interface/io/ring.h

0001 /* SPDX-License-Identifier: MIT */
0002 /******************************************************************************
0003  * ring.h
0004  *
0005  * Shared producer-consumer ring macros.
0006  *
0007  * Tim Deegan and Andrew Warfield November 2004.
0008  */
0009
0010 #ifndef __XEN_PUBLIC_IO_RING_H__
0011 #define __XEN_PUBLIC_IO_RING_H__
0012
0013 /*
0014  * When #include'ing this header, you need to provide the following
0015  * declaration upfront:
0016  * - standard integers types (uint8_t, uint16_t, etc)
0017  * They are provided by stdint.h of the standard headers.
0018  *
0019  * In addition, if you intend to use the FLEX macros, you also need to
0020  * provide the following, before invoking the FLEX macros:
0021  * - size_t
0022  * - memcpy
0023  * - grant_ref_t
0024  * These declarations are provided by string.h of the standard headers,
0025  * and grant_table.h from the Xen public headers.
0026  */
0027
0028 #include <xen/interface/grant_table.h>
0029
0030 typedef unsigned int RING_IDX;
0031
0032 /* Round a 32-bit unsigned constant down to the nearest power of two. */
0033 #define __RD2(_x)  (((_x) & 0x00000002) ? 0x2                  : ((_x) & 0x1))
0034 #define __RD4(_x)  (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2    : __RD2(_x))
0035 #define __RD8(_x)  (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4    : __RD4(_x))
0036 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8    : __RD8(_x))
0037 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
0038
0039 /*
0040  * Calculate size of a shared ring, given the total available space for the
0041  * ring and indexes (_sz), and the name tag of the request/response structure.
0042  * A ring contains as many entries as will fit, rounded down to the nearest
0043  * power of two (so we can mask with (size-1) to loop around).
0044  */
0045 #define __CONST_RING_SIZE(_s, _sz) \
0046     (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
0047         sizeof(((struct _s##_sring *)0)->ring[0])))
0048 /*
0049  * The same for passing in an actual pointer instead of a name tag.
0050  */
0051 #define __RING_SIZE(_s, _sz) \
0052     (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
0053
0054 /*
0055  * Macros to make the correct C datatypes for a new kind of ring.
0056  *
0057  * To make a new ring datatype, you need to have two message structures,
0058  * let's say request_t, and response_t already defined.
0059  *
0060  * In a header where you want the ring datatype declared, you then do:
0061  *
0062  *     DEFINE_RING_TYPES(mytag, request_t, response_t);
0063  *
0064  * These expand out to give you a set of types, as you can see below.
0065  * The most important of these are:
0066  *
0067  *     mytag_sring_t      - The shared ring.
0068  *     mytag_front_ring_t - The 'front' half of the ring.
0069  *     mytag_back_ring_t  - The 'back' half of the ring.
0070  *
0071  * To initialize a ring in your code you need to know the location and size
0072  * of the shared memory area (PAGE_SIZE, for instance). To initialise
0073  * the front half:
0074  *
0075  *     mytag_front_ring_t ring;
0076  *     XEN_FRONT_RING_INIT(&ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
0077  *
0078  * Initializing the back follows similarly (note that only the front
0079  * initializes the shared ring):
0080  *
0081  *     mytag_back_ring_t back_ring;
0082  *     BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
0083  */
0084
0085 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)                     \
0086                                                                         \
0087 /* Shared ring entry */                                                 \
0088 union __name##_sring_entry {                                            \
0089     __req_t req;                                                        \
0090     __rsp_t rsp;                                                        \
0091 };                                                                      \
0092                                                                         \
0093 /* Shared ring page */                                                  \
0094 struct __name##_sring {                                                 \
0095     RING_IDX req_prod, req_event;                                       \
0096     RING_IDX rsp_prod, rsp_event;                                       \
0097     uint8_t __pad[48];                                                  \
0098     union __name##_sring_entry ring[1]; /* variable-length */           \
0099 };                                                                      \
0100                                                                         \
0101 /* "Front" end's private variables */                                   \
0102 struct __name##_front_ring {                                            \
0103     RING_IDX req_prod_pvt;                                              \
0104     RING_IDX rsp_cons;                                                  \
0105     unsigned int nr_ents;                                               \
0106     struct __name##_sring *sring;                                       \
0107 };                                                                      \
0108                                                                         \
0109 /* "Back" end's private variables */                                    \
0110 struct __name##_back_ring {                                             \
0111     RING_IDX rsp_prod_pvt;                                              \
0112     RING_IDX req_cons;                                                  \
0113     unsigned int nr_ents;                                               \
0114     struct __name##_sring *sring;                                       \
0115 };                                                                      \
0116                                                                         \
0117 /*
0118  * Macros for manipulating rings.
