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a42089dd JF |
1 | /****************************************************************************** |
2 | * ring.h | |
3 | * | |
4 | * Shared producer-consumer ring macros. | |
5 | * | |
6 | * Tim Deegan and Andrew Warfield November 2004. | |
7 | */ | |
8 | ||
9 | #ifndef __XEN_PUBLIC_IO_RING_H__ | |
10 | #define __XEN_PUBLIC_IO_RING_H__ | |
11 | ||
12 | typedef unsigned int RING_IDX; | |
13 | ||
14 | /* Round a 32-bit unsigned constant down to the nearest power of two. */ | |
15 | #define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1)) | |
16 | #define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x)) | |
17 | #define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x)) | |
18 | #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x)) | |
19 | #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x)) | |
20 | ||
21 | /* | |
22 | * Calculate size of a shared ring, given the total available space for the | |
23 | * ring and indexes (_sz), and the name tag of the request/response structure. | |
24 | * A ring contains as many entries as will fit, rounded down to the nearest | |
25 | * power of two (so we can mask with (size-1) to loop around). | |
26 | */ | |
667c78af JF |
27 | #define __CONST_RING_SIZE(_s, _sz) \ |
28 | (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \ | |
29 | sizeof(((struct _s##_sring *)0)->ring[0]))) | |
30 | ||
31 | /* | |
32 | * The same for passing in an actual pointer instead of a name tag. | |
33 | */ | |
34 | #define __RING_SIZE(_s, _sz) \ | |
35 | (__RD32(((_sz) - (long)&(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0]))) | |
a42089dd JF |
36 | |
37 | /* | |
38 | * Macros to make the correct C datatypes for a new kind of ring. | |
39 | * | |
40 | * To make a new ring datatype, you need to have two message structures, | |
41 | * let's say struct request, and struct response already defined. | |
42 | * | |
43 | * In a header where you want the ring datatype declared, you then do: | |
44 | * | |
45 | * DEFINE_RING_TYPES(mytag, struct request, struct response); | |
46 | * | |
47 | * These expand out to give you a set of types, as you can see below. | |
48 | * The most important of these are: | |
49 | * | |
50 | * struct mytag_sring - The shared ring. | |
51 | * struct mytag_front_ring - The 'front' half of the ring. | |
52 | * struct mytag_back_ring - The 'back' half of the ring. | |
53 | * | |
54 | * To initialize a ring in your code you need to know the location and size | |
55 | * of the shared memory area (PAGE_SIZE, for instance). To initialise | |
56 | * the front half: | |
57 | * | |
58 | * struct mytag_front_ring front_ring; | |
59 | * SHARED_RING_INIT((struct mytag_sring *)shared_page); | |
60 | * FRONT_RING_INIT(&front_ring, (struct mytag_sring *)shared_page, | |
61 | * PAGE_SIZE); | |
62 | * | |
63 | * Initializing the back follows similarly (note that only the front | |
64 | * initializes the shared ring): | |
65 | * | |
66 | * struct mytag_back_ring back_ring; | |
67 | * BACK_RING_INIT(&back_ring, (struct mytag_sring *)shared_page, | |
68 | * PAGE_SIZE); | |
69 | */ | |
70 | ||
71 | #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \ | |
72 | \ | |
73 | /* Shared ring entry */ \ | |
74 | union __name##_sring_entry { \ | |
75 | __req_t req; \ | |
76 | __rsp_t rsp; \ | |
77 | }; \ | |
78 | \ | |
79 | /* Shared ring page */ \ | |
80 | struct __name##_sring { \ | |
81 | RING_IDX req_prod, req_event; \ | |
82 | RING_IDX rsp_prod, rsp_event; \ | |
83 | uint8_t pad[48]; \ | |
84 | union __name##_sring_entry ring[1]; /* variable-length */ \ | |
85 | }; \ | |
86 | \ | |
87 | /* "Front" end's private variables */ \ | |
88 | struct __name##_front_ring { \ | |
89 | RING_IDX req_prod_pvt; \ | |
90 | RING_IDX rsp_cons; \ | |
91 | unsigned int nr_ents; \ | |
92 | struct __name##_sring *sring; \ | |
93 | }; \ | |
94 | \ | |
95 | /* "Back" end's private variables */ \ | |
96 | struct __name##_back_ring { \ | |
97 | RING_IDX rsp_prod_pvt; \ | |
98 | RING_IDX req_cons; \ | |
99 | unsigned int nr_ents; \ | |
100 | struct __name##_sring *sring; \ | |
101 | }; | |
102 | ||
103 | /* | |
