Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/xen/interface/io/ring.h
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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 __CONST_RING_SIZE(_s, _sz) \ 60 (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \ 61 sizeof(((struct _s##_sring *)0)->ring[0]))) 62 /* 63 * The same for passing in an actual pointer instead of a name tag. 64 */ 65 #define __RING_SIZE(_s, _sz) \ 66 (__RD32(((_sz) - __RING_HEADER_SIZE(_s)) / sizeof((_s)->ring[0]))) 67 68 /* 69 * The number of pages needed to support a given number of request/reponse 70 * entries. The entry count is rounded down to the nearest power of two 71 * as required by the ring macros. 72 */ 73 #define __RING_PAGES(_s, _entries) \ 74 ((__RING_HEADER_SIZE(_s) \ 75 + (__RD32(_entries) * sizeof((_s)->ring[0])) \ 76 + PAGE_SIZE - 1) / PAGE_SIZE) 77 78 /* 79 * Macros to make the correct C datatypes for a new kind of ring. 80 * 81 * To make a new ring datatype, you need to have two message structures, 82 * let's say request_t, and response_t already defined. 83 * 84 * In a header where you want the ring datatype declared, you then do: 85 * 86 * DEFINE_RING_TYPES(mytag, request_t, response_t); 87 * 88 * These expand out to give you a set of types, as you can see below. 89 * The most important of these are: 90 * 91 * mytag_sring_t - The shared ring. 92 * mytag_front_ring_t - The 'front' half of the ring. 93 * mytag_back_ring_t - The 'back' half of the ring. 94 * 95 * To initialize a ring in your code you need to know the location and size 96 * of the shared memory area (PAGE_SIZE, for instance). To initialise 97 * the front half: 98 * 99 * mytag_front_ring_t front_ring; 100 * SHARED_RING_INIT((mytag_sring_t *)shared_page); 101 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 102 * 103 * Initializing the back follows similarly (note that only the front 104 * initializes the shared ring): 105 * 106 * mytag_back_ring_t back_ring; 107 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 108 */ 109 110 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ 111 \ 112 /* Shared ring entry */ \ 113 union __name##_sring_entry { \ 114 __req_t req; \ 115 __rsp_t rsp; \ 116 }; \ 117 \ 118 /* Shared ring page */ \ 119 struct __name##_sring { \ 120 RING_IDX req_prod, req_event; \ 121 RING_IDX rsp_prod, rsp_event; \ 122 union { \ 123 struct { \ 124 uint8_t smartpoll_active; \ 125 } netif; \ 126 struct { \ 127 uint8_t msg; \ 128 } tapif_user; \ 129 uint8_t pvt_pad[4]; \ 130 } private; \ 131 uint8_t __pad[44]; \ 132 union __name##_sring_entry ring[1]; /* variable-length */ \ 133 }; \ 134 \ 135 /* "Front" end's private variables */ \ 136 struct __name##_front_ring { \ 137 RING_IDX req_prod_pvt; \ 138 RING_IDX rsp_cons; \ 139 unsigned int nr_ents; \ 140 struct __name##_sring *sring; \ 141 }; \ 142 \ 143 /* "Back" end's private variables */ \ 144 struct __name##_back_ring { \ 145 RING_IDX rsp_prod_pvt; \ 146 RING_IDX req_cons; \ 147 unsigned int nr_ents; \ 148 struct __name##_sring *sring; \ 149 }; \ 150 \ 151 /* Syntactic sugar */ \ 152 typedef struct __name##_sring __name##_sring_t; \ 153 typedef struct __name##_front_ring __name##_front_ring_t; \ 154 typedef struct __name##_back_ring __name##_back_ring_t 155 156 /* 157 * Macros for manipulating rings. 158 * 159 * FRONT_RING_whatever works on the "front end" of a ring: here 160 * requests are pushed on to the ring and responses taken off it. 161 * 162 * BACK_RING_whatever works on the "back end" of a ring: here 163 * requests are taken off the ring and responses put on. 164 * 165 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. 166 * This is OK in 1-for-1 request-response situations where the 167 * requestor (front end) never has more than RING_SIZE()-1 168 * outstanding requests. 169 */ 170 171 /* Initialising empty rings */ 172 #define SHARED_RING_INIT(_s) do { \ 173 (_s)->req_prod = (_s)->rsp_prod = 0; \ 174 (_s)->req_event = (_s)->rsp_event = 1; \ 175 (void)memset((_s)->private.pvt_pad, 0, sizeof((_s)->private.pvt_pad)); \ 176 (void)memset((_s)->__pad, 0, sizeof((_s)->__pad)); \ 177 } while(0) 178 179 #define FRONT_RING_INIT(_r, _s, __size) do { \ 180 (_r)->req_prod_pvt = 0; \ 181 (_r)->rsp_cons = 0; \ 182 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 183 (_r)->sring = (_s); \ 184 } while (0) 185 186 #define BACK_RING_INIT(_r, _s, __size) do { \ 187 (_r)->rsp_prod_pvt = 0; \ 188 (_r)->req_cons = 0; \ 189 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 190 (_r)->sring = (_s); \ 191 } while (0) 192 193 /* Initialize to existing shared indexes -- for recovery */ 194 #define FRONT_RING_ATTACH(_r, _s, __size) do { \ 195 (_r)->sring = (_s); \ 196 (_r)->req_prod_pvt = (_s)->req_prod; \ 197 (_r)->rsp_cons = (_s)->rsp_prod; \ 198 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 199 } while (0) 200 201 #define BACK_RING_ATTACH(_r, _s, __size) do { \ 202 (_r)->sring = (_s); \ 203 (_r)->rsp_prod_pvt = (_s)->rsp_prod; \ 204 (_r)->req_cons = (_s)->req_prod; \ 205 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 206 } while (0) 207 208 /* How big is this ring? */ 209 #define RING_SIZE(_r) \ 210 ((_r)->nr_ents) 211 212 /* Number of free requests (for use on front side only). */ 213 #define RING_FREE_REQUESTS(_r) \ 214 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) 215 216 /* Test if there is an empty slot available on the front ring. 217 * (This is only meaningful from the front. ) 218 */ 219 #define RING_FULL(_r) \ 220 (RING_FREE_REQUESTS(_r) == 0) 221 222 /* Test if there are outstanding messages to be processed on a ring. */ 223 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \ 224 ((_r)->sring->rsp_prod - (_r)->rsp_cons) 225 226 #ifdef __GNUC__ 227 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \ 228 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \ 229 unsigned int rsp = RING_SIZE(_r) - \ 230 ((_r)->req_cons - (_r)->rsp_prod_pvt); \ 231 req < rsp ? req : rsp; \ 232 }) 233 #else 234 /* Same as above, but without the nice GCC ({ ... }) syntax. */ 235 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \ 236 ((((_r)->sring->req_prod - (_r)->req_cons) < \ 237 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \ 238 ((_r)->sring->req_prod - (_r)->req_cons) : \ 239 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) 240 #endif 241 242 /* Direct access to individual ring elements, by index. */ 243 #define RING_GET_REQUEST(_r, _idx) \ 244 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) 245 246 #define RING_GET_RESPONSE(_r, _idx) \ 247 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) 248 249 /* Loop termination condition: Would the specified index overflow the ring? */ 250 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ 251 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) 252 253 #define RING_PUSH_REQUESTS(_r) do { \ 254 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 255 (_r)->sring->req_prod = (_r)->req_prod_pvt; \ 256 } while (0) 257 258 #define RING_PUSH_RESPONSES(_r) do { \ 259 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 260 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ 261 } while (0) 262 263 /* 264 * Notification hold-off (req_event and rsp_event): 265 * 266 * When queueing requests or responses on a shared ring, it may not always be 267 * necessary to notify the remote end. For example, if requests are in flight 268 * in a backend, the front may be able to queue further requests without 269 * notifying the back (if the back checks for new requests when it queues 270 * responses). 271 * 272 * When enqueuing requests or responses: 273 * 274 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument 275 * is a boolean return value. True indicates that the receiver requires an 276 * asynchronous notification. 277 * 278 * After dequeuing requests or responses (before sleeping the connection): 279 * 280 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). 281 * The second argument is a boolean return value. True indicates that there 282 * are pending messages on the ring (i.e., the connection should not be put 283 * to sleep). 284 * 285 * These macros will set the req_event/rsp_event field to trigger a 286 * notification on the very next message that is enqueued. If you want to 287 * create batches of work (i.e., only receive a notification after several 288 * messages have been enqueued) then you will need to create a customised 289 * version of the FINAL_CHECK macro in your own code, which sets the event 290 * field appropriately. 291 */ 292 293 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ 294 RING_IDX __old = (_r)->sring->req_prod; \ 295 RING_IDX __new = (_r)->req_prod_pvt; \ 296 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 297 (_r)->sring->req_prod = __new; \ 298 xen_mb(); /* back sees new requests /before/ we check req_event */ \ 299 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ 300 (RING_IDX)(__new - __old)); \ 301 } while (0) 302 303 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ 304 RING_IDX __old = (_r)->sring->rsp_prod; \ 305 RING_IDX __new = (_r)->rsp_prod_pvt; \ 306 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 307 (_r)->sring->rsp_prod = __new; \ 308 xen_mb(); /* front sees new resps /before/ we check rsp_event */ \ 309 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ 310 (RING_IDX)(__new - __old)); \ 311 } while (0) 312 313 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ 314 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 315 if (_work_to_do) break; \ 316 (_r)->sring->req_event = (_r)->req_cons + 1; \ 317 xen_mb(); \ 318 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 319 } while (0) 320 321 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ 322 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 323 if (_work_to_do) break; \ 324 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ 325 xen_mb(); \ 326 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 327 } while (0) 328 329 #endif /* __XEN_PUBLIC_IO_RING_H__ */ 330 331 /* 332 * Local variables: 333 * mode: C 334 * c-set-style: "BSD" 335 * c-basic-offset: 4 336 * tab-width: 4 337 * indent-tabs-mode: nil 338 * End: 339 */
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