0119  *
0120  * FRONT_RING_whatever works on the "front end" of a ring: here
0121  * requests are pushed on to the ring and responses taken off it.
0122  *
0123  * BACK_RING_whatever works on the "back end" of a ring: here
0124  * requests are taken off the ring and responses put on.
0125  *
0126  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
0127  * This is OK in 1-for-1 request-response situations where the
0128  * requestor (front end) never has more than RING_SIZE()-1
0129  * outstanding requests.
0130  */
0131
0132 /* Initialising empty rings */
0133 #define SHARED_RING_INIT(_s) do {                                       \
0134     (_s)->req_prod  = (_s)->rsp_prod  = 0;                              \
0135     (_s)->req_event = (_s)->rsp_event = 1;                              \
0136     (void)memset((_s)->__pad, 0, sizeof((_s)->__pad));                  \
0137 } while(0)
0138
0139 #define FRONT_RING_ATTACH(_r, _s, _i, __size) do {                      \
0140     (_r)->req_prod_pvt = (_i);                                          \
0141     (_r)->rsp_cons = (_i);                                              \
0142     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
0143     (_r)->sring = (_s);                                                 \
0144 } while (0)
0145
0146 #define FRONT_RING_INIT(_r, _s, __size) FRONT_RING_ATTACH(_r, _s, 0, __size)
0147
0148 #define XEN_FRONT_RING_INIT(r, s, size) do {                            \
0149     SHARED_RING_INIT(s);                                                \
0150     FRONT_RING_INIT(r, s, size);                                        \
0151 } while (0)
0152
0153 #define BACK_RING_ATTACH(_r, _s, _i, __size) do {                       \
0154     (_r)->rsp_prod_pvt = (_i);                                          \
0155     (_r)->req_cons = (_i);                                              \
0156     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
0157     (_r)->sring = (_s);                                                 \
0158 } while (0)
0159
0160 #define BACK_RING_INIT(_r, _s, __size) BACK_RING_ATTACH(_r, _s, 0, __size)
0161
0162 /* How big is this ring? */
0163 #define RING_SIZE(_r)                                                   \
0164     ((_r)->nr_ents)
0165
0166 /* Number of free requests (for use on front side only). */
0167 #define RING_FREE_REQUESTS(_r)                                          \
0168     (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
0169
0170 /* Test if there is an empty slot available on the front ring.
0171  * (This is only meaningful from the front. )
0172  */
0173 #define RING_FULL(_r)                                                   \
0174     (RING_FREE_REQUESTS(_r) == 0)
0175
0176 /* Test if there are outstanding messages to be processed on a ring. */
0177 #define XEN_RING_NR_UNCONSUMED_RESPONSES(_r)                            \
0178     ((_r)->sring->rsp_prod - (_r)->rsp_cons)
0179
0180 #define XEN_RING_NR_UNCONSUMED_REQUESTS(_r) ({                          \
0181     unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;          \
0182     unsigned int rsp = RING_SIZE(_r) -                                  \
0183         ((_r)->req_cons - (_r)->rsp_prod_pvt);                          \
0184     req < rsp ? req : rsp;                                              \
0185 })
0186
0187 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \
0188     (!!XEN_RING_NR_UNCONSUMED_RESPONSES(_r))
0189 #define RING_HAS_UNCONSUMED_REQUESTS(_r)  \
0190     (!!XEN_RING_NR_UNCONSUMED_REQUESTS(_r))
0191
0192 /* Direct access to individual ring elements, by index. */
0193 #define RING_GET_REQUEST(_r, _idx)                                      \
0194     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
0195
0196 #define RING_GET_RESPONSE(_r, _idx)                                     \
0197     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
0198
0199 /*
0200  * Get a local copy of a request/response.
0201  *
0202  * Use this in preference to RING_GET_{REQUEST,RESPONSE}() so all processing is
0203  * done on a local copy that cannot be modified by the other end.
0204  *
0205  * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
0206  * to be ineffective where dest is a struct which consists of only bitfields.
