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/cvs/libev/ev_linuxaio.c
Revision: 1.10
Committed: Sun Jun 23 02:02:24 2019 UTC (4 years, 10 months ago) by root
Content type: text/plain
Branch: MAIN
Changes since 1.9: +113 -3 lines
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# Content
1 /*
2 * libev linux aio fd activity backend
3 *
4 * Copyright (c) 2019 Marc Alexander Lehmann <libev@schmorp.de>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without modifica-
8 * tion, are permitted provided that the following conditions are met:
9 *
10 * 1. Redistributions of source code must retain the above copyright notice,
11 * this list of conditions and the following disclaimer.
12 *
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
18 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
19 * CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
20 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
21 * CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
22 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
23 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
24 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
25 * ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
26 * OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Alternatively, the contents of this file may be used under the terms of
29 * the GNU General Public License ("GPL") version 2 or any later version,
30 * in which case the provisions of the GPL are applicable instead of
31 * the above. If you wish to allow the use of your version of this file
32 * only under the terms of the GPL and not to allow others to use your
33 * version of this file under the BSD license, indicate your decision
34 * by deleting the provisions above and replace them with the notice
35 * and other provisions required by the GPL. If you do not delete the
36 * provisions above, a recipient may use your version of this file under
37 * either the BSD or the GPL.
38 */
39
40 #define EPOLL_FALLBACK 1
41
42 #include <sys/time.h> /* actually linux/time.h, but we must assume they are compatible */
43 #include <poll.h>
44 #include <linux/aio_abi.h>
45
46 #if EPOLL_FALLBACK
47 # include <sys/epoll.h>
48 #endif
49
50 /* we try to fill 4kB pages exactly.
51 * the ring buffer header is 32 bytes, every io event is 32 bytes.
52 * the kernel takes the io event number, doubles it, adds 2, adds the ring buffer.
53 * therefore the calculation below will use "exactly" 4kB for the ring buffer
54 */
55 #define EV_LINUXAIO_DEPTH (128 / 2 - 2 - 1) /* max. number of io events per batch */
56
57 /*****************************************************************************/
58 /* syscall wrapdadoop */
59
60 #include <sys/syscall.h> /* no glibc wrappers */
61
62 /* aio_abi.h is not versioned in any way, so we cannot test for its existance */
63 #define IOCB_CMD_POLL 5
64
65 /* taken from linux/fs/aio.c */
66 #define AIO_RING_MAGIC 0xa10a10a1
67 #define AIO_RING_INCOMPAT_FEATURES 0
68 struct aio_ring
69 {
70 unsigned id; /* kernel internal index number */
71 unsigned nr; /* number of io_events */
72 unsigned head; /* Written to by userland or by kernel. */
73 unsigned tail;
74
75 unsigned magic;
76 unsigned compat_features;
77 unsigned incompat_features;
78 unsigned header_length; /* size of aio_ring */
79
80 struct io_event io_events[0];
81 };
82
83 inline_size
84 int
85 ev_io_setup (unsigned nr_events, aio_context_t *ctx_idp)
86 {
87 return syscall (SYS_io_setup, nr_events, ctx_idp);
88 }
89
90 inline_size
91 int
92 ev_io_destroy (aio_context_t ctx_id)
93 {
94 return syscall (SYS_io_destroy, ctx_id);
95 }
96
97 inline_size
98 int
