ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/libev/ev_iouring.c
Revision: 1.7
Committed: Sun Dec 22 15:05:32 2019 UTC (4 years, 6 months ago) by root
Content type: text/plain
Branch: MAIN
Changes since 1.6: +5 -1 lines
Log Message:
*** empty log message ***

File Contents

# User Rev Content
1 root 1.1 /*
2     * libev linux io_uring 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     /*
41     * general notes about linux io_uring:
42     *
43     * a) it's the best interface I have seen so far. on linux.
44     * b) best is not necessarily very good.
45     * c) it's better than the aio mess, doesn't suffer from the fork problems
46     * of linux aio or epoll and so on and so on. and you could do event stuff
47     * without any syscalls. what's not to like?
48     * d) ok, it's vastly more complex, but that's ok, really.
49     * e) why 3 mmaps instead of one? one would be more space-efficient,
50     * and I can't see what benefit three would have (other than being
51     * somehow resizable/relocatable, but that's apparently not possible).
52 root 1.7 * (FIXME: newer kernels can use 2 mmaps only, need to look into this).
53 root 1.1 * f) hmm, it's practiclaly undebuggable (gdb can't access the memory, and
54 root 1.7 * the bizarre way structure offsets are communicated makes it hard to
55 root 1.1 * just print the ring buffer heads, even *iff* the memory were visible
56     * in gdb. but then, that's also ok, really.
57     * g) well, you cannot specify a timeout when waiting for events. no,
58     * seriously, the interface doesn't support a timeout. never seen _that_
59     * before. sure, you can use a timerfd, but that's another syscall
60     * you could have avoided. overall, this bizarre omission smells
61     * like a ยต-optimisation by the io_uring author for his personal
62     * applications, to the detriment of everybody else who just wants
63     * an event loop. but, umm, ok, if that's all, it could be worse.
64 root 1.7 * (FIXME: jens mentioned timeout commands, need to investigate)
65 root 1.1 * h) there is a hardcoded limit of 4096 outstanding events. okay,
66     * at least there is no arbitrary low system-wide limit...
67 root 1.7 * (FIXME: apparently, this was increased to 32768 in later kernels(
68 root 1.1 * i) unlike linux aio, you *can* register more then the limit
69     * of fd events, and the kernel will "gracefully" signal an
70     * overflow, after which you could destroy and recreate the kernel
71     * state, a bit bigger, or fall back to e.g. poll. thats not
72     * totally insane, but kind of questions the point a high
73     * performance I/O framework when it doesn't really work
74     * under stress.
75 root 1.7 * (FIXME: iouring should no longer drop events, need to investigate)
76 root 1.1 * j) but, oh my! is has exactly the same bugs as the linux aio backend,
77     * where some undocumented poll combinations just fail.
78     * so we need epoll AGAIN as a fallback. AGAIN! epoll!! and of course,
79     * this is completely undocumented, have I mantioned this already?
80     * k) overall, the *API* itself is, I dare to say, not a total trainwreck.
81     * the big isuess with it are the bugs requiring epoll, which might
82     * or might not get fixed (do I hold my breath?).
