1 /******************************************************************************
2 * ring.h
3 *
4 * Shared producer-consumer ring macros.
5 *
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:
12 *
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
15 *
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.
23 *
24 * Tim Deegan and Andrew Warfield November 2004.
25 */
26
27 #ifndef __XEN_PUBLIC_IO_RING_H__
28 #define __XEN_PUBLIC_IO_RING_H__
29
30 #include "../xen-compat.h"
31
32 #if __XEN_INTERFACE_VERSION__ < 0x00030208
33 #define xen_mb() mb()
34 #define xen_rmb() rmb()
35 #define xen_wmb() wmb()
36 #endif
37
38 typedef unsigned int RING_IDX;
39
40 /* Round a 32-bit unsigned constant down to the nearest power of two. */
41 #define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1))
42 #define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x))
43 #define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x))
44 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x))
45 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
46
47 /*
48 * The amount of space reserved in the shared ring for accounting information.
49 */
50 #define __RING_HEADER_SIZE(_s) \
51 ((intptr_t)(_s)->ring - (intptr_t)(_s))
52
53 /*
54 * Calculate size of a shared ring, given the total available space for the
55 * ring and indexes (_sz), and the name tag of the request/response structure.
56 * A ring contains as many entries as will fit, rounded down to the nearest
57 * power of two (so we can mask with (size-1) to loop around).
58 */
59 #define __CONST_RING_SIZE(_s, _sz) \
60 (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
61 sizeof(((struct _s##_sring *)0)->ring[0])))
62 /*
63 * The same for passing in an actual pointer instead of a name tag.
64 */
65 #define __RING_SIZE(_s, _sz) \
66 (__RD32(((_sz) - __RING_HEADER_SIZE(_s)) / sizeof((_s)->ring[0])))
67
68 /*
69 * The number of pages needed to support a given number of request/reponse
70 * entries. The entry count is rounded down to the nearest power of two
71 * as required by the ring macros.
72 */
73 #define __RING_PAGES(_s, _entries) \
74 ((__RING_HEADER_SIZE(_s) \
75 + (__RD32(_entries) * sizeof((_s)->ring[0])) \
76 + PAGE_SIZE - 1) / PAGE_SIZE)
77
78 /*
79 * Macros to make the correct C datatypes for a new kind of ring.
80 *
81 * To make a new ring datatype, you need to have two message structures,
82 * let's say request_t, and response_t already defined.
83 *
84 * In a header where you want the ring datatype declared, you then do:
85 *
86 * DEFINE_RING_TYPES(mytag, request_t, response_t);
87 *
88 * These expand out to give you a set of types, as you can see below.
89 * The most important of these are:
90 *
91 * mytag_sring_t - The shared ring.
92 * mytag_front_ring_t - The 'front' half of the ring.
93 * mytag_back_ring_t - The 'back' half of the ring.
94 *
95 * To initialize a ring in your code you need to know the location and size
96 * of the shared memory area (PAGE_SIZE, for instance). To initialise
97 * the front half:
98 *
99 * mytag_front_ring_t front_ring;
100 * SHARED_RING_INIT((mytag_sring_t *)shared_page);
101 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
102 *
103 * Initializing the back follows similarly (note that only the front
104 * initializes the shared ring):
105 *
106 * mytag_back_ring_t back_ring;
107 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
108 */
109
110 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
111 \
112 /* Shared ring entry */ \
113 union __name##_sring_entry { \
114 __req_t req; \
115 __rsp_t rsp; \
116 }; \
117 \
118 /* Shared ring page */ \
119 struct __name##_sring { \
120 RING_IDX req_prod, req_event; \
121 RING_IDX rsp_prod, rsp_event; \
122 union { \
123 struct { \
124 uint8_t smartpoll_active; \
125 } netif; \
126 struct { \
127 uint8_t msg; \
128 } tapif_user; \
129 uint8_t pvt_pad[4]; \
130 } private; \
131 uint8_t __pad[44]; \
132 union __name##_sring_entry ring[1]; /* variable-length */ \
133 }; \
134 \
135 /* "Front" end's private variables */ \
136 struct __name##_front_ring { \
137 RING_IDX req_prod_pvt; \
138 RING_IDX rsp_cons; \
139 unsigned int nr_ents; \
140 struct __name##_sring *sring; \
141 }; \
142 \
143 /* "Back" end's private variables */ \
144 struct __name##_back_ring { \
145 RING_IDX rsp_prod_pvt; \
146 RING_IDX req_cons; \
147 unsigned int nr_ents; \
148 struct __name##_sring *sring; \
149 }; \
150 \
151 /* Syntactic sugar */ \
152 typedef struct __name##_sring __name##_sring_t; \
153 typedef struct __name##_front_ring __name##_front_ring_t; \
154 typedef struct __name##_back_ring __name##_back_ring_t
155
156 /*
157 * Macros for manipulating rings.