0207  */
0208 #define RING_COPY_(type, r, idx, dest) do {             \
0209     /* Use volatile to force the copy into dest. */         \
0210     *(dest) = *(volatile typeof(dest))RING_GET_##type(r, idx);  \
0211 } while (0)
0212
0213 #define RING_COPY_REQUEST(r, idx, req)  RING_COPY_(REQUEST, r, idx, req)
0214 #define RING_COPY_RESPONSE(r, idx, rsp) RING_COPY_(RESPONSE, r, idx, rsp)
0215
0216 /* Loop termination condition: Would the specified index overflow the ring? */
0217 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)                           \
0218     (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
0219
0220 /* Ill-behaved frontend determination: Can there be this many requests? */
0221 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod)                           \
0222     (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
0223
0224 /* Ill-behaved backend determination: Can there be this many responses? */
0225 #define RING_RESPONSE_PROD_OVERFLOW(_r, _prod)                          \
0226     (((_prod) - (_r)->rsp_cons) > RING_SIZE(_r))
0227
0228 #define RING_PUSH_REQUESTS(_r) do {                                     \
0229     virt_wmb(); /* back sees requests /before/ updated producer index */\
0230     (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
0231 } while (0)
0232
0233 #define RING_PUSH_RESPONSES(_r) do {                                    \
0234     virt_wmb(); /* front sees resps /before/ updated producer index */  \
0235     (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;                         \
0236 } while (0)
0237
0238 /*
0239  * Notification hold-off (req_event and rsp_event):
0240  *
0241  * When queueing requests or responses on a shared ring, it may not always be
0242  * necessary to notify the remote end. For example, if requests are in flight
0243  * in a backend, the front may be able to queue further requests without
0244  * notifying the back (if the back checks for new requests when it queues
0245  * responses).
0246  *
0247  * When enqueuing requests or responses:
0248  *
0249  *  Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
0250  *  is a boolean return value. True indicates that the receiver requires an
0251  *  asynchronous notification.
0252  *
0253  * After dequeuing requests or responses (before sleeping the connection):
0254  *
0255  *  Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
0256  *  The second argument is a boolean return value. True indicates that there
0257  *  are pending messages on the ring (i.e., the connection should not be put
0258  *  to sleep).
0259  *
0260  *  These macros will set the req_event/rsp_event field to trigger a
0261  *  notification on the very next message that is enqueued. If you want to
0262  *  create batches of work (i.e., only receive a notification after several
0263  *  messages have been enqueued) then you will need to create a customised
0264  *  version of the FINAL_CHECK macro in your own code, which sets the event
0265  *  field appropriately.
0266  */
0267
0268 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {           \
0269     RING_IDX __old = (_r)->sring->req_prod;                             \
0270     RING_IDX __new = (_r)->req_prod_pvt;                                \
0271     virt_wmb(); /* back sees requests /before/ updated producer index */\
0272     (_r)->sring->req_prod = __new;                                      \
0273     virt_mb(); /* back sees new requests /before/ we check req_event */ \
0274     (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <           \
0275                  (RING_IDX)(__new - __old));                            \
0276 } while (0)
0277
0278 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {          \
0279     RING_IDX __old = (_r)->sring->rsp_prod;                             \
0280     RING_IDX __new = (_r)->rsp_prod_pvt;                                \
0281     virt_wmb(); /* front sees resps /before/ updated producer index */  \
0282     (_r)->sring->rsp_prod = __new;                                      \
0283     virt_mb(); /* front sees new resps /before/ we check rsp_event */   \
0284     (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <           \
0285                  (RING_IDX)(__new - __old));                            \
0286 } while (0)
0287
0288 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do {             \
0289     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
0290     if (_work_to_do) break;                                             \
0291     (_r)->sring->req_event = (_r)->req_cons + 1;                        \
0292     virt_mb();                                                          \
0293     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
0294 } while (0)
0295
0296 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do {            \
0297     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
0298     if (_work_to_do) break;                                             \
0299     (_r)->sring->rsp_event = (_r)->rsp_cons + 1;                        \
0300     virt_mb();                                                          \
0301     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
0302 } while (0)
0303
0304
0305 /*
0306  * DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and
0307  * functions to check if there is data on the ring, and to read and
0308  * write to them.
0309  *
0310  * DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but
0311  * does not define the indexes page. As different protocols can have
0312  * extensions to the basic format, this macro allow them to define their
0313  * own struct.
0314  *
0315  * XEN_FLEX_RING_SIZE
0316  *   Convenience macro to calculate the size of one of the two rings
0317  *   from the overall order.
0318  *
0319  * $NAME_mask
0320  *   Function to apply the size mask to an index, to reduce the index
0321  *   within the range [0-size].
0322  *
0323  * $NAME_read_packet
0324  *   Function to read data from the ring. The amount of data to read is
0325  *   specified by the "size" argument.
0326  *
0327  * $NAME_write_packet
0328  *   Function to write data to the ring. The amount of data to write is
0329  *   specified by the "size" argument.
0330  *
0331  * $NAME_get_ring_ptr
0332  *   Convenience function that returns a pointer to read/write to the
0333  *   ring at the right location.
0334  *
0335  * $NAME_data_intf
0336  *   Indexes page, shared between frontend and backend. It also
0337  *   contains the array of grant refs.
