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