83     */
84    
85     #include <sys/timerfd.h>
86     #include <sys/mman.h>
87     #include <poll.h>
88    
89     #define IOURING_INIT_ENTRIES 32
90    
91     /*****************************************************************************/
92     /* syscall wrapdadoop - this section has the raw api/abi definitions */
93    
94     #include <linux/fs.h>
95     #include <linux/types.h>
96    
97     /* mostly directly taken from the kernel or documentation */
98    
99     struct io_uring_sqe
100     {
101     __u8 opcode;
102     __u8 flags;
103     __u16 ioprio;
104     __s32 fd;
105     __u64 off;
106     __u64 addr;
107     __u32 len;
108     union {
109     __kernel_rwf_t rw_flags;
110     __u32 fsync_flags;
111     __u16 poll_events;
112     __u32 sync_range_flags;
113     __u32 msg_flags;
114     };
115     __u64 user_data;
116     union {
117     __u16 buf_index;
118     __u64 __pad2[3];
119     };
120     };
121    
122     struct io_uring_cqe
123     {
124     __u64 user_data;
125     __s32 res;
126     __u32 flags;
127     };
128    
129     struct io_sqring_offsets
130     {
131     __u32 head;
132     __u32 tail;
133     __u32 ring_mask;
134     __u32 ring_entries;
135     __u32 flags;
136     __u32 dropped;
137     __u32 array;
138     __u32 resv1;
139     __u64 resv2;
140     };
141    
142     struct io_cqring_offsets
143     {
144     __u32 head;
145     __u32 tail;
146     __u32 ring_mask;
147     __u32 ring_entries;
148     __u32 overflow;
149     __u32 cqes;
150     __u64 resv[2];
151     };
152    
153     struct io_uring_params
154     {
155     __u32 sq_entries;
156     __u32 cq_entries;
157     __u32 flags;
158     __u32 sq_thread_cpu;
159     __u32 sq_thread_idle;
160     __u32 resv[5];
161     struct io_sqring_offsets sq_off;
162     struct io_cqring_offsets cq_off;
163     };
164    
165     #define IORING_OP_POLL_ADD 6
166     #define IORING_OP_POLL_REMOVE 7
167    
168     #define IORING_ENTER_GETEVENTS 0x01
169    
170     #define IORING_OFF_SQ_RING 0x00000000ULL
171     #define IORING_OFF_CQ_RING 0x08000000ULL
172     #define IORING_OFF_SQES 0x10000000ULL
173    
174     inline_size
175     int
176     evsys_io_uring_setup (unsigned entries, struct io_uring_params *params)
177     {
178     return ev_syscall2 (SYS_io_uring_setup, entries, params);
179     }
180    
181     inline_size
182     int
183     evsys_io_uring_enter (int fd, unsigned to_submit, unsigned min_complete, unsigned flags, const sigset_t *sig, size_t sigsz)
184     {
185     return ev_syscall6 (SYS_io_uring_enter, fd, to_submit, min_complete, flags, sig, sigsz);
186     }
187    
188     /*****************************************************************************/
189     /* actual backed implementation */
190    
191     /* we hope that volatile will make the compiler access this variables only once */
192     #define EV_SQ_VAR(name) *(volatile unsigned *)((char *)iouring_sq_ring + iouring_sq_ ## name)
193     #define EV_CQ_VAR(name) *(volatile unsigned *)((char *)iouring_cq_ring + iouring_cq_ ## name)
194    
195     /* the index array */
196     #define EV_SQ_ARRAY ((unsigned *)((char *)iouring_sq_ring + iouring_sq_array))
197    
198     /* the submit/completion queue entries */
199     #define EV_SQES ((struct io_uring_sqe *) iouring_sqes)
200     #define EV_CQES ((struct io_uring_cqe *)((char *)iouring_cq_ring + iouring_cq_cqes))
201    
202     static
203     struct io_uring_sqe *
204     iouring_sqe_get (EV_P)
205     {
206     unsigned tail = EV_SQ_VAR (tail);
207    
208     if (tail + 1 - EV_SQ_VAR (head) > EV_SQ_VAR (ring_entries))
209     {
210     /* queue full, flush */
211     evsys_io_uring_enter (iouring_fd, iouring_to_submit, 0, 0, 0, 0);
212     iouring_to_submit = 0;
213     }
214    
215     assert (("libev: io_uring queue full after flush", tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries)));
216    
217     return EV_SQES + (tail & EV_SQ_VAR (ring_mask));
218     }
219    
220     inline_size
221     struct io_uring_sqe *
222     iouring_sqe_submit (EV_P_ struct io_uring_sqe *sqe)
223     {
224     unsigned idx = sqe - EV_SQES;
225    
226     EV_SQ_ARRAY [idx] = idx;
227     ECB_MEMORY_FENCE_RELEASE;
228     ++EV_SQ_VAR (tail);
229     /*ECB_MEMORY_FENCE_RELEASE; /* for the time being we assume this is not needed */
230     ++iouring_to_submit;
231     }
232    
233     /*****************************************************************************/
234    
235     /* when the timerfd expires we simply note the fact,
236     * as the purpose of the timerfd is to wake us up, nothing else.
