1/* SPDX-License-Identifier: GPL-2.0 */
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#include <xen/interface/grant_table.h>
14
15typedef unsigned int RING_IDX;
16
17/* Round a 32-bit unsigned constant down to the nearest power of two. */
18#define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1))
19#define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x))
20#define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x))
21#define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x))
22#define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
23
24/*
25 * Calculate size of a shared ring, given the total available space for the
26 * ring and indexes (_sz), and the name tag of the request/response structure.
27 * A ring contains as many entries as will fit, rounded down to the nearest
28 * power of two (so we can mask with (size-1) to loop around).
29 */
30#define __CONST_RING_SIZE(_s, _sz) \
31 (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
32 sizeof(((struct _s##_sring *)0)->ring[0])))
33
34/*
35 * The same for passing in an actual pointer instead of a name tag.
36 */
37#define __RING_SIZE(_s, _sz) \
38 (__RD32(((_sz) - (long)&(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
39
40/*
41 * Macros to make the correct C datatypes for a new kind of ring.
42 *
43 * To make a new ring datatype, you need to have two message structures,
44 * let's say struct request, and struct response already defined.
45 *
46 * In a header where you want the ring datatype declared, you then do:
47 *
48 * DEFINE_RING_TYPES(mytag, struct request, struct response);
49 *
50 * These expand out to give you a set of types, as you can see below.
51 * The most important of these are:
52 *
53 * struct mytag_sring - The shared ring.
54 * struct mytag_front_ring - The 'front' half of the ring.
55 * struct mytag_back_ring - The 'back' half of the ring.
56 *
57 * To initialize a ring in your code you need to know the location and size
58 * of the shared memory area (PAGE_SIZE, for instance). To initialise
59 * the front half:
60 *
61 * struct mytag_front_ring front_ring;
62 * SHARED_RING_INIT((struct mytag_sring *)shared_page);
63 * FRONT_RING_INIT(&front_ring, (struct mytag_sring *)shared_page,
64 * PAGE_SIZE);
65 *
66 * Initializing the back follows similarly (note that only the front
67 * initializes the shared ring):
68 *
69 * struct mytag_back_ring back_ring;
70 * BACK_RING_INIT(&back_ring, (struct mytag_sring *)shared_page,
71 * PAGE_SIZE);
72 */
73
74#define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
75 \
76/* Shared ring entry */ \
77union __name##_sring_entry { \
78 __req_t req; \
79 __rsp_t rsp; \
80}; \
81 \
82/* Shared ring page */ \
83struct __name##_sring { \
84 RING_IDX req_prod, req_event; \
85 RING_IDX rsp_prod, rsp_event; \
86 uint8_t pad[48]; \
87 union __name##_sring_entry ring[1]; /* variable-length */ \
88}; \
89 \
90/* "Front" end's private variables */ \
91struct __name##_front_ring { \
92 RING_IDX req_prod_pvt; \
93 RING_IDX rsp_cons; \
94 unsigned int nr_ents; \
95 struct __name##_sring *sring; \
96}; \
97 \
98/* "Back" end's private variables */ \
99struct __name##_back_ring { \
100 RING_IDX rsp_prod_pvt; \
101 RING_IDX req_cons; \
102 unsigned int nr_ents; \
103 struct __name##_sring *sring; \
104};
105
106/*
107 * Macros for manipulating rings.
108 *
109 * FRONT_RING_whatever works on the "front end" of a ring: here
110 * requests are pushed on to the ring and responses taken off it.
111 *
112 * BACK_RING_whatever works on the "back end" of a ring: here
113 * requests are taken off the ring and responses put on.
114 *
115 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
116 * This is OK in 1-for-1 request-response situations where the
117 * requestor (front end) never has more than RING_SIZE()-1
118 * outstanding requests.
119 */
120
121/* Initialising empty rings */
122#define SHARED_RING_INIT(_s) do { \
123 (_s)->req_prod = (_s)->rsp_prod = 0; \
124 (_s)->req_event = (_s)->rsp_event = 1; \
125 memset((_s)->pad, 0, sizeof((_s)->pad)); \
126} while(0)
127
128#define FRONT_RING_INIT(_r, _s, __size) do { \
129 (_r)->req_prod_pvt = 0; \
130 (_r)->rsp_cons = 0; \
131 (_r)->nr_ents = __RING_SIZE(_s, __size); \
132 (_r)->sring = (_s); \
133} while (0)
134
135#define BACK_RING_INIT(_r, _s, __size) do { \
136 (_r)->rsp_prod_pvt = 0; \
137 (_r)->req_cons = 0; \
138 (_r)->nr_ents = __RING_SIZE(_s, __size); \
139 (_r)->sring = (_s); \
140} while (0)
141
142/* Initialize to existing shared indexes -- for recovery */
143#define FRONT_RING_ATTACH(_r, _s, __size) do { \
144 (_r)->sring = (_s); \
145 (_r)->req_prod_pvt = (_s)->req_prod; \
146 (_r)->rsp_cons = (_s)->rsp_prod; \
147 (_r)->nr_ents = __RING_SIZE(_s, __size); \
148} while (0)
149
150#define BACK_RING_ATTACH(_r, _s, __size) do { \
151 (_r)->sring = (_s); \
152 (_r)->rsp_prod_pvt = (_s)->rsp_prod; \
153 (_r)->req_cons = (_s)->req_prod; \
154 (_r)->nr_ents = __RING_SIZE(_s, __size); \
155} while (0)
156
157/* How big is this ring? */
158#define RING_SIZE(_r) \
159 ((_r)->nr_ents)
160
161/* Number of free requests (for use on front side only). */
162#define RING_FREE_REQUESTS(_r) \
163 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
164
165/* Test if there is an empty slot available on the front ring.
