1/* SPDX-License-Identifier: MIT 2 * 3 * ring.h 4 * 5 * Shared producer-consumer ring macros. 6 * 7 * Tim Deegan and Andrew Warfield November 2004. 8 */ 9 10#ifndef __XEN_PUBLIC_IO_RING_H__ 11#define __XEN_PUBLIC_IO_RING_H__ 12 13/* 14 * When #include'ing this header, you need to provide the following 15 * declaration upfront: 16 * - standard integers types (u8, u16, etc) 17 * They are provided by stdint.h of the standard headers. 18 * 19 * In addition, if you intend to use the FLEX macros, you also need to 20 * provide the following, before invoking the FLEX macros: 21 * - size_t 22 * - memcpy 23 * - grant_ref_t 24 * These declarations are provided by string.h of the standard headers, 25 * and grant_table.h from the Xen public headers. 26 */ 27 28#include <xen/interface/grant_table.h> 29 30typedef unsigned int RING_IDX; 31 32/* Round a 32-bit unsigned constant down to the nearest power of two. */ 33#define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1)) 34#define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x) >> 2) << 2 : __RD2(_x)) 35#define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x) >> 4) << 4 : __RD4(_x)) 36#define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x) >> 8) << 8 : __RD8(_x)) 37#define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x) >> 16) << 16 : __RD16(_x)) 38 39/* 40 * Calculate size of a shared ring, given the total available space for the 41 * ring and indexes (_sz), and the name tag of the request/response structure. 42 * A ring contains as many entries as will fit, rounded down to the nearest 43 * power of two (so we can mask with (size-1) to loop around). 44 */ 45#define __CONST_RING_SIZE(_s, _sz) \ 46 (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \ 47 sizeof(((struct _s##_sring *)0)->ring[0]))) 48/* 49 * The same for passing in an actual pointer instead of a name tag. 50 */ 51#define __RING_SIZE(_s, _sz) \ 52 (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0]))) 53 54/* 55 * Macros to make the correct C datatypes for a new kind of ring. 56 * 57 * To make a new ring datatype, you need to have two message structures, 58 * let's say request_t, and response_t already defined. 59 * 60 * In a header where you want the ring datatype declared, you then do: 61 * 62 * DEFINE_RING_TYPES(mytag, request_t, response_t); 63 * 64 * These expand out to give you a set of types, as you can see below. 65 * The most important of these are: 66 * 67 * mytag_sring_t - The shared ring. 68 * mytag_front_ring_t - The 'front' half of the ring. 69 * mytag_back_ring_t - The 'back' half of the ring. 70 * 71 * To initialize a ring in your code you need to know the location and size 72 * of the shared memory area (PAGE_SIZE, for instance). To initialise 73 * the front half: 74 * 75 * mytag_front_ring_t front_ring; 76 * SHARED_RING_INIT((mytag_sring_t *)shared_page); 77 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 78 * 79 * Initializing the back follows similarly (note that only the front 80 * initializes the shared ring): 81 * 82 * mytag_back_ring_t back_ring; 83 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); 84 */ 85 86#define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ 87 \ 88/* Shared ring entry */ \ 89union __name##_sring_entry { \ 90 __req_t req; \ 91 __rsp_t rsp; \ 92}; \ 93 \ 94/* Shared ring page */ \ 95struct __name##_sring { \ 96 RING_IDX req_prod, req_event; \ 97 RING_IDX rsp_prod, rsp_event; \ 98 union { \ 99 struct { \ 100 u8 smartpoll_active; \ 101 } netif; \ 102 struct { \ 103 u8 msg; \ 104 } tapif_user; \ 105 u8 pvt_pad[4]; \ 106 } pvt; \ 107 u8 __pad[44]; \ 108 union __name##_sring_entry ring[1]; /* variable-length */ \ 109}; \ 110 \ 111/* "Front" end's private variables */ \ 112struct __name##_front_ring { \ 113 RING_IDX req_prod_pvt; \ 114 RING_IDX rsp_cons; \ 115 unsigned int nr_ents; \ 116 struct __name##_sring *sring; \ 117}; \ 118 \ 119/* "Back" end's private variables */ \ 120struct __name##_back_ring { \ 121 RING_IDX rsp_prod_pvt; \ 122 RING_IDX req_cons; \ 123 unsigned int nr_ents; \ 124 struct __name##_sring *sring; \ 125}; \ 126 \ 127/* Syntactic sugar */ \ 128typedef struct __name##_sring __name##_sring_t; \ 129typedef struct __name##_front_ring __name##_front_ring_t; \ 130typedef struct __name##_back_ring __name##_back_ring_t 131 132/* 133 * Macros for manipulating rings. 