| 1 | /* $NetBSD: ring.h,v 1.3 2016/01/06 15:28:40 bouyer Exp $ */ |
| 2 | /****************************************************************************** |
| 3 | * ring.h |
| 4 | * |
| 5 | * Shared producer-consumer ring macros. |
| 6 | * |
| 7 | * Permission is hereby granted, free of charge, to any person obtaining a copy |
| 8 | * of this software and associated documentation files (the "Software"), to |
| 9 | * deal in the Software without restriction, including without limitation the |
| 10 | * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or |
| 11 | * sell copies of the Software, and to permit persons to whom the Software is |
| 12 | * furnished to do so, subject to the following conditions: |
| 13 | * |
| 14 | * The above copyright notice and this permission notice shall be included in |
| 15 | * all copies or substantial portions of the Software. |
| 16 | * |
| 17 | * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
| 18 | * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
| 19 | * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE |
| 20 | * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
| 21 | * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING |
| 22 | * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER |
| 23 | * DEALINGS IN THE SOFTWARE. |
| 24 | * |
| 25 | * Tim Deegan and Andrew Warfield November 2004. |
| 26 | */ |
| 27 | |
| 28 | #ifndef __XEN_PUBLIC_IO_RING_H__ |
| 29 | #define __XEN_PUBLIC_IO_RING_H__ |
| 30 | |
| 31 | #include "../xen-compat.h" |
| 32 | |
| 33 | #if __XEN_INTERFACE_VERSION__ < 0x00030208 |
| 34 | #if defined(__Linux__) |
| 35 | #define xen_mb() mb() |
| 36 | #define xen_rmb() rmb() |
| 37 | #define xen_wmb() wmb() |
| 38 | #endif |
| 39 | #endif |
| 40 | |
| 41 | #if defined(__NetBSD__) |
| 42 | #define xen_mb() x86_mfence() |
| 43 | #define xen_rmb() x86_lfence() |
| 44 | #define xen_wmb() x86_sfence() |
| 45 | #endif |
| 46 | |
| 47 | typedef unsigned int RING_IDX; |
| 48 | |
| 49 | /* Round a 32-bit unsigned constant down to the nearest power of two. */ |
| 50 | #define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1)) |
| 51 | #define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x)) |
| 52 | #define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x)) |
| 53 | #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x)) |
| 54 | #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x)) |
| 55 | |
| 56 | /* |
| 57 | * Calculate size of a shared ring, given the total available space for the |
| 58 | * ring and indexes (_sz), and the name tag of the request/response structure. |
| 59 | * A ring contains as many entries as will fit, rounded down to the nearest |
| 60 | * power of two (so we can mask with (size-1) to loop around). |
| 61 | */ |
| 62 | #define __CONST_RING_SIZE(_s, _sz) \ |
| 63 | (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \ |
| 64 | sizeof(((struct _s##_sring *)0)->ring[0]))) |
| 65 | /* |
| 66 | * The same for passing in an actual pointer instead of a name tag. |
| 67 | */ |
| 68 | #define __RING_SIZE(_s, _sz) \ |
| 69 | (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0]))) |
| 70 | |
| 71 | /* |
| 72 | * Macros to make the correct C datatypes for a new kind of ring. |
| 73 | * |
| 74 | * To make a new ring datatype, you need to have two message structures, |
| 75 | * let's say request_t, and response_t already defined. |
| 76 | * |
| 77 | * In a header where you want the ring datatype declared, you then do: |
| 78 | * |
| 79 | * DEFINE_RING_TYPES(mytag, request_t, response_t); |
| 80 | * |
| 81 | * These expand out to give you a set of types, as you can see below. |
| 82 | * The most important of these are: |
