meta-openembedded/meta-oe/recipes-devtools/nodejs/nodejs/0002-Revert-io_uring-changes-from-libuv-1.45.0.patch

From 6d2ef4c8ba2304ee4941a6719b3ad9bd63e415a9 Mon Sep 17 00:00:00 2001
From: Martin Jansa <martin.jansa@gmail.com>
Date: Wed, 18 Oct 2023 21:09:44 +0200
Subject: [PATCH] Revert io_uring changes from libuv-1.45.0

This reverts https://github.com/libuv/libuv/pull/3952/commits/26c79a942b92573a1388c0ee8a6ad4397f009318

Included in nodejs-20.3.0 with the libuv upgrade to 1.45.0 in:
https://github.com/nodejs/node/commit/bfcb3d1d9a876f399013d326bd65804f9eda77e4

Reverted libuv commits:
Revert "linux: fix WRITEV with lots of bufs using io_uring (#4004)"
This reverts commit ef6a9a624df0a00687037474025a3608472f722a.
Revert "linux: work around EOWNERDEAD io_uring kernel bug (#4002)"
This reverts commit d23a20f62cc50b9fd7694992263f1d296d8f5cb4.
Revert "unix: handle CQ overflow in iou ring (#3991)"
This reverts commit 30fc896cc1b5822e9f1eb462587fe4b368a6215c.
Revert "unix: constrained_memory should return UINT64_MAX (#3753)"
This reverts commit 6ad347fae4520f39520d34bd7c7f5ddafab13a69.
Revert "linux: use io_uring to batch epoll_ctl calls (#3979)"
This reverts commit 6e073ef5daf93b708a654008959b823b58029e88.
Revert "linux: fix logic bug in sqe ring space check (#3980)"
This reverts commit f27208224084fc972b9d2802486d97ef31b51a39.
Revert "src: fix events/events_waiting metrics counter (#3957)"
This reverts commit e02642cf3b768b2c58a41f97fa38507e032ae415.
Revert "linux: remove bug workaround for obsolete kernels (#3965)"
This reverts commit 1c935a34454167b23f8eef7f0f63d7119f0de747.
Revert "linux: add IORING_OP_CLOSE support (#3964)"
This reverts commit dfae365f844e127621128a76bce7165e3f99a8d9.
Revert "linux: add IORING_OP_OPENAT support (#3963)"
This reverts commit 5ca5e475bb1711e65323ef1594a31818e5a1a9eb.
Revert "linux: fix academic valgrind warning (#3960)"
This reverts commit a7ff759ca1deacb2e0e6ae3c2d3dce91cc637dfe.
Revert "linux: introduce io_uring support (#3952)"
This reverts commit d2c31f429b87b476a7f1344d145dad4752a406d4.

Dropped deps/uv/docs deps/uv/test changes as these dirs aren't included
in nodejs tarballs.

Signed-off-by: Martin Jansa <martin.jansa@gmail.com>
---
Upstream-Status: Inappropriate [OE specific]

 deps/uv/docs/src/fs.rst               |   6 -
 deps/uv/docs/src/misc.rst             |   5 +-
 deps/uv/src/threadpool.c              |  21 -
 deps/uv/src/unix/aix.c                |  11 +-
 deps/uv/src/unix/fs.c                 |  57 +-
 deps/uv/src/unix/internal.h           |  23 -
 deps/uv/src/unix/kqueue.c             |  10 +-
 deps/uv/src/unix/linux.c              | 998 +++-----------------------
 deps/uv/src/unix/os390.c              |  11 +-
 deps/uv/src/unix/posix-poll.c         |  11 +-
 deps/uv/src/uv-common.h               |  28 -
 deps/uv/src/win/core.c                |  20 +-
 deps/uv/test/test-fs.c                |  33 -
 deps/uv/test/test-list.h              |   4 -
 deps/uv/test/test-metrics.c           | 151 ----
 deps/uv/test/test-threadpool-cancel.c |  34 +-
 16 files changed, 138 insertions(+), 1285 deletions(-)

diff --git a/deps/uv/src/threadpool.c b/deps/uv/src/threadpool.c
index 51962bf0021..a3da53026f9 100644
--- a/deps/uv/src/threadpool.c
+++ b/deps/uv/src/threadpool.c
@@ -275,13 +275,9 @@ void uv__work_submit(uv_loop_t* loop,
 }
 
 
-/* TODO(bnoordhuis) teach libuv how to cancel file operations
- * that go through io_uring instead of the thread pool.
- */
 static int uv__work_cancel(uv_loop_t* loop, uv_req_t* req, struct uv__work* w) {
   int cancelled;
 
-  uv_once(&once, init_once);  /* Ensure |mutex| is initialized. */
   uv_mutex_lock(&mutex);
   uv_mutex_lock(&w->loop->wq_mutex);
 