237     * the next iteration should re-set it.
238     */
239     static void
240     iouring_tfd_cb (EV_P_ struct ev_io *w, int revents)
241     {
242     iouring_tfd_to = EV_TSTAMP_HUGE;
243     }
244    
245     static void
246     iouring_epoll_cb (EV_P_ struct ev_io *w, int revents)
247     {
248     epoll_poll (EV_A_ 0);
249     }
250    
251     /* called for full and partial cleanup */
252     ecb_cold
253     static int
254     iouring_internal_destroy (EV_P)
255     {
256     close (iouring_tfd);
257     close (iouring_fd);
258    
259     if (iouring_sq_ring != MAP_FAILED) munmap (iouring_sq_ring, iouring_sq_ring_size);
260     if (iouring_cq_ring != MAP_FAILED) munmap (iouring_cq_ring, iouring_cq_ring_size);
261     if (iouring_sqes != MAP_FAILED) munmap (iouring_sqes , iouring_sqes_size );
262    
263     if (ev_is_active (&iouring_epoll_w)) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_epoll_w);
264     if (ev_is_active (&iouring_tfd_w )) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_tfd_w );
265     }
266    
267     ecb_cold
268     static int
269     iouring_internal_init (EV_P)
270     {
271     struct io_uring_params params = { 0 };
272    
273     iouring_to_submit = 0;
274    
275     iouring_tfd = -1;
276     iouring_sq_ring = MAP_FAILED;
277     iouring_cq_ring = MAP_FAILED;
278     iouring_sqes = MAP_FAILED;
279    
280     for (;;)
281     {
282     iouring_fd = evsys_io_uring_setup (iouring_entries, &params);
283    
284     if (iouring_fd >= 0)
285     break; /* yippie */
286    
287     if (errno != EINVAL)
288     return -1; /* we failed */
289    
290     /* EINVAL: lots of possible reasons, but maybe
291     * it is because we hit the unqueryable hardcoded size limit
292     */
293    
294     /* we hit the limit already, give up */
295     if (iouring_max_entries)
296     return -1;
297    
298     /* first time we hit EINVAL? assume we hit the limit, so go back and retry */
299     iouring_entries >>= 1;
300     iouring_max_entries = iouring_entries;
301     }
302    
303     iouring_sq_ring_size = params.sq_off.array + params.sq_entries * sizeof (unsigned);
304     iouring_cq_ring_size = params.cq_off.cqes + params.cq_entries * sizeof (struct io_uring_cqe);
305     iouring_sqes_size = params.sq_entries * sizeof (struct io_uring_sqe);
306    
307     iouring_sq_ring = mmap (0, iouring_sq_ring_size, PROT_READ | PROT_WRITE,
308     MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQ_RING);
309     iouring_cq_ring = mmap (0, iouring_cq_ring_size, PROT_READ | PROT_WRITE,
310     MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_CQ_RING);
311     iouring_sqes = mmap (0, iouring_sqes_size, PROT_READ | PROT_WRITE,
312     MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQES);
313    
314     if (iouring_sq_ring == MAP_FAILED || iouring_cq_ring == MAP_FAILED || iouring_sqes == MAP_FAILED)
315     return -1;
316    
317     iouring_sq_head = params.sq_off.head;
318     iouring_sq_tail = params.sq_off.tail;
319     iouring_sq_ring_mask = params.sq_off.ring_mask;
320     iouring_sq_ring_entries = params.sq_off.ring_entries;