104 | * Macros for manipulating rings. | |
105 | * | |
106 | * FRONT_RING_whatever works on the "front end" of a ring: here | |
107 | * requests are pushed on to the ring and responses taken off it. | |
108 | * | |
109 | * BACK_RING_whatever works on the "back end" of a ring: here | |
110 | * requests are taken off the ring and responses put on. | |
111 | * | |
112 | * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL. | |
113 | * This is OK in 1-for-1 request-response situations where the | |
114 | * requestor (front end) never has more than RING_SIZE()-1 | |
115 | * outstanding requests. | |
116 | */ | |
117 | ||
118 | /* Initialising empty rings */ | |
119 | #define SHARED_RING_INIT(_s) do { \ | |
120 | (_s)->req_prod = (_s)->rsp_prod = 0; \ | |
121 | (_s)->req_event = (_s)->rsp_event = 1; \ | |
122 | memset((_s)->pad, 0, sizeof((_s)->pad)); \ | |
123 | } while(0) | |
124 | ||
125 | #define FRONT_RING_INIT(_r, _s, __size) do { \ | |
126 | (_r)->req_prod_pvt = 0; \ | |
127 | (_r)->rsp_cons = 0; \ | |
128 | (_r)->nr_ents = __RING_SIZE(_s, __size); \ | |
129 | (_r)->sring = (_s); \ | |
130 | } while (0) | |
131 | ||
132 | #define BACK_RING_INIT(_r, _s, __size) do { \ | |
133 | (_r)->rsp_prod_pvt = 0; \ | |
134 | (_r)->req_cons = 0; \ | |
135 | (_r)->nr_ents = __RING_SIZE(_s, __size); \ | |
136 | (_r)->sring = (_s); \ | |
137 | } while (0) | |
138 | ||
139 | /* Initialize to existing shared indexes -- for recovery */ | |
140 | #define FRONT_RING_ATTACH(_r, _s, __size) do { \ | |
141 | (_r)->sring = (_s); \ | |
142 | (_r)->req_prod_pvt = (_s)->req_prod; \ | |
143 | (_r)->rsp_cons = (_s)->rsp_prod; \ | |
144 | (_r)->nr_ents = __RING_SIZE(_s, __size); \ | |
145 | } while (0) | |
146 | ||
147 | #define BACK_RING_ATTACH(_r, _s, __size) do { \ | |
148 | (_r)->sring = (_s); \ | |
149 | (_r)->rsp_prod_pvt = (_s)->rsp_prod; \ | |
150 | (_r)->req_cons = (_s)->req_prod; \ | |
151 | (_r)->nr_ents = __RING_SIZE(_s, __size); \ | |
152 | } while (0) | |
153 | ||
154 | /* How big is this ring? */ | |
155 | #define RING_SIZE(_r) \ | |
156 | ((_r)->nr_ents) | |
157 | ||
158 | /* Number of free requests (for use on front side only). */ | |
159 | #define RING_FREE_REQUESTS(_r) \ | |
160 | (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons)) | |
161 | ||
162 | /* Test if there is an empty slot available on the front ring. | |
163 | * (This is only meaningful from the front. ) | |
164 | */ | |
165 | #define RING_FULL(_r) \ | |
166 | (RING_FREE_REQUESTS(_r) == 0) | |
167 | ||
168 | /* Test if there are outstanding messages to be processed on a ring. */ | |
169 | #define RING_HAS_UNCONSUMED_RESPONSES(_r) \ | |
170 | ((_r)->sring->rsp_prod - (_r)->rsp_cons) | |
171 | ||
172 | #define RING_HAS_UNCONSUMED_REQUESTS(_r) \ | |
173 | ({ \ | |
174 | unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \ | |
175 | unsigned int rsp = RING_SIZE(_r) - \ | |
176 | ((_r)->req_cons - (_r)->rsp_prod_pvt); \ | |
177 | req < rsp ? req : rsp; \ | |
178 | }) | |
179 | ||
180 | /* Direct access to individual ring elements, by index. */ | |
181 | #define RING_GET_REQUEST(_r, _idx) \ | |
182 | (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) | |
183 | ||
454d5d88 DV |
184 | /* |
185 | * Get a local copy of a request. | |
186 | * | |
187 | * Use this in preference to RING_GET_REQUEST() so all processing is | |
188 | * done on a local copy that cannot be modified by the other end. | |
189 | * | |
190 | * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this | |
191 | * to be ineffective where _req is a struct which consists of only bitfields. | |
192 | */ | |
193 | #define RING_COPY_REQUEST(_r, _idx, _req) do { \ | |
194 | /* Use volatile to force the copy into _req. */ \ | |
195 | *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx); \ | |
196 | } while (0) | |
197 | ||
a42089dd JF |
198 | #define RING_GET_RESPONSE(_r, _idx) \ |
199 | (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) | |
200 | ||
201 | /* Loop termination condition: Would the specified index overflow the ring? */ | |
202 | #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \ | |
203 | (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r)) | |
204 | ||
8d925690 JB |
