Adding upstream version 3.8.1.upstream/3.8.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 697 insertions, 0 deletions

diff --git a/contrib/libev/ev_iouring.c b/contrib/libev/ev_iouring.c
new file mode 100644
index 0000000..612391b
--- /dev/null
+++ b/contrib/libev/ev_iouring.c
@@ -0,0 +1,697 @@
+/*
+ * libev linux io_uring fd activity backend
+ *
+ * Copyright (c) 2019-2020 Marc Alexander Lehmann <libev@schmorp.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modifica-
+ * tion, are permitted provided that the following conditions are met:
+ *
+ *   1.  Redistributions of source code must retain the above copyright notice,
+ *       this list of conditions and the following disclaimer.
+ *
+ *   2.  Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
+ * CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO
+ * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
+ * CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
+ * ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * the GNU General Public License ("GPL") version 2 or any later version,
+ * in which case the provisions of the GPL are applicable instead of
+ * the above. If you wish to allow the use of your version of this file
+ * only under the terms of the GPL and not to allow others to use your
+ * version of this file under the BSD license, indicate your decision
+ * by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL. If you do not delete the
+ * provisions above, a recipient may use your version of this file under
+ * either the BSD or the GPL.
+ */
+
+/*
+ * general notes about linux io_uring:
+ *
+ * a) it's the best interface I have seen so far. on linux.
+ * b) best is not necessarily very good.
+ * c) it's better than the aio mess, doesn't suffer from the fork problems
+ *    of linux aio or epoll and so on and so on. and you could do event stuff
+ *    without any syscalls. what's not to like?
+ * d) ok, it's vastly more complex, but that's ok, really.
+ * e) why two mmaps instead of one? one would be more space-efficient,
+ *    and I can't see what benefit two would have (other than being
+ *    somehow resizable/relocatable, but that's apparently not possible).
+ * f) hmm, it's practically undebuggable (gdb can't access the memory, and
+ *    the bizarre way structure offsets are communicated makes it hard to
+ *    just print the ring buffer heads, even *iff* the memory were visible
+ *    in gdb. but then, that's also ok, really.
+ * g) well, you cannot specify a timeout when waiting for events. no,
+ *    seriously, the interface doesn't support a timeout. never seen _that_
+ *    before. sure, you can use a timerfd, but that's another syscall
+ *    you could have avoided. overall, this bizarre omission smells
+ *    like a µ-optimisation by the io_uring author for his personal
+ *    applications, to the detriment of everybody else who just wants
+ *    an event loop. but, umm, ok, if that's all, it could be worse.
+ *    (from what I gather from the author Jens Axboe, it simply didn't
+ *    occur to him, and he made good on it by adding an unlimited nuber
+ *    of timeouts later :).
+ * h) initially there was a hardcoded limit of 4096 outstanding events.
+ *    later versions not only bump this to 32k, but also can handle
+ *    an unlimited amount of events, so this only affects the batch size.
+ * i) unlike linux aio, you *can* register more then the limit
+ *    of fd events. while early verisons of io_uring signalled an overflow
+ *    and you ended up getting wet. 5.5+ does not do this anymore.
+ * j) but, oh my! it had exactly the same bugs as the linux aio backend,
+ *    where some undocumented poll combinations just fail. fortunately,
+ *    after finally reaching the author, he was more than willing to fix
+ *    this probably in 5.6+.
+ * k) overall, the *API* itself is, I dare to say, not a total trainwreck.
+ *    once the bugs ae fixed (probably in 5.6+), it will be without
+ *    competition.