99 ev_io_submit (aio_context_t ctx_id, long nr, struct iocb *cbp[])
100 {
101 return syscall (SYS_io_submit, ctx_id, nr, cbp);
102 }
103
104 inline_size
105 int
106 ev_io_cancel (aio_context_t ctx_id, struct iocb *cbp, struct io_event *result)
107 {
108 return syscall (SYS_io_cancel, ctx_id, cbp, result);
109 }
110
111 inline_size
112 int
113 ev_io_getevents (aio_context_t ctx_id, long min_nr, long nr, struct io_event *events, struct timespec *timeout)
114 {
115 return syscall (SYS_io_getevents, ctx_id, min_nr, nr, events, timeout);
116 }
117
118 /*****************************************************************************/
119 /* actual backed implementation */
120
121 /* we use out own wrapper structure in acse we ever want to do something "clever" */
122 typedef struct aniocb
123 {
124 struct iocb io;
125 /*int inuse;*/
126 } *ANIOCBP;
127
128 inline_size
129 void
130 linuxaio_array_needsize_iocbp (ANIOCBP *base, int count)
131 {
132 /* TODO: quite the overhead to allocate every iocb separately, maybe use our own alocator? */
133 while (count--)
134 {
135 *base = (ANIOCBP)ev_malloc (sizeof (**base));
136 /* TODO: full zero initialize required? */
137 memset (*base, 0, sizeof (**base));
138 /* would be nice to initialize fd/data as well, but array_needsize API doesn't support that */
139 (*base)->io.aio_lio_opcode = IOCB_CMD_POLL;
140 ++base;
141 }
142 }
143
144 ecb_cold
145 static void
146 linuxaio_free_iocbp (EV_P)
147 {
148 while (linuxaio_iocbpmax--)
149 ev_free (linuxaio_iocbps [linuxaio_iocbpmax]);
150
151 linuxaio_iocbpmax = 0; /* next resize will completely reallocate the array, at some overhead */
152 }
153
154 static void
155 linuxaio_modify (EV_P_ int fd, int oev, int nev)
156 {
157 array_needsize (ANIOCBP, linuxaio_iocbps, linuxaio_iocbpmax, fd + 1, linuxaio_array_needsize_iocbp);
158 struct aniocb *iocb = linuxaio_iocbps [fd];
159
160 #if EPOLL_FALLBACK
161 if (iocb->io.aio_reqprio < 0)
162 {
163 epoll_ctl (backend_fd, EPOLL_CTL_DEL, fd, 0);
164 iocb->io.aio_reqprio = 0;
165 }
166 #endif
167
168 if (iocb->io.aio_buf)
169 ev_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0); /* always returns an error relevant kernels */
170
171 if (nev)
172 {
173 iocb->io.aio_data = fd;
174 iocb->io.aio_fildes = fd;
175 iocb->io.aio_buf =
176 (nev & EV_READ ? POLLIN : 0)
177 | (nev & EV_WRITE ? POLLOUT : 0);
178
179 /* queue iocb up for io_submit */
180 /* this assumes we only ever get one call per fd per loop iteration */
181 ++linuxaio_submitcnt;
182 array_needsize (struct iocb *, linuxaio_submits, linuxaio_submitmax, linuxaio_submitcnt, array_needsize_noinit);
183 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io;
184 }
185 }
186
187 static void
188 linuxaio_parse_events (EV_P_ struct io_event *ev, int nr)
189 {
190 while (nr)
191 {
192 int fd = ev->data;
193 int res = ev->res;
194
195 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
196
197 /* linux aio is oneshot: rearm fd */
198 linuxaio_iocbps [fd]->io.aio_buf = 0;
199 anfds [fd].events = 0;
200 fd_change (EV_A_ fd, 0);
201
202 /* feed events, we do not expect or handle POLLNVAL */
203 if (ecb_expect_false (res & POLLNVAL))
204 fd_kill (EV_A_ fd);
205 else
206 fd_event (
207 EV_A_
208 fd,
209 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
210 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
211 );
212
213 --nr;
214 ++ev;
215 }
216 }
217
218 /* get any events from ringbuffer, return true if any were handled */
219 static int
220 linuxaio_get_events_from_ring (EV_P)
221 {
222 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
223
224 unsigned head = ring->head;
