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__
30 #include "../xen-compat.h"
32 #if __XEN_INTERFACE_VERSION__ < 0x00030208
34 #define xen_rmb() rmb()
35 #define xen_wmb() wmb()
38 typedef unsigned int RING_IDX;
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))
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).
53 #define __RING_SIZE(_s, _sz) \
54 (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
57 * Macros to make the correct C datatypes for a new kind of ring.
59 * To make a new ring datatype, you need to have two message structures,
60 * let's say request_t, and response_t already defined.
62 * In a header where you want the ring datatype declared, you then do:
64 * DEFINE_RING_TYPES(mytag, request_t, response_t);
66 * These expand out to give you a set of types, as you can see below.
67 * The most important of these are:
69 * mytag_sring_t - The shared ring.
70 * mytag_front_ring_t - The 'front' half of the ring.
71 * mytag_back_ring_t - The 'back' half of the ring.
73 * To initialize a ring in your code you need to know the location and size
74 * of the shared memory area (PAGE_SIZE, for instance). To initialise
77 * mytag_front_ring_t front_ring;
78 * SHARED_RING_INIT((mytag_sring_t *)shared_page);
79 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
81 * Initializing the back follows similarly (note that only the front
82 * initializes the shared ring):
84 * mytag_back_ring_t back_ring;
85 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
88 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
90 /* Shared ring entry */ \
91 union __name##_sring_entry { \
96 /* Shared ring page */ \
97 struct __name##_sring { \
98 RING_IDX req_prod, req_event; \
99 RING_IDX rsp_prod, rsp_event; \
101 union __name##_sring_entry ring[1]; /* variable-length */ \
104 /* "Front" end's private variables */ \
105 struct __name##_front_ring { \
106 RING_IDX req_prod_pvt; \
108 unsigned int nr_ents; \
109 struct __name##_sring *sring; \
112 /* "Back" end's private variables */ \
113 struct __name##_back_ring { \
114 RING_IDX rsp_prod_pvt; \
116 unsigned int nr_ents; \
117 struct __name##_sring *sring; \
120 /* Syntactic sugar */ \
121 typedef struct __name##_sring __name##_sring_t; \
122 typedef struct __name##_front_ring __name##_front_ring_t; \
123 typedef struct __name##_back_ring __name##_back_ring_t
126 * Macros for manipulating rings.
128 * FRONT_RING_whatever works on the "front end" of a ring: here
129 * requests are pushed on to the ring and responses taken off it.
131 * BACK_RING_whatever works on the "back end" of a ring: here
132 * requests are taken off the ring and responses put on.
134 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
135 * This is OK in 1-for-1 request-response situations where the
136 * requestor (front end) never has more than RING_SIZE()-1
137 * outstanding requests.
140 /* Initialising empty rings */
141 #define SHARED_RING_INIT(_s) do { \
142 (_s)->req_prod = (_s)->rsp_prod = 0; \
143 (_s)->req_event = (_s)->rsp_event = 1; \
144 (void)memset((_s)->pad, 0, sizeof((_s)->pad)); \
147 #define FRONT_RING_INIT(_r, _s, __size) do { \
148 (_r)->req_prod_pvt = 0; \
149 (_r)->rsp_cons = 0; \
150 (_r)->nr_ents = __RING_SIZE(_s, __size); \
151 (_r)->sring = (_s); \
154 #define BACK_RING_INIT(_r, _s, __size) do { \
155 (_r)->rsp_prod_pvt = 0; \
156 (_r)->req_cons = 0; \
157 (_r)->nr_ents = __RING_SIZE(_s, __size); \
158 (_r)->sring = (_s); \
161 /* Initialize to existing shared indexes -- for recovery */
162 #define FRONT_RING_ATTACH(_r, _s, __size) do { \
163 (_r)->sring = (_s); \
164 (_r)->req_prod_pvt = (_s)->req_prod; \
165 (_r)->rsp_cons = (_s)->rsp_prod; \
166 (_r)->nr_ents = __RING_SIZE(_s, __size); \
169 #define BACK_RING_ATTACH(_r, _s, __size) do { \
170 (_r)->sring = (_s); \
171 (_r)->rsp_prod_pvt = (_s)->rsp_prod; \
172 (_r)->req_cons = (_s)->req_prod; \
173 (_r)->nr_ents = __RING_SIZE(_s, __size); \
176 /* How big is this ring? */
177 #define RING_SIZE(_r) \
180 /* Number of free requests (for use on front side only). */
181 #define RING_FREE_REQUESTS(_r) \
182 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
184 /* Test if there is an empty slot available on the front ring.