321     iouring_sq_flags = params.sq_off.flags;
322     iouring_sq_dropped = params.sq_off.dropped;
323     iouring_sq_array = params.sq_off.array;
324    
325     iouring_cq_head = params.cq_off.head;
326     iouring_cq_tail = params.cq_off.tail;
327     iouring_cq_ring_mask = params.cq_off.ring_mask;
328     iouring_cq_ring_entries = params.cq_off.ring_entries;
329     iouring_cq_overflow = params.cq_off.overflow;
330     iouring_cq_cqes = params.cq_off.cqes;
331    
332     iouring_tfd = timerfd_create (CLOCK_MONOTONIC, TFD_CLOEXEC);
333    
334     if (iouring_tfd < 0)
335     return iouring_tfd;
336    
337     iouring_tfd_to = EV_TSTAMP_HUGE;
338    
339     return 0;
340     }
341    
342     ecb_cold
343     static void
344     iouring_fork (EV_P)
345     {
346     iouring_internal_destroy (EV_A);
347    
348     while (iouring_internal_init (EV_A) < 0)
349     ev_syserr ("(libev) io_uring_setup");
350    
351     /* forking epoll should also effectively unregister all fds from the backend */
352     epoll_fork (EV_A);
353     /* epoll_fork already did this. hopefully */
354     /*fd_rearm_all (EV_A);*/
355    
356     ev_io_stop (EV_A_ &iouring_epoll_w);
357     ev_io_set (EV_A_ &iouring_epoll_w, backend_fd, EV_READ);
358     ev_io_start (EV_A_ &iouring_epoll_w);
359    
360     ev_io_stop (EV_A_ &iouring_tfd_w);
361     ev_io_set (EV_A_ &iouring_tfd_w, iouring_tfd, EV_READ);
362     ev_io_start (EV_A_ &iouring_tfd_w);
363     }
364    
365     /*****************************************************************************/
366    
367     static void
368     iouring_modify (EV_P_ int fd, int oev, int nev)
369     {
370     if (ecb_expect_false (anfds [fd].eflags))
371     {
372     /* we handed this fd over to epoll, so undo this first */
373     /* we do it manually because the optimisations on epoll_modify won't do us any good */
374     epoll_ctl (iouring_fd, EPOLL_CTL_DEL, fd, 0);
375     anfds [fd].eflags = 0;
376     oev = 0;
377     }
378    
379     if (oev)
380     {
381     /* we assume the sqe's are all "properly" initialised */
382     struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
383     sqe->opcode = IORING_OP_POLL_REMOVE;
384     sqe->fd = fd;
385     sqe->user_data = -1;
386     iouring_sqe_submit (EV_A_ sqe);
387 root 1.2
388     /* increment generation counter to avoid handling old events */
389     ++anfds [fd].egen;
390 root 1.1 }
391    
392     if (nev)
393     {
394     struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
395     sqe->opcode = IORING_OP_POLL_ADD;
396     sqe->fd = fd;
397 root 1.2 sqe->user_data = (uint32_t)fd | ((__u64)(uint32_t)anfds [fd].egen << 32);
398 root 1.1 sqe->poll_events =
399     (nev & EV_READ ? POLLIN : 0)
400     | (nev & EV_WRITE ? POLLOUT : 0);
401     iouring_sqe_submit (EV_A_ sqe);
402     }
403     }
404    
405     inline_size
406     void
407     iouring_tfd_update (EV_P_ ev_tstamp timeout)
408     {
409     ev_tstamp tfd_to = mn_now + timeout;
410    
411     /* we assume there will be many iterations per timer change, so
412     * we only re-set the timerfd when we have to because its expiry
413     * is too late.
