libev/ev_iouring.c

/*
 * libev linux io_uring fd activity backend
 *
 * Copyright (c) 2019 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 3 mmaps instead of one? one would be more space-efficient,
 *    and I can't see what benefit three would have (other than being
 *    somehow resizable/relocatable, but that's apparently not possible).
 *    (FIXME: newer kernels can use 2 mmaps only, need to look into this).
 * f) hmm, it's practiclaly 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.
 *    (FIXME: jens mentioned timeout commands, need to investigate)
 * h) there is a hardcoded limit of 4096 outstanding events. okay,
 *    at least there is no arbitrary low system-wide limit...
 *    (FIXME: apparently, this was increased to 32768 in later kernels(
 * i) unlike linux aio, you *can* register more then the limit
 *    of fd events, and the kernel will "gracefully" signal an
 *    overflow, after which you could destroy and recreate the kernel
 *    state, a bit bigger, or fall back to e.g. poll. thats not
 *    totally insane, but kind of questions the point a high
 *    performance I/O framework when it doesn't really work
 *    under stress.
 *    (FIXME: iouring should no longer drop events, need to investigate)
 * j) but, oh my! is has exactly the same bugs as the linux aio backend,
 *    where some undocumented poll combinations just fail.
 *    so we need epoll AGAIN as a fallback. AGAIN! epoll!! and of course,
 *    this is completely undocumented, have I mantioned this already?
 * k) overall, the *API* itself is, I dare to say, not a total trainwreck.
 *    the big isuess with it are the bugs requiring epoll, which might
 *    or might not get fixed (do I hold my breath?).
 */

#include <sys/timerfd.h>
#include <sys/mman.h>
#include <poll.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_OP_POLL_ADD    6
#define IORING_OP_POLL_REMOVE 7

#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   0x1
#define IORING_FEAT_NODROP        0x2
#define IORING_FEAT_SUBMIT_STABLE 0x4

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))

static
struct io_uring_sqe *
iouring_sqe_get (EV_P)
{
  unsigned tail = EV_SQ_VAR (tail);

  if (tail + 1 - EV_SQ_VAR (head) > EV_SQ_VAR (ring_entries))
    {
      /* queue full, flush */
      evsys_io_uring_enter (iouring_fd, iouring_to_submit, 0, 0, 0, 0);
      iouring_to_submit = 0;
    }

  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;
}

/*****************************************************************************/

/* 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);
    }
}

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;

  for (;;)
    {
      iouring_fd = evsys_io_uring_setup (iouring_entries, &params);

      if (iouring_fd >= 0)
        break; /* yippie */

      if (errno != EINVAL)
        return -1; /* we failed */

      /* 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;
      sqe->user_data = -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->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;

  /* ignore fd removal events, if there are any. TODO: verify */
  if (cqe->user_data == (__u64)-1)
    abort ();//D

  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 */
  /* 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)
      //TODO: EBUSY happens when?

      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 tghe 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.
       * since we use epoll anyways, go epoll.
       */

      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 */
  if (iouring_handle_cq (EV_A))
    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;

      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);
      iouring_to_submit = 0;

      EV_ACQUIRE_CB;

      if (ecb_expect_false (res < 0))
        if (errno == EINTR)
          /* 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);
}

