include/xen/interface/io/ring.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   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 #include <xen/interface/grant_table.h>
  14
  15 typedef unsigned int RING_IDX;
  16
  17 /* Round a 32-bit unsigned constant down to the nearest power of two. */
  18 #define __RD2(_x)  (((_x) & 0x00000002) ? 0x2                  : ((_x) & 0x1))
  19 #define __RD4(_x)  (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2    : __RD2(_x))
  20 #define __RD8(_x)  (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4    : __RD4(_x))
  21 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8    : __RD8(_x))
  22 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
  23
  24 /*
  25  * Calculate size of a shared ring, given the total available space for the
  26  * ring and indexes (_sz), and the name tag of the request/response structure.
  27  * A ring contains as many entries as will fit, rounded down to the nearest
  28  * power of two (so we can mask with (size-1) to loop around).
  29  */
  30 #define __CONST_RING_SIZE(_s, _sz)                              \
  31         (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) /   \
  32                 sizeof(((struct _s##_sring *)0)->ring[0])))
  33
  34 /*
  35  * The same for passing in an actual pointer instead of a name tag.
  36  */
  37 #define __RING_SIZE(_s, _sz)                                            \
  38         (__RD32(((_sz) - (long)&(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
  39
  40 /*
  41  * Macros to make the correct C datatypes for a new kind of ring.
  42  *
  43  * To make a new ring datatype, you need to have two message structures,
  44  * let's say struct request, and struct response already defined.
  45  *
  46  * In a header where you want the ring datatype declared, you then do:
  47  *
  48  *     DEFINE_RING_TYPES(mytag, struct request, struct response);
  49  *
  50  * These expand out to give you a set of types, as you can see below.
  51  * The most important of these are:
  52  *
  53  *     struct mytag_sring      - The shared ring.
  54  *     struct mytag_front_ring - The 'front' half of the ring.
  55  *     struct mytag_back_ring  - The 'back' half of the ring.
  56  *
  57  * To initialize a ring in your code you need to know the location and size
  58  * of the shared memory area (PAGE_SIZE, for instance). To initialise
  59  * the front half:
  60  *
  61  *     struct mytag_front_ring front_ring;
  62  *     SHARED_RING_INIT((struct mytag_sring *)shared_page);
  63  *     FRONT_RING_INIT(&front_ring, (struct mytag_sring *)shared_page,
  64  *                     PAGE_SIZE);
  65  *
  66  * Initializing the back follows similarly (note that only the front
  67  * initializes the shared ring):
  68  *
  69  *     struct mytag_back_ring back_ring;
  70  *     BACK_RING_INIT(&back_ring, (struct mytag_sring *)shared_page,
  71  *                    PAGE_SIZE);
  72  */
  73
  74 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)                     \
  75                                                                         \
  76 /* Shared ring entry */                                                 \
  77 union __name##_sring_entry {                                            \
  78     __req_t req;                                                        \
  79     __rsp_t rsp;                                                        \
  80 };                                                                      \
  81                                                                         \
  82 /* Shared ring page */                                                  \
  83 struct __name##_sring {                                                 \
  84     RING_IDX req_prod, req_event;                                       \
  85     RING_IDX rsp_prod, rsp_event;                                       \
  86     uint8_t  pad[48];                                                   \
  87     union __name##_sring_entry ring[1]; /* variable-length */           \
  88 };                                                                      \
  89                                                                         \
  90 /* "Front" end's private variables */                                   \
  91 struct __name##_front_ring {                                            \
  92     RING_IDX req_prod_pvt;                                              \
  93     RING_IDX rsp_cons;                                                  \
  94     unsigned int nr_ents;                                               \
  95     struct __name##_sring *sring;                                       \
  96 };                                                                      \
  97                                                                         \
  98 /* "Back" end's private variables */                                    \
  99 struct __name##_back_ring {                                             \
 100     RING_IDX rsp_prod_pvt;                                              \
 101     RING_IDX req_cons;                                                  \
 102     unsigned int nr_ents;                                               \
 103     struct __name##_sring *sring;                                       \
 104 };
 105
 106 /*
 107  * Macros for manipulating rings.
 108  *
 109  * FRONT_RING_whatever works on the "front end" of a ring: here
 110  * requests are pushed on to the ring and responses taken off it.
 111  *
 112  * BACK_RING_whatever works on the "back end" of a ring: here
 113  * requests are taken off the ring and responses put on.