134 * 135 * FRONT_RING_whatever works on the "front end" of a ring: here 136 * requests are pushed on to the ring and responses taken off it. 137 * 138 * BACK_RING_whatever works on the "back end" of a ring: here 139 * requests are taken off the ring and responses put on. 140 * 141 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. 142 * This is OK in 1-for-1 request-response situations where the 143 * requestor (front end) never has more than RING_SIZE()-1 144 * outstanding requests. 145 */ 146 147/* Initialising empty rings */ 148#define SHARED_RING_INIT(_s) do { \ 149 (_s)->req_prod = (_s)->rsp_prod = 0; \ 150 (_s)->req_event = (_s)->rsp_event = 1; \ 151 (void)memset((_s)->pvt.pvt_pad, 0, sizeof((_s)->pvt.pvt_pad)); \ 152 (void)memset((_s)->__pad, 0, sizeof((_s)->__pad)); \ 153} while (0) 154 155#define FRONT_RING_INIT(_r, _s, __size) do { \ 156 (_r)->req_prod_pvt = 0; \ 157 (_r)->rsp_cons = 0; \ 158 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 159 (_r)->sring = (_s); \ 160} while (0) 161 162#define BACK_RING_INIT(_r, _s, __size) do { \ 163 (_r)->rsp_prod_pvt = 0; \ 164 (_r)->req_cons = 0; \ 165 (_r)->nr_ents = __RING_SIZE(_s, __size); \ 166 (_r)->sring = (_s); \ 167} while (0) 168 169/* How big is this ring? */ 170#define RING_SIZE(_r) \ 171 ((_r)->nr_ents) 172 173/* Number of free requests (for use on front side only). */ 174#define RING_FREE_REQUESTS(_r) \ 175 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) 176 177/* Test if there is an empty slot available on the front ring. 178 * (This is only meaningful from the front. ) 179 */ 180#define RING_FULL(_r) \ 181 (RING_FREE_REQUESTS(_r) == 0) 182 183/* Test if there are outstanding messages to be processed on a ring. */ 184#define RING_HAS_UNCONSUMED_RESPONSES(_r) \ 185 ((_r)->sring->rsp_prod - (_r)->rsp_cons) 186 187#ifdef __GNUC__ 188#define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \ 189 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \ 190 unsigned int rsp = RING_SIZE(_r) - \ 191 ((_r)->req_cons - (_r)->rsp_prod_pvt); \ 192 req < rsp ? req : rsp; \ 193}) 194#else 195/* Same as above, but without the nice GCC ({ ... }) syntax. */ 196#define RING_HAS_UNCONSUMED_REQUESTS(_r) \ 197 ((((_r)->sring->req_prod - (_r)->req_cons) < \ 198 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \ 199 ((_r)->sring->req_prod - (_r)->req_cons) : \ 200 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) 201#endif 202 203/* Direct access to individual ring elements, by index. */ 204#define RING_GET_REQUEST(_r, _idx) \ 205 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) 206 207/* 208 * Get a local copy of a request. 209 * 210 * Use this in preference to RING_GET_REQUEST() so all processing is 211 * done on a local copy that cannot be modified by the other end. 212 * 213 * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this 214 * to be ineffective where _req is a struct which consists of only bitfields. 