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 * The amount of space reserved in the shared ring for accounting information.
50 #define __RING_HEADER_SIZE(_s) \
51 ((intptr_t)(_s)->ring - (intptr_t)(_s))
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).
59 #define __RING_SIZE(_s, _sz) \
60 (__RD32(((_sz) - __RING_HEADER_SIZE(_s)) / sizeof((_s)->ring[0])))
63 * The number of pages needed to support a given number of request/reponse
64 * entries. The entry count is rounded down to the nearest power of two
65 * as required by the ring macros.
67 #define __RING_PAGES(_s, _entries) \
68 ((__RING_HEADER_SIZE(_s) \
69 + (__RD32(_entries) * sizeof((_s)->ring[0])) \
70 + PAGE_SIZE - 1) / PAGE_SIZE)
73 * Macros to make the correct C datatypes for a new kind of ring.
75 * To make a new ring datatype, you need to have two message structures,
76 * let's say request_t, and response_t already defined.
78 * In a header where you want the ring datatype declared, you then do:
80 * DEFINE_RING_TYPES(mytag, request_t, response_t);
82 * These expand out to give you a set of types, as you can see below.
83 * The most important of these are:
85 * mytag_sring_t - The shared ring.
86 * mytag_front_ring_t - The 'front' half of the ring.
87 * mytag_back_ring_t - The 'back' half of the ring.
89 * To initialize a ring in your code you need to know the location and size
90 * of the shared memory area (PAGE_SIZE, for instance). To initialise
93 * mytag_front_ring_t front_ring;
94 * SHARED_RING_INIT((mytag_sring_t *)shared_page);
95 * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
97 * Initializing the back follows similarly (note that only the front
98 * initializes the shared ring):
100 * mytag_back_ring_t back_ring;
101 * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
104 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
106 /* Shared ring entry */ \
107 union __name##_sring_entry { \
112 /* Shared ring page */ \
113 struct __name##_sring { \
114 RING_IDX req_prod, req_event; \
115 RING_IDX rsp_prod, rsp_event; \
117 union __name##_sring_entry ring[1]; /* variable-length */ \
120 /* "Front" end's private variables */ \
121 struct __name##_front_ring { \
122 RING_IDX req_prod_pvt; \
124 unsigned int nr_ents; \
125 struct __name##_sring *sring; \
128 /* "Back" end's private variables */ \
129 struct __name##_back_ring { \
130 RING_IDX rsp_prod_pvt; \
132 unsigned int nr_ents; \
133 struct __name##_sring *sring; \
136 /* Syntactic sugar */ \
137 typedef struct __name##_sring __name##_sring_t; \
138 typedef struct __name##_front_ring __name##_front_ring_t; \
139 typedef struct __name##_back_ring __name##_back_ring_t
142 * Macros for manipulating rings.
144 * FRONT_RING_whatever works on the "front end" of a ring: here
145 * requests are pushed on to the ring and responses taken off it.
147 * BACK_RING_whatever works on the "back end" of a ring: here
148 * requests are taken off the ring and responses put on.
150 * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
151 * This is OK in 1-for-1 request-response situations where the
152 * requestor (front end) never has more than RING_SIZE()-1
153 * outstanding requests.
156 /* Initialising empty rings */
157 #define SHARED_RING_INIT(_s) do { \
158 (_s)->req_prod = (_s)->rsp_prod = 0; \
159 (_s)->req_event = (_s)->rsp_event = 1; \
160 (void)memset((_s)->pad, 0, sizeof((_s)->pad)); \
163 #define FRONT_RING_INIT(_r, _s, __size) do { \
164 (_r)->req_prod_pvt = 0; \
165 (_r)->rsp_cons = 0; \
166 (_r)->nr_ents = __RING_SIZE(_s, __size); \
167 (_r)->sring = (_s); \
170 #define BACK_RING_INIT(_r, _s, __size) do { \
171 (_r)->rsp_prod_pvt = 0; \
172 (_r)->req_cons = 0; \
173 (_r)->nr_ents = __RING_SIZE(_s, __size); \
174 (_r)->sring = (_s); \
177 /* Initialize to existing shared indexes -- for recovery */
178 #define FRONT_RING_ATTACH(_r, _s, __size) do { \
179 (_r)->sring = (_s); \
180 (_r)->req_prod_pvt = (_s)->req_prod; \
181 (_r)->rsp_cons = (_s)->rsp_prod; \
182 (_r)->nr_ents = __RING_SIZE(_s, __size); \
185 #define BACK_RING_ATTACH(_r, _s, __size) do { \
186 (_r)->sring = (_s); \
187 (_r)->rsp_prod_pvt = (_s)->rsp_prod; \
188 (_r)->req_cons = (_s)->req_prod; \
189 (_r)->nr_ents = __RING_SIZE(_s, __size); \
192 /* How big is this ring? */
193 #define RING_SIZE(_r) \
196 /* Number of free requests (for use on front side only). */
197 #define RING_FREE_REQUESTS(_r) \
198 (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
200 /* Test if there is an empty slot available on the front ring.