 114  *
 115  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
 116  * This is OK in 1-for-1 request-response situations where the
 117  * requestor (front end) never has more than RING_SIZE()-1
 118  * outstanding requests.
 119  */
 120
 121 /* Initialising empty rings */
 122 #define SHARED_RING_INIT(_s) do {                                       \
 123     (_s)->req_prod  = (_s)->rsp_prod  = 0;                              \
 124     (_s)->req_event = (_s)->rsp_event = 1;                              \
 125     memset((_s)->pad, 0, sizeof((_s)->pad));                            \
 126 } while(0)
 127
 128 #define FRONT_RING_INIT(_r, _s, __size) do {                            \
 129     (_r)->req_prod_pvt = 0;                                             \
 130     (_r)->rsp_cons = 0;                                                 \
 131     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 132     (_r)->sring = (_s);                                                 \
 133 } while (0)
 134
 135 #define BACK_RING_INIT(_r, _s, __size) do {                             \
 136     (_r)->rsp_prod_pvt = 0;                                             \
 137     (_r)->req_cons = 0;                                                 \
 138     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 139     (_r)->sring = (_s);                                                 \
 140 } while (0)
 141
 142 /* Initialize to existing shared indexes -- for recovery */
 143 #define FRONT_RING_ATTACH(_r, _s, __size) do {                          \
 144     (_r)->sring = (_s);                                                 \
 145     (_r)->req_prod_pvt = (_s)->req_prod;                                \
 146     (_r)->rsp_cons = (_s)->rsp_prod;                                    \
 147     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 148 } while (0)
 149
 150 #define BACK_RING_ATTACH(_r, _s, __size) do {                           \
 151     (_r)->sring = (_s);                                                 \
 152     (_r)->rsp_prod_pvt = (_s)->rsp_prod;                                \
 153     (_r)->req_cons = (_s)->req_prod;                                    \
 154     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 155 } while (0)
 156
 157 /* How big is this ring? */
 158 #define RING_SIZE(_r)                                                   \
 159     ((_r)->nr_ents)
 160
 161 /* Number of free requests (for use on front side only). */
 162 #define RING_FREE_REQUESTS(_r)                                          \
 163     (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
 164
 165 /* Test if there is an empty slot available on the front ring.
 166  * (This is only meaningful from the front. )
 167  */
 168 #define RING_FULL(_r)                                                   \
 169     (RING_FREE_REQUESTS(_r) == 0)
 170
 171 /* Test if there are outstanding messages to be processed on a ring. */
 172 #define RING_HAS_UNCONSUMED_RESPONSES(_r)                               \
 173     ((_r)->sring->rsp_prod - (_r)->rsp_cons)
 174
 175 #define RING_HAS_UNCONSUMED_REQUESTS(_r)                                \
 176     ({                                                                  \
 177         unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;      \
 178         unsigned int rsp = RING_SIZE(_r) -                              \
 179                            ((_r)->req_cons - (_r)->rsp_prod_pvt);       \
 180         req < rsp ? req : rsp;                                          \
 181     })
 182
 183 /* Direct access to individual ring elements, by index. */
 184 #define RING_GET_REQUEST(_r, _idx)                                      \
 185     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
 186
 187 /*
 188  * Get a local copy of a request.
 189  *
 190  * Use this in preference to RING_GET_REQUEST() so all processing is
 191  * done on a local copy that cannot be modified by the other end.
 192  *
 193  * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
 194  * to be ineffective where _req is a struct which consists of only bitfields.
 195  */
 196 #define RING_COPY_REQUEST(_r, _idx, _req) do {                          \
 197         /* Use volatile to force the copy into _req. */                 \
 198         *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx);   \
 199 } while (0)
 200
 201 #define RING_GET_RESPONSE(_r, _idx)                                     \
 202     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
 203
 204 /* Loop termination condition: Would the specified index overflow the ring? */
 205 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)                           \
 206     (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
 207
 208 /* Ill-behaved frontend determination: Can there be this many requests? */
 209 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod)               \
 210     (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
 211
 212
 213 #define RING_PUSH_REQUESTS(_r) do {                                     \
 214     virt_wmb(); /* back sees requests /before/ updated producer index */        \
 215     (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
 216 } while (0)
 217
 218 #define RING_PUSH_RESPONSES(_r) do {                                    \
 219     virt_wmb(); /* front sees responses /before/ updated producer index */      \
 220     (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;                         \
 221 } while (0)
 222
 223 /*
 224  * Notification hold-off (req_event and rsp_event):
 225  *
 226  * When queueing requests or responses on a shared ring, it may not always be
 227  * necessary to notify the remote end. For example, if requests are in flight
 228  * in a backend, the front may be able to queue further requests without
 229  * notifying the back (if the back checks for new requests when it queues
 230  * responses).
