File Coverage

libev/ev_linuxaio.c
Criterion Covered Total %
statement 0 198 0.0
branch 0 86 0.0
condition n/a
subroutine n/a
pod n/a
total 0 284 0.0


line stmt bran cond sub pod time code
1             /*
2             * libev linux aio fd activity backend
3             *
4             * Copyright (c) 2019 Marc Alexander Lehmann
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             /*
41             * general notes about linux aio:
42             *
43             * a) at first, the linux aio IOCB_CMD_POLL functionality introduced in
44             * 4.18 looks too good to be true: both watchers and events can be
45             * batched, and events can even be handled in userspace using
46             * a ring buffer shared with the kernel. watchers can be canceled
47             * regardless of whether the fd has been closed. no problems with fork.
48             * ok, the ring buffer is 200% undocumented (there isn't even a
49             * header file), but otherwise, it's pure bliss!
50             * b) ok, watchers are one-shot, so you have to re-arm active ones
51             * on every iteration. so much for syscall-less event handling,
52             * but at least these re-arms can be batched, no big deal, right?
53             * c) well, linux as usual: the documentation lies to you: io_submit
54             * sometimes returns EINVAL because the kernel doesn't feel like
55             * handling your poll mask - ttys can be polled for POLLOUT,
56             * POLLOUT|POLLIN, but polling for POLLIN fails. just great,
57             * so we have to fall back to something else (hello, epoll),
58             * but at least the fallback can be slow, because these are
59             * exceptional cases, right?
60             * d) hmm, you have to tell the kernel the maximum number of watchers
61             * you want to queue when initialising the aio context. but of
62             * course the real limit is magically calculated in the kernel, and
63             * is often higher then we asked for. so we just have to destroy
64             * the aio context and re-create it a bit larger if we hit the limit.
65             * (starts to remind you of epoll? well, it's a bit more deterministic
66             * and less gambling, but still ugly as hell).
67             * e) that's when you find out you can also hit an arbitrary system-wide
68             * limit. or the kernel simply doesn't want to handle your watchers.
69             * what the fuck do we do then? you guessed it, in the middle
70             * of event handling we have to switch to 100% epoll polling. and
71             * that better is as fast as normal epoll polling, so you practically
72             * have to use the normal epoll backend with all its quirks.
73             * f) end result of this train wreck: it inherits all the disadvantages
74             * from epoll, while adding a number on its own. why even bother to use
75             * it? because if conditions are right and your fds are supported and you
76             * don't hit a limit, this backend is actually faster, doesn't gamble with
77             * your fds, batches watchers and events and doesn't require costly state
78             * recreates. well, until it does.
79             * g) all of this makes this backend use almost twice as much code as epoll.
80             * which in turn uses twice as much code as poll. and that#s not counting
81             * the fact that this backend also depends on the epoll backend, making
82             * it three times as much code as poll, or kqueue.
83             * h) bleah. why can't linux just do kqueue. sure kqueue is ugly, but by now
84             * it's clear that whatever linux comes up with is far, far, far worse.
85             */
86              
87             #include /* actually linux/time.h, but we must assume they are compatible */
88             #include
89             #include
90              
91             /*****************************************************************************/
92             /* syscall wrapdadoop - this section has the raw api/abi definitions */
93              
94             #include /* no glibc wrappers */
95              
96             /* aio_abi.h is not versioned in any way, so we cannot test for its existance */
97             #define IOCB_CMD_POLL 5
98              
99             /* taken from linux/fs/aio.c. yup, that's a .c file.
100             * not only is this totally undocumented, not even the source code
101             * can tell you what the future semantics of compat_features and
102             * incompat_features are, or what header_length actually is for.