@@ -311,15 +307,12 @@ void uv__work_done(uv_async_t* handle) {
   QUEUE* q;
   QUEUE wq;
   int err;
-  int nevents;
 
   loop = container_of(handle, uv_loop_t, wq_async);
   uv_mutex_lock(&loop->wq_mutex);
   QUEUE_MOVE(&loop->wq, &wq);
   uv_mutex_unlock(&loop->wq_mutex);
 
-  nevents = 0;
-
   while (!QUEUE_EMPTY(&wq)) {
     q = QUEUE_HEAD(&wq);
     QUEUE_REMOVE(q);
@@ -327,20 +320,6 @@ void uv__work_done(uv_async_t* handle) {
     w = container_of(q, struct uv__work, wq);
     err = (w->work == uv__cancelled) ? UV_ECANCELED : 0;
     w->done(w, err);
-    nevents++;
-  }
-
-  /* This check accomplishes 2 things:
-   * 1. Even if the queue was empty, the call to uv__work_done() should count
-   *    as an event. Which will have been added by the event loop when
-   *    calling this callback.
-   * 2. Prevents accidental wrap around in case nevents == 0 events == 0.
-   */
-  if (nevents > 1) {
-    /* Subtract 1 to counter the call to uv__work_done(). */
-    uv__metrics_inc_events(loop, nevents - 1);
-    if (uv__get_internal_fields(loop)->current_timeout == 0)
-      uv__metrics_inc_events_waiting(loop, nevents - 1);
   }
 }
 
diff --git a/deps/uv/src/unix/aix.c b/deps/uv/src/unix/aix.c
index f1afbed49ec..b855282ebc8 100644
--- a/deps/uv/src/unix/aix.c
+++ b/deps/uv/src/unix/aix.c
@@ -131,7 +131,6 @@ int uv__io_check_fd(uv_loop_t* loop, int fd) {
 
 
 void uv__io_poll(uv_loop_t* loop, int timeout) {
-  uv__loop_internal_fields_t* lfields;
   struct pollfd events[1024];
   struct pollfd pqry;
   struct pollfd* pe;
@@ -155,8 +154,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     return;
   }
 
-  lfields = uv__get_internal_fields(loop);
-
   while (!QUEUE_EMPTY(&loop->watcher_queue)) {
     q = QUEUE_HEAD(&loop->watcher_queue);
     QUEUE_REMOVE(q);
@@ -220,7 +217,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
   base = loop->time;
   count = 48; /* Benchmarks suggest this gives the best throughput. */
 
-  if (lfields->flags & UV_METRICS_IDLE_TIME) {
+  if (uv__get_internal_fields(loop)->flags & UV_METRICS_IDLE_TIME) {
     reset_timeout = 1;
     user_timeout = timeout;
     timeout = 0;
@@ -235,12 +232,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     if (timeout != 0)
       uv__metrics_set_provider_entry_time(loop);
 
-    /* Store the current timeout in a location that's globally accessible so
-     * other locations like uv__work_done() can determine whether the queue
-     * of events in the callback were waiting when poll was called.
-     */
-    lfields->current_timeout = timeout;
-
     nfds = pollset_poll(loop->backend_fd,
                         events,
                         ARRAY_SIZE(events),
diff --git a/deps/uv/src/unix/fs.c b/deps/uv/src/unix/fs.c
index 00d385c24b7..c696a8d5500 100644
--- a/deps/uv/src/unix/fs.c
+++ b/deps/uv/src/unix/fs.c
@@ -61,11 +61,10 @@
 #endif
 
 #if defined(__linux__)
-# include <sys/sendfile.h>
-# include <sys/utsname.h>
+# include "sys/utsname.h"
 #endif
 
-#if defined(__sun)
+#if defined(__linux__) || defined(__sun)
 # include <sys/sendfile.h>
 # include <sys/sysmacros.h>
 #endif
@@ -1554,7 +1553,26 @@ static int uv__fs_statx(int fd,
     return UV_ENOSYS;
   }
 
-  uv__statx_to_stat(&statxbuf, buf);
+  buf->st_dev = makedev(statxbuf.stx_dev_major, statxbuf.stx_dev_minor);
+  buf->st_mode = statxbuf.stx_mode;
+  buf->st_nlink = statxbuf.stx_nlink;
+  buf->st_uid = statxbuf.stx_uid;
+  buf->st_gid = statxbuf.stx_gid;
+  buf->st_rdev = makedev(statxbuf.stx_rdev_major, statxbuf.stx_rdev_minor);
+  buf->st_ino = statxbuf.stx_ino;
+  buf->st_size = statxbuf.stx_size;
+  buf->st_blksize = statxbuf.stx_blksize;
+  buf->st_blocks = statxbuf.stx_blocks;
+  buf->st_atim.tv_sec = statxbuf.stx_atime.tv_sec;
+  buf->st_atim.tv_nsec = statxbuf.stx_atime.tv_nsec;
+  buf->st_mtim.tv_sec = statxbuf.stx_mtime.tv_sec;
+  buf->st_mtim.tv_nsec = statxbuf.stx_mtime.tv_nsec;
+  buf->st_ctim.tv_sec = statxbuf.stx_ctime.tv_sec;
+  buf->st_ctim.tv_nsec = statxbuf.stx_ctime.tv_nsec;
+  buf->st_birthtim.tv_sec = statxbuf.stx_btime.tv_sec;
+  buf->st_birthtim.tv_nsec = statxbuf.stx_btime.tv_nsec;
+  buf->st_flags = 0;
+  buf->st_gen = 0;
 
   return 0;
 #else
@@ -1798,9 +1816,6 @@ int uv_fs_chown(uv_loop_t* loop,
 int uv_fs_close(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb) {
   INIT(CLOSE);
   req->file = file;
-  if (cb != NULL)
-    if (uv__iou_fs_close(loop, req))
-      return 0;
   POST;
 }
 
