1 /* SPDX-License-Identifier: MIT */
2 /******************************************************************************
3 * ring.h
4 *
5 * Shared producer-consumer ring macros.
6 *
7 * Tim Deegan and Andrew Warfield November 2004.
8 */
9
10 #ifndef __XEN_PUBLIC_IO_RING_H__
11 #define __XEN_PUBLIC_IO_RING_H__
12
13 /*
14 * When #include'ing this header, you need to provide the following
15 * declaration upfront:
16 * - standard integers types (uint8_t, uint16_t, etc)
17 * They are provided by stdint.h of the standard headers.
18 *
19 * In addition, if you intend to use the FLEX macros, you also need to
20 * provide the following, before invoking the FLEX macros:
21 * - size_t
22 * - memcpy
23 * - grant_ref_t
24 * These declarations are provided by string.h of the standard headers,
25 * and grant_table.h from the Xen public headers.
26 */
27
28 #include <xen/interface/grant_table.h>
29
30 typedef unsigned int RING_IDX;
31
32 /* Round a 32-bit unsigned constant down to the nearest power of two. */
33 #define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1))
34 #define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x))
35 #define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x))
36 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x))
37 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
38
39 /*
40 * Calculate size of a shared ring, given the total available space for the
41 * ring and indexes (_sz), and the name tag of the request/response structure.
42 * A ring contains as many entries as will fit, rounded down to the nearest
43 * power of two (so we can mask with (size-1) to loop around).
44 */
45 #define __CONST_RING_SIZE(_s, _sz) \
46 (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
47 sizeof(((struct _s##_sring *)0)->ring[0])))
48 /*
49 * The same for passing in an actual pointer instead of a name tag.
50 */
51 #define __RING_SIZE(_s, _sz) \
52 (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
53
54 /*
55 * Macros to make the correct C datatypes for a new kind of ring.
56 *
57 * To make a new ring datatype, you need to have two message structures,
58 * let's say request_t, and response_t already defined.
59 *
60 * In a header where you want the ring datatype declared, you then do:
61 *
62 * DEFINE_RING_TYPES(mytag, request_t, response_t);
63 *
64 * These expand out to give you a set of types, as you can see below.
65 * The most important of these are:
66 *
67 * mytag_sring_t - The shared ring.
68 * mytag_front_ring_t - The 'front' half of the ring.
69 * mytag_back_ring_t - The 'back' half of the ring.
70 *
71 * To initialize a ring in your code you need to know the location and size
72 * of the shared memory area (PAGE_SIZE, for instance). To initialise
73 * the front half:
74 *
75 * mytag_front_ring_t ring;
76 * XEN_FRONT_RING_INIT(&ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
77 *
78 * Initializing the back follows similarly (note that only the front
79 * initializes the shared ring):
80 *
81 * mytag_back_ring_t back_ring;
82 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
83 */
84
85 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
86 \
87 /* Shared ring entry */ \
88 union __name##_sring_entry { \
89 __req_t req; \
90 __rsp_t rsp; \
91 }; \
92 \
93 /* Shared ring page */ \
94 struct __name##_sring { \
95 RING_IDX req_prod, req_event; \
96 RING_IDX rsp_prod, rsp_event; \
97 uint8_t __pad[48]; \
98 union __name##_sring_entry ring[]; \
99 }; \
100 \
101 /* "Front" end's private variables */ \
102 struct __name##_front_ring { \
103 RING_IDX req_prod_pvt; \
104 RING_IDX rsp_cons; \
105 unsigned int nr_ents; \
106 struct __name##_sring *sring; \
107 }; \
108 \
109 /* "Back" end's private variables */ \
110 struct __name##_back_ring { \
111 RING_IDX rsp_prod_pvt; \
112 RING_IDX req_cons; \
113 unsigned int nr_ents; \
114 struct __name##_sring *sring; \
115 }; \
116 \
117 /*
118 * Macros for manipulating rings.
119 *
120 * FRONT_RING_whatever works on the "front end" of a ring: here
121 * requests are pushed on to the ring and responses taken off it.