| 83 | * |
| 84 | * mytag_sring_t - The shared ring. |
| 85 | * mytag_front_ring_t - The 'front' half of the ring. |
| 86 | * mytag_back_ring_t - The 'back' half of the ring. |
| 87 | * |
| 88 | * To initialize a ring in your code you need to know the location and size |
| 89 | * of the shared memory area (PAGE_SIZE, for instance). To initialise |
| 90 | * the front half: |
| 91 | * |
| 92 | * mytag_front_ring_t front_ring; |
| 93 | * SHARED_RING_INIT((mytag_sring_t *)shared_page); |
| 94 | * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); |
| 95 | * |
| 96 | * Initializing the back follows similarly (note that only the front |
| 97 | * initializes the shared ring): |
| 98 | * |
| 99 | * mytag_back_ring_t back_ring; |
| 100 | * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE); |
| 101 | */ |
| 102 | |
| 103 | #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ |
| 104 | \ |
| 105 | /* Shared ring entry */ \ |
| 106 | union __name##_sring_entry { \ |
| 107 | __req_t req; \ |
| 108 | __rsp_t rsp; \ |
| 109 | }; \ |
| 110 | \ |
| 111 | /* Shared ring page */ \ |
| 112 | struct __name##_sring { \ |
| 113 | RING_IDX req_prod, req_event; \ |
| 114 | RING_IDX rsp_prod, rsp_event; \ |
| 115 | union { \ |
| 116 | struct { \ |
| 117 | uint8_t smartpoll_active; \ |
| 118 | } netif; \ |
| 119 | struct { \ |
| 120 | uint8_t msg; \ |
| 121 | } tapif_user; \ |
| 122 | uint8_t pvt_pad[4]; \ |
| 123 | } private; \ |
| 124 | uint8_t __pad[44]; \ |
| 125 | union __name##_sring_entry ring[1]; /* variable-length */ \ |
| 126 | }; \ |
| 127 | \ |
| 128 | /* "Front" end's private variables */ \ |
| 129 | struct __name##_front_ring { \ |
| 130 | RING_IDX req_prod_pvt; \ |
| 131 | RING_IDX rsp_cons; \ |
| 132 | unsigned int nr_ents; \ |
| 133 | struct __name##_sring *sring; \ |
| 134 | }; \ |
| 135 | \ |
| 136 | /* "Back" end's private variables */ \ |
| 137 | struct __name##_back_ring { \ |
| 138 | RING_IDX rsp_prod_pvt; \ |
| 139 | RING_IDX req_cons; \ |
| 140 | unsigned int nr_ents; \ |
| 141 | struct __name##_sring *sring; \ |
| 142 | }; \ |
| 143 | \ |
| 144 | /* Syntactic sugar */ \ |
| 145 | typedef struct __name##_sring __name##_sring_t; \ |
| 146 | typedef struct __name##_front_ring __name##_front_ring_t; \ |
| 147 | typedef struct __name##_back_ring __name##_back_ring_t |
| 148 | |
| 149 | /* |
| 150 | * Macros for manipulating rings. |
| 151 | * |
| 152 | * FRONT_RING_whatever works on the "front end" of a ring: here |
| 153 | * requests are pushed on to the ring and responses taken off it. |
| 154 | * |
| 155 | * BACK_RING_whatever works on the "back end" of a ring: here |
| 156 | * requests are taken off the ring and responses put on. |
| 157 | * |
| 158 | * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. |
| 159 | * This is OK in 1-for-1 request-response situations where the |
| 160 | * requestor (front end) never has more than RING_SIZE()-1 |
| 161 | * outstanding requests. |
| 162 | */ |
| 163 | |
| 164 | /* Initialising empty rings */ |
| 165 | #define SHARED_RING_INIT(_s) do { \ |
| 166 | (_s)->req_prod = (_s)->rsp_prod = 0; \ |
| 167 | (_s)->req_event = (_s)->rsp_event = 1; \ |
| 168 | (void)memset((_s)->private.pvt_pad, 0, sizeof((_s)->private.pvt_pad)); \ |
| 169 | (void)memset((_s)->__pad, 0, sizeof((_s)->__pad)); \ |
| 170 | } while(0) |
| 171 | |
| 172 | #define FRONT_RING_INIT(_r, _s, __size) do { \ |
| 173 | (_r)->req_prod_pvt = 0; \ |
| 174 | (_r)->rsp_cons = 0; \ |
| 175 | (_r)->nr_ents = __RING_SIZE(_s, __size); \ |
| 176 | (_r)->sring = (_s); \ |
| 177 | } while (0) |
| 178 | |
| 179 | #define BACK_RING_INIT(_r, _s, __size) do { \ |
| 180 | (_r)->rsp_prod_pvt = 0; \ |
