include/xen/interface/io/ring.h

   1 /******************************************************************************
   2  * ring.h
   3  *
   4  * Shared producer-consumer ring macros.
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to
   8  * deal in the Software without restriction, including without limitation the
   9  * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
  10  * sell copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  22  * DEALINGS IN THE SOFTWARE.
  23  *
  24  * Tim Deegan and Andrew Warfield November 2004.
  25  */
  26
  27 #ifndef __XEN_PUBLIC_IO_RING_H__
  28 #define __XEN_PUBLIC_IO_RING_H__
  29
  30 /*
  31  * When #include'ing this header, you need to provide the following
  32  * declaration upfront:
  33  * - standard integers types (uint8_t, uint16_t, etc)
  34  * They are provided by stdint.h of the standard headers.
  35  *
  36  * In addition, if you intend to use the FLEX macros, you also need to
  37  * provide the following, before invoking the FLEX macros:
  38  * - size_t
  39  * - memcpy
  40  * - grant_ref_t
  41  * These declarations are provided by string.h of the standard headers,
  42  * and grant_table.h from the Xen public headers.
  43  */
  44
  45 #include <xen/interface/grant_table.h>
  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     uint8_t __pad[48];                                                  \
 116     union __name##_sring_entry ring[1]; /* variable-length */           \
 117 };                                                                      \
 118                                                                         \
 119 /* "Front" end's private variables */                                   \
 120 struct __name##_front_ring {                                            \
 121     RING_IDX req_prod_pvt;                                              \
 122     RING_IDX rsp_cons;                                                  \
 123     unsigned int nr_ents;                                               \
 124     struct __name##_sring *sring;                                       \
 125 };                                                                      \
 126                                                                         \
 127 /* "Back" end's private variables */                                    \
 128 struct __name##_back_ring {                                             \
 129     RING_IDX rsp_prod_pvt;                                              \
 130     RING_IDX req_cons;                                                  \
 131     unsigned int nr_ents;                                               \
 132     struct __name##_sring *sring;                                       \
 133 };                                                                      \
 134                                                                         \
 135 /*
 136  * Macros for manipulating rings.
 137  *
 138  * FRONT_RING_whatever works on the "front end" of a ring: here
 139  * requests are pushed on to the ring and responses taken off it.
 140  *
 141  * BACK_RING_whatever works on the "back end" of a ring: here
 142  * requests are taken off the ring and responses put on.
 143  *
 144  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
 145  * This is OK in 1-for-1 request-response situations where the
 146  * requestor (front end) never has more than RING_SIZE()-1
 147  * outstanding requests.
 148  */
 149
 150 /* Initialising empty rings */
 151 #define SHARED_RING_INIT(_s) do {                                       \
 152     (_s)->req_prod  = (_s)->rsp_prod  = 0;                              \
 153     (_s)->req_event = (_s)->rsp_event = 1;                              \
 154     (void)memset((_s)->__pad, 0, sizeof((_s)->__pad));                  \
 155 } while(0)
 156
 157 #define FRONT_RING_ATTACH(_r, _s, _i, __size) do {                      \
 158     (_r)->req_prod_pvt = (_i);                                          \
 159     (_r)->rsp_cons = (_i);                                              \
 160     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 161     (_r)->sring = (_s);                                                 \
 162 } while (0)
 163
 164 #define FRONT_RING_INIT(_r, _s, __size) FRONT_RING_ATTACH(_r, _s, 0, __size)
 165
 166 #define BACK_RING_ATTACH(_r, _s, _i, __size) do {                       \
 167     (_r)->rsp_prod_pvt = (_i);                                          \
 168     (_r)->req_cons = (_i);                                              \
 169     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 170     (_r)->sring = (_s);                                                 \
 171 } while (0)
 172
 173 #define BACK_RING_INIT(_r, _s, __size) BACK_RING_ATTACH(_r, _s, 0, __size)
 174
 175 /* How big is this ring? */
 176 #define RING_SIZE(_r)                                                   \
 177     ((_r)->nr_ents)
 178
 179 /* Number of free requests (for use on front side only). */
 180 #define RING_FREE_REQUESTS(_r)                                          \
 181     (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
 182
 183 /* Test if there is an empty slot available on the front ring.
 184  * (This is only meaningful from the front. )
 185  */
 186 #define RING_FULL(_r)                                                   \
 187     (RING_FREE_REQUESTS(_r) == 0)
 188
 189 /* Test if there are outstanding messages to be processed on a ring. */
 190 #define RING_HAS_UNCONSUMED_RESPONSES(_r)                               \
 191     ((_r)->sring->rsp_prod - (_r)->rsp_cons)
 192
 193 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({                             \
 194     unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;          \
 195     unsigned int rsp = RING_SIZE(_r) -                                  \
 196         ((_r)->req_cons - (_r)->rsp_prod_pvt);                          \
 197     req < rsp ? req : rsp;                                              \
 198 })
 199
 200 /* Direct access to individual ring elements, by index. */
 201 #define RING_GET_REQUEST(_r, _idx)                                      \
 202     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
 203
 204 #define RING_GET_RESPONSE(_r, _idx)                                     \
 205     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
 206
 207 /*
 208  * Get a local copy of a request/response.