205 | /* Ill-behaved frontend determination: Can there be this many requests? */ |
206 | #define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \ | |
207 | (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r)) | |
208 | ||
209 | ||
a42089dd | 210 | #define RING_PUSH_REQUESTS(_r) do { \ |
506b02eb | 211 | virt_wmb(); /* back sees requests /before/ updated producer index */ \ |
a42089dd JF |
212 | (_r)->sring->req_prod = (_r)->req_prod_pvt; \ |
213 | } while (0) | |
214 | ||
215 | #define RING_PUSH_RESPONSES(_r) do { \ | |
506b02eb | 216 | virt_wmb(); /* front sees responses /before/ updated producer index */ \ |
a42089dd JF |
217 | (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ |
218 | } while (0) | |
219 | ||
220 | /* | |
221 | * Notification hold-off (req_event and rsp_event): | |
222 | * | |
223 | * When queueing requests or responses on a shared ring, it may not always be | |
224 | * necessary to notify the remote end. For example, if requests are in flight | |
225 | * in a backend, the front may be able to queue further requests without | |
226 | * notifying the back (if the back checks for new requests when it queues | |
227 | * responses). | |
228 | * | |
229 | * When enqueuing requests or responses: | |
230 | * | |
231 | * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument | |
232 | * is a boolean return value. True indicates that the receiver requires an | |
233 | * asynchronous notification. | |
234 | * | |
235 | * After dequeuing requests or responses (before sleeping the connection): | |
236 | * | |
237 | * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES(). | |
238 | * The second argument is a boolean return value. True indicates that there | |
239 | * are pending messages on the ring (i.e., the connection should not be put | |
240 | * to sleep). | |
241 | * | |
242 | * These macros will set the req_event/rsp_event field to trigger a | |
243 | * notification on the very next message that is enqueued. If you want to | |
244 | * create batches of work (i.e., only receive a notification after several | |
245 | * messages have been enqueued) then you will need to create a customised | |
246 | * version of the FINAL_CHECK macro in your own code, which sets the event | |
247 | * field appropriately. | |
248 | */ | |
249 | ||
250 | #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ | |
251 | RING_IDX __old = (_r)->sring->req_prod; \ | |
252 | RING_IDX __new = (_r)->req_prod_pvt; \ | |
506b02eb | 253 | virt_wmb(); /* back sees requests /before/ updated producer index */ \ |
a42089dd | 254 | (_r)->sring->req_prod = __new; \ |
506b02eb | 255 | virt_mb(); /* back sees new requests /before/ we check req_event */ \ |
a42089dd JF |
256 | (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ |
257 | (RING_IDX)(__new - __old)); \ | |
258 | } while (0) | |
259 | ||
260 | #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ | |
261 | RING_IDX __old = (_r)->sring->rsp_prod; \ | |
262 | RING_IDX __new = (_r)->rsp_prod_pvt; \ | |
506b02eb | 263 | virt_wmb(); /* front sees responses /before/ updated producer index */ \ |
a42089dd | 264 | (_r)->sring->rsp_prod = __new; \ |
506b02eb | 265 | virt_mb(); /* front sees new responses /before/ we check rsp_event */ \ |
a42089dd JF |
266 | (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ |
267 | (RING_IDX)(__new - __old)); \ | |
268 | } while (0) | |
269 | ||
270 | #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \ | |
271 | (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ | |
272 | if (_work_to_do) break; \ | |
273 | (_r)->sring->req_event = (_r)->req_cons + 1; \ | |
506b02eb | 274 | virt_mb(); \ |
a42089dd JF |
275 | (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ |
276 | } while (0) | |
277 | ||
278 | #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \ | |
279 | (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ | |
280 | if (_work_to_do) break; \ | |
281 | (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ | |
506b02eb | 282 | virt_mb(); \ |
a42089dd JF |
283 | (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ |
284 | } while (0) | |
285 | ||
286 | #endif /* __XEN_PUBLIC_IO_RING_H__ */ |