sys/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  * The amount of space reserved in the shared ring for accounting information.
  49  */
  50 #define __RING_HEADER_SIZE(_s) \
  51     ((intptr_t)(_s)->ring - (intptr_t)(_s))
  52
  53 /*
  54  * Calculate size of a shared ring, given the total available space for the
  55  * ring and indexes (_sz), and the name tag of the request/response structure.
  56  * A ring contains as many entries as will fit, rounded down to the nearest
  57  * power of two (so we can mask with (size-1) to loop around).
  58  */
  59 #define __CONST_RING_SIZE(_s, _sz) \
  60     (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
  61             sizeof(((struct _s##_sring *)0)->ring[0])))
  62 /*
  63  * The same for passing in an actual pointer instead of a name tag.
  64  */
  65 #define __RING_SIZE(_s, _sz) \
  66     (__RD32(((_sz) - __RING_HEADER_SIZE(_s)) / sizeof((_s)->ring[0])))
  67
  68 /*
  69  * The number of pages needed to support a given number of request/reponse
  70  * entries.  The entry count is rounded down to the nearest power of two
  71  * as required by the ring macros.
  72  */
  73 #define __RING_PAGES(_s, _entries)              \
  74     ((__RING_HEADER_SIZE(_s)                    \
  75    + (__RD32(_entries) * sizeof((_s)->ring[0])) \
  76    + PAGE_SIZE - 1) / PAGE_SIZE)
  77
  78 /*
  79  * Macros to make the correct C datatypes for a new kind of ring.
  80  *
  81  * To make a new ring datatype, you need to have two message structures,
  82  * let's say request_t, and response_t already defined.
  83  *
  84  * In a header where you want the ring datatype declared, you then do:
  85  *
  86  *     DEFINE_RING_TYPES(mytag, request_t, response_t);
  87  *
  88  * These expand out to give you a set of types, as you can see below.
  89  * The most important of these are:
  90  *
  91  *     mytag_sring_t      - The shared ring.
  92  *     mytag_front_ring_t - The 'front' half of the ring.
  93  *     mytag_back_ring_t  - The 'back' half of the ring.
  94  *
  95  * To initialize a ring in your code you need to know the location and size
  96  * of the shared memory area (PAGE_SIZE, for instance). To initialise
  97  * the front half:
  98  *
  99  *     mytag_front_ring_t front_ring;
 100  *     SHARED_RING_INIT((mytag_sring_t *)shared_page);
 101  *     FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
 102  *
 103  * Initializing the back follows similarly (note that only the front
 104  * initializes the shared ring):
 105  *
 106  *     mytag_back_ring_t back_ring;
 107  *     BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
 108  */
 109
 110 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)                     \
 111                                                                         \
 112 /* Shared ring entry */                                                 \
 113 union __name##_sring_entry {                                            \
 114     __req_t req;                                                        \
 115     __rsp_t rsp;                                                        \
 116 };                                                                      \
 117                                                                         \
 118 /* Shared ring page */                                                  \
 119 struct __name##_sring {                                                 \
 120     RING_IDX req_prod, req_event;                                       \
 121     RING_IDX rsp_prod, rsp_event;                                       \
 122     union {                                                             \
 123         struct {                                                        \
 124             uint8_t smartpoll_active;                                   \
 125         } netif;                                                        \
 126         struct {                                                        \
 127             uint8_t msg;                                                \
 128         } tapif_user;                                                   \
 129         uint8_t pvt_pad[4];                                             \
 130     } private;                                                          \
 131     uint8_t __pad[44];                                                  \
 132     union __name##_sring_entry ring[1]; /* variable-length */           \
 133 };                                                                      \
 134                                                                         \
 135 /* "Front" end's private variables */                                   \
 136 struct __name##_front_ring {                                            \
 137     RING_IDX req_prod_pvt;                                              \
 138     RING_IDX rsp_cons;                                                  \
 139     unsigned int nr_ents;                                               \
 140     struct __name##_sring *sring;                                       \
 141 };                                                                      \
 142                                                                         \
 143 /* "Back" end's private variables */                                    \
 144 struct __name##_back_ring {                                             \
 145     RING_IDX rsp_prod_pvt;                                              \
 146     RING_IDX req_cons;                                                  \
 147     unsigned int nr_ents;                                               \
 148     struct __name##_sring *sring;                                       \
 149 };                                                                      \
 150                                                                         \
 151 /* Syntactic sugar */                                                   \
 152 typedef struct __name##_sring __name##_sring_t;                         \
 153 typedef struct __name##_front_ring __name##_front_ring_t;               \
 154 typedef struct __name##_back_ring __name##_back_ring_t
 155
 156 /*
 157  * Macros for manipulating rings.
