include/hw/xen/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 #if __XEN_INTERFACE_VERSION__ < 0x00030208
  46 #define xen_mb()  mb()
  47 #define xen_rmb() rmb()
  48 #define xen_wmb() wmb()
  49 #endif
  50
  51 typedef unsigned int RING_IDX;
  52
  53 /* Round a 32-bit unsigned constant down to the nearest power of two. */
  54 #define __RD2(_x)  (((_x) & 0x00000002) ? 0x2                  : ((_x) & 0x1))
  55 #define __RD4(_x)  (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2    : __RD2(_x))
  56 #define __RD8(_x)  (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4    : __RD4(_x))
  57 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8    : __RD8(_x))
  58 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
  59
  60 /*
  61  * Calculate size of a shared ring, given the total available space for the
  62  * ring and indexes (_sz), and the name tag of the request/response structure.
  63  * A ring contains as many entries as will fit, rounded down to the nearest
  64  * power of two (so we can mask with (size-1) to loop around).
  65  */
  66 #define __CONST_RING_SIZE(_s, _sz) \
  67     (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
  68             sizeof_field(struct _s##_sring, ring[0])))
  69 /*
  70  * The same for passing in an actual pointer instead of a name tag.
  71  */
  72 #define __RING_SIZE(_s, _sz) \
  73     (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
  74
  75 /*
  76  * Macros to make the correct C datatypes for a new kind of ring.
  77  *
  78  * To make a new ring datatype, you need to have two message structures,
  79  * let's say request_t, and response_t already defined.
  80  *
  81  * In a header where you want the ring datatype declared, you then do:
  82  *
  83  *     DEFINE_RING_TYPES(mytag, request_t, response_t);
  84  *
  85  * These expand out to give you a set of types, as you can see below.
  86  * The most important of these are:
  87  *
  88  *     mytag_sring_t      - The shared ring.
  89  *     mytag_front_ring_t - The 'front' half of the ring.
  90  *     mytag_back_ring_t  - The 'back' half of the ring.
  91  *
  92  * To initialize a ring in your code you need to know the location and size
  93  * of the shared memory area (PAGE_SIZE, for instance). To initialise
  94  * the front half:
  95  *
  96  *     mytag_front_ring_t front_ring;
  97  *     SHARED_RING_INIT((mytag_sring_t *)shared_page);
  98  *     FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
  99  *
 100  * Initializing the back follows similarly (note that only the front
 101  * initializes the shared ring):
 102  *
 103  *     mytag_back_ring_t back_ring;
 104  *     BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
 105  */
 106
 107 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)                     \
 108                                                                         \
 109 /* Shared ring entry */                                                 \
 110 union __name##_sring_entry {                                            \
 111     __req_t req;                                                        \
 112     __rsp_t rsp;                                                        \
 113 };                                                                      \
 114                                                                         \
 115 /* Shared ring page */                                                  \
 116 struct __name##_sring {                                                 \
 117     RING_IDX req_prod, req_event;                                       \
 118     RING_IDX rsp_prod, rsp_event;                                       \
 119     union {                                                             \
 120         struct {                                                        \
 121             uint8_t smartpoll_active;                                   \
 122         } netif;                                                        \
 123         struct {                                                        \
 124             uint8_t msg;                                                \
 125         } tapif_user;                                                   \
 126         uint8_t pvt_pad[4];                                             \
 127     } pvt;                                                              \
 128     uint8_t __pad[44];                                                  \
 129     union __name##_sring_entry ring[1]; /* variable-length */           \
 130 };                                                                      \
 131                                                                         \
 132 /* "Front" end's private variables */                                   \
 133 struct __name##_front_ring {                                            \
 134     RING_IDX req_prod_pvt;                                              \
 135     RING_IDX rsp_cons;                                                  \
 136     unsigned int nr_ents;                                               \
 137     struct __name##_sring *sring;                                       \
 138 };                                                                      \
 139                                                                         \
 140 /* "Back" end's private variables */                                    \
 141 struct __name##_back_ring {                                             \
 142     RING_IDX rsp_prod_pvt;                                              \
 143     RING_IDX req_cons;                                                  \
 144     unsigned int nr_ents;                                               \
 145     struct __name##_sring *sring;                                       \
 146 };                                                                      \
 147                                                                         \
 148 /* Syntactic sugar */                                                   \
 149 typedef struct __name##_sring __name##_sring_t;                         \
 150 typedef struct __name##_front_ring __name##_front_ring_t;               \
 151 typedef struct __name##_back_ring __name##_back_ring_t
 152
 153 /*
 154  * Macros for manipulating rings.
