xref: /titanic_41/usr/src/uts/common/xen/public/io/ring.h (revision 349b53dd4e695e3d833b5380540385145b2d3ae8)
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 __RING_SIZE(_s, _sz) \
54     (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
55 
56 /*
57  * Macros to make the correct C datatypes for a new kind of ring.
58  *
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.
61  *
62  * In a header where you want the ring datatype declared, you then do:
63  *
64  *     DEFINE_RING_TYPES(mytag, request_t, response_t);
65  *
66  * These expand out to give you a set of types, as you can see below.
67  * The most important of these are:
68  *
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.
72  *
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
75  * the front half:
76  *
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);
80  *
81  * Initializing the back follows similarly (note that only the front
82  * initializes the shared ring):
83  *
84  *     mytag_back_ring_t back_ring;
85  *     BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
86  */
87 
88 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)                     \
89                                                                         \
90 /* Shared ring entry */                                                 \
91 union __name##_sring_entry {                                            \
92     __req_t req;                                                        \
93     __rsp_t rsp;                                                        \
94 };                                                                      \
95                                                                         \
96 /* Shared ring page */                                                  \
97 struct __name##_sring {                                                 \
98     RING_IDX req_prod, req_event;                                       \
99     RING_IDX rsp_prod, rsp_event;                                       \
100     uint8_t  pad[48];                                                   \
101     union __name##_sring_entry ring[1]; /* variable-length */           \
102 };                                                                      \
103                                                                         \
104 /* "Front" end's private variables */                                   \
105 struct __name##_front_ring {                                            \
106     RING_IDX req_prod_pvt;                                              \
107     RING_IDX rsp_cons;                                                  \
108     unsigned int nr_ents;                                               \
109     struct __name##_sring *sring;                                       \
110 };                                                                      \
111                                                                         \
112 /* "Back" end's private variables */                                    \
113 struct __name##_back_ring {                                             \
114     RING_IDX rsp_prod_pvt;                                              \
115     RING_IDX req_cons;                                                  \
116     unsigned int nr_ents;                                               \
117     struct __name##_sring *sring;                                       \
118 };                                                                      \
119                                                                         \
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
124 
125 /*
126  * Macros for manipulating rings.
127  *
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.
130  *
131  * BACK_RING_whatever works on the "back end" of a ring: here
132  * requests are taken off the ring and responses put on.
133  *
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.
138  */
139 
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));                      \
145 } while(0)
146 
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);                                                 \
152 } while (0)
153 
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);                                                 \
159 } while (0)
160 
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);                            \
167 } while (0)
168 
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);                            \
174 } while (0)
175 
176 /* How big is this ring? */
177 #define RING_SIZE(_r)                                                   \
178     ((_r)->nr_ents)
179 
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))
183 
184 /* Test if there is an empty slot available on the front ring.
185  * (This is only meaningful from the front. )
186  */
187 #define RING_FULL(_r)                                                   \
188     (RING_FREE_REQUESTS(_r) == 0)
189 
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)
193 
194 #ifdef __GNUC__
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;                                              \
200 })
201 #else
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)))
208 #endif
209 
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))
213 
214 #define RING_GET_RESPONSE(_r, _idx)                                     \
215     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
216 
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))
220 
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;                         \
224 } while (0)
225 
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;                         \
229 } while (0)
230 
231 /*
232  * Notification hold-off (req_event and rsp_event):
233  *
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
238  * responses).
239  *
240  * When enqueuing requests or responses:
241  *
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.
245  *
246  * After dequeuing requests or responses (before sleeping the connection):
247  *
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
251  *  to sleep).
252  *
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.
259  */
260 
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));                            \
269 } while (0)
270 
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));                            \
279 } while (0)
280 
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;                        \
285     xen_mb();                                                           \
286     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
287 } while (0)
288 
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;                        \
293     xen_mb();                                                           \
294     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
295 } while (0)
296 
297 #endif /* __XEN_PUBLIC_IO_RING_H__ */
298 
299 /*
300  * Local variables:
301  * mode: C
302  * c-set-style: "BSD"
303  * c-basic-offset: 4
304  * tab-width: 4
305  * indent-tabs-mode: nil
306  * End:
307  */
308