1 /******************************************************************************
4 * Shared producer-consumer ring macros.
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:
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
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.
24 * Tim Deegan and Andrew Warfield November 2004.
27 #ifndef __XEN_PUBLIC_IO_RING_H__
28 #define __XEN_PUBLIC_IO_RING_H__
31 * When #include'ing this header, you need to provide the following
32 * declaration upfront:
33 * - standard integers types (uint8_t, uint16_t, etc)
34 * They are provided by stdint.h of the standard headers.
36 * In addition, if you intend to use the FLEX macros, you also need to
37 * provide the following, before invoking the FLEX macros:
41 * These declarations are provided by string.h of the standard headers,
42 * and grant_table.h from the Xen public headers.
45 #include <xen/interface/grant_table.h>
47 typedef unsigned int RING_IDX;
49 /* Round a 32-bit unsigned constant down to the nearest power of two. */
50 #define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1))
51 #define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x))
52 #define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x))
53 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x))
54 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
57 * Calculate size of a shared ring, given the total available space for the
58 * ring and indexes (_sz), and the name tag of the request/response structure.
59 * A ring contains as many entries as will fit, rounded down to the nearest
60 * power of two (so we can mask with (size-1) to loop around).
62 #define __CONST_RING_SIZE(_s, _sz) \
63 (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
64 sizeof(((struct _s##_sring *)0)->ring[0])))
66 * The same for passing in an actual pointer instead of a name tag.
68 #define __RING_SIZE(_s, _sz) \
69 (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
72 * Macros to make the correct C datatypes for a new kind of ring.
74 * To make a new ring datatype, you need to have two message structures,
75 * let's say request_t, and response_t already defined.
77 * In a header where you want the ring datatype declared, you then do:
79 * DEFINE_RING_TYPES(mytag, request_t, response_t);
81 * These expand out to give you a set of types, as you can see below.
82 * The most important of these are:
84 * mytag_sring_t - The shared ring.
85 * mytag_front_ring_t - The 'front' half of the ring.
86 * mytag_back_ring_t - The 'back' half of the ring.
88 * To initialize a ring in your code you need to know the location and size
89 * of the shared memory area (PAGE_SIZE, for instance). To initialise
92 * mytag_front_ring_t front_ring;
93 * SHARED_RING_INIT((mytag_sring_t *)shared_page);
94 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
96 * Initializing the back follows similarly (note that only the front
97 * initializes the shared ring):
99 * mytag_back_ring_t back_ring;
100 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
103 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
105 /* Shared ring entry */ \
106 union __name##_sring_entry { \
111 /* Shared ring page */ \
112 struct __name##_sring { \
113 RING_IDX req_prod, req_event; \
114 RING_IDX rsp_prod, rsp_event; \
116 union __name##_sring_entry ring[1]; /* variable-length */ \
119 /* "Front" end's private variables */ \
120 struct __name##_front_ring { \
121 RING_IDX req_prod_pvt; \
123 unsigned int nr_ents; \
124 struct __name##_sring *sring; \
127 /* "Back" end's private variables */ \
128 struct __name##_back_ring { \
129 RING_IDX rsp_prod_pvt; \
131 unsigned int nr_ents; \
132 struct __name##_sring *sring; \
136 * Macros for manipulating rings.
138 * FRONT_RING_whatever works on the "front end" of a ring: here
139 * requests are pushed on to the ring and responses taken off it.
141 * BACK_RING_whatever works on the "back end" of a ring: here
142 * requests are taken off the ring and responses put on.
144 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
145 * This is OK in 1-for-1 request-response situations where the
146 * requestor (front end) never has more than RING_SIZE()-1
147 * outstanding requests.