 155  *
 156  * FRONT_RING_whatever works on the "front end" of a ring: here
 157  * requests are pushed on to the ring and responses taken off it.
 158  *
 159  * BACK_RING_whatever works on the "back end" of a ring: here
 160  * requests are taken off the ring and responses put on.
 161  *
 162  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
 163  * This is OK in 1-for-1 request-response situations where the
 164  * requestor (front end) never has more than RING_SIZE()-1
 165  * outstanding requests.
 166  */
 167
 168 /* Initialising empty rings */
 169 #define SHARED_RING_INIT(_s) do {                                       \
 170     (_s)->req_prod  = (_s)->rsp_prod  = 0;                              \
 171     (_s)->req_event = (_s)->rsp_event = 1;                              \
 172     (void)memset((_s)->pvt.pvt_pad, 0, sizeof((_s)->pvt.pvt_pad));      \
 173     (void)memset((_s)->__pad, 0, sizeof((_s)->__pad));                  \
 174 } while(0)
 175
 176 #define FRONT_RING_INIT(_r, _s, __size) do {                            \
 177     (_r)->req_prod_pvt = 0;                                             \
 178     (_r)->rsp_cons = 0;                                                 \
 179     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 180     (_r)->sring = (_s);                                                 \
 181 } while (0)
 182
 183 #define BACK_RING_INIT(_r, _s, __size) do {                             \
 184     (_r)->rsp_prod_pvt = 0;                                             \
 185     (_r)->req_cons = 0;                                                 \
 186     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 187     (_r)->sring = (_s);                                                 \
 188 } while (0)
 189
 190 /* How big is this ring? */
 191 #define RING_SIZE(_r)                                                   \
 192     ((_r)->nr_ents)
 193
 194 /* Number of free requests (for use on front side only). */
 195 #define RING_FREE_REQUESTS(_r)                                          \
 196     (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
 197
 198 /* Test if there is an empty slot available on the front ring.
 199  * (This is only meaningful from the front. )
 200  */
 201 #define RING_FULL(_r)                                                   \
 202     (RING_FREE_REQUESTS(_r) == 0)
 203
 204 /* Test if there are outstanding messages to be processed on a ring. */
 205 #define RING_HAS_UNCONSUMED_RESPONSES(_r)                               \
 206     ((_r)->sring->rsp_prod - (_r)->rsp_cons)
 207
 208 #ifdef __GNUC__
 209 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({                             \
 210     unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;          \
 211     unsigned int rsp = RING_SIZE(_r) -                                  \
 212         ((_r)->req_cons - (_r)->rsp_prod_pvt);                          \
 213     req < rsp ? req : rsp;                                              \
 214 })
 215 #else
 216 /* Same as above, but without the nice GCC ({ ... }) syntax. */
 217 #define RING_HAS_UNCONSUMED_REQUESTS(_r)                                \
 218     ((((_r)->sring->req_prod - (_r)->req_cons) <                        \
 219       (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ?        \
 220      ((_r)->sring->req_prod - (_r)->req_cons) :                         \
 221      (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
 222 #endif
 223
 224 /* Direct access to individual ring elements, by index. */
 225 #define RING_GET_REQUEST(_r, _idx)                                      \
 226     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
 227
 228 /*
 229  * Get a local copy of a request.
 230  *
 231  * Use this in preference to RING_GET_REQUEST() so all processing is
 232  * done on a local copy that cannot be modified by the other end.
 233  *
 234  * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
 235  * to be ineffective where _req is a struct which consists of only bitfields.
 236  */
 237 #define RING_COPY_REQUEST(_r, _idx, _req) do {                          \
 238         /* Use volatile to force the copy into _req. */                 \
 239         *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx);   \
 240 } while (0)
 241
 242 #define RING_GET_RESPONSE(_r, _idx)                                     \
 243     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
 244
 245 /* Loop termination condition: Would the specified index overflow the ring? */
 246 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)                           \
 247     (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
 248
 249 /* Ill-behaved frontend determination: Can there be this many requests? */
 250 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod)                           \
 251     (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
 252
 253 #define RING_PUSH_REQUESTS(_r) do {                                     \
 254     xen_wmb(); /* back sees requests /before/ updated producer index */ \
 255     (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
 256 } while (0)
 257
 258 #define RING_PUSH_RESPONSES(_r) do {                                    \
 259     xen_wmb(); /* front sees resps /before/ updated producer index */   \
 260     (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;                         \
 261 } while (0)
 262
 263 /*
 264  * Notification hold-off (req_event and rsp_event):
 265  *
 266  * When queueing requests or responses on a shared ring, it may not always be
 267  * necessary to notify the remote end. For example, if requests are in flight
 268  * in a backend, the front may be able to queue further requests without
 269  * notifying the back (if the back checks for new requests when it queues
 270  * responses).