215 */ 216#define RING_COPY_REQUEST(_r, _idx, _req) do { \ 217 /* Use volatile to force the copy into _req. */ \ 218 *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx); \ 219} while (0) 220 221#define RING_GET_RESPONSE(_r, _idx) \ 222 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) 223 224/* Loop termination condition: Would the specified index overflow the ring? */ 225#define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ 226 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) 227 228/* Ill-behaved frontend determination: Can there be this many requests? */ 229#define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \ 230 (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r)) 231 232#define RING_PUSH_REQUESTS(_r) do { \ 233 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 234 (_r)->sring->req_prod = (_r)->req_prod_pvt; \ 235} while (0) 236 237#define RING_PUSH_RESPONSES(_r) do { \ 238 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 239 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ 240} while (0) 241 242/* 243 * Notification hold-off (req_event and rsp_event): 244 * 245 * When queueing requests or responses on a shared ring, it may not always be 246 * necessary to notify the remote end. For example, if requests are in flight 247 * in a backend, the front may be able to queue further requests without 248 * notifying the back (if the back checks for new requests when it queues 249 * responses). 250 * 251 * When enqueuing requests or responses: 252 * 253 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument 254 * is a boolean return value. True indicates that the receiver requires an 255 * asynchronous notification. 256 * 257 * After dequeuing requests or responses (before sleeping the connection): 258 * 259 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). 260 * The second argument is a boolean return value. True indicates that there 261 * are pending messages on the ring (i.e., the connection should not be put 262 * to sleep). 263 * 264 * These macros will set the req_event/rsp_event field to trigger a 265 * notification on the very next message that is enqueued. If you want to 266 * create batches of work (i.e., only receive a notification after several 267 * messages have been enqueued) then you will need to create a customised 268 * version of the FINAL_CHECK macro in your own code, which sets the event 269 * field appropriately. 270 */ 271 272#define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ 273 RING_IDX __old = (_r)->sring->req_prod; \ 274 RING_IDX __new = (_r)->req_prod_pvt; \ 275 xen_wmb(); /* back sees requests /before/ updated producer index */ \ 276 (_r)->sring->req_prod = __new; \ 277 xen_mb(); /* back sees new requests /before/ we check req_event */ \ 278 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ 279 (RING_IDX)(__new - __old)); \ 280} while (0) 281 282#define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ 283 RING_IDX __old = (_r)->sring->rsp_prod; \ 284 RING_IDX __new = (_r)->rsp_prod_pvt; \ 285 xen_wmb(); /* front sees resps /before/ updated producer index */ \ 286 (_r)->sring->rsp_prod = __new; \ 287 xen_mb(); /* front sees new resps /before/ we check rsp_event */ \ 288 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ 289 (RING_IDX)(__new - __old)); \ 290} while (0) 291 292#define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ 293 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 294 if (_work_to_do) \ 295 break; \ 296 (_r)->sring->req_event = (_r)->req_cons + 1; \ 297 xen_mb(); \ 298 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ 299} while (0) 300 301#define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ 302 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 303 if (_work_to_do) \ 304 break; \ 305 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ 306 xen_mb(); \ 307 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ 308} while (0) 309 310/* 311 * DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and 312 * functions to check if there is data on the ring, and to read and 313 * write to them. 314 * 315 * DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but 316 * does not define the indexes page. As different protocols can have 317 * extensions to the basic format, this macro allow them to define their 318 * own struct. 319 * 320 * XEN_FLEX_RING_SIZE 321 * Convenience macro to calculate the size of one of the two rings 322 * from the overall order. 