+ */
+
+/* TODO: use internal TIMEOUT */
+/* TODO: take advantage of single mmap, NODROP etc. */
+/* TODO: resize cq/sq size independently */
+
+#include <sys/timerfd.h>
+#include <sys/mman.h>
+#include <poll.h>
+#include <stdint.h>
+
+#define IOURING_INIT_ENTRIES 32
+
+/*****************************************************************************/
+/* syscall wrapdadoop - this section has the raw api/abi definitions */
+
+#include <linux/fs.h>
+#include <linux/types.h>
+
+/* mostly directly taken from the kernel or documentation */
+
+struct io_uring_sqe
+{
+  __u8 opcode;
+  __u8 flags;
+  __u16 ioprio;
+  __s32 fd;
+  union {
+    __u64 off;
+    __u64 addr2;
+  };
+  __u64 addr;
+  __u32 len;
+  union {
+    __kernel_rwf_t rw_flags;
+    __u32 fsync_flags;
+    __u16 poll_events;
+    __u32 sync_range_flags;
+    __u32 msg_flags;
+    __u32 timeout_flags;
+    __u32 accept_flags;
+    __u32 cancel_flags;
+    __u32 open_flags;
+    __u32 statx_flags;
+  };
+  __u64 user_data;
+  union {
+    __u16 buf_index;
+    __u64 __pad2[3];
+  };
+};
+
+struct io_uring_cqe
+{
+  __u64 user_data;
+  __s32 res;
+  __u32 flags;
+};
+
+struct io_sqring_offsets
+{
+  __u32 head;
+  __u32 tail;
+  __u32 ring_mask;
+  __u32 ring_entries;
+  __u32 flags;
+  __u32 dropped;
+  __u32 array;
+  __u32 resv1;
+  __u64 resv2;
+};
+
+struct io_cqring_offsets
+{
+  __u32 head;
+  __u32 tail;
+  __u32 ring_mask;
+  __u32 ring_entries;
+  __u32 overflow;
+  __u32 cqes;
+  __u64 resv[2];
+};
+
+struct io_uring_params
+{
+  __u32 sq_entries;
+  __u32 cq_entries;
+  __u32 flags;
+  __u32 sq_thread_cpu;
+  __u32 sq_thread_idle;
+  __u32 features;
+  __u32 resv[4];
+  struct io_sqring_offsets sq_off;
+  struct io_cqring_offsets cq_off;
+};
+
+#define IORING_SETUP_CQSIZE 0x00000008
+
+#define IORING_OP_POLL_ADD        6
+#define IORING_OP_POLL_REMOVE     7
+#define IORING_OP_TIMEOUT        11
+#define IORING_OP_TIMEOUT_REMOVE 12
+
+/* relative or absolute, reference clock is CLOCK_MONOTONIC */
+struct iouring_kernel_timespec
+{
+  int64_t tv_sec;
+  long long tv_nsec;
+};
+
+#define IORING_TIMEOUT_ABS 0x00000001
+
+#define IORING_ENTER_GETEVENTS 0x01
+
+#define IORING_OFF_SQ_RING 0x00000000ULL
+#define IORING_OFF_CQ_RING 0x08000000ULL
+#define IORING_OFF_SQES	   0x10000000ULL
+
+#define IORING_FEAT_SINGLE_MMAP   0x00000001
+#define IORING_FEAT_NODROP        0x00000002
+#define IORING_FEAT_SUBMIT_STABLE 0x00000004
+
+inline_size
+int
+evsys_io_uring_setup (unsigned entries, struct io_uring_params *params)
+{
+  return ev_syscall2 (SYS_io_uring_setup, entries, params);
+}
+
+inline_size
+int
+evsys_io_uring_enter (int fd, unsigned to_submit, unsigned min_complete, unsigned flags, const sigset_t *sig, size_t sigsz)
+{
+  return ev_syscall6 (SYS_io_uring_enter, fd, to_submit, min_complete, flags, sig, sigsz);
+}
+
+/*****************************************************************************/
+/* actual backed implementation */
+
+/* we hope that volatile will make the compiler access this variables only once */
+#define EV_SQ_VAR(name) *(volatile unsigned *)((char *)iouring_sq_ring + iouring_sq_ ## name)
+#define EV_CQ_VAR(name) *(volatile unsigned *)((char *)iouring_cq_ring + iouring_cq_ ## name)
+
+/* the index array */
+#define EV_SQ_ARRAY     ((unsigned *)((char *)iouring_sq_ring + iouring_sq_array))
+
+/* the submit/completion queue entries */
+#define EV_SQES         ((struct io_uring_sqe *)         iouring_sqes)
