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Annotation of Gnu-Mach/xen/public/io/ring.h, revision 1.1

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

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