225 unsigned tail = *(volatile unsigned *)&ring->tail;
226
227 if (head == tail)
228 return 0;
229
230 /* bail out if the ring buffer doesn't match the expected layout */
231 if (ecb_expect_false (ring->magic != AIO_RING_MAGIC)
232 || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES
233 || ring->header_length != sizeof (struct aio_ring)) /* TODO: or use it to find io_event[0]? */
234 return 0;
235
236 ECB_MEMORY_FENCE_ACQUIRE;
237
238 /* parse all available events, but only once, to avoid starvation */
239 if (tail > head) /* normal case around */
240 linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head);
241 else /* wrapped around */
242 {
243 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
244 linuxaio_parse_events (EV_A_ ring->io_events, tail);
245 }
246
247 ring->head = tail;
248
249 return 1;
250 }
251
252 /* read at least one event from kernel, or timeout */
253 inline_size
254 void
255 linuxaio_get_events (EV_P_ ev_tstamp timeout)
256 {
257 struct timespec ts;
258 struct io_event ioev;
259 int res;
260
261 if (linuxaio_get_events_from_ring (EV_A))
262 return;
263
264 /* no events, so wait for at least one, then poll ring buffer again */
265 /* this degrades to one event per loop iteration */
266 /* if the ring buffer changes layout, but so be it */
267
268 ts.tv_sec = (long)timeout;
269 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9);
270
271 res = ev_io_getevents (linuxaio_ctx, 1, 1, &ioev, &ts);
272
273 if (res < 0)
274 if (errno == EINTR)
275 /* ignored */;
276 else
277 ev_syserr ("(libev) linuxaio io_getevents");
278 else if (res)
279 {
280 /* at least one event received, handle it and any remaining ones in the ring buffer */
281 linuxaio_parse_events (EV_A_ &ioev, 1);
282 linuxaio_get_events_from_ring (EV_A);
283 }
284 }
285
286 #if EPOLL_FALLBACK
287 static void
288 linuxaio_rearm_epoll (EV_P_ struct iocb *iocb, int op)
289 {
290 struct epoll_event eev;
291
292 eev.events = EPOLLONESHOT;
293 if (iocb->aio_buf & POLLIN ) eev.events |= EPOLLIN ;
294 if (iocb->aio_buf & POLLOUT) eev.events |= EPOLLOUT;
295 eev.data.fd = iocb->aio_fildes;
296
297 if (epoll_ctl (backend_fd, op, iocb->aio_fildes, &eev) < 0)
298 ev_syserr ("(libeio) linuxaio epoll_ctl");
299 }
300 #endif
301
302 static void
303 linuxaio_poll (EV_P_ ev_tstamp timeout)
304 {
305 int submitted;
306
307 /* first phase: submit new iocbs */
308
309 /* io_submit might return less than the requested number of iocbs */
310 /* this is, afaics, only because of errors, but we go by the book and use a loop, */
311 /* which allows us to pinpoint the errornous iocb */
312 for (submitted = 0; submitted < linuxaio_submitcnt; )
313 {
314 int res = ev_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted);
315
316 if (ecb_expect_false (res < 0))
317 if (errno == EAGAIN)
318 {
319 /* This happens when the ring buffer is full, at least. I assume this means
320 * that the event was queued synchronously during io_submit, and thus
321 * the buffer overflowed.
322 * In this case, we just try in next loop iteration.
323 * This should not result in a few fds taking priority, as the interface
324 * is one-shot, and we submit iocb's in a round-robin fashion.
325 */
326 memmove (linuxaio_submits, linuxaio_submits + submitted, (linuxaio_submitcnt - submitted) * sizeof (*linuxaio_submits));
327 linuxaio_submitcnt -= submitted;
328 timeout = 0;
329 break;
330 }
331 #if EPOLL_FALLBACK
332 else if (errno == EINVAL)
333 {
334 /* This hapĆ¼pens for unsupported fds, officially, but in my testing,
335 * also randomly happens for supported fds. We fall back to good old
336 * poll() here, under the assumption that this is a very rare case.