+#define EV_CQES         ((struct io_uring_cqe *)((char *)iouring_cq_ring + iouring_cq_cqes))
+
+inline_speed
+int
+iouring_enter (EV_P_ ev_tstamp timeout)
+{
+  int res;
+
+  EV_RELEASE_CB;
+
+  res = evsys_io_uring_enter (iouring_fd, iouring_to_submit, 1,
+                              timeout > EV_TS_CONST (0.) ? IORING_ENTER_GETEVENTS : 0, 0, 0);
+
+  assert (("libev: io_uring_enter did not consume all sqes", (res < 0 || res == iouring_to_submit)));
+
+  iouring_to_submit = 0;
+
+  EV_ACQUIRE_CB;
+
+  return res;
+}
+
+/* TODO: can we move things around so we don't need this forward-reference? */
+static void
+iouring_poll (EV_P_ ev_tstamp timeout);
+
+static
+struct io_uring_sqe *
+iouring_sqe_get (EV_P)
+{
+  unsigned tail;
+
+  for (;;)
+    {
+      tail = EV_SQ_VAR (tail);
+
+      if (ecb_expect_true (tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries)))
+        break; /* whats the problem, we have free sqes */
+
+      /* queue full, need to flush and possibly handle some events */
+
+#if EV_FEATURE_CODE
+      /* first we ask the kernel nicely, most often this frees up some sqes */
+      int res = iouring_enter (EV_A_ EV_TS_CONST (0.));
+
+      ECB_MEMORY_FENCE_ACQUIRE; /* better safe than sorry */
+
+      if (res >= 0)
+        continue; /* yes, it worked, try again */
+#endif
+
+      /* some problem, possibly EBUSY - do the full poll and let it handle any issues */
+
+      iouring_poll (EV_A_ EV_TS_CONST (0.));
+      /* iouring_poll should have done ECB_MEMORY_FENCE_ACQUIRE for us */
+    }
+
+  /*assert (("libev: io_uring queue full after flush", tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries)));*/
+
+  return EV_SQES + (tail & EV_SQ_VAR (ring_mask));
+}
+
+inline_size
+struct io_uring_sqe *
+iouring_sqe_submit (EV_P_ struct io_uring_sqe *sqe)
+{
+  unsigned idx = sqe - EV_SQES;
+
+  EV_SQ_ARRAY [idx] = idx;
+  ECB_MEMORY_FENCE_RELEASE;
+  ++EV_SQ_VAR (tail);
+  // ECB_MEMORY_FENCE_RELEASE; /* for the time being we assume this is not needed */
+  ++iouring_to_submit;
+  return sqe;
+}
+
+/*****************************************************************************/
+
+/* when the timerfd expires we simply note the fact,
+ * as the purpose of the timerfd is to wake us up, nothing else.
+ * the next iteration should re-set it.
+ */
+static void
+iouring_tfd_cb (EV_P_ struct ev_io *w, int revents)
+{
+  iouring_tfd_to = EV_TSTAMP_HUGE;
+}
+
+/* called for full and partial cleanup */
+ecb_cold
+static int
+iouring_internal_destroy (EV_P)
+{
+  close (iouring_tfd);
+  close (iouring_fd);
+
+  if (iouring_sq_ring != MAP_FAILED) munmap (iouring_sq_ring, iouring_sq_ring_size);
+  if (iouring_cq_ring != MAP_FAILED) munmap (iouring_cq_ring, iouring_cq_ring_size);
+  if (iouring_sqes    != MAP_FAILED) munmap (iouring_sqes   , iouring_sqes_size   );
+
+  if (ev_is_active (&iouring_tfd_w))
+    {
+      ev_ref (EV_A);
+      ev_io_stop (EV_A_ &iouring_tfd_w);
+    }
+
+  return 0;
+}
+
+ecb_cold
+static int
+iouring_internal_init (EV_P)
+{
+  struct io_uring_params params = { 0 };
+
+  iouring_to_submit = 0;
+
+  iouring_tfd     = -1;
+  iouring_sq_ring = MAP_FAILED;
+  iouring_cq_ring = MAP_FAILED;
+  iouring_sqes    = MAP_FAILED;
+
+  if (!have_monotonic) /* cannot really happen, but what if11 */
+    return -1;
+
+  for (;;)
+    {
+      iouring_fd = evsys_io_uring_setup (iouring_entries, &params);
+
+      if (iouring_fd >= 0)
+        break; /* yippie */
+
+      if (errno != EINVAL)