 231  *
 232  * When enqueuing requests or responses:
 233  *
 234  *  Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
 235  *  is a boolean return value. True indicates that the receiver requires an
 236  *  asynchronous notification.
 237  *
 238  * After dequeuing requests or responses (before sleeping the connection):
 239  *
 240  *  Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
 241  *  The second argument is a boolean return value. True indicates that there
 242  *  are pending messages on the ring (i.e., the connection should not be put
 243  *  to sleep).
 244  *
 245  *  These macros will set the req_event/rsp_event field to trigger a
 246  *  notification on the very next message that is enqueued. If you want to
 247  *  create batches of work (i.e., only receive a notification after several
 248  *  messages have been enqueued) then you will need to create a customised
 249  *  version of the FINAL_CHECK macro in your own code, which sets the event
 250  *  field appropriately.
 251  */
 252
 253 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {           \
 254     RING_IDX __old = (_r)->sring->req_prod;                             \
 255     RING_IDX __new = (_r)->req_prod_pvt;                                \
 256     virt_wmb(); /* back sees requests /before/ updated producer index */        \
 257     (_r)->sring->req_prod = __new;                                      \
 258     virt_mb(); /* back sees new requests /before/ we check req_event */ \
 259     (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <           \
 260                  (RING_IDX)(__new - __old));                            \
 261 } while (0)
 262
 263 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {          \
 264     RING_IDX __old = (_r)->sring->rsp_prod;                             \
 265     RING_IDX __new = (_r)->rsp_prod_pvt;                                \
 266     virt_wmb(); /* front sees responses /before/ updated producer index */      \
 267     (_r)->sring->rsp_prod = __new;                                      \
 268     virt_mb(); /* front sees new responses /before/ we check rsp_event */       \
 269     (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <           \
 270                  (RING_IDX)(__new - __old));                            \
 271 } while (0)
 272
 273 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do {             \
 274     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 275     if (_work_to_do) break;                                             \
 276     (_r)->sring->req_event = (_r)->req_cons + 1;                        \
 277     virt_mb();                                                          \
 278     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 279 } while (0)
 280
 281 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do {            \
 282     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 283     if (_work_to_do) break;                                             \
 284     (_r)->sring->rsp_event = (_r)->rsp_cons + 1;                        \
 285     virt_mb();                                                          \
 286     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 287 } while (0)
 288
 289
 290 /*
 291  * DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and
 292  * functions to check if there is data on the ring, and to read and
 293  * write to them.
 294  *
 295  * DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but
 296  * does not define the indexes page. As different protocols can have
 297  * extensions to the basic format, this macro allow them to define their
 298  * own struct.
 299  *
 300  * XEN_FLEX_RING_SIZE
 301  *   Convenience macro to calculate the size of one of the two rings
 302  *   from the overall order.
 303  *
 304  * $NAME_mask
 305  *   Function to apply the size mask to an index, to reduce the index
 306  *   within the range [0-size].
 307  *
 308  * $NAME_read_packet
 309  *   Function to read data from the ring. The amount of data to read is
 310  *   specified by the "size" argument.
 311  *
 312  * $NAME_write_packet
 313  *   Function to write data to the ring. The amount of data to write is
 314  *   specified by the "size" argument.
 315  *
 316  * $NAME_get_ring_ptr
 317  *   Convenience function that returns a pointer to read/write to the
 318  *   ring at the right location.
 319  *
 320  * $NAME_data_intf
 321  *   Indexes page, shared between frontend and backend. It also
 322  *   contains the array of grant refs.
 323  *
 324  * $NAME_queued
 325  *   Function to calculate how many bytes are currently on the ring,
 326  *   ready to be read. It can also be used to calculate how much free
 327  *   space is currently on the ring (XEN_FLEX_RING_SIZE() -
 328  *   $NAME_queued()).