122 *
123 * BACK_RING_whatever works on the "back end" of a ring: here
124 * requests are taken off the ring and responses put on.
125 *
126 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
127 * This is OK in 1-for-1 request-response situations where the
128 * requestor (front end) never has more than RING_SIZE()-1
129 * outstanding requests.
130 */
131
132 /* Initialising empty rings */
133 #define SHARED_RING_INIT(_s) do { \
134 (_s)->req_prod = (_s)->rsp_prod = 0; \
135 (_s)->req_event = (_s)->rsp_event = 1; \
136 (void)memset((_s)->__pad, 0, sizeof((_s)->__pad)); \
137 } while(0)
138
139 #define FRONT_RING_ATTACH(_r, _s, _i, __size) do { \
140 (_r)->req_prod_pvt = (_i); \
141 (_r)->rsp_cons = (_i); \
142 (_r)->nr_ents = __RING_SIZE(_s, __size); \
143 (_r)->sring = (_s); \
144 } while (0)
145
146 #define FRONT_RING_INIT(_r, _s, __size) FRONT_RING_ATTACH(_r, _s, 0, __size)
147
148 #define XEN_FRONT_RING_INIT(r, s, size) do { \
149 SHARED_RING_INIT(s); \
150 FRONT_RING_INIT(r, s, size); \
151 } while (0)
152
153 #define BACK_RING_ATTACH(_r, _s, _i, __size) do { \
154 (_r)->rsp_prod_pvt = (_i); \
155 (_r)->req_cons = (_i); \
156 (_r)->nr_ents = __RING_SIZE(_s, __size); \
157 (_r)->sring = (_s); \
158 } while (0)
159
160 #define BACK_RING_INIT(_r, _s, __size) BACK_RING_ATTACH(_r, _s, 0, __size)
161
162 /* How big is this ring? */
163 #define RING_SIZE(_r) \
164 ((_r)->nr_ents)
165
166 /* Number of free requests (for use on front side only). */
167 #define RING_FREE_REQUESTS(_r) \
168 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
169
170 /* Test if there is an empty slot available on the front ring.
171 * (This is only meaningful from the front. )
172 */
173 #define RING_FULL(_r) \
174 (RING_FREE_REQUESTS(_r) == 0)
175
176 /* Test if there are outstanding messages to be processed on a ring. */
177 #define XEN_RING_NR_UNCONSUMED_RESPONSES(_r) \
178 ((_r)->sring->rsp_prod - (_r)->rsp_cons)
179
180 #define XEN_RING_NR_UNCONSUMED_REQUESTS(_r) ({ \
181 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
182 unsigned int rsp = RING_SIZE(_r) - \
183 ((_r)->req_cons - (_r)->rsp_prod_pvt); \
184 req < rsp ? req : rsp; \
185 })
186
187 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \
188 (!!XEN_RING_NR_UNCONSUMED_RESPONSES(_r))
189 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \
190 (!!XEN_RING_NR_UNCONSUMED_REQUESTS(_r))
191
192 /* Direct access to individual ring elements, by index. */
193 #define RING_GET_REQUEST(_r, _idx) \
194 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
195
196 #define RING_GET_RESPONSE(_r, _idx) \
197 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
198
199 /*
200 * Get a local copy of a request/response.
201 *
202 * Use this in preference to RING_GET_{REQUEST,RESPONSE}() so all processing is
203 * done on a local copy that cannot be modified by the other end.
204 *
205 * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
206 * to be ineffective where dest is a struct which consists of only bitfields.
