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 #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 /*
  58  * The same for passing in an actual pointer instead of a name tag.
  59  */
  60 #define __RING_SIZE(_s, _sz)                                            \
  61         (__RD32(((_sz) - (long)&(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
  62
  63 /*
  64  * Macros to make the correct C datatypes for a new kind of ring.
  65  *
  66  * To make a new ring datatype, you need to have two message structures,
  67  * let's say request_t, and response_t already defined.
  68  *
  69  * In a header where you want the ring datatype declared, you then do:
  70  *
  71  *     DEFINE_RING_TYPES(mytag, request_t, response_t);
  72  *
  73  * These expand out to give you a set of types, as you can see below.
  74  * The most important of these are:
  75  *
  76  *     mytag_sring_t      - The shared ring.
  77  *     mytag_front_ring_t - The 'front' half of the ring.
  78  *     mytag_back_ring_t  - The 'back' half of the ring.
  79  *
  80  * To initialize a ring in your code you need to know the location and size
  81  * of the shared memory area (PAGE_SIZE, for instance). To initialise
  82  * the front half:
  83  *
  84  *     mytag_front_ring_t front_ring;
  85  *     SHARED_RING_INIT((mytag_sring_t *)shared_page);
  86  *     FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
  87  *
  88  * Initializing the back follows similarly (note that only the front
  89  * initializes the shared ring):
  90  *
  91  *     mytag_back_ring_t back_ring;
  92  *     BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
  93  */
  94
  95 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)                     \
  96                                                                         \
  97 /* Shared ring entry */                                                 \
  98 union __name##_sring_entry {                                            \
  99     __req_t req;                                                        \
 100     __rsp_t rsp;                                                        \
 101 };                                                                      \
 102                                                                         \
 103 /* Shared ring page */                                                  \
 104 struct __name##_sring {                                                 \
 105     RING_IDX req_prod, req_event;                                       \
 106     RING_IDX rsp_prod, rsp_event;                                       \
 107     union {                                                             \
 108         struct {                                                        \
 109             uint8_t smartpoll_active;                                   \
 110         } netif;                                                        \
 111         struct {                                                        \
 112             uint8_t msg;                                                \
 113         } tapif_user;                                                   \
 114         uint8_t pvt_pad[4];                                             \
 115     } private;                                                          \
 116     uint8_t __pad[44];                                                  \
 117     union __name##_sring_entry ring[1]; /* variable-length */           \
 118 };                                                                      \
 119                                                                         \
 120 /* "Front" end's private variables */                                   \
 121 struct __name##_front_ring {                                            \
 122     RING_IDX req_prod_pvt;                                              \
 123     RING_IDX rsp_cons;                                                  \
 124     unsigned int nr_ents;                                               \
 125     struct __name##_sring *sring;                                       \
 126 };                                                                      \
 127                                                                         \
 128 /* "Back" end's private variables */                                    \
 129 struct __name##_back_ring {                                             \
 130     RING_IDX rsp_prod_pvt;                                              \
 131     RING_IDX req_cons;                                                  \
 132     unsigned int nr_ents;                                               \
 133     struct __name##_sring *sring;                                       \
 134 };                                                                      \
 135                                                                         \
 136 /* Syntactic sugar */                                                   \
 137 typedef struct __name##_sring __name##_sring_t;                 \
 138 typedef struct __name##_front_ring __name##_front_ring_t;               \
 139 typedef struct __name##_back_ring __name##_back_ring_t
 140
 141 /*
 142  * Macros for manipulating rings.
 143  *
 144  * FRONT_RING_whatever works on the "front end" of a ring: here
 145  * requests are pushed on to the ring and responses taken off it.
 146  *
 147  * BACK_RING_whatever works on the "back end" of a ring: here
 148  * requests are taken off the ring and responses put on.
 149  *
 150  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
 151  * This is OK in 1-for-1 request-response situations where the
 152  * requestor (front end) never has more than RING_SIZE()-1
 153  * outstanding requests.
 154  */
 155
 156 /* Initialising empty rings */
 157 #define SHARED_RING_INIT(_s) do {                                       \
 158     (_s)->req_prod  = (_s)->rsp_prod  = 0;                              \
 159     (_s)->req_event = (_s)->rsp_event = 1;                              \
 160     (void)memset((_s)->private.pvt_pad, 0, sizeof((_s)->private.pvt_pad)); \
 161     (void)memset((_s)->__pad, 0, sizeof((_s)->__pad));                  \
 162 } while(0)
 163
 164 #define FRONT_RING_INIT(_r, _s, __size) do {                            \
 165     (_r)->req_prod_pvt = 0;                                             \
 166     (_r)->rsp_cons = 0;                                                 \
 167     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 168     (_r)->sring = (_s);                                                 \
 169 } while (0)
 170
 171 #define BACK_RING_INIT(_r, _s, __size) do {                             \
 172     (_r)->rsp_prod_pvt = 0;                                             \
 173     (_r)->req_cons = 0;                                                 \
 174     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 175     (_r)->sring = (_s);                                                 \
 176 } while (0)
 177
 178 /* Initialize to existing shared indexes -- for recovery */
 179 #define FRONT_RING_ATTACH(_r, _s, __size) do {                          \
 180     (_r)->sring = (_s);                                                 \
 181     (_r)->req_prod_pvt = (_s)->req_prod;                                \
 182     (_r)->rsp_cons = (_s)->rsp_prod;                                    \
 183     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 184 } while (0)
 185
 186 #define BACK_RING_ATTACH(_r, _s, __size) do {                           \
 187     (_r)->sring = (_s);                                                 \
 188     (_r)->rsp_prod_pvt = (_s)->rsp_prod;                                \
 189     (_r)->req_cons = (_s)->req_prod;                                    \
 190     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 191 } while (0)
 192
 193 /* How big is this ring? */
 194 #define RING_SIZE(_r)                                                   \
 195     ((_r)->nr_ents)
 196
 197 /* Number of free requests (for use on front side only). */
 198 #define RING_FREE_REQUESTS(_r)                                          \
 199     (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
 200
 201 /* Test if there is an empty slot available on the front ring.
