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