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 30 typedef 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 /* Solaris equivalents */ 49 #ifdef _SOLARIS 50 #define wmb membar_producer 51 #define mb membar_enter 52 #endif 53 54 /* 55 * Macros to make the correct C datatypes for a new kind of ring. 56 * 57 * To make a new ring datatype, you need to have two message structures, 58 * let's say request_t, and response_t already defined. 59 * 60 * In a header where you want the ring datatype declared, you then do: 61 * 62 * DEFINE_RING_TYPES(mytag, request_t, response_t); 63 * 64 * These expand out to give you a set of types, as you can see below. 65 * The most important of these are: 66 * 67 * mytag_sring_t - The shared ring. 68 * mytag_front_ring_t - The 'front' half of the ring. 69 * mytag_back_ring_t - The 'back' half of the ring. 70 * 71 * To initialize a ring in your code you need to know the location and size 72 * of the shared memory area (PAGE_SIZE, for instance). To initialise 73 * the front half: 74 * 75 * mytag_front_ring_t front_ring; 76 * SHARED_RING_INIT((mytag_sring_t *)shared_page); 77 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 78 * 79 * Initializing the back follows similarly (note that only the front 80 * initializes the shared ring): 81 * 82 * mytag_back_ring_t back_ring; 83 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 84 */ 85 86 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ 87 \ 88 /* Shared ring entry */ \ 89 union __name##_sring_entry { \ 90 __req_t req; \ 91 __rsp_t rsp; \ 92 }; \ 93 \ 94 /* Shared ring page */ \ 95 struct __name##_sring { \ 96 RING_IDX req_prod, req_event; \ 97 RING_IDX rsp_prod, rsp_event; \ 98 uint8_t pad[48]; \ 99 union __name##_sring_entry ring[1]; /* variable-length */ \ 100 }; \ 101 \ 102 /* "Front" end's private variables */ \ 103 struct __name##_front_ring { \ 104 RING_IDX req_prod_pvt; \ 105 RING_IDX rsp_cons; \ 106 unsigned int nr_ents; \ 107 struct __name##_sring *sring; \ 108 }; \ 109 \ 110 /* "Back" end's private variables */ \ 111 struct __name##_back_ring { \ 112 RING_IDX rsp_prod_pvt; \ 113 RING_IDX req_cons; \ 114 unsigned int nr_ents; \ 115 struct __name##_sring *sring; \ 116 }; \ 117 \ 118 /* Syntactic sugar */ \ 119 typedef struct __name##_sring __name##_sring_t; \ 120 typedef struct __name##_front_ring __name##_front_ring_t; \ 121 typedef struct __name##_back_ring __name##_back_ring_t 122 123 /* 124 * Macros for manipulating rings. 125 * 126 * FRONT_RING_whatever works on the "front end" of a ring: here 127 * requests are pushed on to the ring and responses taken off it. 128 * 129 * BACK_RING_whatever works on the "back end" of a ring: here 130 * requests are taken off the ring and responses put on. 131 * 132 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. 133 * This is OK in 1-for-1 request-response situations where the 134 * requestor (front end) never has more than RING_SIZE()-1 135 * outstanding requests. 136 */ 137 138 /* Initialising empty rings */ 139 #define SHARED_RING_INIT(_s) do { \ 140 (_s)->req_prod = (_s)->rsp_prod = 0; \ 141 (_s)->req_event = (_s)->rsp_event = 1; \ 142 (void)memset((_s)->pad, 0, sizeof((_s)->pad)); \ 143 } while(0) 144 145 #define FRONT_RING_INIT(_r, _s, __size) do { \ 146 (_r)->req_prod_pvt = 0; \ 147 (_r)->rsp_cons = 0; \ 148 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 149 (_r)->sring = (_s); \ 150 } while (0) 151 152 #define BACK_RING_INIT(_r, _s, __size) do { \ 153 (_r)->rsp_prod_pvt = 0; \ 154 (_r)->req_cons = 0; \ 155 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 156 (_r)->sring = (_s); \ 157 } while (0) 158 159 /* Initialize to existing shared indexes -- for recovery */ 160 #define FRONT_RING_ATTACH(_r, _s, __size) do { \ 161 (_r)->sring = (_s); \ 162 (_r)->req_prod_pvt = (_s)->req_prod; \ 163 (_r)->rsp_cons = (_s)->rsp_prod; \ 164 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 165 } while (0) 166 167 #define BACK_RING_ATTACH(_r, _s, __size) do { \ 168 (_r)->sring = (_s); \ 169 (_r)->rsp_prod_pvt = (_s)->rsp_prod; \ 170 (_r)->req_cons = (_s)->req_prod; \ 171 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 172 } while (0) 173 174 /* How big is this ring? */ 175 #define RING_SIZE(_r) \ 176 ((_r)->nr_ents) 177 178 /* Number of free requests (for use on front side only). */ 179 #define RING_FREE_REQUESTS(_r) \ 180 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) 181 182 /* Test if there is an empty slot available on the front ring. 183 * (This is only meaningful from the front. ) 184 */ 185 #define RING_FULL(_r) \ 186 (RING_FREE_REQUESTS(_r) == 0) 187 188 /* Test if there are outstanding messages to