 271  *
 272  * When enqueuing requests or responses:
 273  *
 274  *  Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
 275  *  is a boolean return value. True indicates that the receiver requires an
 276  *  asynchronous notification.
 277  *
 278  * After dequeuing requests or responses (before sleeping the connection):
 279  *
 280  *  Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
 281  *  The second argument is a boolean return value. True indicates that there
 282  *  are pending messages on the ring (i.e., the connection should not be put
 283  *  to sleep).
 284  *
 285  *  These macros will set the req_event/rsp_event field to trigger a
 286  *  notification on the very next message that is enqueued. If you want to
 287  *  create batches of work (i.e., only receive a notification after several
 288  *  messages have been enqueued) then you will need to create a customised
 289  *  version of the FINAL_CHECK macro in your own code, which sets the event
 290  *  field appropriately.
 291  */
 292
 293 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {           \
 294     RING_IDX __old = (_r)->sring->req_prod;                             \
 295     RING_IDX __new = (_r)->req_prod_pvt;                                \
 296     xen_wmb(); /* back sees requests /before/ updated producer index */ \
 297     (_r)->sring->req_prod = __new;                                      \
 298     xen_mb(); /* back sees new requests /before/ we check req_event */  \
 299     (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <           \
 300                  (RING_IDX)(__new - __old));                            \
 301 } while (0)
 302
 303 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {          \
 304     RING_IDX __old = (_r)->sring->rsp_prod;                             \
 305     RING_IDX __new = (_r)->rsp_prod_pvt;                                \
 306     xen_wmb(); /* front sees resps /before/ updated producer index */   \
 307     (_r)->sring->rsp_prod = __new;                                      \
 308     xen_mb(); /* front sees new resps /before/ we check rsp_event */    \
 309     (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <           \
 310                  (RING_IDX)(__new - __old));                            \
 311 } while (0)
 312
 313 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do {             \
 314     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 315     if (_work_to_do) break;                                             \
 316     (_r)->sring->req_event = (_r)->req_cons + 1;                        \
 317     xen_mb();                                                           \
 318     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 319 } while (0)
 320
 321 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do {            \
 322     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 323     if (_work_to_do) break;                                             \
 324     (_r)->sring->rsp_event = (_r)->rsp_cons + 1;                        \
 325     xen_mb();                                                           \
 326     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 327 } while (0)
 328
 329
 330 /*
 331  * DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and
 332  * functions to check if there is data on the ring, and to read and
 333  * write to them.
 334  *
 335  * DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but
 336  * does not define the indexes page. As different protocols can have
 337  * extensions to the basic format, this macro allow them to define their
 338  * own struct.
 339  *
 340  * XEN_FLEX_RING_SIZE
 341  *   Convenience macro to calculate the size of one of the two rings
 342  *   from the overall order.
 343  *
 344  * $NAME_mask
 345  *   Function to apply the size mask to an index, to reduce the index
 346  *   within the range [0-size].
 347  *
 348  * $NAME_read_packet
 349  *   Function to read data from the ring. The amount of data to read is
 350  *   specified by the "size" argument.
 351  *
 352  * $NAME_write_packet
 353  *   Function to write data to the ring. The amount of data to write is
 354  *   specified by the "size" argument.
 355  *
 356  * $NAME_get_ring_ptr
 357  *   Convenience function that returns a pointer to read/write to the
 358  *   ring at the right location.
 359  *
 360  * $NAME_data_intf
 361  *   Indexes page, shared between frontend and backend. It also
 362  *   contains the array of grant refs.
 363  *
 364  * $NAME_queued
 365  *   Function to calculate how many bytes are currently on the ring,
 366  *   ready to be read. It can also be used to calculate how much free
 367  *   space is currently on the ring (XEN_FLEX_RING_SIZE() -
 368  *   $NAME_queued()).
 369  */
 370
 371 #ifndef XEN_PAGE_SHIFT
 372 /* The PAGE_SIZE for ring protocols and hypercall interfaces is always
 373  * 4K, regardless of the architecture, and page granularity chosen by
 374  * operating systems.
