usr/src/uts/common/xen/public/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 #include "../xen-compat.h"
  31
  32 #if __XEN_INTERFACE_VERSION__ < 0x00030208
  33 #define xen_mb()  mb()
  34 #define xen_rmb() rmb()
  35 #define xen_wmb() wmb()
  36 #endif
  37
  38 typedef unsigned int RING_IDX;
  39
  40 /* Round a 32-bit unsigned constant down to the nearest power of two. */
  41 #define __RD2(_x)  (((_x) & 0x00000002) ? 0x2                  : ((_x) & 0x1))
  42 #define __RD4(_x)  (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2    : __RD2(_x))
  43 #define __RD8(_x)  (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4    : __RD4(_x))
  44 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8    : __RD8(_x))
  45 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
  46
  47 /*
  48  * Calculate size of a shared ring, given the total available space for the
  49  * ring and indexes (_sz), and the name tag of the request/response structure.
  50  * A ring contains as many entries as will fit, rounded down to the nearest
  51  * power of two (so we can mask with (size-1) to loop around).
  52  */
  53 #define __CONST_RING_SIZE(_s, _sz) \
  54     (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
  55        sizeof(((struct _s##_sring *)0)->ring[0])))
  56 /*
  57  * The same for passing in an actual pointer instead of a name tag.
  58  */
  59 #define __RING_SIZE(_s, _sz) \
  60     (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
  61
  62 /*
  63  * Macros to make the correct C datatypes for a new kind of ring.
  64  *
  65  * To make a new ring datatype, you need to have two message structures,
  66  * let's say request_t, and response_t already defined.
  67  *
  68  * In a header where you want the ring datatype declared, you then do:
  69  *
  70  *     DEFINE_RING_TYPES(mytag, request_t, response_t);
  71  *
  72  * These expand out to give you a set of types, as you can see below.
  73  * The most important of these are:
  74  *
  75  *     mytag_sring_t      - The shared ring.
  76  *     mytag_front_ring_t - The 'front' half of the ring.
  77  *     mytag_back_ring_t  - The 'back' half of the ring.
  78  *
  79  * To initialize a ring in your code you need to know the location and size
  80  * of the shared memory area (PAGE_SIZE, for instance). To initialise
  81  * the front half:
  82  *
  83  *     mytag_front_ring_t front_ring;
  84  *     SHARED_RING_INIT((mytag_sring_t *)shared_page);
  85  *     FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
  86  *
  87  * Initializing the back follows similarly (note that only the front
  88  * initializes the shared ring):
  89  *
  90  *     mytag_back_ring_t back_ring;
  91  *     BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
  92  */
  93
  94 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)                     \
  95                                                                         \
  96 /* Shared ring entry */                                                 \
  97 union __name##_sring_entry {                                            \
  98     __req_t req;                                                        \
  99     __rsp_t rsp;                                                        \
 100 };                                                                      \
 101                                                                         \
 102 /* Shared ring page */                                                  \
 103 struct __name##_sring {                                                 \
 104     RING_IDX req_prod, req_event;                                       \
 105     RING_IDX rsp_prod, rsp_event;                                       \
 106     uint8_t  pad[48];                                                   \
 107     union __name##_sring_entry ring[1]; /* variable-length */           \
 108 };                                                                      \
 109                                                                         \
 110 /* "Front" end's private variables */                                   \
 111 struct __name##_front_ring {                                            \
 112     RING_IDX req_prod_pvt;                                              \
 113     RING_IDX rsp_cons;                                                  \
 114     unsigned int nr_ents;                                               \
 115     struct __name##_sring *sring;                                       \
 116 };                                                                      \
 117                                                                         \
 118 /* "Back" end's private variables */                                    \
 119 struct __name##_back_ring {                                             \
 120     RING_IDX rsp_prod_pvt;                                              \
 121     RING_IDX req_cons;                                                  \
 122     unsigned int nr_ents;                                               \
 123     struct __name##_sring *sring;                                       \
 124 };                                                                      \
 125                                                                         \
 126 /* Syntactic sugar */                                                   \
 127 typedef struct __name##_sring __name##_sring_t;                         \
 128 typedef struct __name##_front_ring __name##_front_ring_t;               \
 129 typedef struct __name##_back_ring __name##_back_ring_t
 130
 131 /*
 132  * Macros for manipulating rings.