 158  *
 159  * FRONT_RING_whatever works on the "front end" of a ring: here
 160  * requests are pushed on to the ring and responses taken off it.
 161  *
 162  * BACK_RING_whatever works on the "back end" of a ring: here
 163  * requests are taken off the ring and responses put on.
 164  *
 165  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
 166  * This is OK in 1-for-1 request-response situations where the
 167  * requestor (front end) never has more than RING_SIZE()-1
 168  * outstanding requests.
 169  */
 170
 171 /* Initialising empty rings */
 172 #define SHARED_RING_INIT(_s) do {                                       \
 173     (_s)->req_prod  = (_s)->rsp_prod  = 0;                              \
 174     (_s)->req_event = (_s)->rsp_event = 1;                              \
 175     (void)memset((_s)->private.pvt_pad, 0, sizeof((_s)->private.pvt_pad)); \
 176     (void)memset((_s)->__pad, 0, sizeof((_s)->__pad));                  \
 177 } while(0)
 178
 179 #define FRONT_RING_INIT(_r, _s, __size) do {                            \
 180     (_r)->req_prod_pvt = 0;                                             \
 181     (_r)->rsp_cons = 0;                                                 \
 182     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 183     (_r)->sring = (_s);                                                 \
 184 } while (0)
 185
 186 #define BACK_RING_INIT(_r, _s, __size) do {                             \
 187     (_r)->rsp_prod_pvt = 0;                                             \
 188     (_r)->req_cons = 0;                                                 \
 189     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 190     (_r)->sring = (_s);                                                 \
 191 } while (0)
 192
 193 /* Initialize to existing shared indexes -- for recovery */
 194 #define FRONT_RING_ATTACH(_r, _s, __size) do {                          \
 195     (_r)->sring = (_s);                                                 \
 196     (_r)->req_prod_pvt = (_s)->req_prod;                                \
 197     (_r)->rsp_cons = (_s)->rsp_prod;                                    \
 198     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 199 } while (0)
 200
 201 #define BACK_RING_ATTACH(_r, _s, __size) do {                           \
 202     (_r)->sring = (_s);                                                 \
 203     (_r)->rsp_prod_pvt = (_s)->rsp_prod;                                \
 204     (_r)->req_cons = (_s)->req_prod;                                    \
 205     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 206 } while (0)
 207
 208 /* How big is this ring? */
 209 #define RING_SIZE(_r)                                                   \
 210     ((_r)->nr_ents)
 211
 212 /* Number of free requests (for use on front side only). */
 213 #define RING_FREE_REQUESTS(_r)                                          \
 214     (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
 215
 216 /* Test if there is an empty slot available on the front ring.
 217  * (This is only meaningful from the front. )
 218  */
 219 #define RING_FULL(_r)                                                   \
 220     (RING_FREE_REQUESTS(_r) == 0)
 221
 222 /* Test if there are outstanding messages to be processed on a ring. */
 223 #define RING_HAS_UNCONSUMED_RESPONSES(_r)                               \
 224     ((_r)->sring->rsp_prod - (_r)->rsp_cons)
 225
 226 #ifdef __GNUC__
 227 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({                             \
 228     unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;          \
 229     unsigned int rsp = RING_SIZE(_r) -                                  \
 230         ((_r)->req_cons - (_r)->rsp_prod_pvt);                          \
 231     req < rsp ? req : rsp;                                              \
 232 })
 233 #else
 234 /* Same as above, but without the nice GCC ({ ... }) syntax. */
 235 #define RING_HAS_UNCONSUMED_REQUESTS(_r)                                \
 236     ((((_r)->sring->req_prod - (_r)->req_cons) <                        \
 237       (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ?        \
 238      ((_r)->sring->req_prod - (_r)->req_cons) :                         \
 239      (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
 240 #endif
 241
 242 /* Direct access to individual ring elements, by index. */
 243 #define RING_GET_REQUEST(_r, _idx)                                      \
 244     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
 245
 246 #define RING_GET_RESPONSE(_r, _idx)                                     \
 247     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
 248
 249 /* Loop termination condition: Would the specified index overflow the ring? */
 250 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)                           \
 251     (((_cons) - (_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 #endif /* __XEN_PUBLIC_IO_RING_H__ */
 330
 331 /*
 332  * Local variables:
 333  * mode: C
 334  * c-set-style: "BSD"
 335  * c-basic-offset: 4
 336  * tab-width: 4
 337  * indent-tabs-mode: nil
 338  * End:
 339  */