323 * 324 * $NAME_mask 325 * Function to apply the size mask to an index, to reduce the index 326 * within the range [0-size]. 327 * 328 * $NAME_read_packet 329 * Function to read data from the ring. The amount of data to read is 330 * specified by the "size" argument. 331 * 332 * $NAME_write_packet 333 * Function to write data to the ring. The amount of data to write is 334 * specified by the "size" argument. 335 * 336 * $NAME_get_ring_ptr 337 * Convenience function that returns a pointer to read/write to the 338 * ring at the right location. 339 * 340 * $NAME_data_intf 341 * Indexes page, shared between frontend and backend. It also 342 * contains the array of grant refs. 343 * 344 * $NAME_queued 345 * Function to calculate how many bytes are currently on the ring, 346 * ready to be read. It can also be used to calculate how much free 347 * space is currently on the ring (XEN_FLEX_RING_SIZE() - 348 * $NAME_queued()). 349 */ 350 351#ifndef XEN_PAGE_SHIFT 352/* The PAGE_SIZE for ring protocols and hypercall interfaces is always 353 * 4K, regardless of the architecture, and page granularity chosen by 354 * operating systems. 355 */ 356#define XEN_PAGE_SHIFT 12 357#endif 358#define XEN_FLEX_RING_SIZE(order) \ 359 (1UL << ((order) + XEN_PAGE_SHIFT - 1)) 360 361#define DEFINE_XEN_FLEX_RING(name) \ 362static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size) \ 363{ \ 364 return idx & (ring_size - 1); \ 365} \ 366 \ 367static inline unsigned char *name##_get_ring_ptr(unsigned char *buf, \ 368 RING_IDX idx, \ 369 RING_IDX ring_size) \ 370{ \ 371 return buf + name##_mask(idx, ring_size); \ 372} \ 373 \ 374static inline void name##_read_packet(void *opaque, \ 375 const unsigned char *buf, \ 376 size_t size, \ 377 RING_IDX masked_prod, \ 378 RING_IDX *masked_cons, \ 379 RING_IDX ring_size) \ 380{ \ 381 if (*masked_cons < masked_prod || \ 382 size <= ring_size - *masked_cons) { \ 383 memcpy(opaque, buf + *masked_cons, size); \ 384 } else { \ 385 memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons); \ 386 memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf, \ 387 size - (ring_size - *masked_cons)); \ 388 } \ 389 *masked_cons = name##_mask(*masked_cons + size, ring_size); \ 390} \ 391 \ 392static inline void name##_write_packet(unsigned char *buf, \ 393 const void *opaque, \ 394 size_t size, \ 395 RING_IDX *masked_prod, \ 396 RING_IDX masked_cons, \ 397 RING_IDX ring_size) \ 398{ \ 399 if (*masked_prod < masked_cons || \ 400 size <= ring_size - *masked_prod) { \ 401 memcpy(buf + *masked_prod, opaque, size); \ 402 } else { \ 403 memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod); \ 404 memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod), \ 405 size - (ring_size - *masked_prod)); \ 406 } \ 407 *masked_prod = name##_mask(*masked_prod + size, ring_size); \ 408} \ 409 \ 410static inline RING_IDX name##_queued(RING_IDX prod, \ 411 RING_IDX cons, \ 412 RING_IDX ring_size) \ 413{ \ 414 RING_IDX size; \ 415 \ 416 if (prod == cons) \ 417 return 0; \ 418 \ 419 prod = name##_mask(prod, ring_size); \ 420 cons = name##_mask(cons, ring_size); \ 421 \ 422 if (prod == cons) \ 423 return ring_size; \ 424 \ 425 if (prod > cons) \ 426 size = prod - cons; \ 427 else \ 428 size = ring_size - (cons - prod); \ 429 return size; \ 430} \ 431 \ 432struct name##_data { \ 433 unsigned char *in; /* half of the allocation */ \ 434 unsigned char *out; /* half of the allocation */ \ 435} 436 437#define DEFINE_XEN_FLEX_RING_AND_INTF(name) \ 438struct name##_data_intf { \ 439 RING_IDX in_cons, in_prod; \ 440 \ 441 u8 pad1[56]; \ 442 \ 443 RING_IDX out_cons, out_prod; \ 444 \ 445 u8 pad2[56]; \ 446 \ 447 RING_IDX ring_order; \ 448 grant_ref_t ref[]; \ 449}; \ 450DEFINE_XEN_FLEX_RING(name) 451 452#endif /* __XEN_PUBLIC_IO_RING_H__ */ 453 454/* 455 * Local variables: 456 * mode: C 457 * c-file-style: "BSD" 458 * c-basic-offset: 4 459 * tab-width: 8 460 * indent-tabs-mode: nil 461 * End: 462 */ 463