@@ -1848,9 +1863,6 @@ int uv_fs_lchown(uv_loop_t* loop,
 int uv_fs_fdatasync(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb) {
   INIT(FDATASYNC);
   req->file = file;
-  if (cb != NULL)
-    if (uv__iou_fs_fsync_or_fdatasync(loop, req, /* IORING_FSYNC_DATASYNC */ 1))
-      return 0;
   POST;
 }
 
@@ -1858,9 +1870,6 @@ int uv_fs_fdatasync(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb) {
 int uv_fs_fstat(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb) {
   INIT(FSTAT);
   req->file = file;
-  if (cb != NULL)
-    if (uv__iou_fs_statx(loop, req, /* is_fstat */ 1, /* is_lstat */ 0))
-      return 0;
   POST;
 }
 
@@ -1868,9 +1877,6 @@ int uv_fs_fstat(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb) {
 int uv_fs_fsync(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb) {
   INIT(FSYNC);
   req->file = file;
-  if (cb != NULL)
-    if (uv__iou_fs_fsync_or_fdatasync(loop, req, /* no flags */ 0))
-      return 0;
   POST;
 }
 
@@ -1917,9 +1923,6 @@ int uv_fs_lutime(uv_loop_t* loop,
 int uv_fs_lstat(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_fs_cb cb) {
   INIT(LSTAT);
   PATH;
-  if (cb != NULL)
-    if (uv__iou_fs_statx(loop, req, /* is_fstat */ 0, /* is_lstat */ 1))
-      return 0;
   POST;
 }
 
@@ -1981,9 +1984,6 @@ int uv_fs_open(uv_loop_t* loop,
   PATH;
   req->flags = flags;
   req->mode = mode;
-  if (cb != NULL)
-    if (uv__iou_fs_open(loop, req))
-      return 0;
   POST;
 }
 
@@ -2012,11 +2012,6 @@ int uv_fs_read(uv_loop_t* loop, uv_fs_t* req,
   memcpy(req->bufs, bufs, nbufs * sizeof(*bufs));
 
   req->off = off;
-
-  if (cb != NULL)
-    if (uv__iou_fs_read_or_write(loop, req, /* is_read */ 1))
-      return 0;
-
   POST;
 }
 
@@ -2124,9 +2119,6 @@ int uv_fs_sendfile(uv_loop_t* loop,
 int uv_fs_stat(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_fs_cb cb) {
   INIT(STAT);
   PATH;
-  if (cb != NULL)
-    if (uv__iou_fs_statx(loop, req, /* is_fstat */ 0, /* is_lstat */ 0))
-      return 0;
   POST;
 }
 
@@ -2190,11 +2182,6 @@ int uv_fs_write(uv_loop_t* loop,
   memcpy(req->bufs, bufs, nbufs * sizeof(*bufs));
 
   req->off = off;
-
-  if (cb != NULL)
-    if (uv__iou_fs_read_or_write(loop, req, /* is_read */ 0))
-      return 0;
-
   POST;
 }
 
diff --git a/deps/uv/src/unix/internal.h b/deps/uv/src/unix/internal.h
index 6c5822e6a0d..d439ae6dd3d 100644
--- a/deps/uv/src/unix/internal.h
+++ b/deps/uv/src/unix/internal.h
@@ -329,28 +329,6 @@ int uv__random_getentropy(void* buf, size_t buflen);
 int uv__random_readpath(const char* path, void* buf, size_t buflen);
 int uv__random_sysctl(void* buf, size_t buflen);
 
-/* io_uring */
-#ifdef __linux__
-int uv__iou_fs_close(uv_loop_t* loop, uv_fs_t* req);
-int uv__iou_fs_fsync_or_fdatasync(uv_loop_t* loop,
-                                  uv_fs_t* req,
-                                  uint32_t fsync_flags);
-int uv__iou_fs_open(uv_loop_t* loop, uv_fs_t* req);
-int uv__iou_fs_read_or_write(uv_loop_t* loop,
-                             uv_fs_t* req,
-                             int is_read);
-int uv__iou_fs_statx(uv_loop_t* loop,
-                     uv_fs_t* req,
-                     int is_fstat,
-                     int is_lstat);
-#else
-#define uv__iou_fs_close(loop, req) 0
-#define uv__iou_fs_fsync_or_fdatasync(loop, req, fsync_flags) 0
-#define uv__iou_fs_open(loop, req) 0
-#define uv__iou_fs_read_or_write(loop, req, is_read) 0
-#define uv__iou_fs_statx(loop, req, is_fstat, is_lstat) 0
-#endif
-
 #if defined(__APPLE__)
 int uv___stream_fd(const uv_stream_t* handle);
 #define uv__stream_fd(handle) (uv___stream_fd((const uv_stream_t*) (handle)))
@@ -427,7 +405,6 @@ int uv__statx(int dirfd,
               int flags,
               unsigned int mask,
               struct uv__statx* statxbuf);
-void uv__statx_to_stat(const struct uv__statx* statxbuf, uv_stat_t* buf);
 ssize_t uv__getrandom(void* buf, size_t buflen, unsigned flags);
 #endif
 
