1 /****************************************************************************** 2 * ring.h 3 * 4 * Shared producer-consumer ring macros. 5 * 6 * SPDX-License-Identifier: MIT 7 * 8 * Tim Deegan and Andrew Warfield November 2004. 9 */ 10 11 #ifndef __XEN_PUBLIC_IO_RING_H__ 12 #define __XEN_PUBLIC_IO_RING_H__ 13 14 #include "../xen-compat.h" 15 16 #if __XEN_INTERFACE_VERSION__ < 0x00030208 17 #define xen_mb() mb() 18 #define xen_rmb() rmb() 19 #define xen_wmb() wmb() 20 #endif 21 22 typedef UINT32 RING_IDX; 23 24 /* Round a 32-bit unsigned constant down to the nearest power of two. */ 25 #define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1)) 26 #define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x)) 27 #define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x)) 28 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x)) 29 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x)) 30 31 /* 32 * Calculate size of a shared ring, given the total available space for the 33 * ring and indexes (_sz), and the name tag of the request/response structure. 34 * A ring contains as many entries as will fit, rounded down to the nearest 35 * power of two (so we can mask with (size-1) to loop around). 36 */ 37 #define __CONST_RING_SIZE(_s, _sz) \ 38 (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \ 39 sizeof(((struct _s##_sring *)0)->ring[0]))) 40 /* 41 * The same for passing in an actual pointer instead of a name tag. 42 */ 43 #define __RING_SIZE(_s, _sz) \ 44 (__RD32(((_sz) - (INTN)(_s)->ring + (INTN)(_s)) / sizeof((_s)->ring[0]))) 45 46 /* 47 * Macros to make the correct C datatypes for a new kind of ring. 48 * 49 * To make a new ring datatype, you need to have two message structures, 50 * let's say request_t, and response_t already defined. 51 * 52 * In a header where you want the ring datatype declared, you then do: 53 * 54 * DEFINE_RING_TYPES(mytag, request_t, response_t); 55 * 56 * These expand out to give you a set of types, as you can see below. 57 * The most important of these are: 58 * 59 * mytag_sring_t - The shared ring. 60 * mytag_front_ring_t - The 'front' half of the ring. 61 * mytag_back_ring_t - The 'back' half of the ring. 62 * 63 * To initialize a ring in your code you need to know the location and size 64 * of the shared memory area (PAGE_SIZE, for instance). To initialise 65 * the front half: 66 * 67 * mytag_front_ring_t front_ring; 68 * SHARED_RING_INIT((mytag_sring_t *)shared_page); 69 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 70 * 71 * Initializing the back follows similarly (note that only the front 72 * initializes the shared ring): 73 * 74 * mytag_back_ring_t back_ring; 75 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 76 */ 77 78 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ 79 \ 80 /* Shared ring entry */ \ 81 union __name##_sring_entry { \ 82 __req_t req; \ 83 __rsp_t rsp; \ 84 }; \ 85 \ 86 /* Shared ring page */ \ 87 struct __name##_sring { \ 88 RING_IDX req_prod, req_event; \ 89 RING_IDX rsp_prod, rsp_event; \ 90 union { \ 91 struct { \ 92 UINT8 smartpoll_active; \ 93 } netif; \ 94 struct { \ 95 UINT8 msg; \ 96 } tapif_user; \ 97 UINT8 pvt_pad[4]; \ 98 } private; \ 99 UINT8 __pad[44]; \ 100 union __name##_sring_entry ring[1]; /* variable-length */ \ 101 }; \ 102 \ 103 /* "Front" end's private variables */ \ 104 struct __name##_front_ring { \ 105 RING_IDX req_prod_pvt; \ 106 RING_IDX rsp_cons; \ 107 UINT32 nr_ents; \ 108 struct __name##_sring *sring; \ 109 }; \ 110 \ 111 /* "Back" end's private variables */ \ 112 struct __name##_back_ring { \ 113 RING_IDX rsp_prod_pvt; \ 114 RING_IDX req_cons; \ 115 UINT32 nr_ents; \ 116 struct __name##_sring *sring; \ 117 }; \ 118 \ 119 /* Syntactic sugar */ \ 120 typedef struct __name##_sring __name##_sring_t; \ 121 typedef struct __name##_front_ring __name##_front_ring_t; \ 122 typedef struct __name##_back_ring __name##_back_ring_t 123 124 /* 125 * Macros for manipulating rings. 126 * 127 * FRONT_RING_whatever works on the "front end" of a ring: here 128 * requests are pushed on to the ring and responses taken off it. 129 * 130 * BACK_RING_whatever works on the "back end" of a ring: here 131 * requests are taken off the ring and responses put on. 132 * 133 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. 134 * This is OK in 1-for-1 request-response situations where the 135 * requestor (front end) never has more than RING_SIZE()-1 136 * outstanding requests. 137 */ 138 139 /* Initialising empty rings */ 140 #define SHARED_RING_INIT(_s) do { \ 141 (_s)->req_prod = (_s)->rsp_prod = 0; \ 142 (_s)->req_event = (_s)->rsp_event = 1; \ 143 (VOID)ZeroMem((_s)->private.pvt_pad, sizeof((_s)->private.pvt_pad)); \ 144 (VOID)ZeroMem((_s)->__pad, sizeof((_s)->__pad)); \ 145 } while(0) 146 147 #define FRONT_RING_INIT(_r, _s, __size) do { \ 148 (_r)->req_prod_pvt = 0; \ 149 (_r)->rsp_cons = 0; \ 150 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 151 (_r)->sring = (_s); \ 152 } while (0) 153 154 #define BACK_RING_INIT(_r, _s, __size) do { \ 155 (_r)->rsp_prod_pvt = 0; \ 156 (_r)->req_cons = 0; \ 157 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 158 (_r)->sring = (_s); \ 159 } while (0) 160 161 /* How big is this ring? */ 162 #define RING_SIZE(_r) \ 