207 */
208 #define RING_COPY_(type, r, idx, dest) do { \
209 /* Use volatile to force the copy into dest. */ \
210 *(dest) = *(volatile typeof(dest))RING_GET_##type(r, idx); \
211 } while (0)
212
213 #define RING_COPY_REQUEST(r, idx, req) RING_COPY_(REQUEST, r, idx, req)
214 #define RING_COPY_RESPONSE(r, idx, rsp) RING_COPY_(RESPONSE, r, idx, rsp)
215
216 /* Loop termination condition: Would the specified index overflow the ring? */
217 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
218 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
219
220 /* Ill-behaved frontend determination: Can there be this many requests? */
221 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \
222 (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
223
224 /* Ill-behaved backend determination: Can there be this many responses? */
225 #define RING_RESPONSE_PROD_OVERFLOW(_r, _prod) \
226 (((_prod) - (_r)->rsp_cons) > RING_SIZE(_r))
227
228 #define RING_PUSH_REQUESTS(_r) do { \
229 virt_wmb(); /* back sees requests /before/ updated producer index */\
230 (_r)->sring->req_prod = (_r)->req_prod_pvt; \
231 } while (0)
232
233 #define RING_PUSH_RESPONSES(_r) do { \
234 virt_wmb(); /* front sees resps /before/ updated producer index */ \
235 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
236 } while (0)
237
238 /*
239 * Notification hold-off (req_event and rsp_event):
240 *
241 * When queueing requests or responses on a shared ring, it may not always be
242 * necessary to notify the remote end. For example, if requests are in flight
243 * in a backend, the front may be able to queue further requests without
244 * notifying the back (if the back checks for new requests when it queues
245 * responses).
246 *
247 * When enqueuing requests or responses:
248 *
249 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
250 * is a boolean return value. True indicates that the receiver requires an
251 * asynchronous notification.
252 *
253 * After dequeuing requests or responses (before sleeping the connection):
254 *
255 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
256 * The second argument is a boolean return value. True indicates that there
257 * are pending messages on the ring (i.e., the connection should not be put
258 * to sleep).
259 *
260 * These macros will set the req_event/rsp_event field to trigger a
261 * notification on the very next message that is enqueued. If you want to
262 * create batches of work (i.e., only receive a notification after several
263 * messages have been enqueued) then you will need to create a customised
264 * version of the FINAL_CHECK macro in your own code, which sets the event
265 * field appropriately.
266 */
267
268 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
269 RING_IDX __old = (_r)->sring->req_prod; \
270 RING_IDX __new = (_r)->req_prod_pvt; \
271 virt_wmb(); /* back sees requests /before/ updated producer index */\
272 (_r)->sring->req_prod = __new; \
273 virt_mb(); /* back sees new requests /before/ we check req_event */ \
274 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
275 (RING_IDX)(__new - __old)); \
276 } while (0)
277
278 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
279 RING_IDX __old = (_r)->sring->rsp_prod; \
280 RING_IDX __new = (_r)->rsp_prod_pvt; \
281 virt_wmb(); /* front sees resps /before/ updated producer index */ \
282 (_r)->sring->rsp_prod = __new; \
283 virt_mb(); /* front sees new resps /before/ we check rsp_event */ \
284 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
285 (RING_IDX)(__new - __old)); \
286 } while (0)
287
288 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
289 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
290 if (_work_to_do) break; \
291 (_r)->sring->req_event = (_r)->req_cons + 1; \
292 virt_mb(); \
293 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
294 } while (0)
295
296 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
297 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
298 if (_work_to_do) break; \
299 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
300 virt_mb(); \
301 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
302 } while (0)
303
304
305 /*
306 * DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and
307 * functions to check if there is data on the ring, and to read and
308 * write to them.
309 *
310 * DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but
311 * does not define the indexes page. As different protocols can have
312 * extensions to the basic format, this macro allow them to define their
313 * own struct.
314 *
315 * XEN_FLEX_RING_SIZE
316 * Convenience macro to calculate the size of one of the two rings
317 * from the overall order.
318 *
319 * $NAME_mask
320 * Function to apply the size mask to an index, to reduce the index
321 * within the range [0-size].
322 *
323 * $NAME_read_packet
324 * Function to read data from the ring. The amount of data to read is
325 * specified by the "size" argument.
326 *
327 * $NAME_write_packet
328 * Function to write data to the ring. The amount of data to write is
329 * specified by the "size" argument.