diff --git a/deps/uv/src/unix/kqueue.c b/deps/uv/src/unix/kqueue.c
index 82916d65933..deb486bae7a 100644
--- a/deps/uv/src/unix/kqueue.c
+++ b/deps/uv/src/unix/kqueue.c
@@ -127,7 +127,6 @@ static void uv__kqueue_delete(int kqfd, const struct kevent *ev) {
 
 
 void uv__io_poll(uv_loop_t* loop, int timeout) {
-  uv__loop_internal_fields_t* lfields;
   struct kevent events[1024];
   struct kevent* ev;
   struct timespec spec;
@@ -156,7 +155,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     return;
   }
 
-  lfields = uv__get_internal_fields(loop);
   nevents = 0;
 
   while (!QUEUE_EMPTY(&loop->watcher_queue)) {
@@ -224,7 +222,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
   base = loop->time;
   count = 48; /* Benchmarks suggest this gives the best throughput. */
 
-  if (lfields->flags & UV_METRICS_IDLE_TIME) {
+  if (uv__get_internal_fields(loop)->flags & UV_METRICS_IDLE_TIME) {
     reset_timeout = 1;
     user_timeout = timeout;
     timeout = 0;
@@ -247,12 +245,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     if (pset != NULL)
       pthread_sigmask(SIG_BLOCK, pset, NULL);
 
-    /* Store the current timeout in a location that's globally accessible so
-     * other locations like uv__work_done() can determine whether the queue
-     * of events in the callback were waiting when poll was called.
-     */
-    lfields->current_timeout = timeout;
-
     nfds = kevent(loop->backend_fd,
                   events,
                   nevents,
diff --git a/deps/uv/src/unix/linux.c b/deps/uv/src/unix/linux.c
index 5f84ad0eea3..343e37f2527 100644
--- a/deps/uv/src/unix/linux.c
+++ b/deps/uv/src/unix/linux.c
@@ -27,8 +27,6 @@
 #include "internal.h"
 
 #include <inttypes.h>
-#include <stdatomic.h>
-#include <stddef.h>  /* offsetof */
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -40,29 +38,15 @@
 #include <net/if.h>
 #include <sys/epoll.h>
 #include <sys/inotify.h>
-#include <sys/mman.h>
 #include <sys/param.h>
 #include <sys/prctl.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
 #include <sys/sysinfo.h>
-#include <sys/sysmacros.h>
 #include <sys/types.h>
 #include <time.h>
 #include <unistd.h>
 
-#ifndef __NR_io_uring_setup
-# define __NR_io_uring_setup 425
-#endif
-
-#ifndef __NR_io_uring_enter
-# define __NR_io_uring_enter 426
-#endif
-
-#ifndef __NR_io_uring_register
-# define __NR_io_uring_register 427
-#endif
-
 #ifndef __NR_copy_file_range
 # if defined(__x86_64__)
 #  define __NR_copy_file_range 326
@@ -132,129 +116,6 @@
 # include <netpacket/packet.h>
 #endif /* HAVE_IFADDRS_H */
 