337 */
338 struct iocb *iocb = linuxaio_submits [submitted];
339 res = 1; /* skip this iocb */
340
341 linuxaio_rearm_epoll (EV_A_ iocb, EPOLL_CTL_ADD);
342 iocb->aio_reqprio = -1; /* mark iocb as epoll */
343 }
344 #endif
345 else
346 ev_syserr ("(libev) linuxaio io_submit");
347
348 submitted += res;
349 }
350
351 linuxaio_submitcnt = 0;
352
353 /* second phase: fetch and parse events */
354
355 linuxaio_get_events (EV_A_ timeout);
356 }
357
358 #if EPOLL_FALLBACK
359
360 static void
361 linuxaio_epoll_cb (EV_P_ struct ev_io *w, int revents)
362 {
363 struct epoll_event events[16];
364
365 for (;;)
366 {
367 int idx;
368 int res = epoll_wait (backend_fd, events, sizeof (events) / sizeof (events [0]), 0);
369
370 if (ecb_expect_false (res < 0))
371 ev_syserr ("(libev) linuxaio epoll_wait");
372 else if (!res)
373 break;
374
375 for (idx = res; idx--; )
376 {
377 int fd = events [idx].data.fd;
378 uint32_t ev = events [idx].events;
379
380 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
381
382 linuxaio_rearm_epoll (EV_A_ &linuxaio_iocbps [fd]->io, EPOLL_CTL_MOD);
383
384 fd_event (EV_A_ fd,
385 (ev & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)
386 | (ev & (EPOLLIN | EPOLLERR | EPOLLHUP) ? EV_READ : 0));
387 }
388
389 if (res < sizeof (events) / sizeof (events [0]))
390 break;
391 }
392 }
393
394 #endif
395
396 inline_size
397 int
398 linuxaio_init (EV_P_ int flags)
399 {
400 /* would be great to have a nice test for IOCB_CMD_POLL instead */
401 /* also: test some semi-common fd types, such as files and ttys in recommended_backends */
402 if (ev_linux_version () < 0x041200) /* 4.18 introduced IOCB_CMD_POLL */
403 return 0;
404
405 linuxaio_ctx = 0;
406 if (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
407 return 0;
408
409 #if EPOLL_FALLBACK
410 backend_fd = ev_epoll_create ();
411 if (backend_fd < 0)
412 {
413 ev_io_destroy (linuxaio_ctx);
414 return 0;
415 }
416
417 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
418 ev_io_start (EV_A_ &linuxaio_epoll_w);
419 #endif
420
421 backend_modify = linuxaio_modify;
422 backend_poll = linuxaio_poll;
423
424 linuxaio_iocbpmax = 0;
425 linuxaio_iocbps = 0;
426
427 linuxaio_submits = 0;
428 linuxaio_submitmax = 0;
429 linuxaio_submitcnt = 0;
430
431 return EVBACKEND_LINUXAIO;
432 }
433
434 inline_size
435 void
436 linuxaio_destroy (EV_P)
437 {
438 #if EPOLL_FALLBACK
439 close (backend_fd);
440 #endif
441 linuxaio_free_iocbp (EV_A);
442 ev_io_destroy (linuxaio_ctx);
443 }
444
445 inline_size
446 void
447 linuxaio_fork (EV_P)
448 {
449 /* this frees all iocbs, which is very heavy-handed */
450 linuxaio_destroy (EV_A);
451 linuxaio_submitcnt = 0; /* all pointers were invalidated */
452
453 linuxaio_ctx = 0;
454 while (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
455 ev_syserr ("(libev) linuxaio io_setup");
456
457 #if EPOLL_FALLBACK
458 while ((backend_fd = ev_epoll_create ()) < 0)
459 ev_syserr ("(libev) linuxaio epoll_create");
460
461 ev_io_stop (EV_A_ &linuxaio_epoll_w);
462 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
463 ev_io_start (EV_A_ &linuxaio_epoll_w);
464 ev_unref (EV_A); /* watcher should not keep loop alive */
465 #endif
466
467 fd_rearm_all (EV_A);
468 }
469