Revision:	1.8
Committed:	Fri Dec 27 16:08:24 2019 UTC (4 years, 4 months ago) by root
Content type:	text/plain
Branch:	MAIN
Changes since 1.7:	+25 -49 lines
Log Message:	rip out epoll from iouring
#	Content
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	* (FIXME: newer kernels can use 2 mmaps only, need to look into this).
53	* f) hmm, it's practiclaly undebuggable (gdb can't access the memory, and
54	* the bizarre way structure offsets are communicated makes it hard to
55	* 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 µ-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	* (FIXME: jens mentioned timeout commands, need to investigate)
65	* h) there is a hardcoded limit of 4096 outstanding events. okay,
66	* at least there is no arbitrary low system-wide limit...
67	* (FIXME: apparently, this was increased to 32768 in later kernels(
68	* 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	* (FIXME: iouring should no longer drop events, need to investigate)
76	* 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	union {
106	__u64 off;
107	__u64 addr2;
108	};
109	__u64 addr;
110	__u32 len;
111	union {
112	__kernel_rwf_t rw_flags;
113	__u32 fsync_flags;
114	__u16 poll_events;
115	__u32 sync_range_flags;
116	__u32 msg_flags;
117	__u32 timeout_flags;
118	__u32 accept_flags;
119	__u32 cancel_flags;
120	__u32 open_flags;
121	__u32 statx_flags;
122	};
123	__u64 user_data;
124	union {
125	__u16 buf_index;
126	__u64 __pad2[3];
127	};
128	};
129
130	struct io_uring_cqe
131	{
132	__u64 user_data;
133	__s32 res;
134	__u32 flags;
135	};
136
137	struct io_sqring_offsets
138	{
139	__u32 head;
140	__u32 tail;
141	__u32 ring_mask;
142	__u32 ring_entries;
143	__u32 flags;
144	__u32 dropped;
145	__u32 array;
146	__u32 resv1;
147	__u64 resv2;
148	};
149
150	struct io_cqring_offsets
151	{
152	__u32 head;
153	__u32 tail;
154	__u32 ring_mask;
155	__u32 ring_entries;
156	__u32 overflow;
157	__u32 cqes;
158	__u64 resv[2];
159	};
160
161	struct io_uring_params
162	{
163	__u32 sq_entries;
164	__u32 cq_entries;
165	__u32 flags;
166	__u32 sq_thread_cpu;
167	__u32 sq_thread_idle;
168	__u32 features;
169	__u32 resv[4];
170	struct io_sqring_offsets sq_off;
171	struct io_cqring_offsets cq_off;
172	};
173
174	#define IORING_OP_POLL_ADD 6
175	#define IORING_OP_POLL_REMOVE 7
176
177	#define IORING_ENTER_GETEVENTS 0x01
178
179	#define IORING_OFF_SQ_RING 0x00000000ULL
180	#define IORING_OFF_CQ_RING 0x08000000ULL
181	#define IORING_OFF_SQES 0x10000000ULL
182
183	#define IORING_FEAT_SINGLE_MMAP 0x1
184	#define IORING_FEAT_NODROP 0x2
185	#define IORING_FEAT_SUBMIT_STABLE 0x4
186
187	inline_size
188	int
189	evsys_io_uring_setup (unsigned entries, struct io_uring_params *params)
190	{
191	return ev_syscall2 (SYS_io_uring_setup, entries, params);
192	}
193
194	inline_size
195	int
196	evsys_io_uring_enter (int fd, unsigned to_submit, unsigned min_complete, unsigned flags, const sigset_t *sig, size_t sigsz)
197	{
198	return ev_syscall6 (SYS_io_uring_enter, fd, to_submit, min_complete, flags, sig, sigsz);
199	}
200
201	/*****************************************************************************/
202	/* actual backed implementation */
203
204	/* we hope that volatile will make the compiler access this variables only once */
205	#define EV_SQ_VAR(name) (volatile unsigned )((char *)iouring_sq_ring + iouring_sq_ ## name)
206	#define EV_CQ_VAR(name) (volatile unsigned )((char *)iouring_cq_ring + iouring_cq_ ## name)
207
208	/* the index array */
209	#define EV_SQ_ARRAY ((unsigned )((char )iouring_sq_ring + iouring_sq_array))
210
211	/* the submit/completion queue entries */
212	#define EV_SQES ((struct io_uring_sqe *) iouring_sqes)
213	#define EV_CQES ((struct io_uring_cqe )((char )iouring_cq_ring + iouring_cq_cqes))
214
215	static
216	struct io_uring_sqe *
217	iouring_sqe_get (EV_P)