150 /* Initialising empty rings */
151 #define SHARED_RING_INIT(_s) do { \
152 (_s)->req_prod = (_s)->rsp_prod = 0; \
153 (_s)->req_event = (_s)->rsp_event = 1; \
154 (void)memset((_s)->__pad, 0, sizeof((_s)->__pad)); \
157 #define FRONT_RING_ATTACH(_r, _s, _i, __size) do { \
158 (_r)->req_prod_pvt = (_i); \
159 (_r)->rsp_cons = (_i); \
160 (_r)->nr_ents = __RING_SIZE(_s, __size); \
161 (_r)->sring = (_s); \
164 #define FRONT_RING_INIT(_r, _s, __size) FRONT_RING_ATTACH(_r, _s, 0, __size)
166 #define BACK_RING_ATTACH(_r, _s, _i, __size) do { \
167 (_r)->rsp_prod_pvt = (_i); \
168 (_r)->req_cons = (_i); \
169 (_r)->nr_ents = __RING_SIZE(_s, __size); \
170 (_r)->sring = (_s); \
173 #define BACK_RING_INIT(_r, _s, __size) BACK_RING_ATTACH(_r, _s, 0, __size)
175 /* How big is this ring? */
176 #define RING_SIZE(_r) \
179 /* Number of free requests (for use on front side only). */
180 #define RING_FREE_REQUESTS(_r) \
181 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
183 /* Test if there is an empty slot available on the front ring.
184 * (This is only meaningful from the front. )
186 #define RING_FULL(_r) \
187 (RING_FREE_REQUESTS(_r) == 0)
189 /* Test if there are outstanding messages to be processed on a ring. */
190 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \
191 ((_r)->sring->rsp_prod - (_r)->rsp_cons)
193 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \
194 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
195 unsigned int rsp = RING_SIZE(_r) - \
196 ((_r)->req_cons - (_r)->rsp_prod_pvt); \
197 req < rsp ? req : rsp; \
200 /* Direct access to individual ring elements, by index. */
201 #define RING_GET_REQUEST(_r, _idx) \
202 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
204 #define RING_GET_RESPONSE(_r, _idx) \
205 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
208 * Get a local copy of a request/response.
210 * Use this in preference to RING_GET_{REQUEST,RESPONSE}() so all processing is
211 * done on a local copy that cannot be modified by the other end.
213 * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
214 * to be ineffective where dest is a struct which consists of only bitfields.
216 #define RING_COPY_(type, r, idx, dest) do { \
217 /* Use volatile to force the copy into dest. */ \
218 *(dest) = *(volatile typeof(dest))RING_GET_##type(r, idx); \
221 #define RING_COPY_REQUEST(r, idx, req) RING_COPY_(REQUEST, r, idx, req)
222 #define RING_COPY_RESPONSE(r, idx, rsp) RING_COPY_(RESPONSE, r, idx, rsp)
224 /* Loop termination condition: Would the specified index overflow the ring? */
225 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
226 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
228 /* Ill-behaved frontend determination: Can there be this many requests? */
229 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \
230 (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
232 /* Ill-behaved backend determination: Can there be this many responses? */
233 #define RING_RESPONSE_PROD_OVERFLOW(_r, _prod) \
234 (((_prod) - (_r)->rsp_cons) > RING_SIZE(_r))
236 #define RING_PUSH_REQUESTS(_r) do { \
237 virt_wmb(); /* back sees requests /before/ updated producer index */\
238 (_r)->sring->req_prod = (_r)->req_prod_pvt; \
241 #define RING_PUSH_RESPONSES(_r) do { \
242 virt_wmb(); /* front sees resps /before/ updated producer index */ \
243 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
247 * Notification hold-off (req_event and rsp_event):
249 * When queueing requests or responses on a shared ring, it may not always be
250 * necessary to notify the remote end. For example, if requests are in flight
251 * in a backend, the front may be able to queue further requests without
252 * notifying the back (if the back checks for new requests when it queues
255 * When enqueuing requests or responses:
257 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
258 * is a boolean return value. True indicates that the receiver requires an
259 * asynchronous notification.
261 * After dequeuing requests or responses (before sleeping the connection):
263 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
264 * The second argument is a boolean return value. True indicates that there
265 * are pending messages on the ring (i.e., the connection should not be put
268 * These macros will set the req_event/rsp_event field to trigger a
269 * notification on the very next message that is enqueued. If you want to
270 * create batches of work (i.e., only receive a notification after several
271 * messages have been enqueued) then you will need to create a customised
272 * version of the FINAL_CHECK macro in your own code, which sets the event
273 * field appropriately.