103             */
104             #define AIO_RING_MAGIC 0xa10a10a1
105             #define EV_AIO_RING_INCOMPAT_FEATURES 0
106             struct aio_ring
107             {
108             unsigned id; /* kernel internal index number */
109             unsigned nr; /* number of io_events */
110             unsigned head; /* Written to by userland or by kernel. */
111             unsigned tail;
112              
113             unsigned magic;
114             unsigned compat_features;
115             unsigned incompat_features;
116             unsigned header_length; /* size of aio_ring */
117              
118             struct io_event io_events[0];
119             };
120              
121             inline_size
122             int
123 0           evsys_io_setup (unsigned nr_events, aio_context_t *ctx_idp)
124             {
125 0           return ev_syscall2 (SYS_io_setup, nr_events, ctx_idp);
126             }
127              
128             inline_size
129             int
130 0           evsys_io_destroy (aio_context_t ctx_id)
131             {
132 0           return ev_syscall1 (SYS_io_destroy, ctx_id);
133             }
134              
135             inline_size
136             int
137 0           evsys_io_submit (aio_context_t ctx_id, long nr, struct iocb *cbp[])
138             {
139 0           return ev_syscall3 (SYS_io_submit, ctx_id, nr, cbp);
140             }
141              
142             inline_size
143             int
144 0           evsys_io_cancel (aio_context_t ctx_id, struct iocb *cbp, struct io_event *result)
145             {
146 0           return ev_syscall3 (SYS_io_cancel, ctx_id, cbp, result);
147             }
148              
149             inline_size
150             int
151 0           evsys_io_getevents (aio_context_t ctx_id, long min_nr, long nr, struct io_event *events, struct timespec *timeout)
152             {
153 0           return ev_syscall5 (SYS_io_getevents, ctx_id, min_nr, nr, events, timeout);
154             }
155              
156             /*****************************************************************************/
157             /* actual backed implementation */
158              
159             ecb_cold
160             static int
161 0           linuxaio_nr_events (EV_P)
162             {
163             /* we start with 16 iocbs and incraese from there
164             * that's tiny, but the kernel has a rather low system-wide
165             * limit that can be reached quickly, so let's be parsimonious
166             * with this resource.
167             * Rest assured, the kernel generously rounds up small and big numbers
168             * in different ways (but doesn't seem to charge you for it).
169             * The 15 here is because the kernel usually has a power of two as aio-max-nr,
170             * and this helps to take advantage of that limit.
171             */
172              
173             /* we try to fill 4kB pages exactly.
174             * the ring buffer header is 32 bytes, every io event is 32 bytes.
175             * the kernel takes the io requests number, doubles it, adds 2
176             * and adds the ring buffer.
177             * the way we use this is by starting low, and then roughly doubling the
178             * size each time we hit a limit.
179             */
180              
181 0           int requests = 15 << linuxaio_iteration;
182 0           int one_page = (4096
183             / sizeof (struct io_event) ) / 2; /* how many fit into one page */
184 0           int first_page = ((4096 - sizeof (struct aio_ring))
185             / sizeof (struct io_event) - 2) / 2; /* how many fit into the first page */
186              
187             /* if everything fits into one page, use count exactly */
188 0 0         if (requests > first_page)
189             /* otherwise, round down to full pages and add the first page */
190 0           requests = requests / one_page * one_page + first_page;
191              
192 0           return requests;
193             }
194              
195             /* we use out own wrapper structure in case we ever want to do something "clever" */
196             typedef struct aniocb
197             {
198             struct iocb io;
199             /*int inuse;*/
200             } *ANIOCBP;
201              
202             inline_size
203             void
204 0           linuxaio_array_needsize_iocbp (ANIOCBP *base, int offset, int count)
205             {
206 0 0         while (count--)
207             {
208             /* TODO: quite the overhead to allocate every iocb separately, maybe use our own allocator? */
209 0           ANIOCBP iocb = (ANIOCBP)ev_malloc (sizeof (*iocb));
210              
211             /* full zero initialise is probably not required at the moment, but
212             * this is not well documented, so we better do it.