 209  *
 210  * Use this in preference to RING_GET_{REQUEST,RESPONSE}() 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 dest is a struct which consists of only bitfields.
 215  */
 216 #define RING_COPY_(type, r, idx, dest) do {                             \
 217         /* Use volatile to force the copy into dest. */                 \
 218         *(dest) = *(volatile typeof(dest))RING_GET_##type(r, idx);      \
 219 } while (0)
 220
 221 #define RING_COPY_REQUEST(r, idx, req)  RING_COPY_(REQUEST, r, idx, req)
 222 #define RING_COPY_RESPONSE(r, idx, rsp) RING_COPY_(RESPONSE, r, idx, 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 /* Ill-behaved backend determination: Can there be this many responses? */
 233 #define RING_RESPONSE_PROD_OVERFLOW(_r, _prod)                          \
 234     (((_prod) - (_r)->rsp_cons) > RING_SIZE(_r))
 235
 236 #define RING_PUSH_REQUESTS(_r) do {                                     \
 237     virt_wmb(); /* back sees requests /before/ updated producer index */\
 238     (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
 239 } while (0)
 240
 241 #define RING_PUSH_RESPONSES(_r) do {                                    \
 242     virt_wmb(); /* front sees resps /before/ updated producer index */  \
 243     (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;                         \
 244 } while (0)
 245
 246 /*
 247  * Notification hold-off (req_event and rsp_event):
 248  *
 249  * When queueing requests or responses on a shared ring, it may not always be
 250  * necessary to notify the remote end. For example, if requests are in flight
 251  * in a backend, the front may be able to queue further requests without
 252  * notifying the back (if the back checks for new requests when it queues
 253  * responses).
 254  *
 255  * When enqueuing requests or responses:
 256  *
 257  *  Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
 258  *  is a boolean return value. True indicates that the receiver requires an
 259  *  asynchronous notification.
 260  *
 261  * After dequeuing requests or responses (before sleeping the connection):
 262  *
 263  *  Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
 264  *  The second argument is a boolean return value. True indicates that there
 265  *  are pending messages on the ring (i.e., the connection should not be put
 266  *  to sleep).
 267  *
 268  *  These macros will set the req_event/rsp_event field to trigger a
 269  *  notification on the very next message that is enqueued. If you want to
 270  *  create batches of work (i.e., only receive a notification after several
 271  *  messages have been enqueued) then you will need to create a customised
 272  *  version of the FINAL_CHECK macro in your own code, which sets the event
 273  *  field appropriately.
 274  */
 275
 276 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {           \
 277     RING_IDX __old = (_r)->sring->req_prod;                             \
 278     RING_IDX __new = (_r)->req_prod_pvt;                                \
 279     virt_wmb(); /* back sees requests /before/ updated producer index */\
 280     (_r)->sring->req_prod = __new;                                      \
 281     virt_mb(); /* back sees new requests /before/ we check req_event */ \
 282     (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <           \
 283                  (RING_IDX)(__new - __old));                            \
 284 } while (0)
 285
 286 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {          \
 287     RING_IDX __old = (_r)->sring->rsp_prod;                             \
 288     RING_IDX __new = (_r)->rsp_prod_pvt;                                \
 289     virt_wmb(); /* front sees resps /before/ updated producer index */  \
 290     (_r)->sring->rsp_prod = __new;                                      \
 291     virt_mb(); /* front sees new resps /before/ we check rsp_event */   \
 292     (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <           \
 293                  (RING_IDX)(__new - __old));                            \
 294 } while (0)
 295
 296 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do {             \
 297     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 298     if (_work_to_do) break;                                             \
 299     (_r)->sring->req_event = (_r)->req_cons + 1;                        \
 300     virt_mb();                                                          \
 301     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 302 } while (0)
 303
 304 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do {            \
 305     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 306     if (_work_to_do) break;                                             \
 307     (_r)->sring->rsp_event = (_r)->rsp_cons + 1;                        \
 308     virt_mb();                                                          \
 309     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 310 } while (0)
 311
 312
 313 /*
 314  * DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and
 315  * functions to check if there is data on the ring, and to read and
 316  * write to them.
 317  *
 318  * DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but
 319  * does not define the indexes page. As different protocols can have
 320  * extensions to the basic format, this macro allow them to define their
 321  * own struct.
 322  *
 323  * XEN_FLEX_RING_SIZE
 324  *   Convenience macro to calculate the size of one of the two rings
 325  *   from the overall order.
 326  *
 327  * $NAME_mask
 328  *   Function to apply the size mask to an index, to reduce the index
 329  *   within the range [0-size].
 330  *
 331  * $NAME_read_packet
 332  *   Function to read data from the ring. The amount of data to read is
 333  *   specified by the "size" argument.
 334  *
 335  * $NAME_write_packet
 336  *   Function to write data to the ring. The amount of data to write is
 337  *   specified by the "size" argument.
