#define SHARED_RING_INIT(_s) do { \ 134 (_s)->req_prod = (_s)->rsp_prod = 0; \ 135 (_s)->req_event = (_s)->rsp_event = 1; \ 136 (void)memset((_s)->pad, 0, sizeof((_s)->pad)); \ 137} while(0) 138 139#define FRONT_RING_INIT(_r, _s, __size) do { \ 140 (_r)->req_prod_pvt = 0; \ 141 (_r)->rsp_cons = 0; \ 142 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 143 (_r)->sring = (_s); \ 144} while (0) 145 146#define BACK_RING_INIT(_r, _s, __size) do { \ 147 (_r)->rsp_prod_pvt = 0; \ 148 (_r)->req_cons = 0; \ 149 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 150 (_r)->sring = (_s); \ 151} while (0) 152 153/* Initialize to existing shared indexes -- for recovery */ 154#define FRONT_RING_ATTACH(_r, _s, __size) do { \ 155 (_r)->sring = (_s); \ 156 (_r)->req_prod_pvt = (_s)->req_prod; \ 157 (_r)->rsp_cons = (_s)->rsp_prod; \ 158 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 159} while (0) 160 161#define BACK_RING_ATTACH(_r, _s, __size) do { \ 162 (_r)->sring = (_s); \ 163 (_r)->rsp_prod_pvt = (_s)->rsp_prod; \ 164 (_r)->req_cons = (_s)->req_prod; \ 165 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 166} while (0) 167 168/* How big is this ring? */ 169#define RING_SIZE(_r) \ 170 ((_r)->nr_ents) 171 172/* Number of free requests (for use on front side only). */ 173#define RING_FREE_REQUESTS(_r) \ 174 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) 175 176/* Test if there is an empty slot available on the front ring. 177 * (This is only meaningful from the front. ) 178 */ 179#define RING_FULL(_r) \ 180 (RING_FREE_REQUESTS(_r) == 0) 181 182/* Test if there are outstanding messages to be processed on a ring. */ 183#define RING_HAS_UNCONSUMED_RESPONSES(_r) \ 184 ((_r)->sring->rsp_prod - (_r)->rsp_cons) 185 186#ifdef __GNUC__ 187#define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \ 188 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \ 189 unsigned int rsp = RING_SIZE(_r) - \ 190 ((_r)->req_cons - (_r)->rsp_prod_pvt); \ 191 req < rsp ? req : rsp; \ 192}) 193#else 194/* Same as above, but without the nice GCC ({ ... }) syntax. */ 195#define RING_HAS_UNCONSUMED_REQUESTS(_r) \ 196 ((((_r)->sring->req_prod - (_r)->req_cons) < \ 197 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \ 198 ((_r)->sring->req_prod - (_r)->req_cons) : \ 199 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) 200#endif 201 202/* Direct access to individual ring elements, by index. */ 203#define RING_GET_REQUEST(_r, _idx) \ 204 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) 205 206#define RING_GET_RESPONSE(_r, _idx) \ 207 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) 208 209/* Loop termination condition: Would the specified index overflow the ring? */ 210#define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ 211 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) 212 213#define RING_PUSH_REQUESTS(_r) do { \ 214 wmb(); /* back sees requests /before/ updated producer index */ \ 215 (_r)->sring->req_prod = (_r)->req_prod_pvt; \ 216} while (0) 217 218#define RING_PUSH_RESPONSES(_r) do { \ 219 wmb(); /* front sees responses /before/ updated producer index */ \ 220 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ 221} while (0) 222 223/* 224 * Notification hold-off (req_event and rsp_event): 225 * 226 * When queueing requests or responses on a shared ring, it may not always be 227 * necessary to notify the remote end. For example, if requests are in flight 228 * in a backend, the front may be able to queue further requests without 229 * notifying the back (if the back checks for new requests when it queues 230 * responses). 231 * 232 * When enqueuing requests or responses: 233 * 234 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument 235 * is a boolean return value. True indicates that the receiver requires an 236 * asynchronous notification. 237 * 238 * After dequeuing requests or responses (before sleeping the connection): 239 * 240 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). 241 * The second argument is a boolean return value. True indicates that there 242 * are pending messages on the ring (i.e., the connection should not be put 243 * to sleep). 244 * 245 * These macros will set the req_event/rsp_event field to trigger a 246 * notification on the very next message that is enqueued. If you want to 247 * create batches of work (i.e., only receive a notification after several 248 * messages have been enqueued) then you will need to create a customised 249 * version of the FINAL_CHECK macro in your own code, which sets the event 250 * field appropriately. 251 */ 252 253#define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ 254 RING_IDX __old = (_r)->sring->req_prod; \ 255 RING_IDX __new = (_r)->req_prod_pvt; \ 256 wmb(); /* back sees requests /before/ updated producer index */ \ 257 (_r)->sring->req_prod = __new; \ 258 mb(); /* back sees new requests /before/ we check req_event */ \ 259 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ 260 (RING_IDX)(__new - __old)); \ 261} while (0) 262 263#define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ 264 RING_IDX __old = (_r)->sring->rsp_prod; \ 265 RING_IDX __new = (_r)->rsp_prod_pvt; \ 266 wmb(); /* front sees responses /before/ updated producer index */ \ 267 (_r)->sring->rsp_prod = __new; \ 268 mb(); /* front sees new responses /before/ we check rsp_event */ \ 269 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ 270 (RING_IDX)(__new - __old)); \ 271} while (0) 272 273#define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ 274 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 275 if (_work_to_do) break; \ 276 (_r)->sring->req_event = (_r)->req_cons + 1; \ 277 mb(); \ 278 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 279} while (0) 280 281#define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ 282 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 283 if (_work_to_do) break; \ 284 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ 285 mb(); \ 286 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 287} while (0) 288 289#endif /* __XEN_PUBLIC_IO_RING_H__ */ 290 291/* 292 * Local variables: 293 * mode: C 294 * c-set-style: "BSD" 295 * c-basic-offset: 4 296 * tab-width: 4 297 * indent-tabs-mode: nil 298 * End: 299 */ 300