213             */
214 0           memset (iocb, 0, sizeof (*iocb));
215              
216 0           iocb->io.aio_lio_opcode = IOCB_CMD_POLL;
217 0           iocb->io.aio_fildes = offset;
218              
219 0           base [offset++] = iocb;
220             }
221 0           }
222              
223             ecb_cold
224             static void
225 0           linuxaio_free_iocbp (EV_P)
226             {
227 0 0         while (linuxaio_iocbpmax--)
228 0           ev_free (linuxaio_iocbps [linuxaio_iocbpmax]);
229              
230 0           linuxaio_iocbpmax = 0; /* next resize will completely reallocate the array, at some overhead */
231 0           }
232              
233             static void
234 0           linuxaio_modify (EV_P_ int fd, int oev, int nev)
235             {
236 0 0         array_needsize (ANIOCBP, linuxaio_iocbps, linuxaio_iocbpmax, fd + 1, linuxaio_array_needsize_iocbp);
237 0           ANIOCBP iocb = linuxaio_iocbps [fd];
238 0           ANFD *anfd = &anfds [fd];
239              
240 0 0         if (ecb_expect_false (iocb->io.aio_reqprio < 0))
241             {
242             /* we handed this fd over to epoll, so undo this first */
243             /* we do it manually because the optimisations on epoll_modify won't do us any good */
244 0           epoll_ctl (backend_fd, EPOLL_CTL_DEL, fd, 0);
245 0           anfd->emask = 0;
246 0           iocb->io.aio_reqprio = 0;
247             }
248 0 0         else if (ecb_expect_false (iocb->io.aio_buf))
249             {
250             /* iocb active, so cancel it first before resubmit */
251             /* this assumes we only ever get one call per fd per loop iteration */
252             for (;;)
253             {
254             /* on all relevant kernels, io_cancel fails with EINPROGRESS on "success" */
255 0 0         if (ecb_expect_false (evsys_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0) == 0))
256 0           break;
257              
258 0 0         if (ecb_expect_true (errno == EINPROGRESS))
259 0           break;
260              
261             /* the EINPROGRESS test is for nicer error message. clumsy. */
262 0 0         if (errno != EINTR)
263             {
264             assert (("libev: linuxaio unexpected io_cancel failed", errno != EINTR && errno != EINPROGRESS));
265 0           break;
266             }
267 0           }
268              
269             /* increment generation counter to avoid handling old events */
270 0           ++anfd->egen;
271             }
272              
273 0           iocb->io.aio_buf = (nev & EV_READ ? POLLIN : 0)
274 0 0         | (nev & EV_WRITE ? POLLOUT : 0);
275              
276 0 0         if (nev)
277             {
278 0           iocb->io.aio_data = (uint32_t)fd | ((__u64)(uint32_t)anfd->egen << 32);
279              
280             /* queue iocb up for io_submit */
281             /* this assumes we only ever get one call per fd per loop iteration */
282 0           ++linuxaio_submitcnt;
283 0 0         array_needsize (struct iocb *, linuxaio_submits, linuxaio_submitmax, linuxaio_submitcnt, array_needsize_noinit);
284 0           linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io;
285             }
286 0           }
287              
288             static void
289 0           linuxaio_epoll_cb (EV_P_ struct ev_io *w, int revents)
290             {
291 0           epoll_poll (EV_A_ 0);
292 0           }
293              
294             inline_speed
295             void
296 0           linuxaio_fd_rearm (EV_P_ int fd)
297             {
298 0           anfds [fd].events = 0;
299 0           linuxaio_iocbps [fd]->io.aio_buf = 0;
300 0           fd_change (EV_A_ fd, EV_ANFD_REIFY);
301 0           }
302              
303             static void
304 0           linuxaio_parse_events (EV_P_ struct io_event *ev, int nr)
305             {
306 0 0         while (nr)
307             {
308 0           int fd = ev->data & 0xffffffff;
309 0           uint32_t gen = ev->data >> 32;
310 0           int res = ev->res;