+        return -1; /* we failed */
+
+#if TODO
+      if ((~params.features) & (IORING_FEAT_NODROP | IORING_FEATURE_SINGLE_MMAP | IORING_FEAT_SUBMIT_STABLE))
+        return -1; /* we require the above features */
+#endif
+
+      /* EINVAL: lots of possible reasons, but maybe
+       * it is because we hit the unqueryable hardcoded size limit
+       */
+
+      /* we hit the limit already, give up */
+      if (iouring_max_entries)
+        return -1;
+
+      /* first time we hit EINVAL? assume we hit the limit, so go back and retry */
+      iouring_entries >>= 1;
+      iouring_max_entries = iouring_entries;
+    }
+
+  iouring_sq_ring_size = params.sq_off.array + params.sq_entries * sizeof (unsigned);
+  iouring_cq_ring_size = params.cq_off.cqes  + params.cq_entries * sizeof (struct io_uring_cqe);
+  iouring_sqes_size    =                       params.sq_entries * sizeof (struct io_uring_sqe);
+
+  iouring_sq_ring = mmap (0, iouring_sq_ring_size, PROT_READ | PROT_WRITE,
+                          MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQ_RING);
+  iouring_cq_ring = mmap (0, iouring_cq_ring_size, PROT_READ | PROT_WRITE,
+                          MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_CQ_RING);
+  iouring_sqes    = mmap (0, iouring_sqes_size, PROT_READ | PROT_WRITE,
+                          MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQES);
+
+  if (iouring_sq_ring == MAP_FAILED || iouring_cq_ring == MAP_FAILED || iouring_sqes == MAP_FAILED)
+    return -1;
+
+  iouring_sq_head         = params.sq_off.head;
+  iouring_sq_tail         = params.sq_off.tail;
+  iouring_sq_ring_mask    = params.sq_off.ring_mask;
+  iouring_sq_ring_entries = params.sq_off.ring_entries;
+  iouring_sq_flags        = params.sq_off.flags;
+  iouring_sq_dropped      = params.sq_off.dropped;
+  iouring_sq_array        = params.sq_off.array;
+
+  iouring_cq_head         = params.cq_off.head;
+  iouring_cq_tail         = params.cq_off.tail;
+  iouring_cq_ring_mask    = params.cq_off.ring_mask;
+  iouring_cq_ring_entries = params.cq_off.ring_entries;
+  iouring_cq_overflow     = params.cq_off.overflow;
+  iouring_cq_cqes         = params.cq_off.cqes;
+
+  iouring_tfd = timerfd_create (CLOCK_MONOTONIC, TFD_CLOEXEC);
+
+  if (iouring_tfd < 0)
+    return iouring_tfd;
+
+  iouring_tfd_to = EV_TSTAMP_HUGE;
+
+  return 0;
+}
+
+ecb_cold
+static void
+iouring_fork (EV_P)
+{
+  iouring_internal_destroy (EV_A);
+
+  while (iouring_internal_init (EV_A) < 0)
+    ev_syserr ("(libev) io_uring_setup");
+
+  fd_rearm_all (EV_A);
+
+  ev_io_stop  (EV_A_ &iouring_tfd_w);
+  ev_io_set   (EV_A_ &iouring_tfd_w, iouring_tfd, EV_READ);
+  ev_io_start (EV_A_ &iouring_tfd_w);
+}
+
+/*****************************************************************************/
+
+static void
+iouring_modify (EV_P_ int fd, int oev, int nev)
+{
+  if (oev)
+    {
+      /* we assume the sqe's are all "properly" initialised */
+      struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
+      sqe->opcode    = IORING_OP_POLL_REMOVE;
+      sqe->fd        = fd;
+      /* Jens Axboe notified me that user_data is not what is documented, but is
+       * some kind of unique ID that has to match, otherwise the request cannot
+       * be removed. Since we don't *really* have that, we pass in the old
+       * generation counter - if that fails, too bad, it will hopefully be removed
+       * at close time and then be ignored. */