-enum {
-  UV__IORING_SETUP_SQPOLL = 2u,
-};
-
-enum {
-  UV__IORING_FEAT_SINGLE_MMAP = 1u,
-  UV__IORING_FEAT_NODROP = 2u,
-  UV__IORING_FEAT_RSRC_TAGS = 1024u,  /* linux v5.13 */
-};
-
-enum {
-  UV__IORING_OP_READV = 1,
-  UV__IORING_OP_WRITEV = 2,
-  UV__IORING_OP_FSYNC = 3,
-  UV__IORING_OP_OPENAT = 18,
-  UV__IORING_OP_CLOSE = 19,
-  UV__IORING_OP_STATX = 21,
-  UV__IORING_OP_EPOLL_CTL = 29,
-};
-
-enum {
-  UV__IORING_ENTER_GETEVENTS = 1u,
-  UV__IORING_ENTER_SQ_WAKEUP = 2u,
-};
-
-enum {
-  UV__IORING_SQ_NEED_WAKEUP = 1u,
-  UV__IORING_SQ_CQ_OVERFLOW = 2u,
-};
-
-struct uv__io_cqring_offsets {
-  uint32_t head;
-  uint32_t tail;
-  uint32_t ring_mask;
-  uint32_t ring_entries;
-  uint32_t overflow;
-  uint32_t cqes;
-  uint64_t reserved0;
-  uint64_t reserved1;
-};
-
-STATIC_ASSERT(40 == sizeof(struct uv__io_cqring_offsets));
-
-struct uv__io_sqring_offsets {
-  uint32_t head;
-  uint32_t tail;
-  uint32_t ring_mask;
-  uint32_t ring_entries;
-  uint32_t flags;
-  uint32_t dropped;
-  uint32_t array;
-  uint32_t reserved0;
-  uint64_t reserved1;
-};
-
-STATIC_ASSERT(40 == sizeof(struct uv__io_sqring_offsets));
-
-struct uv__io_uring_cqe {
-  uint64_t user_data;
-  int32_t res;
-  uint32_t flags;
-};
-
-STATIC_ASSERT(16 == sizeof(struct uv__io_uring_cqe));
-
-struct uv__io_uring_sqe {
-  uint8_t opcode;
-  uint8_t flags;
-  uint16_t ioprio;
-  int32_t fd;
-  union {
-    uint64_t off;
-    uint64_t addr2;
-  };
-  union {
-    uint64_t addr;
-  };
-  uint32_t len;
-  union {
-    uint32_t rw_flags;
-    uint32_t fsync_flags;
-    uint32_t open_flags;
-    uint32_t statx_flags;
-  };
-  uint64_t user_data;
-  union {
-    uint16_t buf_index;
-    uint64_t pad[3];
-  };
-};
-
-STATIC_ASSERT(64 == sizeof(struct uv__io_uring_sqe));
-STATIC_ASSERT(0 == offsetof(struct uv__io_uring_sqe, opcode));
-STATIC_ASSERT(1 == offsetof(struct uv__io_uring_sqe, flags));
-STATIC_ASSERT(2 == offsetof(struct uv__io_uring_sqe, ioprio));
-STATIC_ASSERT(4 == offsetof(struct uv__io_uring_sqe, fd));
-STATIC_ASSERT(8 == offsetof(struct uv__io_uring_sqe, off));
-STATIC_ASSERT(16 == offsetof(struct uv__io_uring_sqe, addr));
-STATIC_ASSERT(24 == offsetof(struct uv__io_uring_sqe, len));
-STATIC_ASSERT(28 == offsetof(struct uv__io_uring_sqe, rw_flags));
-STATIC_ASSERT(32 == offsetof(struct uv__io_uring_sqe, user_data));
-STATIC_ASSERT(40 == offsetof(struct uv__io_uring_sqe, buf_index));
-
-struct uv__io_uring_params {
-  uint32_t sq_entries;
-  uint32_t cq_entries;
-  uint32_t flags;
-  uint32_t sq_thread_cpu;
-  uint32_t sq_thread_idle;
-  uint32_t features;
-  uint32_t reserved[4];
-  struct uv__io_sqring_offsets sq_off;  /* 40 bytes */
-  struct uv__io_cqring_offsets cq_off;  /* 40 bytes */
-};
-
-STATIC_ASSERT(40 + 40 + 40 == sizeof(struct uv__io_uring_params));
-STATIC_ASSERT(40 == offsetof(struct uv__io_uring_params, sq_off));
-STATIC_ASSERT(80 == offsetof(struct uv__io_uring_params, cq_off));
-
-STATIC_ASSERT(EPOLL_CTL_ADD < 4);
-STATIC_ASSERT(EPOLL_CTL_DEL < 4);
-STATIC_ASSERT(EPOLL_CTL_MOD < 4);
-
 struct watcher_list {
   RB_ENTRY(watcher_list) entry;
   QUEUE watchers;
@@ -276,17 +137,6 @@ static int compare_watchers(const struct watcher_list* a,
 static void maybe_free_watcher_list(struct watcher_list* w,
                                     uv_loop_t* loop);
 
-static void uv__epoll_ctl_flush(int epollfd,
-                                struct uv__iou* ctl,
-                                struct epoll_event (*events)[256]);
-
-static void uv__epoll_ctl_prep(int epollfd,
-                               struct uv__iou* ctl,
-                               struct epoll_event (*events)[256],
-                               int op,
-                               int fd,
-                               struct epoll_event* e);
-
 RB_GENERATE_STATIC(watcher_root, watcher_list, entry, compare_watchers)
 
 
@@ -356,187 +206,7 @@ ssize_t uv__getrandom(void* buf, size_t buflen, unsigned flags) {
 }
 