276 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
277 RING_IDX __old = (_r)->sring->req_prod; \
278 RING_IDX __new = (_r)->req_prod_pvt; \
279 virt_wmb(); /* back sees requests /before/ updated producer index */\
280 (_r)->sring->req_prod = __new; \
281 virt_mb(); /* back sees new requests /before/ we check req_event */ \
282 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
283 (RING_IDX)(__new - __old)); \
286 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
287 RING_IDX __old = (_r)->sring->rsp_prod; \
288 RING_IDX __new = (_r)->rsp_prod_pvt; \
289 virt_wmb(); /* front sees resps /before/ updated producer index */ \
290 (_r)->sring->rsp_prod = __new; \
291 virt_mb(); /* front sees new resps /before/ we check rsp_event */ \
292 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
293 (RING_IDX)(__new - __old)); \
296 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
297 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
298 if (_work_to_do) break; \
299 (_r)->sring->req_event = (_r)->req_cons + 1; \
301 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
304 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
305 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
306 if (_work_to_do) break; \
307 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
309 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
314 * DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and
315 * functions to check if there is data on the ring, and to read and
318 * DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but
319 * does not define the indexes page. As different protocols can have
320 * extensions to the basic format, this macro allow them to define their
324 * Convenience macro to calculate the size of one of the two rings
325 * from the overall order.
328 * Function to apply the size mask to an index, to reduce the index
329 * within the range [0-size].
332 * Function to read data from the ring. The amount of data to read is
333 * specified by the "size" argument.
336 * Function to write data to the ring. The amount of data to write is
337 * specified by the "size" argument.
340 * Convenience function that returns a pointer to read/write to the
341 * ring at the right location.
344 * Indexes page, shared between frontend and backend. It also
345 * contains the array of grant refs.
348 * Function to calculate how many bytes are currently on the ring,
349 * ready to be read. It can also be used to calculate how much free
350 * space is currently on the ring (XEN_FLEX_RING_SIZE() -
354 #ifndef XEN_PAGE_SHIFT
355 /* The PAGE_SIZE for ring protocols and hypercall interfaces is always
356 * 4K, regardless of the architecture, and page granularity chosen by
359 #define XEN_PAGE_SHIFT 12
361 #define XEN_FLEX_RING_SIZE(order) \
362 (1UL << ((order) + XEN_PAGE_SHIFT - 1))
364 #define DEFINE_XEN_FLEX_RING(name) \
365 static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size) \
367 return idx & (ring_size - 1); \
370 static inline unsigned char *name##_get_ring_ptr(unsigned char *buf, \
372 RING_IDX ring_size) \
374 return buf + name##_mask(idx, ring_size); \
377 static inline void name##_read_packet(void *opaque, \
378 const unsigned char *buf, \
380 RING_IDX masked_prod, \
381 RING_IDX *masked_cons, \
382 RING_IDX ring_size) \
384 if (*masked_cons < masked_prod || \
385 size <= ring_size - *masked_cons) { \
386 memcpy(opaque, buf + *masked_cons, size); \
388 memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons); \
389 memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf, \
390 size - (ring_size - *masked_cons)); \
392 *masked_cons = name##_mask(*masked_cons + size, ring_size); \
395 static inline void name##_write_packet(unsigned char *buf, \
396 const void *opaque, \
398 RING_IDX *masked_prod, \
399 RING_IDX masked_cons, \
400 RING_IDX ring_size) \
402 if (*masked_prod < masked_cons || \
403 size <= ring_size - *masked_prod) { \
404 memcpy(buf + *masked_prod, opaque, size); \
406 memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod); \
407 memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod), \
408 size - (ring_size - *masked_prod)); \
410 *masked_prod = name##_mask(*masked_prod + size, ring_size); \
413 static inline RING_IDX name##_queued(RING_IDX prod, \
415 RING_IDX ring_size) \
422 prod = name##_mask(prod, ring_size); \
423 cons = name##_mask(cons, ring_size); \
429 size = prod - cons; \
431 size = ring_size - (cons - prod); \
435 struct name##_data { \
436 unsigned char *in; /* half of the allocation */ \
437 unsigned char *out; /* half of the allocation */ \
440 #define DEFINE_XEN_FLEX_RING_AND_INTF(name) \
441 struct name##_data_intf { \
442 RING_IDX in_cons, in_prod; \
446 RING_IDX out_cons, out_prod; \
450 RING_IDX ring_order; \
453 DEFINE_XEN_FLEX_RING(name)
455 #endif /* __XEN_PUBLIC_IO_RING_H__ */