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 #include "../xen-compat.h" 31 32 #if __XEN_INTERFACE_VERSION__ < 0x00030208 33 #define xen_mb() mb() 34 #define xen_rmb() rmb() 35 #define xen_wmb() wmb() 36 #endif 37 38 typedef unsigned int RING_IDX; 39 40 /* Round a 32-bit unsigned constant down to the nearest power of two. */ 41 #define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1)) 42 #define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x)) 43 #define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x)) 44 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x)) 45 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x)) 46 47 /* 48 * The amount of space reserved in the shared ring for accounting information. 49 */ 50 #define __RING_HEADER_SIZE(_s) \ 51 ((intptr_t)(_s)->ring - (intptr_t)(_s)) 52 53 /* 54 * Calculate size of a shared ring, given the total available space for the 55 * ring and indexes (_sz), and the name tag of the request/response structure. 56 * A ring contains as many entries as will fit, rounded down to the nearest 57 * power of two (so we can mask with (size-1) to loop around). 58 */ 59 #define __RING_SIZE(_s, _sz) \ 60 (__RD32(((_sz) - __RING_HEADER_SIZE(_s)) / sizeof((_s)->ring[0]))) 61 62 /* 63 * The number of pages needed to support a given number of request/reponse 64 * entries. The entry count is rounded down to the nearest power of two 65 * as required by the ring macros. 66 */ 67 #define __RING_PAGES(_s, _entries) \ 68 ((__RING_HEADER_SIZE(_s) \ 69 + (__RD32(_entries) * sizeof((_s)->ring[0])) \ 70 + PAGE_SIZE - 1) / PAGE_SIZE) 71 72 /* 73 * Macros to make the correct C datatypes for a new kind of ring. 74 * 75 * To make a new ring datatype, you need to have two message structures, 76 * let's say request_t, and response_t already defined. 77 * 78 * In a header where you want the ring datatype declared, you then do: 79 * 80 * DEFINE_RING_TYPES(mytag, request_t, response_t); 81 * 82 * These expand out to give you a set of types, as you can see below. 83 * The most important of these are: 84 * 85 * mytag_sring_t - The shared ring. 86 * mytag_front_ring_t - The 'front' half of the ring. 87 * mytag_back_ring_t - The 'back' half of the ring. 88 * 89 * To initialize a ring in your code you need to know the location and size 90 * of the shared memory area (PAGE_SIZE, for instance). To initialise 91 * the front half: 92 * 93 * mytag_front_ring_t front_ring; 94 * SHARED_RING_INIT((mytag_sring_t *)shared_page); 95 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 96 * 97 * Initializing the back follows similarly (note that only the front 98 * initializes the shared ring): 99 * 100 * mytag_back_ring_t back_ring; 101 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 102 */ 103 104 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ 105 \ 106 /* Shared ring entry */ \ 107 union __name##_sring_entry { \ 108 __req_t req; \ 109 __rsp_t rsp; \ 110 }; \ 111 \ 112 /* Shared ring page */ \ 113 struct __name##_sring { \ 114 RING_IDX req_prod, req_event; \ 115 RING_IDX rsp_prod, rsp_event; \ 116 uint8_t pad[48]; \ 117 union __name##_sring_entry ring[1]; /* variable-length */ \ 118 }; \ 119 \ 120 /* "Front" end's private variables */ \ 121 struct __name##_front_ring { \ 122 RING_IDX req_prod_pvt; \ 123 RING_IDX rsp_cons; \ 124 unsigned int nr_ents; \ 125 struct __name##_sring *sring; \ 126 }; \ 127 \ 128 /* "Back" end's private variables */ \ 129 struct __name##_back_ring { \ 130 RING_IDX rsp_prod_pvt; \ 131 RING_IDX req_cons; \ 132 unsigned int nr_ents; \ 133 struct __name##_sring *sring; \ 134 }; \ 135 \ 136 /* Syntactic sugar */ \ 137 typedef struct __name##_sring __name##_sring_t; \ 138 typedef struct __name##_front_ring __name##_front_ring_t; \ 139 typedef struct __name##_back_ring __name##_back_ring_t 140 141 /* 142 * Macros for manipulating rings. 143 * 144 * FRONT_RING_whatever works on the "front end" of a ring: here 145 * requests are pushed on to the ring and responses taken off it. 146 * 147 * BACK_RING_whatever works on the "back end" of a ring: here 148 * requests are taken off the ring and responses put on. 149 * 150 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. 151 * This is OK in 1-for-1 request-response situations where the 152 * requestor (front end) never has more than RING_SIZE()-1 153 * outstanding requests. 154 */ 155 156 /* Initialising empty rings */ 157 #define SHARED_RING_INIT(_s) do { \ 158 (_s)->req_prod = (_s)->rsp_prod = 0; \ 159 (_s)->req_event = (_s)->rsp_event = 1; \ 160 (void)memset((_s)->pad, 0, sizeof((_s)->pad)); \ 161 } while(0) 162 163 #define FRONT_RING_INIT(_r, _s, __size) do { \ 164 (_r)->req_prod_pvt = 0; \ 165 (_r)->rsp_cons = 0; \ 166 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 167 (_r)->sring = (_s); \ 168 } while (0) 169 170 #define BACK_RING_INIT(_r, _s, __size) do { \ 171 (_r)->rsp_prod_pvt = 0; \ 172 (_r)->req_cons = 0; \ 173 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 174 (_r)->sring = (_s); \ 175 } while (0) 176 177 /* Initialize to existing shared indexes -- for recovery */ 178 #define FRONT_RING_ATTACH(_r, _s, __size) do { \ 179 (_r)->sring = (_s); \ 180 (_r)->req_prod_pvt = (_s)->req_prod; \ 181 (_r)->rsp_cons = (_s)->rsp_prod; \ 182 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 183 } while (0) 184 185 #define BACK_RING_ATTACH(_r, _s, __size) do { \ 186 (_r)->sring = (_s); \ 187 (_r)->rsp_prod_pvt = (_s)->rsp_prod; \ 188 (_r)->req_cons = (_s)->req_prod; \ 189 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 190 } while (0) 191 192 /* How big is this ring? */ 193 #define RING_SIZE(_r) \ 194 ((_r)->nr_ents) 195 196 /* Number of free requests (for use on front side only). */ 197 #define RING_FREE_REQUESTS(_r) \ 198 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) 199 200 /* Test if there is an empty slot available on the front ring. 201 * (This is only meaningful from the front. ) 202 */ 203 #define RING_FULL(_r) \ 204 (RING_FREE_REQUESTS(_r) == 0) 205 206 /* Test if there are outstanding messages to be processed on a ring. */ 207 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \ 208 ((_r)->sring->rsp_prod - (_r)->rsp_cons) 209 210 #ifdef __GNUC__ 211 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \ 212 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \ 213 unsigned int rsp = RING_SIZE(_r) - \ 214 ((_r)->req_cons - (_r)->rsp_prod_pvt); \ 215 req < rsp ? req : rsp; \ 216 }) 217 #else 218 /* Same as above, but without the nice GCC ({ ... }) syntax. */ 219 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \ 220 ((((_r)->sring->req_prod - (_r)->req_cons) < \ 221 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \ 222 ((_r)->sring->req_prod - (_r)->req_cons) : \ 223 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) 224 #endif 225 226 /* Direct access to individual ring elements, by index. */ 227 #define RING_GET_REQUEST(_r, _idx) \ 228 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) 229 230 #define RING_GET_RESPONSE(_r, _idx) \ 231 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) 232 233 /* Loop termination condition: Would the specified index overflow the ring? */ 234 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ 235 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) 236 237 #define RING_PUSH_REQUESTS(_r) do { \ 238 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 239 (_r)->sring->req_prod = (_r)->req_prod_pvt; \ 240 } while (0) 241 242 #define RING_PUSH_RESPONSES(_r) do { \ 243 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 244 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ 245 } while (0) 246 247 /* 248 * Notification hold-off (req_event and rsp_event): 249 * 250 * When queueing requests or responses on a shared ring, it may not always be 251 * necessary to notify the remote end. For example, if requests are in flight 252 * in a backend, the front may be able to queue further requests without 253 * notifying the back (if the back checks for new requests when it queues 254 * responses). 255 * 256 * When enqueuing requests or responses: 257 * 258 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument 259 * is a boolean return value. True indicates that the receiver requires an 260 * asynchronous notification. 261 * 262 * After dequeuing requests or responses (before sleeping the connection): 263 * 264 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). 265 * The second argument is a boolean return value. True indicates that there 266 * are pending messages on the ring (i.e., the connection should not be put 267 * to sleep). 268 * 269 * These macros will set the req_event/rsp_event field to trigger a 270 * notification on the very next message that is enqueued. If you want to 271 * create batches of work (i.e., only receive a notification after several 272 * messages have been enqueued) then you will need to create a customised 273 * version of the FINAL_CHECK macro in your own code, which sets the event 274 * field appropriately. 275 */ 276 277 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ 278 RING_IDX __old = (_r)->sring->req_prod; \ 279 RING_IDX __new = (_r)->req_prod_pvt; \ 280 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 281 (_r)->sring->req_prod = __new; \ 282 xen_mb(); /* back sees new requests /before/ we check req_event */ \ 283 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ 284 (RING_IDX)(__new - __old)); \ 285 } while (0) 286 287 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ 288 RING_IDX __old = (_r)->sring->rsp_prod; \ 289 RING_IDX __new = (_r)->rsp_prod_pvt; \ 290 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 291 (_r)->sring->rsp_prod = __new; \ 292 xen_mb(); /* front sees new resps /before/ we check rsp_event */ \ 293 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ 294 (RING_IDX)(__new - __old)); \ 295 } while (0) 296 297 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ 298 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 299 if (_work_to_do) break; \ 300 (_r)->sring->req_event = (_r)->req_cons + 1; \ 301 xen_mb(); \ 302 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 303 } while (0) 304 305 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ 306 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 307 if (_work_to_do) break; \ 308 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ 309 xen_mb(); \ 310 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 311 } while (0) 312 313 #endif /* __XEN_PUBLIC_IO_RING_H__ */ 314 315 /* 316 * Local variables: 317 * mode: C 318 * c-set-style: "BSD" 319 * c-basic-offset: 4 320 * tab-width: 4 321 * indent-tabs-mode: nil 322 * End: 323 */ 324