iPXE
ring.h
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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 FILE_LICENCE ( MIT );
31 
32 #include "../xen-compat.h"
33 
34 #if __XEN_INTERFACE_VERSION__ < 0x00030208
35 #define xen_mb() mb()
36 #define xen_rmb() rmb()
37 #define xen_wmb() wmb()
38 #endif
39 
40 typedef unsigned int RING_IDX;
41 
42 /* Round a 32-bit unsigned constant down to the nearest power of two. */
43 #define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1))
44 #define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x))
45 #define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x))
46 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x))
47 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
48 
49 /*
50  * Calculate size of a shared ring, given the total available space for the
51  * ring and indexes (_sz), and the name tag of the request/response structure.
52  * A ring contains as many entries as will fit, rounded down to the nearest
53  * power of two (so we can mask with (size-1) to loop around).
54  */
55 #define __CONST_RING_SIZE(_s, _sz) \
56  (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
57  sizeof(((struct _s##_sring *)0)->ring[0])))
58 /*
59  * The same for passing in an actual pointer instead of a name tag.
60  */
61 #define __RING_SIZE(_s, _sz) \
62  (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
63 
64 /*
65  * Macros to make the correct C datatypes for a new kind of ring.
66  *
67  * To make a new ring datatype, you need to have two message structures,
68  * let's say request_t, and response_t already defined.
69  *
70  * In a header where you want the ring datatype declared, you then do:
71  *
72  * DEFINE_RING_TYPES(mytag, request_t, response_t);
73  *
74  * These expand out to give you a set of types, as you can see below.
75  * The most important of these are:
76  *
77  * mytag_sring_t - The shared ring.
78  * mytag_front_ring_t - The 'front' half of the ring.
79  * mytag_back_ring_t - The 'back' half of the ring.
80  *
81  * To initialize a ring in your code you need to know the location and size
82  * of the shared memory area (PAGE_SIZE, for instance). To initialise
83  * the front half:
84  *
85  * mytag_front_ring_t front_ring;
86  * SHARED_RING_INIT((mytag_sring_t *)shared_page);
87  * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
88  *
89  * Initializing the back follows similarly (note that only the front
90  * initializes the shared ring):
91  *
92  * mytag_back_ring_t back_ring;
93  * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
94  */
95 
96 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
97  \
98 /* Shared ring entry */ \
99 union __name##_sring_entry { \
100  __req_t req; \
101  __rsp_t rsp; \
102 }; \
103  \
104 /* Shared ring page */ \
105 struct __name##_sring { \
106  RING_IDX req_prod, req_event; \
107  RING_IDX rsp_prod, rsp_event; \
108  union { \
109  struct { \
110  uint8_t smartpoll_active; \
111  } netif; \
112  struct { \
113  uint8_t msg; \
114  } tapif_user; \
115  uint8_t pvt_pad[4]; \
116  } private; \
117  uint8_t __pad[44]; \
118  union __name##_sring_entry ring[1]; /* variable-length */ \
119 }; \
120  \
121 /* "Front" end's private variables */ \
122 struct __name##_front_ring { \
123  RING_IDX req_prod_pvt; \
124  RING_IDX rsp_cons; \
125  unsigned int nr_ents; \
126  struct __name##_sring *sring; \
127 }; \
128  \
129 /* "Back" end's private variables */ \
130 struct __name##_back_ring { \
131  RING_IDX rsp_prod_pvt; \
132  RING_IDX req_cons; \
133  unsigned int nr_ents; \
134  struct __name##_sring *sring; \
135 }; \
136  \
137 /* Syntactic sugar */ \
138 typedef struct __name##_sring __name##_sring_t; \
139 typedef struct __name##_front_ring __name##_front_ring_t; \
140 typedef struct __name##_back_ring __name##_back_ring_t
141 
142 /*
143  * Macros for manipulating rings.
144  *
145  * FRONT_RING_whatever works on the "front end" of a ring: here
146  * requests are pushed on to the ring and responses taken off it.
147  *
148  * BACK_RING_whatever works on the "back end" of a ring: here
149  * requests are taken off the ring and responses put on.
150  *
151  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
152  * This is OK in 1-for-1 request-response situations where the
153  * requestor (front end) never has more than RING_SIZE()-1
154  * outstanding requests.
155  */
156 
157 /* Initialising empty rings */
158 #define SHARED_RING_INIT(_s) do { \
159  (_s)->req_prod = (_s)->rsp_prod = 0; \
160  (_s)->req_event = (_s)->rsp_event = 1; \
161  (void)memset((_s)->private.pvt_pad, 0, sizeof((_s)->private.pvt_pad)); \
162  (void)memset((_s)->__pad, 0, sizeof((_s)->__pad)); \
163 } while(0)
164 
165 #define FRONT_RING_INIT(_r, _s, __size) do { \
166  (_r)->req_prod_pvt = 0; \
167  (_r)->rsp_cons = 0; \
168  (_r)->nr_ents = __RING_SIZE(_s, __size); \
169  (_r)->sring = (_s); \
170 } while (0)
171 
172 #define BACK_RING_INIT(_r, _s, __size) do { \
173  (_r)->rsp_prod_pvt = 0; \
174  (_r)->req_cons = 0; \
175  (_r)->nr_ents = __RING_SIZE(_s, __size); \
176  (_r)->sring = (_s); \
177 } while (0)
178 
179 /* How big is this ring? */
180 #define RING_SIZE(_r) \
181  ((_r)->nr_ents)
182 
183 /* Number of free requests (for use on front side only). */
184 #define RING_FREE_REQUESTS(_r) \
185  (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
186 
187 /* Test if there is an empty slot available on the front ring.