163 ((_r)->nr_ents) 164 165 /* Number of free requests (for use on front side only). */ 166 #define RING_FREE_REQUESTS(_r) \ 167 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) 168 169 /* Test if there is an empty slot available on the front ring. 170 * (This is only meaningful from the front. ) 171 */ 172 #define RING_FULL(_r) \ 173 (RING_FREE_REQUESTS(_r) == 0) 174 175 /* Test if there are outstanding messages to be processed on a ring. */ 176 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \ 177 ((_r)->sring->rsp_prod - (_r)->rsp_cons) 178 179 #ifdef __GNUC__ 180 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \ 181 UINT32 req = (_r)->sring->req_prod - (_r)->req_cons; \ 182 UINT32 rsp = RING_SIZE(_r) - \ 183 ((_r)->req_cons - (_r)->rsp_prod_pvt); \ 184 req < rsp ? req : rsp; \ 185 }) 186 #else 187 /* Same as above, but without the nice GCC ({ ... }) syntax. */ 188 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \ 189 ((((_r)->sring->req_prod - (_r)->req_cons) < \ 190 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \ 191 ((_r)->sring->req_prod - (_r)->req_cons) : \ 192 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) 193 #endif 194 195 /* Direct access to individual ring elements, by index. */ 196 #define RING_GET_REQUEST(_r, _idx) \ 197 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) 198 199 #define RING_GET_RESPONSE(_r, _idx) \ 200 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) 201 202 /* Loop termination condition: Would the specified index overflow the ring? */ 203 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ 204 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) 205 206 /* Ill-behaved frontend determination: Can there be this many requests? */ 207 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \ 208 (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r)) 209 210 #define RING_PUSH_REQUESTS(_r) do { \ 211 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 212 (_r)->sring->req_prod = (_r)->req_prod_pvt; \ 213 } while (0) 214 215 #define RING_PUSH_RESPONSES(_r) do { \ 216 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 217 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ 218 } while (0) 219 220 /* 221 * Notification hold-off (req_event and rsp_event): 222 * 223 * When queueing requests or responses on a shared ring, it may not always be 224 * necessary to notify the remote end. For example, if requests are in flight 225 * in a backend, the front may be able to queue further requests without 226 * notifying the back (if the back checks for new requests when it queues 227 * responses). 228 * 229 * When enqueuing requests or responses: 230 * 231 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument 232 * is a boolean return value. True indicates that the receiver requires an 233 * asynchronous notification. 234 * 235 * After dequeuing requests or responses (before sleeping the connection): 236 * 237 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). 238 * The second argument is a boolean return value. True indicates that there 239 * are pending messages on the ring (i.e., the connection should not be put 240 * to sleep). 241 * 242 * These macros will set the req_event/rsp_event field to trigger a 243 * notification on the very next message that is enqueued. If you want to 244 * create batches of work (i.e., only receive a notification after several 245 * messages have been enqueued) then you will need to create a customised 246 * version of the FINAL_CHECK macro in your own code, which sets the event 247 * field appropriately. 248 */ 249 250 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ 251 RING_IDX __old = (_r)->sring->req_prod; \ 252 RING_IDX __new = (_r)->req_prod_pvt; \ 253 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 254 (_r)->sring->req_prod = __new; \ 255 xen_mb(); /* back sees new requests /before/ we check req_event */ \ 256 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ 257 (RING_IDX)(__new - __old)); \ 258 } while (0) 259 260 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ 261 RING_IDX __old = (_r)->sring->rsp_prod; \ 262 RING_IDX __new = (_r)->rsp_prod_pvt; \ 263 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 264 (_r)->sring->rsp_prod = __new; \ 265 xen_mb(); /* front sees new resps /before/ we check rsp_event */ \ 266 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ 267 (RING_IDX)(__new - __old)); \ 268 } while (0) 269 270 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ 271 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 272 if (_work_to_do) break; \ 273 (_r)->sring->req_event = (_r)->req_cons + 1; \ 274 xen_mb(); \ 275 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 276 } while (0) 277 278 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ 279 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 280 if (_work_to_do) break; \ 281 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ 282 xen_mb(); \ 283 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 284 } while (0) 285 286 #endif /* __XEN_PUBLIC_IO_RING_H__ */ 287 288 /* 289 * Local variables: 290 * mode: C 291 * c-file-style: "BSD" 292 * c-basic-offset: 4 293 * tab-width: 4 294 * indent-tabs-mode: nil 295 * End: 296 */ 297