330 *
331 * $NAME_get_ring_ptr
332 * Convenience function that returns a pointer to read/write to the
333 * ring at the right location.
334 *
335 * $NAME_data_intf
336 * Indexes page, shared between frontend and backend. It also
337 * contains the array of grant refs.
338 *
339 * $NAME_queued
340 * Function to calculate how many bytes are currently on the ring,
341 * ready to be read. It can also be used to calculate how much free
342 * space is currently on the ring (XEN_FLEX_RING_SIZE() -
343 * $NAME_queued()).
344 */
345
346 #ifndef XEN_PAGE_SHIFT
347 /* The PAGE_SIZE for ring protocols and hypercall interfaces is always
348 * 4K, regardless of the architecture, and page granularity chosen by
349 * operating systems.
350 */
351 #define XEN_PAGE_SHIFT 12
352 #endif
353 #define XEN_FLEX_RING_SIZE(order) \
354 (1UL << ((order) + XEN_PAGE_SHIFT - 1))
355
356 #define DEFINE_XEN_FLEX_RING(name) \
357 static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size) \
358 { \
359 return idx & (ring_size - 1); \
360 } \
361 \
362 static inline unsigned char *name##_get_ring_ptr(unsigned char *buf, \
363 RING_IDX idx, \
364 RING_IDX ring_size) \
365 { \
366 return buf + name##_mask(idx, ring_size); \
367 } \
368 \
369 static inline void name##_read_packet(void *opaque, \
370 const unsigned char *buf, \
371 size_t size, \
372 RING_IDX masked_prod, \
373 RING_IDX *masked_cons, \
374 RING_IDX ring_size) \
375 { \
376 if (*masked_cons < masked_prod || \
377 size <= ring_size - *masked_cons) { \
378 memcpy(opaque, buf + *masked_cons, size); \
379 } else { \
380 memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons); \
381 memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf, \
382 size - (ring_size - *masked_cons)); \
383 } \
384 *masked_cons = name##_mask(*masked_cons + size, ring_size); \
385 } \
386 \
387 static inline void name##_write_packet(unsigned char *buf, \
388 const void *opaque, \
389 size_t size, \
390 RING_IDX *masked_prod, \
391 RING_IDX masked_cons, \
392 RING_IDX ring_size) \
393 { \
394 if (*masked_prod < masked_cons || \
395 size <= ring_size - *masked_prod) { \
396 memcpy(buf + *masked_prod, opaque, size); \
397 } else { \
398 memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod); \
399 memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod), \
400 size - (ring_size - *masked_prod)); \
401 } \
402 *masked_prod = name##_mask(*masked_prod + size, ring_size); \
403 } \
404 \
405 static inline RING_IDX name##_queued(RING_IDX prod, \
406 RING_IDX cons, \
407 RING_IDX ring_size) \
408 { \
409 RING_IDX size; \
410 \
411 if (prod == cons) \
412 return 0; \
413 \
414 prod = name##_mask(prod, ring_size); \
415 cons = name##_mask(cons, ring_size); \
416 \
417 if (prod == cons) \
418 return ring_size; \
419 \
420 if (prod > cons) \
421 size = prod - cons; \
422 else \
423 size = ring_size - (cons - prod); \
424 return size; \
425 } \
426 \
427 struct name##_data { \
428 unsigned char *in; /* half of the allocation */ \
429 unsigned char *out; /* half of the allocation */ \
430 }
431
432 #define DEFINE_XEN_FLEX_RING_AND_INTF(name) \
433 struct name##_data_intf { \
434 RING_IDX in_cons, in_prod; \
435 \
436 uint8_t pad1[56]; \
437 \
438 RING_IDX out_cons, out_prod; \
439 \
440 uint8_t pad2[56]; \
441 \
442 RING_IDX ring_order; \
443 grant_ref_t ref[]; \
444 }; \
445 DEFINE_XEN_FLEX_RING(name)
446
447 #endif /* __XEN_PUBLIC_IO_RING_H__ */
448
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