be processed on a ring. */ 189 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \ 190 ((_r)->sring->rsp_prod - (_r)->rsp_cons) 191 192 #ifdef __GNUC__ 193 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \ 194 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \ 195 unsigned int rsp = RING_SIZE(_r) - \ 196 ((_r)->req_cons - (_r)->rsp_prod_pvt); \ 197 req < rsp ? req : rsp; \ 198 }) 199 #else 200 /* Same as above, but without the nice GCC ({ ... }) syntax. */ 201 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \ 202 ((((_r)->sring->req_prod - (_r)->req_cons) < \ 203 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \ 204 ((_r)->sring->req_prod - (_r)->req_cons) : \ 205 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) 206 #endif 207 208 /* Direct access to individual ring elements, by index. */ 209 #define RING_GET_REQUEST(_r, _idx) \ 210 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) 211 212 #define RING_GET_RESPONSE(_r, _idx) \ 213 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) 214 215 /* Loop termination condition: Would the specified index overflow the ring? */ 216 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ 217 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) 218 219 #define RING_PUSH_REQUESTS(_r) do { \ 220 wmb(); /* back sees requests /before/ updated producer index */ \ 221 (_r)->sring->req_prod = (_r)->req_prod_pvt; \ 222 } while (0) 223 224 #define RING_PUSH_RESPONSES(_r) do { \ 225 wmb(); /* front sees responses /before/ updated producer index */ \ 226 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ 227 } while (0) 228 229 /* 230 * Notification hold-off (req_event and rsp_event): 231 * 232 * When queueing requests or responses on a shared ring, it may not always be 233 * necessary to notify the remote end. For example, if requests are in flight 234 * in a backend, the front may be able to queue further requests without 235 * notifying the back (if the back checks for new requests when it queues 236 * responses). 237 * 238 * When enqueuing requests or responses: 239 * 240 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument 241 * is a boolean return value. True indicates that the receiver requires an 242 * asynchronous notification. 243 * 244 * After dequeuing requests or responses (before sleeping the connection): 245 * 246 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). 247 * The second argument is a boolean return value. True indicates that there 248 * are pending messages on the ring (i.e., the connection should not be put 249 * to sleep). 250 * 251 * These macros will set the req_event/rsp_event field to trigger a 252 * notification on the very next message that is enqueued. If you want to 253 * create batches of work (i.e., only receive a notification after several 254 * messages have been enqueued) then you will need to create a customised 255 * version of the FINAL_CHECK macro in your own code, which sets the event 256 * field appropriately. 257 */ 258 259 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ 260 RING_IDX __old = (_r)->sring->req_prod; \ 261 RING_IDX __new = (_r)->req_prod_pvt; \ 262 wmb(); /* back sees requests /before/ updated producer index */ \ 263 (_r)->sring->req_prod = __new; \ 264 mb(); /* back sees new requests /before/ we check req_event */ \ 265 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ 266 (RING_IDX)(__new - __old)); \ 267 } while (0) 268 269 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ 270 RING_IDX __old = (_r)->sring->rsp_prod; \ 271 RING_IDX __new = (_r)->rsp_prod_pvt; \ 272 wmb(); /* front sees responses /before/ updated producer index */ \ 273 (_r)->sring->rsp_prod = __new; \ 274 mb(); /* front sees new responses /before/ we check rsp_event */ \ 275 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ 276 (RING_IDX)(__new - __old)); \ 277 } while (0) 278 279 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ 280 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 281 if (_work_to_do) break; \ 282 (_r)->sring->req_event = (_r)->req_cons + 1; \ 283 mb(); \ 284 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 285 } while (0) 286 287 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ 288 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 289 if (_work_to_do) break; \ 290 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ 291 mb(); \ 292 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 293 } while (0) 294 295 #endif /* __XEN_PUBLIC_IO_RING_H__ */ 296 297 /* 298 * Local variables: 299 * mode: C 300 * c-set-style: "BSD" 301 * c-basic-offset: 4 302 * tab-width: 4 303 * indent-tabs-mode: nil 304 * End: 305 */ 306