 202  * (This is only meaningful from the front. )
 203  */
 204 #define RING_FULL(_r)                                                   \
 205     (RING_FREE_REQUESTS(_r) == 0)
 206
 207 /* Test if there are outstanding messages to be processed on a ring. */
 208 #define RING_HAS_UNCONSUMED_RESPONSES(_r)                               \
 209     ((_r)->sring->rsp_prod - (_r)->rsp_cons)
 210
 211 #ifdef __GNUC__
 212 #define RING_HAS_UNCONSUMED_REQUESTS(_r)                                \
 213     ({                                                                  \
 214         unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;      \
 215         unsigned int rsp = RING_SIZE(_r) -                              \
 216                            ((_r)->req_cons - (_r)->rsp_prod_pvt);       \
 217         req < rsp ? req : rsp;                                          \
 218     })
 219 #else
 220 /* Same as above, but without the nice GCC ({ ... }) syntax. */
 221 #define RING_HAS_UNCONSUMED_REQUESTS(_r)                                \
 222     ((((_r)->sring->req_prod - (_r)->req_cons) <                        \
 223       (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ?        \
 224      ((_r)->sring->req_prod - (_r)->req_cons) :                 \
 225      (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
 226 #endif
 227
 228 /* Direct access to individual ring elements, by index. */
 229 #define RING_GET_REQUEST(_r, _idx)                                      \
 230     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
 231
 232 #define RING_GET_RESPONSE(_r, _idx)                                     \
 233     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
 234
 235 /* Loop termination condition: Would the specified index overflow the ring? */
 236 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)                           \
 237     (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
 238
 239 #define RING_PUSH_REQUESTS(_r) do {                                     \
 240     xen_wmb(); /* back sees requests /before/ updated producer index */ \
 241     (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
 242 } while (0)
 243
 244 #define RING_PUSH_RESPONSES(_r) do {                                    \
 245     xen_wmb(); /* front sees resps /before/ updated producer index */   \
 246     (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;                         \
 247 } while (0)
 248
 249 /*
 250  * Notification hold-off (req_event and rsp_event):
 251  *
 252  * When queueing requests or responses on a shared ring, it may not always be
 253  * necessary to notify the remote end. For example, if requests are in flight
 254  * in a backend, the front may be able to queue further requests without
 255  * notifying the back (if the back checks for new requests when it queues
 256  * responses).
 257  *
 258  * When enqueuing requests or responses:
 259  *
 260  *  Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
 261  *  is a boolean return value. True indicates that the receiver requires an
 262  *  asynchronous notification.
 263  *
 264  * After dequeuing requests or responses (before sleeping the connection):
 265  *
 266  *  Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
 267  *  The second argument is a boolean return value. True indicates that there
 268  *  are pending messages on the ring (i.e., the connection should not be put
 269  *  to sleep).
 270  *
 271  *  These macros will set the req_event/rsp_event field to trigger a
 272  *  notification on the very next message that is enqueued. If you want to
 273  *  create batches of work (i.e., only receive a notification after several
 274  *  messages have been enqueued) then you will need to create a customised
 275  *  version of the FINAL_CHECK macro in your own code, which sets the event
 276  *  field appropriately.
 277  */
 278
 279 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {           \
 280     RING_IDX __old = (_r)->sring->req_prod;                             \
 281     RING_IDX __new = (_r)->req_prod_pvt;                                \
 282     xen_wmb(); /* back sees requests /before/ updated producer index */ \
 283     (_r)->sring->req_prod = __new;                                      \
 284     xen_mb(); /* back sees new requests /before/ we check req_event */  \
 285     (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <           \
 286                  (RING_IDX)(__new - __old));                            \
 287 } while (0)
 288
 289 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {          \
 290     RING_IDX __old = (_r)->sring->rsp_prod;                             \
 291     RING_IDX __new = (_r)->rsp_prod_pvt;                                \
 292     xen_wmb(); /* front sees resps /before/ updated producer index */   \
 293     (_r)->sring->rsp_prod = __new;                                      \
 294     xen_mb(); /* front sees new resps /before/ we check rsp_event */    \
 295     (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <           \
 296                  (RING_IDX)(__new - __old));                            \
 297 } while (0)
 298
 299 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do {             \
 300     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 301     if (_work_to_do) break;                                             \
 302     (_r)->sring->req_event = (_r)->req_cons + 1;                        \
 303     xen_mb();                                                           \
 304     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 305 } while (0)
 306
 307 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do {            \
 308     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 309     if (_work_to_do) break;                                             \
 310     (_r)->sring->rsp_event = (_r)->rsp_cons + 1;                        \
 311     xen_mb();                                                           \
 312     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 313 } while (0)
 314
 315 #endif /* __XEN_PUBLIC_IO_RING_H__ */