218	{
219	unsigned tail = EV_SQ_VAR (tail);
220
221	if (tail + 1 - EV_SQ_VAR (head) > EV_SQ_VAR (ring_entries))
222	{
223	/* queue full, flush */
224	evsys_io_uring_enter (iouring_fd, iouring_to_submit, 0, 0, 0, 0);
225	iouring_to_submit = 0;
226	}
227
228	assert (("libev: io_uring queue full after flush", tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries)));
229
230	return EV_SQES + (tail & EV_SQ_VAR (ring_mask));
231	}
232
233	inline_size
234	struct io_uring_sqe *
235	iouring_sqe_submit (EV_P_ struct io_uring_sqe *sqe)
236	{
237	unsigned idx = sqe - EV_SQES;
238
239	EV_SQ_ARRAY [idx] = idx;
240	ECB_MEMORY_FENCE_RELEASE;
241	++EV_SQ_VAR (tail);
242	/ECB_MEMORY_FENCE_RELEASE; / for the time being we assume this is not needed */
243	++iouring_to_submit;
244	}
245
246	/*****************************************************************************/
247
248	/* when the timerfd expires we simply note the fact,
249	* as the purpose of the timerfd is to wake us up, nothing else.
250	* the next iteration should re-set it.
251	*/
252	static void
253	iouring_tfd_cb (EV_P_ struct ev_io *w, int revents)
254	{
255	iouring_tfd_to = EV_TSTAMP_HUGE;
256	}
257
258	/* called for full and partial cleanup */
259	ecb_cold
260	static int
261	iouring_internal_destroy (EV_P)
262	{
263	close (iouring_tfd);
264	close (iouring_fd);
265
266	if (iouring_sq_ring != MAP_FAILED) munmap (iouring_sq_ring, iouring_sq_ring_size);
267	if (iouring_cq_ring != MAP_FAILED) munmap (iouring_cq_ring, iouring_cq_ring_size);
268	if (iouring_sqes != MAP_FAILED) munmap (iouring_sqes , iouring_sqes_size );
269
270	if (ev_is_active (&iouring_tfd_w))
271	{
272	ev_ref (EV_A);
273	ev_io_stop (EV_A_ &iouring_tfd_w);
274	}
275	}
276
277	ecb_cold
278	static int
279	iouring_internal_init (EV_P)
280	{
281	struct io_uring_params params = { 0 };
282
283	iouring_to_submit = 0;
284
285	iouring_tfd = -1;
286	iouring_sq_ring = MAP_FAILED;
287	iouring_cq_ring = MAP_FAILED;
288	iouring_sqes = MAP_FAILED;
289
290	for (;;)
291	{
292	iouring_fd = evsys_io_uring_setup (iouring_entries, &params);
293
294	if (iouring_fd >= 0)
295	break; /* yippie */
296
297	if (errno != EINVAL)
298	return -1; /* we failed */
299
300	/* EINVAL: lots of possible reasons, but maybe
301	* it is because we hit the unqueryable hardcoded size limit
302	*/
303
304	/* we hit the limit already, give up */
305	if (iouring_max_entries)
306	return -1;
307
308	/* first time we hit EINVAL? assume we hit the limit, so go back and retry */
309	iouring_entries >>= 1;
310	iouring_max_entries = iouring_entries;
311	}
312
313	iouring_sq_ring_size = params.sq_off.array + params.sq_entries * sizeof (unsigned);
314	iouring_cq_ring_size = params.cq_off.cqes + params.cq_entries * sizeof (struct io_uring_cqe);
315	iouring_sqes_size = params.sq_entries * sizeof (struct io_uring_sqe);
316
317	iouring_sq_ring = mmap (0, iouring_sq_ring_size, PROT_READ \| PROT_WRITE,
318	MAP_SHARED \| MAP_POPULATE, iouring_fd, IORING_OFF_SQ_RING);
319	iouring_cq_ring = mmap (0, iouring_cq_ring_size, PROT_READ \| PROT_WRITE,
320	MAP_SHARED \| MAP_POPULATE, iouring_fd, IORING_OFF_CQ_RING);
321	iouring_sqes = mmap (0, iouring_sqes_size, PROT_READ \| PROT_WRITE,
322	MAP_SHARED \| MAP_POPULATE, iouring_fd, IORING_OFF_SQES);
323
324	if (iouring_sq_ring == MAP_FAILED \|\| iouring_cq_ring == MAP_FAILED \|\| iouring_sqes == MAP_FAILED)
325	return -1;
326
327	iouring_sq_head = params.sq_off.head;
328	iouring_sq_tail = params.sq_off.tail;
329	iouring_sq_ring_mask = params.sq_off.ring_mask;
330	iouring_sq_ring_entries = params.sq_off.ring_entries;
331	iouring_sq_flags = params.sq_off.flags;
332	iouring_sq_dropped = params.sq_off.dropped;
333	iouring_sq_array = params.sq_off.array;
334
335	iouring_cq_head = params.cq_off.head;
336	iouring_cq_tail = params.cq_off.tail;