188  * (This is only meaningful from the front. )
189  */
190 #define RING_FULL(_r) \
191  (RING_FREE_REQUESTS(_r) == 0)
192 
193 /* Test if there are outstanding messages to be processed on a ring. */
194 #define RING_HAS_UNCONSUMED_RESPONSES(_r) \
195  ((_r)->sring->rsp_prod - (_r)->rsp_cons)
196 
197 #ifdef __GNUC__
198 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({ \
199  unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
200  unsigned int rsp = RING_SIZE(_r) - \
201  ((_r)->req_cons - (_r)->rsp_prod_pvt); \
202  req < rsp ? req : rsp; \
203 })
204 #else
205 /* Same as above, but without the nice GCC ({ ... }) syntax. */
206 #define RING_HAS_UNCONSUMED_REQUESTS(_r) \
207  ((((_r)->sring->req_prod - (_r)->req_cons) < \
208  (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \
209  ((_r)->sring->req_prod - (_r)->req_cons) : \
210  (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
211 #endif
212 
213 /* Direct access to individual ring elements, by index. */
214 #define RING_GET_REQUEST(_r, _idx) \
215  (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
216 
217 #define RING_GET_RESPONSE(_r, _idx) \
218  (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
219 
220 /* Loop termination condition: Would the specified index overflow the ring? */
221 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
222  (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
223 
224 /* Ill-behaved frontend determination: Can there be this many requests? */
225 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \
226  (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
227 
228 #define RING_PUSH_REQUESTS(_r) do { \
229  xen_wmb(); /* back sees requests /before/ updated producer index */ \
230  (_r)->sring->req_prod = (_r)->req_prod_pvt; \
231 } while (0)
232 
233 #define RING_PUSH_RESPONSES(_r) do { \
234  xen_wmb(); /* front sees resps /before/ updated producer index */ \
235  (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
236 } while (0)
237 
238 /*
239  * Notification hold-off (req_event and rsp_event):
240  *
241  * When queueing requests or responses on a shared ring, it may not always be
242  * necessary to notify the remote end. For example, if requests are in flight
243  * in a backend, the front may be able to queue further requests without
244  * notifying the back (if the back checks for new requests when it queues
245  * responses).
246  *
247  * When enqueuing requests or responses:
248  *
249  * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
250  * is a boolean return value. True indicates that the receiver requires an
251  * asynchronous notification.
252  *
253  * After dequeuing requests or responses (before sleeping the connection):
254  *
255  * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
256  * The second argument is a boolean return value. True indicates that there
257  * are pending messages on the ring (i.e., the connection should not be put
258  * to sleep).
259  *
260  * These macros will set the req_event/rsp_event field to trigger a
261  * notification on the very next message that is enqueued. If you want to
262  * create batches of work (i.e., only receive a notification after several
263  * messages have been enqueued) then you will need to create a customised
264  * version of the FINAL_CHECK macro in your own code, which sets the event
265  * field appropriately.
266  */
267 
268 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
269  RING_IDX __old = (_r)->sring->req_prod; \
270  RING_IDX __new = (_r)->req_prod_pvt; \
271  xen_wmb(); /* back sees requests /before/ updated producer index */ \
272  (_r)->sring->req_prod = __new; \
273  xen_mb(); /* back sees new requests /before/ we check req_event */ \
274  (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
275  (RING_IDX)(__new - __old)); \
276 } while (0)
277 
278 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
279  RING_IDX __old = (_r)->sring->rsp_prod; \
280  RING_IDX __new = (_r)->rsp_prod_pvt; \
281  xen_wmb(); /* front sees resps /before/ updated producer index */ \
282  (_r)->sring->rsp_prod = __new; \
283  xen_mb(); /* front sees new resps /before/ we check rsp_event */ \
284  (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
285  (RING_IDX)(__new - __old)); \
286 } while (0)
287 
288 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
289  (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
290  if (_work_to_do) break; \
291  (_r)->sring->req_event = (_r)->req_cons + 1; \
292  xen_mb(); \
293  (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
294 } while (0)
295 
296 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
297  (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
298  if (_work_to_do) break; \
299  (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
300  xen_mb(); \
301  (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
302 } while (0)
303 
304 #endif /* __XEN_PUBLIC_IO_RING_H__ */
305 
306 /*
307  * Local variables:
308  * mode: C
309  * c-file-style: "BSD"
310  * c-basic-offset: 4
311  * tab-width: 4
312  * indent-tabs-mode: nil
313  * End:
314  */
unsigned int RING_IDX
Definition: ring.h:40
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