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