166 * (This is only meaningful from the front. )
167 */
168#define RING_FULL(_r) \
169 (RING_FREE_REQUESTS(_r) == 0)
170
171/* Test if there are outstanding messages to be processed on a ring. */
172#define RING_HAS_UNCONSUMED_RESPONSES(_r) \
173 ((_r)->sring->rsp_prod - (_r)->rsp_cons)
174
175#define RING_HAS_UNCONSUMED_REQUESTS(_r) \
176 ({ \
177 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
178 unsigned int rsp = RING_SIZE(_r) - \
179 ((_r)->req_cons - (_r)->rsp_prod_pvt); \
180 req < rsp ? req : rsp; \
181 })
182
183/* Direct access to individual ring elements, by index. */
184#define RING_GET_REQUEST(_r, _idx) \
185 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
186
187/*
188 * Get a local copy of a request.
189 *
190 * Use this in preference to RING_GET_REQUEST() so all processing is
191 * done on a local copy that cannot be modified by the other end.
192 *
193 * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
194 * to be ineffective where _req is a struct which consists of only bitfields.
195 */
196#define RING_COPY_REQUEST(_r, _idx, _req) do { \
197 /* Use volatile to force the copy into _req. */ \
198 *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx); \
199} while (0)
200
201#define RING_GET_RESPONSE(_r, _idx) \
202 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
203
204/* Loop termination condition: Would the specified index overflow the ring? */
205#define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
206 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
207
208/* Ill-behaved frontend determination: Can there be this many requests? */
209#define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \
210 (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
211
212
213#define RING_PUSH_REQUESTS(_r) do { \
214 virt_wmb(); /* back sees requests /before/ updated producer index */ \
215 (_r)->sring->req_prod = (_r)->req_prod_pvt; \
216} while (0)
217
218#define RING_PUSH_RESPONSES(_r) do { \
219 virt_wmb(); /* front sees responses /before/ updated producer index */ \
220 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
221} while (0)
222
223/*
224 * Notification hold-off (req_event and rsp_event):
225 *
226 * When queueing requests or responses on a shared ring, it may not always be
227 * necessary to notify the remote end. For example, if requests are in flight
228 * in a backend, the front may be able to queue further requests without
229 * notifying the back (if the back checks for new requests when it queues
230 * responses).
231 *
232 * When enqueuing requests or responses:
233 *
234 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
235 * is a boolean return value. True indicates that the receiver requires an
236 * asynchronous notification.
237 *
238 * After dequeuing requests or responses (before sleeping the connection):
239 *
240 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
241 * The second argument is a boolean return value. True indicates that there
242 * are pending messages on the ring (i.e., the connection should not be put
243 * to sleep).
244 *
245 * These macros will set the req_event/rsp_event field to trigger a
246 * notification on the very next message that is enqueued. If you want to
247 * create batches of work (i.e., only receive a notification after several
248 * messages have been enqueued) then you will need to create a customised
249 * version of the FINAL_CHECK macro in your own code, which sets the event
250 * field appropriately.
251 */
252
253#define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
254 RING_IDX __old = (_r)->sring->req_prod; \
255 RING_IDX __new = (_r)->req_prod_pvt; \
256 virt_wmb(); /* back sees requests /before/ updated producer index */ \
257 (_r)->sring->req_prod = __new; \
258 virt_mb(); /* back sees new requests /before/ we check req_event */ \
259 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
260 (RING_IDX)(__new - __old)); \
261} while (0)
262
263#define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
264 RING_IDX __old = (_r)->sring->rsp_prod; \
265 RING_IDX __new = (_r)->rsp_prod_pvt; \
266 virt_wmb(); /* front sees responses /before/ updated producer index */ \
267 (_r)->sring->rsp_prod = __new; \
268 virt_mb(); /* front sees new responses /before/ we check rsp_event */ \
269 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
270 (RING_IDX)(__new - __old)); \
271} while (0)
272
273#define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
274 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
275 if (_work_to_do) break; \
276 (_r)->sring->req_event = (_r)->req_cons + 1; \
277 virt_mb(); \
278 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
279} while (0)
280
281#define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
282 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
283 if (_work_to_do) break; \
284 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
285 virt_mb(); \
286 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
287} while (0)
288
289
290/*
291 * DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and
292 * functions to check if there is data on the ring, and to read and
293 * write to them.
