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