| 181 | (_r)->req_cons = 0; \ |
| 182 | (_r)->nr_ents = __RING_SIZE(_s, __size); \ |
| 183 | (_r)->sring = (_s); \ |
| 184 | } while (0) |
| 185 | |
| 186 | /* Initialize to existing shared indexes -- for recovery */ |
| 187 | #define FRONT_RING_ATTACH(_r, _s, __size) do { \ |
| 188 | (_r)->sring = (_s); \ |
| 189 | (_r)->req_prod_pvt = (_s)->req_prod; \ |
| 190 | (_r)->rsp_cons = (_s)->rsp_prod; \ |
| 191 | (_r)->nr_ents = __RING_SIZE(_s, __size); \ |
| 192 | } while (0) |
| 193 | |
| 194 | #define BACK_RING_ATTACH(_r, _s, __size) do { \ |
| 195 | (_r)->sring = (_s); \ |
| 196 | (_r)->rsp_prod_pvt = (_s)->rsp_prod; \ |
| 197 | (_r)->req_cons = (_s)->req_prod; \ |
| 198 | (_r)->nr_ents = __RING_SIZE(_s, __size); \ |
| 199 | } while (0) |
| 200 | |
| 201 | /* How big is this ring? */ |
| 202 | #define RING_SIZE(_r) \ |
| 203 | ((_r)->nr_ents) |
| 204 | |
| 205 | /* Number of free requests (for use on front side only). */ |
| 206 | #define RING_FREE_REQUESTS(_r) \ |
| 207 | (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) |
| 208 | |
| 209 | /* Test if there is an empty slot available on the front ring. |
| 210 | * (This is only meaningful from the front. ) |
| 211 | */ |
| 212 | #define RING_FULL(_r) \ |
| 213 | (RING_FREE_REQUESTS(_r) == 0) |
| 214 | |
| 215 | /* Test if there are outstanding messages to be processed on a ring. */ |
| 216 | #define RING_HAS_UNCONSUMED_RESPONSES(_r) \ |
| 217 | ((_r)->sring->rsp_prod - (_r)->rsp_cons) |
| 218 | |
| 219 | #ifdef __GNUC__ |
| 220 | #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \ |
| 221 | unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \ |
| 222 | unsigned int rsp = RING_SIZE(_r) - \ |
| 223 | ((_r)->req_cons - (_r)->rsp_prod_pvt); \ |
| 224 | req < rsp ? req : rsp; \ |
| 225 | }) |
| 226 | #else |
| 227 | /* Same as above, but without the nice GCC ({ ... }) syntax. */ |
| 228 | #define RING_HAS_UNCONSUMED_REQUESTS(_r) \ |
| 229 | ((((_r)->sring->req_prod - (_r)->req_cons) < \ |
| 230 | (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \ |
| 231 | ((_r)->sring->req_prod - (_r)->req_cons) : \ |
| 232 | (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) |
| 233 | #endif |
| 234 | |
| 235 | /* Direct access to individual ring elements, by index. */ |
| 236 | #define RING_GET_REQUEST(_r, _idx) \ |
| 237 | (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) |
| 238 | |
| 239 | /* |
| 240 | * Get a local copy of a request. |
| 241 | * |
| 242 | * Use this in preference to RING_GET_REQUEST() so all processing is |
| 243 | * done on a local copy that cannot be modified by the other end. |
| 244 | * |
| 245 | * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this |
| 246 | * to be ineffective where _req is a struct which consists of only bitfields. |
| 247 | */ |
| 248 | #define RING_COPY_REQUEST(_r, _idx, _req) do { \ |
| 249 | /* Use volatile to force the copy into _req. */ \ |
| 250 | *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx); \ |
| 251 | } while (0) |
| 252 | |
| 253 | #define RING_GET_RESPONSE(_r, _idx) \ |
| 254 | (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) |
| 255 | |
| 256 | /* Loop termination condition: Would the specified index overflow the ring? */ |
| 257 | #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ |
| 258 | (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) |
| 259 | |
| 260 | #define RING_PUSH_REQUESTS(_r) do { \ |
| 261 | xen_wmb(); /* back sees requests /before/ updated producer index */ \ |
| 262 | (_r)->sring->req_prod = (_r)->req_prod_pvt; \ |
| 263 | } while (0) |
| 264 | |
| 265 | #define RING_PUSH_RESPONSES(_r) do { \ |
| 266 | xen_wmb(); /* front sees resps /before/ updated producer index */ \ |