337	iouring_cq_ring_mask = params.cq_off.ring_mask;
338	iouring_cq_ring_entries = params.cq_off.ring_entries;
339	iouring_cq_overflow = params.cq_off.overflow;
340	iouring_cq_cqes = params.cq_off.cqes;
341
342	iouring_tfd = timerfd_create (CLOCK_MONOTONIC, TFD_CLOEXEC);
343
344	if (iouring_tfd < 0)
345	return iouring_tfd;
346
347	iouring_tfd_to = EV_TSTAMP_HUGE;
348
349	return 0;
350	}
351
352	ecb_cold
353	static void
354	iouring_fork (EV_P)
355	{
356	iouring_internal_destroy (EV_A);
357
358	while (iouring_internal_init (EV_A) < 0)
359	ev_syserr ("(libev) io_uring_setup");
360
361	fd_rearm_all (EV_A);
362
363	ev_io_stop (EV_A_ &iouring_tfd_w);
364	ev_io_set (EV_A_ &iouring_tfd_w, iouring_tfd, EV_READ);
365	ev_io_start (EV_A_ &iouring_tfd_w);
366	}
367
368	/*****************************************************************************/
369
370	static void
371	iouring_modify (EV_P_ int fd, int oev, int nev)
372	{
373	if (oev)
374	{
375	/* we assume the sqe's are all "properly" initialised */
376	struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
377	sqe->opcode = IORING_OP_POLL_REMOVE;
378	sqe->fd = fd;
379	sqe->user_data = -1;
380	iouring_sqe_submit (EV_A_ sqe);
381
382	/* increment generation counter to avoid handling old events */
383	++anfds [fd].egen;
384	}
385
386	if (nev)
387	{
388	struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
389	sqe->opcode = IORING_OP_POLL_ADD;
390	sqe->fd = fd;
391	sqe->user_data = (uint32_t)fd \| ((__u64)(uint32_t)anfds [fd].egen << 32);
392	sqe->poll_events =
393	(nev & EV_READ ? POLLIN : 0)
394	\| (nev & EV_WRITE ? POLLOUT : 0);
395	iouring_sqe_submit (EV_A_ sqe);
396	}
397	}
398
399	inline_size
400	void
401	iouring_tfd_update (EV_P_ ev_tstamp timeout)
402	{
403	ev_tstamp tfd_to = mn_now + timeout;
404
405	/* we assume there will be many iterations per timer change, so
406	* we only re-set the timerfd when we have to because its expiry
407	* is too late.
408	*/
409	if (ecb_expect_false (tfd_to < iouring_tfd_to))
410	{
411	struct itimerspec its;
412
413	iouring_tfd_to = tfd_to;
414	EV_TS_SET (its.it_interval, 0.);
415	EV_TS_SET (its.it_value, tfd_to);
416
417	if (timerfd_settime (iouring_tfd, TFD_TIMER_ABSTIME, &its, 0) < 0)
418	assert (("libev: iouring timerfd_settime failed", 0));
419	}
420	}
421
422	inline_size
423	void
424	iouring_process_cqe (EV_P_ struct io_uring_cqe *cqe)
425	{
426	int fd = cqe->user_data & 0xffffffffU;
427	uint32_t gen = cqe->user_data >> 32;
428	int res = cqe->res;
429
430	/* ignore fd removal events, if there are any. TODO: verify */
431	if (cqe->user_data == (__u64)-1)
432	abort ();//D
433
434	assert (("libev: io_uring fd must be in-bounds", fd >= 0 && fd < anfdmax));
435
436	/* documentation lies, of course. the result value is NOT like
437	* normal syscalls, but like linux raw syscalls, i.e. negative
438	* error numbers. fortunate, as otherwise there would be no way
439	* to get error codes at all. still, why not document this?
440	*/
441
442	/* ignore event if generation doesn't match */
443	/* this should actually be very rare */
444	if (ecb_expect_false (gen != (uint32_t)anfds [fd].egen))
445	return;
446
447	if (ecb_expect_false (res < 0))
448	{
449	//TODO: EINVAL handling (was something failed with this fd)
450	//TODO: EBUSY happens when?
451
452	if (res == -EBADF)
453	{
454	assert (("libev: event loop rejected bad fd", res != -EBADF));
455	fd_kill (EV_A_ fd);
456	}
457	else
458	{
459	errno = -res;
460	ev_syserr ("(libev) IORING_OP_POLL_ADD");
461	}
462
463	return;
464	}
465
466	/* feed events, we do not expect or handle POLLNVAL */
467	fd_event (
468	EV_A_
469	fd,
470	(res & (POLLOUT \| POLLERR \| POLLHUP) ? EV_WRITE : 0)
471	\| (res & (POLLIN \| POLLERR \| POLLHUP) ? EV_READ : 0)
472	);
473
474	/* io_uring is oneshot, so we need to re-arm the fd next iteration */