311              
312             assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
313              
314             /* only accept events if generation counter matches */
315 0 0         if (ecb_expect_true (gen == (uint32_t)anfds [fd].egen))
316             {
317             /* feed events, we do not expect or handle POLLNVAL */
318 0           fd_event (
319             EV_A_
320             fd,
321 0 0         (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
322 0           | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
323             );
324              
325             /* linux aio is oneshot: rearm fd. TODO: this does more work than strictly needed */
326 0           linuxaio_fd_rearm (EV_A_ fd);
327             }
328              
329 0           --nr;
330 0           ++ev;
331             }
332 0           }
333              
334             /* get any events from ring buffer, return true if any were handled */
335             static int
336 0           linuxaio_get_events_from_ring (EV_P)
337             {
338 0           struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
339             unsigned head, tail;
340              
341             /* the kernel reads and writes both of these variables, */
342             /* as a C extension, we assume that volatile use here */
343             /* both makes reads atomic and once-only */
344 0           head = *(volatile unsigned *)&ring->head;
345 0           ECB_MEMORY_FENCE_ACQUIRE;
346 0           tail = *(volatile unsigned *)&ring->tail;
347              
348 0 0         if (head == tail)
349 0           return 0;
350              
351             /* parse all available events, but only once, to avoid starvation */
352 0 0         if (ecb_expect_true (tail > head)) /* normal case around */
353 0           linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head);
354             else /* wrapped around */
355             {
356 0           linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
357 0           linuxaio_parse_events (EV_A_ ring->io_events, tail);
358             }
359              
360 0           ECB_MEMORY_FENCE_RELEASE;
361             /* as an extension to C, we hope that the volatile will make this atomic and once-only */
362 0           *(volatile unsigned *)&ring->head = tail;
363              
364 0           return 1;
365             }
366              
367             inline_size
368             int
369 0           linuxaio_ringbuf_valid (EV_P)
370             {
371 0           struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
372              
373 0           return ecb_expect_true (ring->magic == AIO_RING_MAGIC)
374 0 0         && ring->incompat_features == EV_AIO_RING_INCOMPAT_FEATURES
375 0 0         && ring->header_length == sizeof (struct aio_ring); /* TODO: or use it to find io_event[0]? */
    0          
376             }
377              
378             /* read at least one event from kernel, or timeout */
379             inline_size
380             void
381 0           linuxaio_get_events (EV_P_ ev_tstamp timeout)
382             {
383             struct timespec ts;
384             struct io_event ioev[8]; /* 256 octet stack space */
385 0           int want = 1; /* how many events to request */
386 0           int ringbuf_valid = linuxaio_ringbuf_valid (EV_A);
387              
388 0 0         if (ecb_expect_true (ringbuf_valid))
389             {
390             /* if the ring buffer has any events, we don't wait or call the kernel at all */
391 0 0         if (linuxaio_get_events_from_ring (EV_A))
392 0           return;
393              
394             /* if the ring buffer is empty, and we don't have a timeout, then don't call the kernel */
395 0 0         if (!timeout)
396 0           return;
397             }
398             else
399             /* no ringbuffer, request slightly larger batch */
400 0           want = sizeof (ioev) / sizeof (ioev [0]);
401              