158 *
159 * FRONT_RING_whatever works on the "front end" of a ring: here
160 * requests are pushed on to the ring and responses taken off it.
161 *
162 * BACK_RING_whatever works on the "back end" of a ring: here
163 * requests are taken off the ring and responses put on.
164 *
165 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
166 * This is OK in 1-for-1 request-response situations where the
167 * requestor (front end) never has more than RING_SIZE()-1
168 * outstanding requests.
169 */
170
171 /* Initialising empty rings */
172 #define SHARED_RING_INIT(_s) do { \
173 (_s)->req_prod = (_s)->rsp_prod = 0; \
174 (_s)->req_event = (_s)->rsp_event = 1; \
175 (void)memset((_s)->private.pvt_pad, 0, sizeof((_s)->private.pvt_pad)); \
176 (void)memset((_s)->__pad, 0, sizeof((_s)->__pad)); \
177 } while(0)
178
179 #define FRONT_RING_INIT(_r, _s, __size) do { \
180 (_r)->req_prod_pvt = 0; \
181 (_r)->rsp_cons = 0; \
182 (_r)->nr_ents = __RING_SIZE(_s, __size); \
183 (_r)->sring = (_s); \
184 } while (0)
185
186 #define BACK_RING_INIT(_r, _s, __size) do { \
187 (_r)->rsp_prod_pvt = 0; \
188 (_r)->req_cons = 0; \
189 (_r)->nr_ents = __RING_SIZE(_s, __size); \
190 (_r)->sring = (_s); \
191 } while (0)
192
193 /* Initialize to existing shared indexes -- for recovery */
194 #define FRONT_RING_ATTACH(_r, _s, __size) do { \
195 (_r)->sring = (_s); \
196 (_r)->req_prod_pvt = (_s)->req_prod; \
197 (_r)->rsp_cons = (_s)->rsp_prod; \
198 (_r)->nr_ents = __RING_SIZE(_s, __size); \
199 } while (0)
200
201 #define BACK_RING_ATTACH(_r, _s, __size) do { \
202 (_r)->sring = (_s); \
203 (_r)->rsp_prod_pvt = (_s)->rsp_prod; \
204 (_r)->req_cons = (_s)->req_prod; \
205 (_r)->nr_ents = __RING_SIZE(_s, __size); \
206 } while (0)
207
208 /* How big is this ring? */
209 #define RING_SIZE(_r) \
210 ((_r)->nr_ents)
211
212 /* Number of free requests (for use on front side only). */
213 #define RING_FREE_REQUESTS(_r) \
214 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
215
216 /* Test if there is an empty slot available on the front ring.