185 * (This is only meaningful from the front. )
187 #define RING_FULL(_r) \
188 (RING_FREE_REQUESTS(_r) == 0)
190 /* Test if there are outstanding messages to be processed on a ring. */
191 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \
192 ((_r)->sring->rsp_prod - (_r)->rsp_cons)
195 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \
196 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
197 unsigned int rsp = RING_SIZE(_r) - \
198 ((_r)->req_cons - (_r)->rsp_prod_pvt); \
199 req < rsp ? req : rsp; \
202 /* Same as above, but without the nice GCC ({ ... }) syntax. */
203 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \
204 ((((_r)->sring->req_prod - (_r)->req_cons) < \
205 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \
206 ((_r)->sring->req_prod - (_r)->req_cons) : \
207 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
210 /* Direct access to individual ring elements, by index. */
211 #define RING_GET_REQUEST(_r, _idx) \
212 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
214 #define RING_GET_RESPONSE(_r, _idx) \
215 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
217 /* Loop termination condition: Would the specified index overflow the ring? */
218 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
219 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
221 #define RING_PUSH_REQUESTS(_r) do { \
222 xen_wmb(); /* back sees requests /before/ updated producer index */ \
223 (_r)->sring->req_prod = (_r)->req_prod_pvt; \
226 #define RING_PUSH_RESPONSES(_r) do { \
227 xen_wmb(); /* front sees resps /before/ updated producer index */ \
228 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
232 * Notification hold-off (req_event and rsp_event):
234 * When queueing requests or responses on a shared ring, it may not always be
235 * necessary to notify the remote end. For example, if requests are in flight
236 * in a backend, the front may be able to queue further requests without
237 * notifying the back (if the back checks for new requests when it queues
240 * When enqueuing requests or responses:
242 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
243 * is a boolean return value. True indicates that the receiver requires an
244 * asynchronous notification.
246 * After dequeuing requests or responses (before sleeping the connection):
248 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
249 * The second argument is a boolean return value. True indicates that there
250 * are pending messages on the ring (i.e., the connection should not be put
253 * These macros will set the req_event/rsp_event field to trigger a
254 * notification on the very next message that is enqueued. If you want to
255 * create batches of work (i.e., only receive a notification after several
256 * messages have been enqueued) then you will need to create a customised
257 * version of the FINAL_CHECK macro in your own code, which sets the event
258 * field appropriately.
261 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
262 RING_IDX __old = (_r)->sring->req_prod; \
263 RING_IDX __new = (_r)->req_prod_pvt; \
264 xen_wmb(); /* back sees requests /before/ updated producer index */ \
265 (_r)->sring->req_prod = __new; \
266 xen_mb(); /* back sees new requests /before/ we check req_event */ \
267 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
268 (RING_IDX)(__new - __old)); \
271 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
272 RING_IDX __old = (_r)->sring->rsp_prod; \
273 RING_IDX __new = (_r)->rsp_prod_pvt; \
274 xen_wmb(); /* front sees resps /before/ updated producer index */ \
275 (_r)->sring->rsp_prod = __new; \
276 xen_mb(); /* front sees new resps /before/ we check rsp_event */ \
277 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
278 (RING_IDX)(__new - __old)); \
281 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
282 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
283 if (_work_to_do) break; \
284 (_r)->sring->req_event = (_r)->req_cons + 1; \
286 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
289 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
290 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
291 if (_work_to_do) break; \
292 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
294 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
297 #endif /* __XEN_PUBLIC_IO_RING_H__ */
305 * indent-tabs-mode: nil