1 /****************************************************************************** 2 * ring.h 3 * 4 * Shared producer-consumer ring macros. 5 * 6 * Tim Deegan and Andrew Warfield November 2004. 7 */ 8 9 #ifndef __XEN_PUBLIC_IO_RING_H__ 10 #define __XEN_PUBLIC_IO_RING_H__ 11 12 typedef unsigned int RING_IDX; 13 14 /* Round a 32-bit unsigned constant down to the nearest power of two. */ 15 #define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1)) 16 #define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x)) 17 #define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x)) 18 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x)) 19 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x)) 20 21 /* 22 * Calculate size of a shared ring, given the total available space for the 23 * ring and indexes (_sz), and the name tag of the request/response structure. 24 * A ring contains as many entries as will fit, rounded down to the nearest 25 * power of two (so we can mask with (size-1) to loop around). 26 */ 27 #define __CONST_RING_SIZE(_s, _sz) \ 28 (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \ 29 sizeof(((struct _s##_sring *)0)->ring[0]))) 30 31 /* 32 * The same for passing in an actual pointer instead of a name tag. 33 */ 34 #define __RING_SIZE(_s, _sz) \ 35 (__RD32(((_sz) - (long)&(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0]))) 36 37 /* 38 * Macros to make the correct C datatypes for a new kind of ring. 39 * 40 * To make a new ring datatype, you need to have two message structures, 41 * let's say struct request, and struct response already defined. 42 * 43 * In a header where you want the ring datatype declared, you then do: 44 * 45 * DEFINE_RING_TYPES(mytag, struct request, struct response); 46 * 47 * These expand out to give you a set of types, as you can see below. 48 * The most important of these are: 49 * 50 * struct mytag_sring - The shared ring. 51 * struct mytag_front_ring - The 'front' half of the ring. 52 * struct mytag_back_ring - The 'back' half of the ring. 53 * 54 * To initialize a ring in your code you need to know the location and size 55 * of the shared memory area (PAGE_SIZE, for instance). To initialise 56 * the front half: 57 * 58 * struct mytag_front_ring front_ring; 59 * SHARED_RING_INIT((struct mytag_sring *)shared_page); 60 * FRONT_RING_INIT(&front_ring, (struct mytag_sring *)shared_page, 61 * PAGE_SIZE); 62 * 63 * Initializing the back follows similarly (note that only the front 64 * initializes the shared ring): 65 * 66 * struct mytag_back_ring back_ring; 67 * BACK_RING_INIT(&back_ring, (struct mytag_sring *)shared_page, 68 * PAGE_SIZE); 69 */ 70 71 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ 72 \ 73 /* Shared ring entry */ \ 74 union __name##_sring_entry { \ 75 __req_t req; \ 76 __rsp_t rsp; \ 77 }; \ 78 \ 79 /* Shared ring page */ \ 80 struct __name##_sring { \ 81 RING_IDX req_prod, req_event; \ 82 RING_IDX rsp_prod, rsp_event; \ 83 uint8_t pad[48]; \ 84 union __name##_sring_entry ring[1]; /* variable-length */ \ 85 }; \ 86 \ 87 /* "Front" end's private variables */ \ 88 struct __name##_front_ring { \ 89 RING_IDX req_prod_pvt; \ 90 RING_IDX rsp_cons; \ 91 unsigned int nr_ents; \ 92 struct __name##_sring *sring; \ 93 }; \ 94 \ 95 /* "Back" end's private variables */ \ 96 struct __name##_back_ring { \ 97 RING_IDX rsp_prod_pvt; \ 98 RING_IDX req_cons; \ 99 unsigned int nr_ents; \ 100 struct __name##_sring *sring; \ 101 }; 102 103 /* 104 * Macros for manipulating rings. 105 * 106 * FRONT_RING_whatever works on the "front end" of a ring: here 107 * requests are pushed on to the ring and responses taken off it. 108 * 109 * BACK_RING_whatever works on the "back end" of a ring: here 110 * requests are taken off the ring and responses put on. 111 * 112 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. 113 * This is OK in 1-for-1 request-response situations where the 114 * requestor (front end) never has more than RING_SIZE()-1 115 * outstanding requests. 116 */ 117 118 /* Initialising empty rings */ 119 #define SHARED_RING_INIT(_s) do { \ 120 (_s)->req_prod = (_s)->rsp_prod = 0; \ 121 (_s)->req_event = (_s)->rsp_event = 1; \ 122 memset((_s)->pad, 0, sizeof((_s)->pad)); \ 123 } while(0) 124 125 #define FRONT_RING_INIT(_r, _s, __size) do { \ 126 (_r)->req_prod_pvt = 0; \ 127 (_r)->rsp_cons = 0; \ 128 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 129 (_r)->sring = (_s); \ 130 } while (0) 131 132 #define BACK_RING_INIT(_r, _s, __size) do { \ 133 (_r)->rsp_prod_pvt = 0; \ 134 (_r)->req_cons = 0; \ 135 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 136 (_r)->sring = (_s); \ 137 } while (0) 138 139 /* Initialize to existing shared indexes -- for recovery */ 140 #define FRONT_RING_ATTACH(_r, _s, __size) do { \ 141 (_r)->sring = (_s); \ 142 (_r)->req_prod_pvt = (_s)->req_prod; \ 143 (_r)->rsp_cons = (_s)->rsp_prod; \ 144 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 145 } while (0) 146 147 #define BACK_RING_ATTACH(_r, _s, __size) do { \ 148 (_r)->sring = (_s); \ 149 (_r)->rsp_prod_pvt = (_s)->rsp_prod; \ 150 (_r)->req_cons = (_s)->req_prod; \ 151 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 152 } while (0) 153 154 /* How big is this ring? */ 155 #define RING_SIZE(_r) \ 156 ((_r)->nr_ents) 157 158 /* Number of free requests (for use on front side only). */ 159 #define RING_FREE_REQUESTS(_r) \ 160 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) 161 162 /* Test if there is an empty slot available on the front ring. 163 * (This is only meaningful from the front. ) 164 */ 165 #define RING_FULL(_r) \ 166 (RING_FREE_REQUESTS(_r) == 0) 167 168 /* Test if there are outstanding messages to be processed on a ring. */ 169 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \ 170 ((_r)->sring->rsp_prod - (_r)->rsp_cons) 171 172 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \ 173 ({ \ 174 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \ 175 unsigned int rsp = RING_SIZE(_r) - \ 176 ((_r)->req_cons - (_r)->rsp_prod_pvt); \ 177 req < rsp ? req : rsp; \ 178 }) 179 180 /* Direct access to individual ring elements, by index. */ 181 #define RING_GET_REQUEST(_r, _idx) \ 182 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) 183 184 #define RING_GET_RESPONSE(_r, _idx) \ 185 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) 186 187 /* Loop termination condition: Would the specified index overflow the ring? */ 188 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ 189 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) 190 191 /* Ill-behaved frontend determination: Can there be this many requests? */ 192 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \ 193 (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r)) 194 195 196 #define RING_PUSH_REQUESTS(_r) do { \ 197 wmb(); /* back sees requests /before/ updated producer index */ \ 198 (_r)->sring->req_prod = (_r)->req_prod_pvt; \ 199 } while (0) 200 201 #define RING_PUSH_RESPONSES(_r) do { \ 202 wmb(); /* front sees responses /before/ updated producer index */ \ 203 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ 204 } while (0) 205 206 /* 207 * Notification hold-off (req_event and rsp_event): 208 * 209 * When queueing requests or responses on a shared ring, it may not always be 210 * necessary to notify the remote end. For example, if requests are in flight 211 * in a backend, the front may be able to queue further requests without 212 * notifying the back (if the back checks for new requests when it queues 213 * responses). 214 * 215 * When enqueuing requests or responses: 216 * 217 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument 218 * is a boolean return value. True indicates that the receiver requires an 219 * asynchronous notification. 220 * 221 * After dequeuing requests or responses (before sleeping the connection): 222 * 223 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). 224 * The second argument is a boolean return value. True indicates that there 225 * are pending messages on the ring (i.e., the connection should not be put 226 * to sleep). 227 * 228 * These macros will set the req_event/rsp_event field to trigger a 229 * notification on the very next message that is enqueued. If you want to 230 * create batches of work (i.e., only receive a notification after several 231 * messages have been enqueued) then you will need to create a customised 232 * version of the FINAL_CHECK macro in your own code, which sets the event 233 * field appropriately. 234 */ 235 236 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ 237 RING_IDX __old = (_r)->sring->req_prod; \ 238 RING_IDX __new = (_r)->req_prod_pvt; \ 239 wmb(); /* back sees requests /before/ updated producer index */ \ 240 (_r)->sring->req_prod = __new; \ 241 mb(); /* back sees new requests /before/ we check req_event */ \ 242 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ 243 (RING_IDX)(__new - __old)); \ 244 } while (0) 245 246 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ 247 RING_IDX __old = (_r)->sring->rsp_prod; \ 248 RING_IDX __new = (_r)->rsp_prod_pvt; \ 249 wmb(); /* front sees responses /before/ updated producer index */ \ 250 (_r)->sring->rsp_prod = __new; \ 251 mb(); /* front sees new responses /before/ we check rsp_event */ \ 252 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ 253 (RING_IDX)(__new - __old)); \ 254 } while (0) 255 256 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ 257 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 258 if (_work_to_do) break; \ 259 (_r)->sring->req_event = (_r)->req_cons + 1; \ 260 mb(); \ 261 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 262 } while (0) 263 264 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ 265 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 266 if (_work_to_do) break; \ 267 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ 268 mb(); \ 269 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 270 } while (0) 271 272 #endif /* __XEN_PUBLIC_IO_RING_H__ */ 273