 
-int uv__io_uring_setup(int entries, struct uv__io_uring_params* params) {
-  return syscall(__NR_io_uring_setup, entries, params);
-}
-
-
-int uv__io_uring_enter(int fd,
-                       unsigned to_submit,
-                       unsigned min_complete,
-                       unsigned flags) {
-  /* io_uring_enter used to take a sigset_t but it's unused
-   * in newer kernels unless IORING_ENTER_EXT_ARG is set,
-   * in which case it takes a struct io_uring_getevents_arg.
-   */
-  return syscall(__NR_io_uring_enter,
-                 fd,
-                 to_submit,
-                 min_complete,
-                 flags,
-                 NULL,
-                 0L);
-}
-
-
-int uv__io_uring_register(int fd, unsigned opcode, void* arg, unsigned nargs) {
-  return syscall(__NR_io_uring_register, fd, opcode, arg, nargs);
-}
-
-
-static int uv__use_io_uring(void) {
-  /* Ternary: unknown=0, yes=1, no=-1 */
-  static _Atomic int use_io_uring;
-  char* val;
-  int use;
-
-  use = atomic_load_explicit(&use_io_uring, memory_order_relaxed);
-
-  if (use == 0) {
-    val = getenv("UV_USE_IO_URING");
-    use = val == NULL || atoi(val) ? 1 : -1;
-    atomic_store_explicit(&use_io_uring, use, memory_order_relaxed);
-  }
-
-  return use > 0;
-}
-
-
-static void uv__iou_init(int epollfd,
-                         struct uv__iou* iou,
-                         uint32_t entries,
-                         uint32_t flags) {
-  struct uv__io_uring_params params;
-  struct epoll_event e;
-  size_t cqlen;
-  size_t sqlen;
-  size_t maxlen;
-  size_t sqelen;
-  uint32_t i;
-  char* sq;
-  char* sqe;
-  int ringfd;
-
-  sq = MAP_FAILED;
-  sqe = MAP_FAILED;
-
-  if (!uv__use_io_uring())
-    return;
-
-  /* SQPOLL required CAP_SYS_NICE until linux v5.12 relaxed that requirement.
-   * Mostly academic because we check for a v5.13 kernel afterwards anyway.
-   */
-  memset(&params, 0, sizeof(params));
-  params.flags = flags;
-
-  if (flags & UV__IORING_SETUP_SQPOLL)
-    params.sq_thread_idle = 10;  /* milliseconds */
-
-  /* Kernel returns a file descriptor with O_CLOEXEC flag set. */
-  ringfd = uv__io_uring_setup(entries, &params);
-  if (ringfd == -1)
-    return;
-
-  /* IORING_FEAT_RSRC_TAGS is used to detect linux v5.13 but what we're
-   * actually detecting is whether IORING_OP_STATX works with SQPOLL.
-   */
-  if (!(params.features & UV__IORING_FEAT_RSRC_TAGS))
-    goto fail;
-
-  /* Implied by IORING_FEAT_RSRC_TAGS but checked explicitly anyway. */
-  if (!(params.features & UV__IORING_FEAT_SINGLE_MMAP))
-    goto fail;
-
-  /* Implied by IORING_FEAT_RSRC_TAGS but checked explicitly anyway. */
-  if (!(params.features & UV__IORING_FEAT_NODROP))
-    goto fail;
-
-  sqlen = params.sq_off.array + params.sq_entries * sizeof(uint32_t);
-  cqlen =
-      params.cq_off.cqes + params.cq_entries * sizeof(struct uv__io_uring_cqe);
-  maxlen = sqlen < cqlen ? cqlen : sqlen;
-  sqelen = params.sq_entries * sizeof(struct uv__io_uring_sqe);
-
-  sq = mmap(0,
-            maxlen,
-            PROT_READ | PROT_WRITE,
-            MAP_SHARED | MAP_POPULATE,
-            ringfd,
-            0);  /* IORING_OFF_SQ_RING */
-
-  sqe = mmap(0,
-             sqelen,
-             PROT_READ | PROT_WRITE,
-             MAP_SHARED | MAP_POPULATE,
-             ringfd,
-             0x10000000ull);  /* IORING_OFF_SQES */
-
-  if (sq == MAP_FAILED || sqe == MAP_FAILED)
-    goto fail;
-
-  if (flags & UV__IORING_SETUP_SQPOLL) {
-    /* Only interested in completion events. To get notified when
-     * the kernel pulls items from the submission ring, add POLLOUT.
-     */
-    memset(&e, 0, sizeof(e));
-    e.events = POLLIN;
-    e.data.fd = ringfd;
-
-    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, ringfd, &e))
-      goto fail;
-  }
-
-  iou->sqhead = (uint32_t*) (sq + params.sq_off.head);
-  iou->sqtail = (uint32_t*) (sq + params.sq_off.tail);
-  iou->sqmask = *(uint32_t*) (sq + params.sq_off.ring_mask);
-  iou->sqarray = (uint32_t*) (sq + params.sq_off.array);
-  iou->sqflags = (uint32_t*) (sq + params.sq_off.flags);
-  iou->cqhead = (uint32_t*) (sq + params.cq_off.head);
-  iou->cqtail = (uint32_t*) (sq + params.cq_off.tail);
-  iou->cqmask = *(uint32_t*) (sq + params.cq_off.ring_mask);
-  iou->sq = sq;
-  iou->cqe = sq + params.cq_off.cqes;
-  iou->sqe = sqe;
-  iou->sqlen = sqlen;
-  iou->cqlen = cqlen;
-  iou->maxlen = maxlen;
-  iou->sqelen = sqelen;
-  iou->ringfd = ringfd;
-  iou->in_flight = 0;
-
-  for (i = 0; i <= iou->sqmask; i++)
-    iou->sqarray[i] = i;  /* Slot -> sqe identity mapping. */
-
-  return;
-
-fail:
-  if (sq != MAP_FAILED)
-    munmap(sq, maxlen);
-
-  if (sqe != MAP_FAILED)
-    munmap(sqe, sqelen);
-
-  uv__close(ringfd);
-}
-
-
-static void uv__iou_delete(struct uv__iou* iou) {
-  if (iou->ringfd != -1) {
-    munmap(iou->sq, iou->maxlen);
-    munmap(iou->sqe, iou->sqelen);
-    uv__close(iou->ringfd);
-    iou->ringfd = -1;
-  }
-}
-
-
 int uv__platform_loop_init(uv_loop_t* loop) {
-  uv__loop_internal_fields_t* lfields;
-
-  lfields = uv__get_internal_fields(loop);
-  lfields->ctl.ringfd = -1;
-  lfields->iou.ringfd = -1;
-
   loop->inotify_watchers = NULL;
   loop->inotify_fd = -1;
   loop->backend_fd = epoll_create1(O_CLOEXEC);
@@ -544,9 +214,6 @@ int uv__platform_loop_init(uv_loop_t* loop) {
   if (loop->backend_fd == -1)
     return UV__ERR(errno);
 
