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 UINT32 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 * Calculate size of a shared ring, given the total available space for the 49 * ring and indexes (_sz), and the name tag of the request/response structure. 50 * A ring contains as many entries as will fit, rounded down to the nearest 51 * power of two (so we can mask with (size-1) to loop around). 52 */ 53 #define __CONST_RING_SIZE(_s, _sz) \ 54 (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \ 55 sizeof(((struct _s##_sring *)0)->ring[0]))) 56 /* 57 * The same for passing in an actual pointer instead of a name tag. 58 */ 59 #define __RING_SIZE(_s, _sz) \ 60 (__RD32(((_sz) - (INTN)(_s)->ring + (INTN)(_s)) / sizeof((_s)->ring[0]))) 61 62 /* 63 * Macros to make the correct C datatypes for a new kind of ring. 64 * 65 * To make a new ring datatype, you need to have two message structures, 66 * let's say request_t, and response_t already defined. 67 * 68 * In a header where you want the ring datatype declared, you then do: 69 * 70 * DEFINE_RING_TYPES(mytag, request_t, response_t); 71 * 72 * These expand out to give you a set of types, as you can see below. 73 * The most important of these are: 74 * 75 * mytag_sring_t - The shared ring. 76 * mytag_front_ring_t - The 'front' half of the ring. 77 * mytag_back_ring_t - The 'back' half of the ring. 78 * 79 * To initialize a ring in your code you need to know the location and size 80 * of the shared memory area (PAGE_SIZE, for instance). To initialise 81 * the front half: 82 * 83 * mytag_front_ring_t front_ring; 84 * SHARED_RING_INIT((mytag_sring_t *)shared_page); 85 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 86 * 87 * Initializing the back follows similarly (note that only the front 88 * initializes the shared ring): 89 * 90 * mytag_back_ring_t back_ring; 91 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 92 */ 93 94 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ 95 \ 96 /* Shared ring entry */ \ 97 union __name##_sring_entry { \ 98 __req_t req; \ 99 __rsp_t rsp; \ 100 }; \ 101 \ 102 /* Shared ring page */ \ 103 struct __name##_sring { \ 104 RING_IDX req_prod, req_event; \ 105 RING_IDX rsp_prod, rsp_event; \ 106 union { \ 107 struct { \ 108 UINT8 smartpoll_active; \ 109 } netif; \ 110 struct { \ 111 UINT8 msg; \ 112 } tapif_user; \ 113 UINT8 pvt_pad[4]; \ 114 } private; \ 115 UINT8 __pad[44]; \ 116 union __name##_sring_entry ring[1]; /* variable-length */ \ 117 }; \ 118 \ 119 /* "Front" end's private variables */ \ 120 struct __name##_front_ring { \ 121 RING_IDX req_prod_pvt; \ 122 RING_IDX rsp_cons; \ 123 UINT32 nr_ents; \ 124 struct __name##_sring *sring; \ 125 }; \ 126 \ 127 /* "Back" end's private variables */ \ 128 struct __name##_back_ring { \ 129 RING_IDX rsp_prod_pvt; \ 130 RING_IDX req_cons; \ 131 UINT32 nr_ents; \ 132 struct __name##_sring *sring; \ 133 }; \ 134 \ 135 /* Syntactic sugar */ \ 136 typedef struct __name##_sring __name##_sring_t; \ 137 typedef struct __name##_front_ring __name##_front_ring_t; \ 138 typedef struct __name##_back_ring __name##_back_ring_t 139 140 /* 141 * Macros for manipulating rings. 142 * 143 * FRONT_RING_whatever works on the "front end" of a ring: here 144 * requests are pushed on to the ring and responses taken off it. 145 * 146 * BACK_RING_whatever works on the "back end" of a ring: here 147 * requests are taken off the ring and responses put on. 148 * 149 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. 150 * This is OK in 1-for-1 request-response situations where the 151 * requestor (front end) never has more than RING_SIZE()-1 152 * outstanding requests. 153 */ 154 155 /* Initialising empty rings */ 156 #define SHARED_RING_INIT(_s) do { \ 157 (_s)->req_prod = (_s)->rsp_prod = 0; \ 158 (_s)->req_event = (_s)->rsp_event = 1; \ 159 (VOID)ZeroMem((_s)->private.pvt_pad, sizeof((_s)->private.pvt_pad)); \ 160 (VOID)ZeroMem((_s)->__pad, 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 /* How big is this ring? */ 178 #define RING_SIZE(_r) \ 179 ((_r)->nr_ents) 180 181 /* Number of free requests (for use on front side only). */ 182 #define RING_FREE_REQUESTS(_r) \ 183 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) 184 185 /* Test if there is an empty slot available on the front ring. 186 * (This is only meaningful from the front. ) 187 */ 188 #define RING_FULL(_r) \ 189 (RING_FREE_REQUESTS(_r) == 0) 190 191 /* Test if there are outstanding messages to be processed on a ring. */ 192 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \ 193 ((_r)->sring->rsp_prod - (_r)->rsp_cons) 194 195 #ifdef __GNUC__ 196 