201 * (This is only meaningful from the front. )
203 #define RING_FULL(_r) \
204 (RING_FREE_REQUESTS(_r) == 0)
206 /* Test if there are outstanding messages to be processed on a ring. */
207 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \
208 ((_r)->sring->rsp_prod - (_r)->rsp_cons)
211 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \
212 unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
213 unsigned int rsp = RING_SIZE(_r) - \
214 ((_r)->req_cons - (_r)->rsp_prod_pvt); \
215 req < rsp ? req : rsp; \
218 /* Same as above, but without the nice GCC ({ ... }) syntax. */
219 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \
220 ((((_r)->sring->req_prod - (_r)->req_cons) < \
221 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \
222 ((_r)->sring->req_prod - (_r)->req_cons) : \
223 (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
226 /* Direct access to individual ring elements, by index. */
227 #define RING_GET_REQUEST(_r, _idx) \
228 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
230 #define RING_GET_RESPONSE(_r, _idx) \
231 (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
233 /* Loop termination condition: Would the specified index overflow the ring? */
234 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
235 (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
237 #define RING_PUSH_REQUESTS(_r) do { \
238 xen_wmb(); /* back sees requests /before/ updated producer index */ \
239 (_r)->sring->req_prod = (_r)->req_prod_pvt; \
242 #define RING_PUSH_RESPONSES(_r) do { \
243 xen_wmb(); /* front sees resps /before/ updated producer index */ \
244 (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
248 * Notification hold-off (req_event and rsp_event):
250 * When queueing requests or responses on a shared ring, it may not always be
251 * necessary to notify the remote end. For example, if requests are in flight
252 * in a backend, the front may be able to queue further requests without
253 * notifying the back (if the back checks for new requests when it queues
256 * When enqueuing requests or responses:
258 * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
259 * is a boolean return value. True indicates that the receiver requires an
260 * asynchronous notification.
262 * After dequeuing requests or responses (before sleeping the connection):
264 * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
265 * The second argument is a boolean return value. True indicates that there
266 * are pending messages on the ring (i.e., the connection should not be put
269 * These macros will set the req_event/rsp_event field to trigger a
270 * notification on the very next message that is enqueued. If you want to
271 * create batches of work (i.e., only receive a notification after several
272 * messages have been enqueued) then you will need to create a customised
273 * version of the FINAL_CHECK macro in your own code, which sets the event
274 * field appropriately.
277 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
278 RING_IDX __old = (_r)->sring->req_prod; \
279 RING_IDX __new = (_r)->req_prod_pvt; \
280 xen_wmb(); /* back sees requests /before/ updated producer index */ \
281 (_r)->sring->req_prod = __new; \
282 xen_mb(); /* back sees new requests /before/ we check req_event */ \
283 (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
284 (RING_IDX)(__new - __old)); \
287 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
288 RING_IDX __old = (_r)->sring->rsp_prod; \
289 RING_IDX __new = (_r)->rsp_prod_pvt; \
290 xen_wmb(); /* front sees resps /before/ updated producer index */ \
291 (_r)->sring->rsp_prod = __new; \
292 xen_mb(); /* front sees new resps /before/ we check rsp_event */ \
293 (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
294 (RING_IDX)(__new - __old)); \
297 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
298 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
299 if (_work_to_do) break; \
300 (_r)->sring->req_event = (_r)->req_cons + 1; \
302 (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
305 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
306 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
307 if (_work_to_do) break; \
308 (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
310 (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
313 #endif /* __XEN_PUBLIC_IO_RING_H__ */
321 * indent-tabs-mode: nil