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1.1 root 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: */
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