 375  */
 376 #define XEN_PAGE_SHIFT 12
 377 #endif
 378 #define XEN_FLEX_RING_SIZE(order)                                             \
 379     (1UL << ((order) + XEN_PAGE_SHIFT - 1))
 380
 381 #define DEFINE_XEN_FLEX_RING(name)                                            \
 382 static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size)          \
 383 {                                                                             \
 384     return idx & (ring_size - 1);                                             \
 385 }                                                                             \
 386                                                                               \
 387 static inline unsigned char *name##_get_ring_ptr(unsigned char *buf,          \
 388                                                  RING_IDX idx,                \
 389                                                  RING_IDX ring_size)          \
 390 {                                                                             \
 391     return buf + name##_mask(idx, ring_size);                                 \
 392 }                                                                             \
 393                                                                               \
 394 static inline void name##_read_packet(void *opaque,                           \
 395                                       const unsigned char *buf,               \
 396                                       size_t size,                            \
 397                                       RING_IDX masked_prod,                   \
 398                                       RING_IDX *masked_cons,                  \
 399                                       RING_IDX ring_size)                     \
 400 {                                                                             \
 401     if (*masked_cons < masked_prod ||                                         \
 402         size <= ring_size - *masked_cons) {                                   \
 403         memcpy(opaque, buf + *masked_cons, size);                             \
 404     } else {                                                                  \
 405         memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons);         \
 406         memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf,       \
 407                size - (ring_size - *masked_cons));                            \
 408     }                                                                         \
 409     *masked_cons = name##_mask(*masked_cons + size, ring_size);               \
 410 }                                                                             \
 411                                                                               \
 412 static inline void name##_write_packet(unsigned char *buf,                    \
 413                                        const void *opaque,                    \
 414                                        size_t size,                           \
 415                                        RING_IDX *masked_prod,                 \
 416                                        RING_IDX masked_cons,                  \
 417                                        RING_IDX ring_size)                    \
 418 {                                                                             \
 419     if (*masked_prod < masked_cons ||                                         \
 420         size <= ring_size - *masked_prod) {                                   \
 421         memcpy(buf + *masked_prod, opaque, size);                             \
 422     } else {                                                                  \
 423         memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod);         \
 424         memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod),     \
 425                size - (ring_size - *masked_prod));                            \
 426     }                                                                         \
 427     *masked_prod = name##_mask(*masked_prod + size, ring_size);               \
 428 }                                                                             \
 429                                                                               \
 430 static inline RING_IDX name##_queued(RING_IDX prod,                           \
 431                                      RING_IDX cons,                           \
 432                                      RING_IDX ring_size)                      \
 433 {                                                                             \
 434     RING_IDX size;                                                            \
 435                                                                               \
 436     if (prod == cons)                                                         \
 437         return 0;                                                             \
 438                                                                               \
 439     prod = name##_mask(prod, ring_size);                                      \
 440     cons = name##_mask(cons, ring_size);                                      \
 441                                                                               \
 442     if (prod == cons)                                                         \
 443         return ring_size;                                                     \
 444                                                                               \
 445     if (prod > cons)                                                          \
 446         size = prod - cons;                                                   \
 447     else                                                                      \
 448         size = ring_size - (cons - prod);                                     \
 449     return size;                                                              \
 450 }                                                                             \
 451                                                                               \
 452 struct name##_data {                                                          \
 453     unsigned char *in; /* half of the allocation */                           \
 454     unsigned char *out; /* half of the allocation */                          \
 455 }
 456
 457 #define DEFINE_XEN_FLEX_RING_AND_INTF(name)                                   \
 458 struct name##_data_intf {                                                     \
 459     RING_IDX in_cons, in_prod;                                                \
 460                                                                               \
 461     uint8_t pad1[56];                                                         \
 462                                                                               \
 463     RING_IDX out_cons, out_prod;                                              \
 464                                                                               \
 465     uint8_t pad2[56];                                                         \
 466                                                                               \
 467     RING_IDX ring_order;                                                      \
 468     grant_ref_t ref[];                                                        \
 469 };                                                                            \
 470 DEFINE_XEN_FLEX_RING(name)
 471
 472 #endif /* __XEN_PUBLIC_IO_RING_H__ */
 473
 474 /*
 475  * Local variables:
 476  * mode: C
 477  * c-file-style: "BSD"
 478  * c-basic-offset: 4
 479  * tab-width: 4
 480  * indent-tabs-mode: nil
 481  * End:
 482  */