+      sqe->addr      = (uint32_t)fd | ((__u64)(uint32_t)anfds [fd].egen << 32);
+      sqe->user_data = (uint64_t)-1;
+      iouring_sqe_submit (EV_A_ sqe);
+
+      /* increment generation counter to avoid handling old events */
+      ++anfds [fd].egen;
+    }
+
+  if (nev)
+    {
+      struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
+      sqe->opcode      = IORING_OP_POLL_ADD;
+      sqe->fd          = fd;
+      sqe->addr        = 0;
+      sqe->user_data   = (uint32_t)fd | ((__u64)(uint32_t)anfds [fd].egen << 32);
+      sqe->poll_events =
+        (nev & EV_READ ? POLLIN : 0)
+        | (nev & EV_WRITE ? POLLOUT : 0);
+      iouring_sqe_submit (EV_A_ sqe);
+    }
+}
+
+inline_size
+void
+iouring_tfd_update (EV_P_ ev_tstamp timeout)
+{
+  ev_tstamp tfd_to = mn_now + timeout;
+
+  /* we assume there will be many iterations per timer change, so
+   * we only re-set the timerfd when we have to because its expiry
+   * is too late.
+   */
+  if (ecb_expect_false (tfd_to < iouring_tfd_to))
+    {
+       struct itimerspec its;
+
+       iouring_tfd_to = tfd_to;
+       EV_TS_SET (its.it_interval, 0.);
+       EV_TS_SET (its.it_value, tfd_to);
+
+       if (timerfd_settime (iouring_tfd, TFD_TIMER_ABSTIME, &its, 0) < 0)
+         assert (("libev: iouring timerfd_settime failed", 0));
+    }
+}
+
+inline_size
+void
+iouring_process_cqe (EV_P_ struct io_uring_cqe *cqe)
+{
+  int      fd  = cqe->user_data & 0xffffffffU;
+  uint32_t gen = cqe->user_data >> 32;
+  int      res = cqe->res;
+
+  /* user_data -1 is a remove that we are not atm. interested in */
+  if (cqe->user_data == (uint64_t)-1)
+    return;
+
+  assert (("libev: io_uring fd must be in-bounds", fd >= 0 && fd < anfdmax));
+
+  /* documentation lies, of course. the result value is NOT like
+   * normal syscalls, but like linux raw syscalls, i.e. negative
+   * error numbers. fortunate, as otherwise there would be no way
+   * to get error codes at all. still, why not document this?
+   */
+
+  /* ignore event if generation doesn't match */
+  /* other than skipping removal events, */
+  /* this should actually be very rare */
+  if (ecb_expect_false (gen != (uint32_t)anfds [fd].egen))
+    return;
+
+  if (ecb_expect_false (res < 0))
+    {
+      /*TODO: EINVAL handling (was something failed with this fd)*/
+
+      if (res == -EBADF)
+        {
+          assert (("libev: event loop rejected bad fd", res != -EBADF));
+          fd_kill (EV_A_ fd);
+        }
+      else
+        {
+          errno = -res;
+          ev_syserr ("(libev) IORING_OP_POLL_ADD");
+        }
+
+      return;
+    }
+
+  /* feed events, we do not expect or handle POLLNVAL */
+  fd_event (
+    EV_A_
+    fd,
+    (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
+    | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
+  );
+
+  /* io_uring is oneshot, so we need to re-arm the fd next iteration */
+  /* this also means we usually have to do at least one syscall per iteration */
+  anfds [fd].events = 0;
+  fd_change (EV_A_ fd, EV_ANFD_REIFY);
+}
+
+/* called when the event queue overflows */
+ecb_cold
+static void
+iouring_overflow (EV_P)
+{
+  /* we have two options, resize the queue (by tearing down
+   * everything and recreating it, or living with it
+   * and polling.
+   * we implement this by resizing the queue, and, if that fails,
+   * we just recreate the state on every failure, which
+   * kind of is a very inefficient poll.