294 *
295 * DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but
296 * does not define the indexes page. As different protocols can have
297 * extensions to the basic format, this macro allow them to define their
298 * own struct.
299 *
300 * XEN_FLEX_RING_SIZE
301 * Convenience macro to calculate the size of one of the two rings
302 * from the overall order.
303 *
304 * $NAME_mask
305 * Function to apply the size mask to an index, to reduce the index
306 * within the range [0-size].
307 *
308 * $NAME_read_packet
309 * Function to read data from the ring. The amount of data to read is
310 * specified by the "size" argument.
311 *
312 * $NAME_write_packet
313 * Function to write data to the ring. The amount of data to write is
314 * specified by the "size" argument.
315 *
316 * $NAME_get_ring_ptr
317 * Convenience function that returns a pointer to read/write to the
318 * ring at the right location.
319 *
320 * $NAME_data_intf
321 * Indexes page, shared between frontend and backend. It also
322 * contains the array of grant refs.
323 *
324 * $NAME_queued
325 * Function to calculate how many bytes are currently on the ring,
326 * ready to be read. It can also be used to calculate how much free
327 * space is currently on the ring (XEN_FLEX_RING_SIZE() -
328 * $NAME_queued()).
329 */
330
331#ifndef XEN_PAGE_SHIFT
332/* The PAGE_SIZE for ring protocols and hypercall interfaces is always
333 * 4K, regardless of the architecture, and page granularity chosen by
334 * operating systems.
335 */
336#define XEN_PAGE_SHIFT 12
337#endif
338#define XEN_FLEX_RING_SIZE(order) \
339 (1UL << ((order) + XEN_PAGE_SHIFT - 1))
340
341#define DEFINE_XEN_FLEX_RING(name) \
342static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size) \
343{ \
344 return idx & (ring_size - 1); \
345} \
346 \
347static inline unsigned char *name##_get_ring_ptr(unsigned char *buf, \
348 RING_IDX idx, \
349 RING_IDX ring_size) \
350{ \
351 return buf + name##_mask(idx, ring_size); \
352} \
353 \
354static inline void name##_read_packet(void *opaque, \
355 const unsigned char *buf, \
356 size_t size, \
357 RING_IDX masked_prod, \
358 RING_IDX *masked_cons, \
359 RING_IDX ring_size) \
360{ \
361 if (*masked_cons < masked_prod || \
362 size <= ring_size - *masked_cons) { \
363 memcpy(opaque, buf + *masked_cons, size); \
364 } else { \
365 memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons); \
366 memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf, \
367 size - (ring_size - *masked_cons)); \
368 } \
369 *masked_cons = name##_mask(*masked_cons + size, ring_size); \
370} \
371 \
372static inline void name##_write_packet(unsigned char *buf, \
373 const void *opaque, \
374 size_t size, \
375 RING_IDX *masked_prod, \
376 RING_IDX masked_cons, \
377 RING_IDX ring_size) \
378{ \
379 if (*masked_prod < masked_cons || \
380 size <= ring_size - *masked_prod) { \
381 memcpy(buf + *masked_prod, opaque, size); \
382 } else { \
383 memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod); \
384 memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod), \
385 size - (ring_size - *masked_prod)); \
386 } \
387 *masked_prod = name##_mask(*masked_prod + size, ring_size); \
388} \
389 \
390static inline RING_IDX name##_queued(RING_IDX prod, \
391 RING_IDX cons, \
392 RING_IDX ring_size) \
393{ \
394 RING_IDX size; \
395 \
396 if (prod == cons) \
397 return 0; \
398 \
399 prod = name##_mask(prod, ring_size); \
400 cons = name##_mask(cons, ring_size); \
401 \
402 if (prod == cons) \
403 return ring_size; \
404 \
405 if (prod > cons) \
406 size = prod - cons; \
407 else \
408 size = ring_size - (cons - prod); \
409 return size; \
410} \
411 \
412struct name##_data { \
413 unsigned char *in; /* half of the allocation */ \
414 unsigned char *out; /* half of the allocation */ \
415}
416
417#define DEFINE_XEN_FLEX_RING_AND_INTF(name) \
418struct name##_data_intf { \
419 RING_IDX in_cons, in_prod; \
420 \
421 uint8_t pad1[56]; \
422 \
423 RING_IDX out_cons, out_prod; \
424 \
425 uint8_t pad2[56]; \
426 \
427 RING_IDX ring_order; \
428 grant_ref_t ref[]; \
429}; \
430DEFINE_XEN_FLEX_RING(name)
431
432#endif /* __XEN_PUBLIC_IO_RING_H__ */
433