-  uv__iou_init(loop->backend_fd, &lfields->iou, 64, UV__IORING_SETUP_SQPOLL);
-  uv__iou_init(loop->backend_fd, &lfields->ctl, 256, 0);
-
   return 0;
 }
 
@@ -559,8 +226,6 @@ int uv__io_fork(uv_loop_t* loop) {
 
   uv__close(loop->backend_fd);
   loop->backend_fd = -1;
-
-  /* TODO(bnoordhuis) Loses items from the submission and completion rings. */
   uv__platform_loop_delete(loop);
 
   err = uv__platform_loop_init(loop);
@@ -572,62 +237,42 @@ int uv__io_fork(uv_loop_t* loop) {
 
 
 void uv__platform_loop_delete(uv_loop_t* loop) {
-  uv__loop_internal_fields_t* lfields;
-
-  lfields = uv__get_internal_fields(loop);
-  uv__iou_delete(&lfields->ctl);
-  uv__iou_delete(&lfields->iou);
-
-  if (loop->inotify_fd != -1) {
-    uv__io_stop(loop, &loop->inotify_read_watcher, POLLIN);
-    uv__close(loop->inotify_fd);
-    loop->inotify_fd = -1;
-  }
+  if (loop->inotify_fd == -1) return;
+  uv__io_stop(loop, &loop->inotify_read_watcher, POLLIN);
+  uv__close(loop->inotify_fd);
+  loop->inotify_fd = -1;
 }
 
 
-struct uv__invalidate {
-  struct epoll_event (*prep)[256];
-  struct epoll_event* events;
-  int nfds;
-};
-
-
 void uv__platform_invalidate_fd(uv_loop_t* loop, int fd) {
-  uv__loop_internal_fields_t* lfields;
-  struct uv__invalidate* inv;
+  struct epoll_event* events;
   struct epoll_event dummy;
-  int i;
+  uintptr_t i;
+  uintptr_t nfds;
 
-  lfields = uv__get_internal_fields(loop);
-  inv = lfields->inv;
+  assert(loop->watchers != NULL);
+  assert(fd >= 0);
 
-  /* Invalidate events with same file descriptor */
-  if (inv != NULL)
-    for (i = 0; i < inv->nfds; i++)
-      if (inv->events[i].data.fd == fd)
-        inv->events[i].data.fd = -1;
+  events = (struct epoll_event*) loop->watchers[loop->nwatchers];
+  nfds = (uintptr_t) loop->watchers[loop->nwatchers + 1];
+  if (events != NULL)
+    /* Invalidate events with same file descriptor */
+    for (i = 0; i < nfds; i++)
+      if (events[i].data.fd == fd)
+        events[i].data.fd = -1;
 
   /* Remove the file descriptor from the epoll.
    * This avoids a problem where the same file description remains open
    * in another process, causing repeated junk epoll events.
    *
    * We pass in a dummy epoll_event, to work around a bug in old kernels.
-   *
-   * Work around a bug in kernels 3.10 to 3.19 where passing a struct that
-   * has the EPOLLWAKEUP flag set generates spurious audit syslog warnings.
    */
-  memset(&dummy, 0, sizeof(dummy));
-
-  if (inv == NULL) {
+  if (loop->backend_fd >= 0) {
+    /* Work around a bug in kernels 3.10 to 3.19 where passing a struct that
+     * has the EPOLLWAKEUP flag set generates spurious audit syslog warnings.
+     */
+    memset(&dummy, 0, sizeof(dummy));
     epoll_ctl(loop->backend_fd, EPOLL_CTL_DEL, fd, &dummy);
-  } else {
-    uv__epoll_ctl_prep(loop->backend_fd,
-                       &lfields->ctl,
-                       inv->prep,
-                       EPOLL_CTL_DEL,
-                       fd,
-                       &dummy);
   }
 }
 