402             /* no events, so wait for some
403             * for fairness reasons, we do this in a loop, to fetch all events
404             */
405             for (;;)
406             {
407             int res;
408              
409 0 0         EV_RELEASE_CB;
410              
411 0           EV_TS_SET (ts, timeout);
412 0           res = evsys_io_getevents (linuxaio_ctx, 1, want, ioev, &ts);
413              
414 0 0         EV_ACQUIRE_CB;
415              
416 0 0         if (res < 0)
417 0 0         if (errno == EINTR)
418             /* ignored, retry */;
419             else
420 0           ev_syserr ("(libev) linuxaio io_getevents");
421 0 0         else if (res)
422             {
423             /* at least one event available, handle them */
424 0           linuxaio_parse_events (EV_A_ ioev, res);
425              
426 0 0         if (ecb_expect_true (ringbuf_valid))
427             {
428             /* if we have a ring buffer, handle any remaining events in it */
429 0           linuxaio_get_events_from_ring (EV_A);
430              
431             /* at this point, we should have handled all outstanding events */
432 0           break;
433             }
434 0 0         else if (res < want)
435             /* otherwise, if there were fewere events than we wanted, we assume there are no more */
436 0           break;
437             }
438             else
439 0           break; /* no events from the kernel, we are done */
440              
441 0           timeout = EV_TS_CONST (0.); /* only wait in the first iteration */
442 0           }
443             }
444              
445             inline_size
446             int
447 0           linuxaio_io_setup (EV_P)
448             {
449 0           linuxaio_ctx = 0;
450 0           return evsys_io_setup (linuxaio_nr_events (EV_A), &linuxaio_ctx);
451             }
452              
453             static void
454 0           linuxaio_poll (EV_P_ ev_tstamp timeout)
455             {
456             int submitted;
457              
458             /* first phase: submit new iocbs */
459              
460             /* io_submit might return less than the requested number of iocbs */
461             /* this is, afaics, only because of errors, but we go by the book and use a loop, */
462             /* which allows us to pinpoint the erroneous iocb */
463 0 0         for (submitted = 0; submitted < linuxaio_submitcnt; )
464             {
465 0           int res = evsys_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted);
466              
467 0 0         if (ecb_expect_false (res < 0))
468 0 0         if (errno == EINVAL)
469             {
470             /* This happens for unsupported fds, officially, but in my testing,
471             * also randomly happens for supported fds. We fall back to good old
472             * poll() here, under the assumption that this is a very rare case.
473             * See https://lore.kernel.org/patchwork/patch/1047453/ to see
474             * discussion about such a case (ttys) where polling for POLLIN
475             * fails but POLLIN|POLLOUT works.
476             */
477 0           struct iocb *iocb = linuxaio_submits [submitted];
478 0           epoll_modify (EV_A_ iocb->aio_fildes, 0, anfds [iocb->aio_fildes].events);
479 0           iocb->aio_reqprio = -1; /* mark iocb as epoll */
480              
481 0           res = 1; /* skip this iocb - another iocb, another chance */
482             }
483 0 0         else if (errno == EAGAIN)
484             {
485             /* This happens when the ring buffer is full, or some other shit we
486             * don't know and isn't documented. Most likely because we have too
487             * many requests and linux aio can't be assed to handle them.
488             * In this case, we try to allocate a larger ring buffer, freeing
489             * ours first. This might fail, in which case we have to fall back to 100%
490             * epoll.
491             * God, how I hate linux not getting its act together. Ever.