 338  *
 339  * $NAME_get_ring_ptr
 340  *   Convenience function that returns a pointer to read/write to the
 341  *   ring at the right location.
 342  *
 343  * $NAME_data_intf
 344  *   Indexes page, shared between frontend and backend. It also
 345  *   contains the array of grant refs.
 346  *
 347  * $NAME_queued
 348  *   Function to calculate how many bytes are currently on the ring,
 349  *   ready to be read. It can also be used to calculate how much free
 350  *   space is currently on the ring (XEN_FLEX_RING_SIZE() -
 351  *   $NAME_queued()).
 352  */
 353
 354 #ifndef XEN_PAGE_SHIFT
 355 /* The PAGE_SIZE for ring protocols and hypercall interfaces is always
 356  * 4K, regardless of the architecture, and page granularity chosen by
 357  * operating systems.
 358  */
 359 #define XEN_PAGE_SHIFT 12
 360 #endif
 361 #define XEN_FLEX_RING_SIZE(order)                                             \
 362     (1UL << ((order) + XEN_PAGE_SHIFT - 1))
 363
 364 #define DEFINE_XEN_FLEX_RING(name)                                            \
 365 static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size)          \
 366 {                                                                             \
 367     return idx & (ring_size - 1);                                             \
 368 }                                                                             \
 369                                                                               \
 370 static inline unsigned char *name##_get_ring_ptr(unsigned char *buf,          \
 371                                                  RING_IDX idx,                \
 372                                                  RING_IDX ring_size)          \
 373 {                                                                             \
 374     return buf + name##_mask(idx, ring_size);                                 \
 375 }                                                                             \
 376                                                                               \
 377 static inline void name##_read_packet(void *opaque,                           \
 378                                       const unsigned char *buf,               \
 379                                       size_t size,                            \
 380                                       RING_IDX masked_prod,                   \
 381                                       RING_IDX *masked_cons,                  \
 382                                       RING_IDX ring_size)                     \
 383 {                                                                             \
 384     if (*masked_cons < masked_prod ||                                         \
 385         size <= ring_size - *masked_cons) {                                   \
 386         memcpy(opaque, buf + *masked_cons, size);                             \
 387     } else {                                                                  \
 388         memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons);         \
 389         memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf,       \
 390                size - (ring_size - *masked_cons));                            \
 391     }                                                                         \
 392     *masked_cons = name##_mask(*masked_cons + size, ring_size);               \
 393 }                                                                             \
 394                                                                               \
 395 static inline void name##_write_packet(unsigned char *buf,                    \
 396                                        const void *opaque,                    \
 397                                        size_t size,                           \
 398                                        RING_IDX *masked_prod,                 \
 399                                        RING_IDX masked_cons,                  \
 400                                        RING_IDX ring_size)                    \
 401 {                                                                             \
 402     if (*masked_prod < masked_cons ||                                         \
 403         size <= ring_size - *masked_prod) {                                   \
 404         memcpy(buf + *masked_prod, opaque, size);                             \
 405     } else {                                                                  \
 406         memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod);         \
 407         memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod),     \
 408                size - (ring_size - *masked_prod));                            \
 409     }                                                                         \
 410     *masked_prod = name##_mask(*masked_prod + size, ring_size);               \
 411 }                                                                             \
 412                                                                               \
 413 static inline RING_IDX name##_queued(RING_IDX prod,                           \
 414                                      RING_IDX cons,                           \
 415                                      RING_IDX ring_size)                      \
 416 {                                                                             \
 417     RING_IDX size;                                                            \
 418                                                                               \
 419     if (prod == cons)                                                         \
 420         return 0;                                                             \
 421                                                                               \
 422     prod = name##_mask(prod, ring_size);                                      \
 423     cons = name##_mask(cons, ring_size);                                      \
 424                                                                               \
 425     if (prod == cons)                                                         \
 426         return ring_size;                                                     \
 427                                                                               \
 428     if (prod > cons)                                                          \
 429         size = prod - cons;                                                   \
 430     else                                                                      \
 431         size = ring_size - (cons - prod);                                     \
 432     return size;                                                              \
 433 }                                                                             \
 434                                                                               \
 435 struct name##_data {                                                          \
 436     unsigned char *in; /* half of the allocation */                           \
 437     unsigned char *out; /* half of the allocation */                          \
 438 }
 439
 440 #define DEFINE_XEN_FLEX_RING_AND_INTF(name)                                   \
 441 struct name##_data_intf {                                                     \
 442     RING_IDX in_cons, in_prod;                                                \
 443                                                                               \
 444     uint8_t pad1[56];                                                         \
 445                                                                               \
 446     RING_IDX out_cons, out_prod;                                              \
 447                                                                               \
 448     uint8_t pad2[56];                                                         \
 449                                                                               \
 450     RING_IDX ring_order;                                                      \
 451     grant_ref_t ref[];                                                        \
 452 };                                                                            \
 453 DEFINE_XEN_FLEX_RING(name)
 454
 455 #endif /* __XEN_PUBLIC_IO_RING_H__ */