 133  *
 134  * FRONT_RING_whatever works on the "front end" of a ring: here
 135  * requests are pushed on to the ring and responses taken off it.
 136  *
 137  * BACK_RING_whatever works on the "back end" of a ring: here
 138  * requests are taken off the ring and responses put on.
 139  *
 140  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
 141  * This is OK in 1-for-1 request-response situations where the
 142  * requestor (front end) never has more than RING_SIZE()-1
 143  * outstanding requests.
 144  */
 145
 146 /* Initialising empty rings */
 147 #define SHARED_RING_INIT(_s) do {                                       \
 148     (_s)->req_prod  = (_s)->rsp_prod  = 0;                              \
 149     (_s)->req_event = (_s)->rsp_event = 1;                              \
 150     (void)memset((_s)->pad, 0, sizeof((_s)->pad));                      \
 151 } while(0)
 152
 153 #define FRONT_RING_INIT(_r, _s, __size) do {                            \
 154     (_r)->req_prod_pvt = 0;                                             \
 155     (_r)->rsp_cons = 0;                                                 \
 156     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 157     (_r)->sring = (_s);                                                 \
 158 } while (0)
 159
 160 #define BACK_RING_INIT(_r, _s, __size) do {                             \
 161     (_r)->rsp_prod_pvt = 0;                                             \
 162     (_r)->req_cons = 0;                                                 \
 163     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 164     (_r)->sring = (_s);                                                 \
 165 } while (0)
 166
 167 /* Initialize to existing shared indexes -- for recovery */
 168 #define FRONT_RING_ATTACH(_r, _s, __size) do {                          \
 169     (_r)->sring = (_s);                                                 \
 170     (_r)->req_prod_pvt = (_s)->req_prod;                                \
 171     (_r)->rsp_cons = (_s)->rsp_prod;                                    \
 172     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 173 } while (0)
 174
 175 #define BACK_RING_ATTACH(_r, _s, __size) do {                           \
 176     (_r)->sring = (_s);                                                 \
 177     (_r)->rsp_prod_pvt = (_s)->rsp_prod;                                \
 178     (_r)->req_cons = (_s)->req_prod;                                    \
 179     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 180 } while (0)
 181
 182 /* How big is this ring? */
 183 #define RING_SIZE(_r)                                                   \
 184     ((_r)->nr_ents)
 185
 186 /* Number of free requests (for use on front side only). */
 187 #define RING_FREE_REQUESTS(_r)                                          \
 188     (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
 189
 190 /* Test if there is an empty slot available on the front ring.