 329  */
 330
 331 #ifndef XEN_PAGE_SHIFT
 332 /* The PAGE_SIZE for ring protocols and hypercall interfaces is always
 333  * 4K, regardless of the architecture, and page granularity chosen by
 334  * operating systems.
 335  */
 336 #define XEN_PAGE_SHIFT 12
 337 #endif
 338 #define XEN_FLEX_RING_SIZE(order)                                             \
 339     (1UL << ((order) + XEN_PAGE_SHIFT - 1))
 340
 341 #define DEFINE_XEN_FLEX_RING(name)                                            \
 342 static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size)          \
 343 {                                                                             \
 344     return idx & (ring_size - 1);                                             \
 345 }                                                                             \
 346                                                                               \
 347 static inline unsigned char *name##_get_ring_ptr(unsigned char *buf,          \
 348                                                  RING_IDX idx,                \
 349                                                  RING_IDX ring_size)          \
 350 {                                                                             \
 351     return buf + name##_mask(idx, ring_size);                                 \
 352 }                                                                             \
 353                                                                               \
 354 static inline void name##_read_packet(void *opaque,                           \
 355                                       const unsigned char *buf,               \
 356                                       size_t size,                            \
 357                                       RING_IDX masked_prod,                   \
 358                                       RING_IDX *masked_cons,                  \
 359                                       RING_IDX ring_size)                     \
 360 {                                                                             \
 361     if (*masked_cons < masked_prod ||                                         \
 362         size <= ring_size - *masked_cons) {                                   \
 363         memcpy(opaque, buf + *masked_cons, size);                             \
 364     } else {                                                                  \
 365         memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons);         \
 366         memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf,       \
 367                size - (ring_size - *masked_cons));                            \
 368     }                                                                         \
 369     *masked_cons = name##_mask(*masked_cons + size, ring_size);               \
 370 }                                                                             \
 371                                                                               \
 372 static inline void name##_write_packet(unsigned char *buf,                    \
 373                                        const void *opaque,                    \
 374                                        size_t size,                           \
 375                                        RING_IDX *masked_prod,                 \
 376                                        RING_IDX masked_cons,                  \
 377                                        RING_IDX ring_size)                    \
 378 {                                                                             \
 379     if (*masked_prod < masked_cons ||                                         \
 380         size <= ring_size - *masked_prod) {                                   \
 381         memcpy(buf + *masked_prod, opaque, size);                             \
 382     } else {                                                                  \
 383         memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod);         \
 384         memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod),     \
 385                size - (ring_size - *masked_prod));                            \
 386     }                                                                         \
 387     *masked_prod = name##_mask(*masked_prod + size, ring_size);               \
 388 }                                                                             \
 389                                                                               \
 390 static inline RING_IDX name##_queued(RING_IDX prod,                           \
 391                                      RING_IDX cons,                           \
 392                                      RING_IDX ring_size)                      \
 393 {                                                                             \
 394     RING_IDX size;                                                            \
 395                                                                               \
 396     if (prod == cons)                                                         \
 397         return 0;                                                             \
 398                                                                               \
 399     prod = name##_mask(prod, ring_size);                                      \
 400     cons = name##_mask(cons, ring_size);                                      \
 401                                                                               \
 402     if (prod == cons)                                                         \
 403         return ring_size;                                                     \
 404                                                                               \
 405     if (prod > cons)                                                          \
 406         size = prod - cons;                                                   \
 407     else                                                                      \
 408         size = ring_size - (cons - prod);                                     \
 409     return size;                                                              \
 410 }                                                                             \
 411                                                                               \
 412 struct name##_data {                                                          \
 413     unsigned char *in; /* half of the allocation */                           \
 414     unsigned char *out; /* half of the allocation */                          \
 415 }
 416
 417 #define DEFINE_XEN_FLEX_RING_AND_INTF(name)                                   \
 418 struct name##_data_intf {                                                     \
 419     RING_IDX in_cons, in_prod;                                                \
 420                                                                               \
 421     uint8_t pad1[56];                                                         \
 422                                                                               \
 423     RING_IDX out_cons, out_prod;                                              \
 424                                                                               \
 425     uint8_t pad2[56];                                                         \
 426                                                                               \
 427     RING_IDX ring_order;                                                      \
 428     grant_ref_t ref[];                                                        \
 429 };                                                                            \
 430 DEFINE_XEN_FLEX_RING(name)
 431
 432 #endif /* __XEN_PUBLIC_IO_RING_H__ */