| 267 | (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ |
| 268 | } while (0) |
| 269 | |
| 270 | /* |
| 271 | * Notification hold-off (req_event and rsp_event): |
| 272 | * |
| 273 | * When queueing requests or responses on a shared ring, it may not always be |
| 274 | * necessary to notify the remote end. For example, if requests are in flight |
| 275 | * in a backend, the front may be able to queue further requests without |
| 276 | * notifying the back (if the back checks for new requests when it queues |
| 277 | * responses). |
| 278 | * |
| 279 | * When enqueuing requests or responses: |
| 280 | * |
| 281 | * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument |
| 282 | * is a boolean return value. True indicates that the receiver requires an |
| 283 | * asynchronous notification. |
| 284 | * |
| 285 | * After dequeuing requests or responses (before sleeping the connection): |
| 286 | * |
| 287 | * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). |
| 288 | * The second argument is a boolean return value. True indicates that there |
| 289 | * are pending messages on the ring (i.e., the connection should not be put |
| 290 | * to sleep). |
| 291 | * |
| 292 | * These macros will set the req_event/rsp_event field to trigger a |
| 293 | * notification on the very next message that is enqueued. If you want to |
| 294 | * create batches of work (i.e., only receive a notification after several |
| 295 | * messages have been enqueued) then you will need to create a customised |
| 296 | * version of the FINAL_CHECK macro in your own code, which sets the event |
| 297 | * field appropriately. |
| 298 | */ |
| 299 | |
| 300 | #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ |
| 301 | RING_IDX __old = (_r)->sring->req_prod; \ |
| 302 | RING_IDX __new = (_r)->req_prod_pvt; \ |
| 303 | xen_wmb(); /* back sees requests /before/ updated producer index */ \ |
| 304 | (_r)->sring->req_prod = __new; \ |
| 305 | xen_mb(); /* back sees new requests /before/ we check req_event */ \ |
| 306 | (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ |
| 307 | (RING_IDX)(__new - __old)); \ |
| 308 | } while (0) |
| 309 | |
| 310 | #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ |
| 311 | RING_IDX __old = (_r)->sring->rsp_prod; \ |
| 312 | RING_IDX __new = (_r)->rsp_prod_pvt; \ |
| 313 | xen_wmb(); /* front sees resps /before/ updated producer index */ \ |
| 314 | (_r)->sring->rsp_prod = __new; \ |
| 315 | xen_mb(); /* front sees new resps /before/ we check rsp_event */ \ |
| 316 | (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ |
| 317 | (RING_IDX)(__new - __old)); \ |
| 318 | } while (0) |
| 319 | |
| 320 | #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ |
| 321 | (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ |
| 322 | if (_work_to_do) break; \ |
| 323 | (_r)->sring->req_event = (_r)->req_cons + 1; \ |
| 324 | xen_mb(); \ |
| 325 | (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ |
| 326 | } while (0) |
| 327 | |
| 328 | #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ |
| 329 | (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ |
| 330 | if (_work_to_do) break; \ |
| 331 | (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ |
| 332 | xen_mb(); \ |
| 333 | (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ |
| 334 | } while (0) |
| 335 | |
| 336 | #endif /* __XEN_PUBLIC_IO_RING_H__ */ |
| 337 | |
| 338 | /* |
| 339 | * Local variables: |
| 340 | * mode: C |
| 341 | * c-set-style: "BSD" |
| 342 | * c-basic-offset: 4 |
| 343 | * tab-width: 4 |
| 344 | * indent-tabs-mode: nil |
| 345 | * End: |
| 346 | */ |
| 347 | |