 191  * (This is only meaningful from the front. )
 192  */
 193 #define RING_FULL(_r)                                                   \
 194     (RING_FREE_REQUESTS(_r) == 0)
 195
 196 /* Test if there are outstanding messages to be processed on a ring. */
 197 #define RING_HAS_UNCONSUMED_RESPONSES(_r)                               \
 198     ((_r)->sring->rsp_prod - (_r)->rsp_cons)
 199
 200 #ifdef __GNUC__
 201 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({                             \
 202     unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;          \
 203     unsigned int rsp = RING_SIZE(_r) -                                  \
 204         ((_r)->req_cons - (_r)->rsp_prod_pvt);                          \
 205     req < rsp ? req : rsp;                                              \
 206 })
 207 #else
 208 /* Same as above, but without the nice GCC ({ ... }) syntax. */
 209 #define RING_HAS_UNCONSUMED_REQUESTS(_r)                                \
 210     ((((_r)->sring->req_prod - (_r)->req_cons) <                        \
 211       (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ?        \
 212      ((_r)->sring->req_prod - (_r)->req_cons) :                         \
 213      (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
 214 #endif
 215
 216 /* Direct access to individual ring elements, by index. */
 217 #define RING_GET_REQUEST(_r, _idx)                                      \
 218     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
 219
 220 #define RING_GET_RESPONSE(_r, _idx)                                     \
 221     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
 222
 223 /* Loop termination condition: Would the specified index overflow the ring? */
 224 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)                           \
 225     (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
 226
 227 #define RING_PUSH_REQUESTS(_r) do {                                     \
 228     xen_wmb(); /* back sees requests /before/ updated producer index */ \
 229     (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
 230 } while (0)
 231
 232 #define RING_PUSH_RESPONSES(_r) do {                                    \
 233     xen_wmb(); /* front sees resps /before/ updated producer index */   \
 234     (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;                         \
 235 } while (0)
 236
 237 /*
 238  * Notification hold-off (req_event and rsp_event):
 239  *
 240  * When queueing requests or responses on a shared ring, it may not always be
 241  * necessary to notify the remote end. For example, if requests are in flight
 242  * in a backend, the front may be able to queue further requests without
 243  * notifying the back (if the back checks for new requests when it queues
 244  * responses).
 245  *
 246  * When enqueuing requests or responses:
 247  *
 248  *  Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
 249  *  is a boolean return value. True indicates that the receiver requires an
 250  *  asynchronous notification.
 251  *
 252  * After dequeuing requests or responses (before sleeping the connection):
 253  *
 254  *  Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
 255  *  The second argument is a boolean return value. True indicates that there
 256  *  are pending messages on the ring (i.e., the connection should not be put
 257  *  to sleep).
 258  *
 259  *  These macros will set the req_event/rsp_event field to trigger a
 260  *  notification on the very next message that is enqueued. If you want to
 261  *  create batches of work (i.e., only receive a notification after several
 262  *  messages have been enqueued) then you will need to create a customised
 263  *  version of the FINAL_CHECK macro in your own code, which sets the event
 264  *  field appropriately.
 265  */
 266
 267 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {           \
 268     RING_IDX __old = (_r)->sring->req_prod;                             \
 269     RING_IDX __new = (_r)->req_prod_pvt;                                \
 270     xen_wmb(); /* back sees requests /before/ updated producer index */ \
 271     (_r)->sring->req_prod = __new;                                      \
 272     xen_mb(); /* back sees new requests /before/ we check req_event */  \
 273     (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <           \
 274                  (RING_IDX)(__new - __old));                            \
 275 } while (0)
 276
 277 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {          \
 278     RING_IDX __old = (_r)->sring->rsp_prod;                             \
 279     RING_IDX __new = (_r)->rsp_prod_pvt;                                \
 280     xen_wmb(); /* front sees resps /before/ updated producer index */   \
 281     (_r)->sring->rsp_prod = __new;                                      \
 282     xen_mb(); /* front sees new resps /before/ we check rsp_event */    \
 283     (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <           \
 284                  (RING_IDX)(__new - __old));                            \
 285 } while (0)
 286
 287 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do {             \
 288     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 289     if (_work_to_do) break;                                             \
 290     (_r)->sring->req_event = (_r)->req_cons + 1;                        \
 291     xen_mb();                                                           \
 292     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 293 } while (0)
 294
 295 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do {            \
 296     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 297     if (_work_to_do) break;                                             \
 298     (_r)->sring->rsp_event = (_r)->rsp_cons + 1;                        \
 299     xen_mb();                                                           \
 300     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 301 } while (0)
 302
 303 #endif /* __XEN_PUBLIC_IO_RING_H__ */
 304
 305 /*
 306  * Local variables:
 307  * mode: C
 308  * c-set-style: "BSD"
 309  * c-basic-offset: 4
 310  * tab-width: 4
 311  * indent-tabs-mode: nil
 312  * End:
 313  */