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \ 197 UINT32 req = (_r)->sring->req_prod - (_r)->req_cons; \ 198 UINT32 rsp = RING_SIZE(_r) - \ 199 ((_r)->req_cons - (_r)->rsp_prod_pvt); \ 200 req < rsp ? req : rsp; \ 201 }) 202 #else 203 /* Same as above, but without the nice GCC ({ ... }) syntax. */ 204 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \ 205 ((((_r)->sring->req_prod - (_r)->req_cons) < \ 206 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \ 207 ((_r)->sring->req_prod - (_r)->req_cons) : \ 208 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) 209 #endif 210 211 /* Direct access to individual ring elements, by index. */ 212 #define RING_GET_REQUEST(_r, _idx) \ 213 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) 214 215 #define RING_GET_RESPONSE(_r, _idx) \ 216 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) 217 218 /* Loop termination condition: Would the specified index overflow the ring? */ 219 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ 220 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) 221 222 /* Ill-behaved frontend determination: Can there be this many requests? */ 223 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \ 224 (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r)) 225 226 #define RING_PUSH_REQUESTS(_r) do { \ 227 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 228 (_r)->sring->req_prod = (_r)->req_prod_pvt; \ 229 } while (0) 230 231 #define RING_PUSH_RESPONSES(_r) do { \ 232 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 233 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ 234 } while (0) 235 236 /* 237 * Notification hold-off (req_event and rsp_event): 238 * 239 * When queueing requests or responses on a shared ring, it may not always be 240 * necessary to notify the remote end. For example, if requests are in flight 241 * in a backend, the front may be able to queue further requests without 242 * notifying the back (if the back checks for new requests when it queues 243 * responses). 244 * 245 * When enqueuing requests or responses: 246 * 247 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument 248 * is a boolean return value. True indicates that the receiver requires an 249 * asynchronous notification. 250 * 251 * After dequeuing requests or responses (before sleeping the connection): 252 * 253 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). 254 * The second argument is a boolean return value. True indicates that there 255 * are pending messages on the ring (i.e., the connection should not be put 256 * to sleep). 257 * 258 * These macros will set the req_event/rsp_event field to trigger a 259 * notification on the very next message that is enqueued. If you want to 260 * create batches of work (i.e., only receive a notification after several 261 * messages have been enqueued) then you will need to create a customised 262 * version of the FINAL_CHECK macro in your own code, which sets the event 263 * field appropriately. 264 */ 265 266 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ 267 RING_IDX __old = (_r)->sring->req_prod; \ 268 RING_IDX __new = (_r)->req_prod_pvt; \ 269 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 270 (_r)->sring->req_prod = __new; \ 271 xen_mb(); /* back sees new requests /before/ we check req_event */ \ 272 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ 273 (RING_IDX)(__new - __old)); \ 274 } while (0) 275 276 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ 277 RING_IDX __old = (_r)->sring->rsp_prod; \ 278 RING_IDX __new = (_r)->rsp_prod_pvt; \ 279 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 280 (_r)->sring->rsp_prod = __new; \ 281 xen_mb(); /* front sees new resps /before/ we check rsp_event */ \ 282 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ 283 (RING_IDX)(__new - __old)); \ 284 } while (0) 285 286 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ 287 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 288 if (_work_to_do) break; \ 289 (_r)->sring->req_event = (_r)->req_cons + 1; \ 290 xen_mb(); \ 291 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 292 } while (0) 293 294 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ 295 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 296 if (_work_to_do) break; \ 297 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ 298 xen_mb(); \ 299 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 300 } while (0) 301 302 #endif /* __XEN_PUBLIC_IO_RING_H__ */ 303 304 /* 305 * Local variables: 306 * mode: C 307 * c-file-style: "BSD" 308 * c-basic-offset: 4 309 * tab-width: 4 310 * indent-tabs-mode: nil 311 * End: 312 */ 313