+   * one danger is, due to the bios toward lower fds,
+   * we will only really get events for those, so
+   * maybe we need a poll() fallback, after all.
+   */
+  /*EV_CQ_VAR (overflow) = 0;*/ /* need to do this if we keep the state and poll manually */
+
+  fd_rearm_all (EV_A);
+
+  /* we double the size until we hit the hard-to-probe maximum */
+  if (!iouring_max_entries)
+    {
+      iouring_entries <<= 1;
+      iouring_fork (EV_A);
+    }
+  else
+    {
+      /* we hit the kernel limit, we should fall back to something else.
+       * we can either poll() a few times and hope for the best,
+       * poll always, or switch to epoll.
+       * TODO: is this necessary with newer kernels?
+       */
+
+      iouring_internal_destroy (EV_A);
+
+      /* this should make it so that on return, we don't call any uring functions */
+      iouring_to_submit = 0;
+
+      for (;;)
+        {
+          backend = epoll_init (EV_A_ 0);
+
+          if (backend)
+            break;
+
+          ev_syserr ("(libev) iouring switch to epoll");
+        }
+    }
+}
+
+/* handle any events in the completion queue, return true if there were any */
+static int
+iouring_handle_cq (EV_P)
+{
+  unsigned head, tail, mask;
+
+  head = EV_CQ_VAR (head);
+  ECB_MEMORY_FENCE_ACQUIRE;
+  tail = EV_CQ_VAR (tail);
+
+  if (head == tail)
+    return 0;
+
+  /* it can only overflow if we have events, yes, yes? */
+  if (ecb_expect_false (EV_CQ_VAR (overflow)))
+    {
+      iouring_overflow (EV_A);
+      return 1;
+    }
+
+  mask = EV_CQ_VAR (ring_mask);
+
+  do
+    iouring_process_cqe (EV_A_ &EV_CQES [head++ & mask]);
+  while (head != tail);
+
+  EV_CQ_VAR (head) = head;
+  ECB_MEMORY_FENCE_RELEASE;
+
+  return 1;
+}
+
+static void
+iouring_poll (EV_P_ ev_tstamp timeout)
+{
+  /* if we have events, no need for extra syscalls, but we might have to queue events */
+  /* we also clar the timeout if there are outstanding fdchanges */
+  /* the latter should only happen if both the sq and cq are full, most likely */
+  /* because we have a lot of event sources that immediately complete */
+  /* TODO: fdchacngecnt is always 0 because fd_reify does not have two buffers yet */
+  if (iouring_handle_cq (EV_A) || fdchangecnt)
+    timeout = EV_TS_CONST (0.);
+  else
+    /* no events, so maybe wait for some */
+    iouring_tfd_update (EV_A_ timeout);
+
+  /* only enter the kernel if we have something to submit, or we need to wait */
+  if (timeout || iouring_to_submit)
+    {
+      int res = iouring_enter (EV_A_ timeout);
+
+      if (ecb_expect_false (res < 0))
+        if (errno == EINTR)
+          /* ignore */;
+        else if (errno == EBUSY)
+          /* cq full, cannot submit - should be rare because we flush the cq first, so simply ignore */;
+        else
+          ev_syserr ("(libev) iouring setup");
+      else
+        iouring_handle_cq (EV_A);
+    }
+}
+
+inline_size
+int
+iouring_init (EV_P_ int flags)
+{
+  iouring_entries     = IOURING_INIT_ENTRIES;
+  iouring_max_entries = 0;
+
+  if (iouring_internal_init (EV_A) < 0)
+    {
+      iouring_internal_destroy (EV_A);
+      return 0;
+    }
+
+  ev_io_init  (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ);
+  ev_set_priority (&iouring_tfd_w, EV_MINPRI);
+  ev_io_start (EV_A_ &iouring_tfd_w);
+  ev_unref (EV_A); /* watcher should not keep loop alive */
+
+  backend_modify = iouring_modify;
+  backend_poll   = iouring_poll;
+
+  return EVBACKEND_IOURING;
+}
+
+inline_size
+void
+iouring_destroy (EV_P)
+{
+  iouring_internal_destroy (EV_A);
+}
+