414     */
415     if (ecb_expect_false (tfd_to < iouring_tfd_to))
416     {
417     struct itimerspec its;
418    
419     iouring_tfd_to = tfd_to;
420     EV_TS_SET (its.it_interval, 0.);
421     EV_TS_SET (its.it_value, tfd_to);
422    
423     if (timerfd_settime (iouring_tfd, TFD_TIMER_ABSTIME, &its, 0) < 0)
424     assert (("libev: iouring timerfd_settime failed", 0));
425     }
426     }
427    
428     inline_size
429     void
430     iouring_process_cqe (EV_P_ struct io_uring_cqe *cqe)
431     {
432     int fd = cqe->user_data & 0xffffffffU;
433     uint32_t gen = cqe->user_data >> 32;
434     int res = cqe->res;
435    
436     /* ignore fd removal events, if there are any. TODO: verify */
437     if (cqe->user_data == (__u64)-1)
438     abort ();//D
439    
440     assert (("libev: io_uring fd must be in-bounds", fd >= 0 && fd < anfdmax));
441    
442     /* documentation lies, of course. the result value is NOT like
443     * normal syscalls, but like linux raw syscalls, i.e. negative
444     * error numbers. fortunate, as otherwise there would be no way
445     * to get error codes at all. still, why not document this?
446     */
447    
448     /* ignore event if generation doesn't match */
449     /* this should actually be very rare */
450 root 1.2 if (ecb_expect_false (gen != (uint32_t)anfds [fd].egen))
451 root 1.1 return;
452    
453     if (ecb_expect_false (res < 0))
454     {
455     if (res == -EINVAL)
456     {
457     /* we assume this error code means the fd/poll combination is buggy
458     * and fall back to epoll.
459     * this error code might also indicate a bug, but the kernel doesn't
460     * distinguish between those two conditions, so... sigh...
461     */
462    
463     epoll_modify (EV_A_ fd, 0, anfds [fd].events);
464     }
465     else if (res == -EBADF)
466     {
467     assert (("libev: event loop rejected bad fd", res != -EBADF));
468     fd_kill (EV_A_ fd);
469     }
470     else
471     {
472     errno = -res;
473     ev_syserr ("(libev) IORING_OP_POLL_ADD");
474     }
475    
476     return;
477     }
478    
479     /* feed events, we do not expect or handle POLLNVAL */
480     fd_event (
481     EV_A_
482     fd,
483     (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
484     | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
485     );
486    
487     /* io_uring is oneshot, so we need to re-arm the fd next iteration */
488     /* this also means we usually have to do at least one syscall per iteration */
489     anfds [fd].events = 0;
490     fd_change (EV_A_ fd, EV_ANFD_REIFY);
491     }
492    
493     /* called when the event queue overflows */
494     ecb_cold
495     static void
496     iouring_overflow (EV_P)
497     {
498     /* we have two options, resize the queue (by tearing down
499     * everything and recreating it, or living with it
500     * and polling.
501     * we implement this by resizing tghe queue, and, if that fails,
502     * we just recreate the state on every failure, which
503     * kind of is a very inefficient poll.
504     * one danger is, due to the bios toward lower fds,
505     * we will only really get events for those, so
506     * maybe we need a poll() fallback, after all.
507     */
508     /*EV_CQ_VAR (overflow) = 0;*/ /* need to do this if we keep the state and poll manually */
509    
510     fd_rearm_all (EV_A);
511    
512     /* we double the size until we hit the hard-to-probe maximum */
513     if (!iouring_max_entries)
514     {
515     iouring_entries <<= 1;
516     iouring_fork (EV_A);
517     }
518     else
519     {
520     /* we hit the kernel limit, we should fall back to something else.
521     * we can either poll() a few times and hope for the best,
522     * poll always, or switch to epoll.
523     * since we use epoll anyways, go epoll.