475	/* this also means we usually have to do at least one syscall per iteration */
476	anfds [fd].events = 0;
477	fd_change (EV_A_ fd, EV_ANFD_REIFY);
478	}
479
480	/* called when the event queue overflows */
481	ecb_cold
482	static void
483	iouring_overflow (EV_P)
484	{
485	/* we have two options, resize the queue (by tearing down
486	* everything and recreating it, or living with it
487	* and polling.
488	* we implement this by resizing tghe queue, and, if that fails,
489	* we just recreate the state on every failure, which
490	* kind of is a very inefficient poll.
491	* one danger is, due to the bios toward lower fds,
492	* we will only really get events for those, so
493	* maybe we need a poll() fallback, after all.
494	*/
495	/EV_CQ_VAR (overflow) = 0;/ /* need to do this if we keep the state and poll manually */
496
497	fd_rearm_all (EV_A);
498
499	/* we double the size until we hit the hard-to-probe maximum */
500	if (!iouring_max_entries)
501	{
502	iouring_entries <<= 1;
503	iouring_fork (EV_A);
504	}
505	else
506	{
507	/* we hit the kernel limit, we should fall back to something else.
508	* we can either poll() a few times and hope for the best,
509	* poll always, or switch to epoll.
510	* since we use epoll anyways, go epoll.
511	*/
512
513	iouring_internal_destroy (EV_A);
514
515	/* this should make it so that on return, we don'T call any uring functions */
516	iouring_to_submit = 0;
517
518	for (;;)
519	{
520	backend = epoll_init (EV_A_ 0);
521
522	if (backend)
523	break;
524
525	ev_syserr ("(libev) iouring switch to epoll");
526	}
527	}
528	}
529
530	/* handle any events in the completion queue, return true if there were any */
531	static int
532	iouring_handle_cq (EV_P)
533	{
534	unsigned head, tail, mask;
535
536	head = EV_CQ_VAR (head);
537	ECB_MEMORY_FENCE_ACQUIRE;
538	tail = EV_CQ_VAR (tail);
539
540	if (head == tail)
541	return 0;
542
543	/* it can only overflow if we have events, yes, yes? */
544	if (ecb_expect_false (EV_CQ_VAR (overflow)))
545	{
546	iouring_overflow (EV_A);
547	return 1;
548	}
549
550	mask = EV_CQ_VAR (ring_mask);
551
552	do
553	iouring_process_cqe (EV_A_ &EV_CQES [head++ & mask]);
554	while (head != tail);
555
556	EV_CQ_VAR (head) = head;
557	ECB_MEMORY_FENCE_RELEASE;
558
559	return 1;
560	}
561
562	static void
563	iouring_poll (EV_P_ ev_tstamp timeout)
564	{
565	/* if we have events, no need for extra syscalls, but we might have to queue events */
566	if (iouring_handle_cq (EV_A))
567	timeout = EV_TS_CONST (0.);
568	else
569	/* no events, so maybe wait for some */
570	iouring_tfd_update (EV_A_ timeout);
571
572	/* only enter the kernel if we have something to submit, or we need to wait */
573	if (timeout \|\| iouring_to_submit)
574	{
575	int res;
576
577	EV_RELEASE_CB;
578
579	res = evsys_io_uring_enter (iouring_fd, iouring_to_submit, 1,
580	timeout > EV_TS_CONST (0.) ? IORING_ENTER_GETEVENTS : 0, 0, 0);
581	iouring_to_submit = 0;
582
583	EV_ACQUIRE_CB;
584
585	if (ecb_expect_false (res < 0))
586	if (errno == EINTR)
587	/* ignore */;
588	else
589	ev_syserr ("(libev) iouring setup");
590	else
591	iouring_handle_cq (EV_A);
592	}
593	}
594
595	inline_size
596	int
597	iouring_init (EV_P_ int flags)
598	{
599	iouring_entries = IOURING_INIT_ENTRIES;
600	iouring_max_entries = 0;
601
602	if (iouring_internal_init (EV_A) < 0)
603	{
604	iouring_internal_destroy (EV_A);
605	return 0;
606	}
607
608	ev_io_init (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ);
609	ev_set_priority (&iouring_tfd_w, EV_MINPRI);
610	ev_io_start (EV_A_ &iouring_tfd_w);
611	ev_unref (EV_A); /* watcher should not keep loop alive */
612
613	backend_modify = iouring_modify;
614	backend_poll = iouring_poll;
615
616	return EVBACKEND_IOURING;
617	}
618
619	inline_size
620	void
621	iouring_destroy (EV_P)
622	{
623	iouring_internal_destroy (EV_A);
624	}
625