217 * (This is only meaningful from the front. )
218 */
219 #define RING_FULL(_r) \
220 (RING_FREE_REQUESTS(_r) == 0)
221
222 /* Test if there are outstanding messages to be processed on a ring. */
223 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \
224 ((_r)->sring->rsp_prod - (_r)->rsp_cons)
225
226 #ifdef __GNUC__
227 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \
228 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
229 unsigned int rsp = RING_SIZE(_r) - \
230 ((_r)->req_cons - (_r)->rsp_prod_pvt); \
231 req < rsp ? req : rsp; \
232 })
233 #else
234 /* Same as above, but without the nice GCC ({ ... }) syntax. */
235 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \
236 ((((_r)->sring->req_prod - (_r)->req_cons) < \
237 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \
238 ((_r)->sring->req_prod - (_r)->req_cons) : \
239 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
240 #endif
241
242 /* Direct access to individual ring elements, by index. */
243 #define RING_GET_REQUEST(_r, _idx) \
244 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
245
246 #define RING_GET_RESPONSE(_r, _idx) \
247 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
248
249 /* Loop termination condition: Would the specified index overflow the ring? */
250 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
251 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
252
253 #define RING_PUSH_REQUESTS(_r) do { \
254 xen_wmb(); /* back sees requests /before/ updated producer index */ \
255 (_r)->sring->req_prod = (_r)->req_prod_pvt; \
256 } while (0)
257
258 #define RING_PUSH_RESPONSES(_r) do { \
259 xen_wmb(); /* front sees resps /before/ updated producer index */ \
260 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
261 } while (0)
262
263 /*
264 * Notification hold-off (req_event and rsp_event):
265 *
266 * When queueing requests or responses on a shared ring, it may not always be
267 * necessary to notify the remote end. For example, if requests are in flight
268 * in a backend, the front may be able to queue further requests without
269 * notifying the back (if the back checks for new requests when it queues
270 * responses).
271 *
272 * When enqueuing requests or responses:
273 *
274 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
275 * is a boolean return value. True indicates that the receiver requires an
276 * asynchronous notification.
277 *
278 * After dequeuing requests or responses (before sleeping the connection):
279 *
280 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
281 * The second argument is a boolean return value. True indicates that there
282 * are pending messages on the ring (i.e., the connection should not be put
283 * to sleep).
284 *
285 * These macros will set the req_event/rsp_event field to trigger a
286 * notification on the very next message that is enqueued. If you want to
287 * create batches of work (i.e., only receive a notification after several
288 * messages have been enqueued) then you will need to create a customised
289 * version of the FINAL_CHECK macro in your own code, which sets the event
290 * field appropriately.
291 */
292
293 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
294 RING_IDX __old = (_r)->sring->req_prod; \
295 RING_IDX __new = (_r)->req_prod_pvt; \
296 xen_wmb(); /* back sees requests /before/ updated producer index */ \
297 (_r)->sring->req_prod = __new; \
298 xen_mb(); /* back sees new requests /before/ we check req_event */ \
299 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
300 (RING_IDX)(__new - __old)); \
301 } while (0)
302
303 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
304 RING_IDX __old = (_r)->sring->rsp_prod; \
305 RING_IDX __new = (_r)->rsp_prod_pvt; \
306 xen_wmb(); /* front sees resps /before/ updated producer index */ \
307 (_r)->sring->rsp_prod = __new; \
308 xen_mb(); /* front sees new resps /before/ we check rsp_event */ \
309 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
310 (RING_IDX)(__new - __old)); \
311 } while (0)
312
313 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
314 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
315 if (_work_to_do) break; \
316 (_r)->sring->req_event = (_r)->req_cons + 1; \
317 xen_mb(); \
318 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
319 } while (0)
320
321 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
322 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
323 if (_work_to_do) break; \
324 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
325 xen_mb(); \
326 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
327 } while (0)
328
329 #endif /* __XEN_PUBLIC_IO_RING_H__ */
330
331 /*
332 * Local variables:
333 * mode: C
334 * c-set-style: "BSD"
335 * c-basic-offset: 4
336 * tab-width: 4
337 * indent-tabs-mode: nil
338 * End:
339 */
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