0338  *
0339  * $NAME_queued
0340  *   Function to calculate how many bytes are currently on the ring,
0341  *   ready to be read. It can also be used to calculate how much free
0342  *   space is currently on the ring (XEN_FLEX_RING_SIZE() -
0343  *   $NAME_queued()).
0344  */
0345
0346 #ifndef XEN_PAGE_SHIFT
0347 /* The PAGE_SIZE for ring protocols and hypercall interfaces is always
0348  * 4K, regardless of the architecture, and page granularity chosen by
0349  * operating systems.
0350  */
0351 #define XEN_PAGE_SHIFT 12
0352 #endif
0353 #define XEN_FLEX_RING_SIZE(order)                                             \
0354     (1UL << ((order) + XEN_PAGE_SHIFT - 1))
0355
0356 #define DEFINE_XEN_FLEX_RING(name)                                            \
0357 static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size)          \
0358 {                                                                             \
0359     return idx & (ring_size - 1);                                             \
0360 }                                                                             \
0361                                                                               \
0362 static inline unsigned char *name##_get_ring_ptr(unsigned char *buf,          \
0363                                                  RING_IDX idx,                \
0364                                                  RING_IDX ring_size)          \
0365 {                                                                             \
0366     return buf + name##_mask(idx, ring_size);                                 \
0367 }                                                                             \
0368                                                                               \
0369 static inline void name##_read_packet(void *opaque,                           \
0370                                       const unsigned char *buf,               \
0371                                       size_t size,                            \
0372                                       RING_IDX masked_prod,                   \
0373                                       RING_IDX *masked_cons,                  \
0374                                       RING_IDX ring_size)                     \
0375 {                                                                             \
0376     if (*masked_cons < masked_prod ||                                         \
0377         size <= ring_size - *masked_cons) {                                   \
0378         memcpy(opaque, buf + *masked_cons, size);                             \
0379     } else {                                                                  \
0380         memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons);         \
0381         memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf,       \
0382                size - (ring_size - *masked_cons));                            \
0383     }                                                                         \
0384     *masked_cons = name##_mask(*masked_cons + size, ring_size);               \
0385 }                                                                             \
0386                                                                               \
0387 static inline void name##_write_packet(unsigned char *buf,                    \
0388                                        const void *opaque,                    \
0389                                        size_t size,                           \
0390                                        RING_IDX *masked_prod,                 \
0391                                        RING_IDX masked_cons,                  \
0392                                        RING_IDX ring_size)                    \
0393 {                                                                             \
0394     if (*masked_prod < masked_cons ||                                         \
0395         size <= ring_size - *masked_prod) {                                   \
0396         memcpy(buf + *masked_prod, opaque, size);                             \
0397     } else {                                                                  \
0398         memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod);         \
0399         memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod),     \
0400                size - (ring_size - *masked_prod));                            \
0401     }                                                                         \
0402     *masked_prod = name##_mask(*masked_prod + size, ring_size);               \
0403 }                                                                             \
0404                                                                               \
0405 static inline RING_IDX name##_queued(RING_IDX prod,                           \
0406                                      RING_IDX cons,                           \
0407                                      RING_IDX ring_size)                      \
0408 {                                                                             \
0409     RING_IDX size;                                                            \
0410                                                                               \
0411     if (prod == cons)                                                         \
0412         return 0;                                                             \
0413                                                                               \
0414     prod = name##_mask(prod, ring_size);                                      \
0415     cons = name##_mask(cons, ring_size);                                      \
0416                                                                               \
0417     if (prod == cons)                                                         \
0418         return ring_size;                                                     \
0419                                                                               \
0420     if (prod > cons)                                                          \
0421         size = prod - cons;                                                   \
0422     else                                                                      \
0423         size = ring_size - (cons - prod);                                     \
0424     return size;                                                              \
0425 }                                                                             \
0426                                                                               \
0427 struct name##_data {                                                          \
0428     unsigned char *in; /* half of the allocation */                           \
0429     unsigned char *out; /* half of the allocation */                          \
0430 }
0431
0432 #define DEFINE_XEN_FLEX_RING_AND_INTF(name)                                   \
0433 struct name##_data_intf {                                                     \
0434     RING_IDX in_cons, in_prod;                                                \
0435                                                                               \
0436     uint8_t pad1[56];                                                         \
0437                                                                               \
0438     RING_IDX out_cons, out_prod;                                              \
0439                                                                               \
0440     uint8_t pad2[56];                                                         \
0441                                                                               \
0442     RING_IDX ring_order;                                                      \
0443     grant_ref_t ref[];                                                        \
0444 };                                                                            \
0445 DEFINE_XEN_FLEX_RING(name)
0446
0447 #endif /* __XEN_PUBLIC_IO_RING_H__ */