524     */
525    
526     iouring_internal_destroy (EV_A);
527    
528     /* this should make it so that on return, we don'T call any uring functions */
529     iouring_to_submit = 0;
530    
531     for (;;)
532     {
533     backend = epoll_init (EV_A_ 0);
534    
535     if (backend)
536     break;
537    
538     ev_syserr ("(libev) iouring switch to epoll");
539     }
540     }
541     }
542    
543     /* handle any events in the completion queue, return true if there were any */
544     static int
545     iouring_handle_cq (EV_P)
546     {
547     unsigned head, tail, mask;
548    
549     head = EV_CQ_VAR (head);
550     ECB_MEMORY_FENCE_ACQUIRE;
551     tail = EV_CQ_VAR (tail);
552    
553     if (head == tail)
554     return 0;
555    
556     /* it can only overflow if we have events, yes, yes? */
557     if (ecb_expect_false (EV_CQ_VAR (overflow)))
558     {
559     iouring_overflow (EV_A);
560     return 1;
561     }
562    
563     mask = EV_CQ_VAR (ring_mask);
564    
565     do
566     iouring_process_cqe (EV_A_ &EV_CQES [head++ & mask]);
567     while (head != tail);
568    
569     EV_CQ_VAR (head) = head;
570     ECB_MEMORY_FENCE_RELEASE;
571    
572     return 1;
573     }
574    
575     static void
576     iouring_poll (EV_P_ ev_tstamp timeout)
577     {
578     /* if we have events, no need for extra syscalls, but we might have to queue events */
579     if (iouring_handle_cq (EV_A))
580 root 1.3 timeout = EV_TS_CONST (0.);
581 root 1.1 else
582     /* no events, so maybe wait for some */
583     iouring_tfd_update (EV_A_ timeout);
584    
585 root 1.6 /* only enter the kernel if we have something to submit, or we need to wait */
586 root 1.1 if (timeout || iouring_to_submit)
587     {
588     int res;
589    
590     EV_RELEASE_CB;
591    
592     res = evsys_io_uring_enter (iouring_fd, iouring_to_submit, 1,
593 root 1.3 timeout > EV_TS_CONST (0.) ? IORING_ENTER_GETEVENTS : 0, 0, 0);
594 root 1.1 iouring_to_submit = 0;
595    
596     EV_ACQUIRE_CB;
597    
598     if (ecb_expect_false (res < 0))
599     if (errno == EINTR)
600     /* ignore */;
601     else
602     ev_syserr ("(libev) iouring setup");
603     else
604     iouring_handle_cq (EV_A);
605     }
606     }
607    
608     inline_size
609     int
610     iouring_init (EV_P_ int flags)
611     {
612     if (!epoll_init (EV_A_ 0))
613     return 0;
614    
615     iouring_entries = IOURING_INIT_ENTRIES;
616     iouring_max_entries = 0;
617    
618     if (iouring_internal_init (EV_A) < 0)
619     {
620     iouring_internal_destroy (EV_A);
621     return 0;
622     }
623    
624 root 1.6 ev_io_init (&iouring_epoll_w, iouring_epoll_cb, backend_fd, EV_READ);
625     ev_set_priority (&iouring_epoll_w, EV_MAXPRI);
626    
627     ev_io_init (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ);
628     ev_set_priority (&iouring_tfd_w, EV_MAXPRI);
629    
630 root 1.1 ev_io_start (EV_A_ &iouring_epoll_w);
631     ev_unref (EV_A); /* watcher should not keep loop alive */
632    
633     ev_io_start (EV_A_ &iouring_tfd_w);
634     ev_unref (EV_A); /* watcher should not keep loop alive */
635    
636     backend_modify = iouring_modify;
637     backend_poll = iouring_poll;
638    
639     return EVBACKEND_IOURING;
640     }
641    
642     inline_size
643     void
644     iouring_destroy (EV_P)
645     {
646     iouring_internal_destroy (EV_A);
647     epoll_destroy (EV_A);
648     }
649