492             */
493 0           evsys_io_destroy (linuxaio_ctx);
494 0           linuxaio_submitcnt = 0;
495              
496             /* rearm all fds with active iocbs */
497             {
498             int fd;
499 0 0         for (fd = 0; fd < linuxaio_iocbpmax; ++fd)
500 0 0         if (linuxaio_iocbps [fd]->io.aio_buf)
501 0           linuxaio_fd_rearm (EV_A_ fd);
502             }
503              
504 0           ++linuxaio_iteration;
505 0 0         if (linuxaio_io_setup (EV_A) < 0)
506             {
507             /* TODO: rearm all and recreate epoll backend from scratch */
508             /* TODO: might be more prudent? */
509              
510             /* to bad, we can't get a new aio context, go 100% epoll */
511 0           linuxaio_free_iocbp (EV_A);
512 0           ev_io_stop (EV_A_ &linuxaio_epoll_w);
513 0           ev_ref (EV_A);
514 0           linuxaio_ctx = 0;
515              
516 0           backend = EVBACKEND_EPOLL;
517 0           backend_modify = epoll_modify;
518 0           backend_poll = epoll_poll;
519             }
520              
521 0           timeout = EV_TS_CONST (0.);
522             /* it's easiest to handle this mess in another iteration */
523 0           return;
524             }
525 0 0         else if (errno == EBADF)
526             {
527             assert (("libev: event loop rejected bad fd", errno != EBADF));
528 0           fd_kill (EV_A_ linuxaio_submits [submitted]->aio_fildes);
529              
530 0           res = 1; /* skip this iocb */
531             }
532 0 0         else if (errno == EINTR) /* not seen in reality, not documented */
533 0           res = 0; /* silently ignore and retry */
534             else
535             {
536 0           ev_syserr ("(libev) linuxaio io_submit");
537 0           res = 0;
538             }
539              
540 0           submitted += res;
541             }
542              
543 0           linuxaio_submitcnt = 0;
544              
545             /* second phase: fetch and parse events */
546              
547 0           linuxaio_get_events (EV_A_ timeout);
548             }
549              
550             inline_size
551             int
552 0           linuxaio_init (EV_P_ int flags)
553             {
554             /* would be great to have a nice test for IOCB_CMD_POLL instead */
555             /* also: test some semi-common fd types, such as files and ttys in recommended_backends */
556             /* 4.18 introduced IOCB_CMD_POLL, 4.19 made epoll work, and we need that */
557 0 0         if (ev_linux_version () < 0x041300)
558 0           return 0;
559              
560 0 0         if (!epoll_init (EV_A_ 0))
561 0           return 0;
562              
563 0           linuxaio_iteration = 0;
564              
565 0 0         if (linuxaio_io_setup (EV_A) < 0)
566             {
567 0           epoll_destroy (EV_A);
568 0           return 0;
569             }
570              
571 0           ev_io_init (&linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
572 0           ev_set_priority (&linuxaio_epoll_w, EV_MAXPRI);
573 0           ev_io_start (EV_A_ &linuxaio_epoll_w);
574 0           ev_unref (EV_A); /* watcher should not keep loop alive */
575              
576 0           backend_modify = linuxaio_modify;
577 0           backend_poll = linuxaio_poll;
578              
579 0           linuxaio_iocbpmax = 0;
580 0           linuxaio_iocbps = 0;
581              
582 0           linuxaio_submits = 0;
583 0           linuxaio_submitmax = 0;
584 0           linuxaio_submitcnt = 0;
585              
586 0           return EVBACKEND_LINUXAIO;
587             }
588              
589             inline_size
590             void
591 0           linuxaio_destroy (EV_P)
592             {
593 0           epoll_destroy (EV_A);
594 0           linuxaio_free_iocbp (EV_A);
595 0           evsys_io_destroy (linuxaio_ctx); /* fails in child, aio context is destroyed */
596 0           }
597              
598             ecb_cold
599             static void
600 0           linuxaio_fork (EV_P)
601             {
602 0           linuxaio_submitcnt = 0; /* all pointers were invalidated */
603 0           linuxaio_free_iocbp (EV_A); /* this frees all iocbs, which is very heavy-handed */
604 0           evsys_io_destroy (linuxaio_ctx); /* fails in child, aio context is destroyed */
605              
606 0           linuxaio_iteration = 0; /* we start over in the child */
607              
608 0 0         while (linuxaio_io_setup (EV_A) < 0)
609 0           ev_syserr ("(libev) linuxaio io_setup");
610              
611             /* forking epoll should also effectively unregister all fds from the backend */
612 0           epoll_fork (EV_A);
613             /* epoll_fork already did this. hopefully */
614             /*fd_rearm_all (EV_A);*/
615              
616 0           ev_io_stop (EV_A_ &linuxaio_epoll_w);
617 0           ev_io_set (EV_A_ &linuxaio_epoll_w, backend_fd, EV_READ);
618 0           ev_io_start (EV_A_ &linuxaio_epoll_w);
619 0           }
620