@@ -653,454 +298,27 @@ int uv__io_check_fd(uv_loop_t* loop, int fd) {
 }
 
 
-/* Caller must initialize SQE and call uv__iou_submit(). */
-static struct uv__io_uring_sqe* uv__iou_get_sqe(struct uv__iou* iou,
-                                                uv_loop_t* loop,
-                                                uv_fs_t* req) {
-  struct uv__io_uring_sqe* sqe;
-  uint32_t head;
-  uint32_t tail;
-  uint32_t mask;
-  uint32_t slot;
-
-  if (iou->ringfd == -1)
-    return NULL;
-
-  head = atomic_load_explicit((_Atomic uint32_t*) iou->sqhead,
-                              memory_order_acquire);
-  tail = *iou->sqtail;
-  mask = iou->sqmask;
-
-  if ((head & mask) == ((tail + 1) & mask))
-    return NULL;  /* No room in ring buffer. TODO(bnoordhuis) maybe flush it? */
-
-  slot = tail & mask;
-  sqe = iou->sqe;
-  sqe = &sqe[slot];
-  memset(sqe, 0, sizeof(*sqe));
-  sqe->user_data = (uintptr_t) req;
-
-  /* Pacify uv_cancel(). */
-  req->work_req.loop = loop;
-  req->work_req.work = NULL;
-  req->work_req.done = NULL;
-  QUEUE_INIT(&req->work_req.wq);
-
-  uv__req_register(loop, req);
-  iou->in_flight++;
-
-  return sqe;
-}
-
-
-static void uv__iou_submit(struct uv__iou* iou) {
-  uint32_t flags;
-
-  atomic_store_explicit((_Atomic uint32_t*) iou->sqtail,
-                        *iou->sqtail + 1,
-                        memory_order_release);
-
-  flags = atomic_load_explicit((_Atomic uint32_t*) iou->sqflags,
-                               memory_order_acquire);
-
-  if (flags & UV__IORING_SQ_NEED_WAKEUP)
-    if (uv__io_uring_enter(iou->ringfd, 0, 0, UV__IORING_ENTER_SQ_WAKEUP))
-      if (errno != EOWNERDEAD)  /* Kernel bug. Harmless, ignore. */
-        perror("libuv: io_uring_enter(wakeup)");  /* Can't happen. */
-}
-
-
-int uv__iou_fs_close(uv_loop_t* loop, uv_fs_t* req) {
-  struct uv__io_uring_sqe* sqe;
-  struct uv__iou* iou;
-
-  iou = &uv__get_internal_fields(loop)->iou;
-
-  sqe = uv__iou_get_sqe(iou, loop, req);
-  if (sqe == NULL)
-    return 0;
-
-  sqe->fd = req->file;
-  sqe->opcode = UV__IORING_OP_CLOSE;
-
-  uv__iou_submit(iou);
-
-  return 1;
-}
-
-
-int uv__iou_fs_fsync_or_fdatasync(uv_loop_t* loop,
-                                  uv_fs_t* req,
-                                  uint32_t fsync_flags) {
-  struct uv__io_uring_sqe* sqe;
-  struct uv__iou* iou;
-
-  iou = &uv__get_internal_fields(loop)->iou;
-
-  sqe = uv__iou_get_sqe(iou, loop, req);
-  if (sqe == NULL)
-    return 0;
-
-  /* Little known fact: setting seq->off and seq->len turns
-   * it into an asynchronous sync_file_range() operation.
-   */
-  sqe->fd = req->file;
-  sqe->fsync_flags = fsync_flags;
-  sqe->opcode = UV__IORING_OP_FSYNC;
-
-  uv__iou_submit(iou);
-
-  return 1;
-}
-
-
-int uv__iou_fs_open(uv_loop_t* loop, uv_fs_t* req) {
-  struct uv__io_uring_sqe* sqe;
-  struct uv__iou* iou;
-
-  iou = &uv__get_internal_fields(loop)->iou;
-
-  sqe = uv__iou_get_sqe(iou, loop, req);
-  if (sqe == NULL)
-    return 0;
-
-  sqe->addr = (uintptr_t) req->path;
-  sqe->fd = AT_FDCWD;
-  sqe->len = req->mode;
-  sqe->opcode = UV__IORING_OP_OPENAT;
-  sqe->open_flags = req->flags | O_CLOEXEC;
-
-  uv__iou_submit(iou);
-
-  return 1;
-}
-
-
-int uv__iou_fs_read_or_write(uv_loop_t* loop,
-                             uv_fs_t* req,
-                             int is_read) {
-  struct uv__io_uring_sqe* sqe;
-  struct uv__iou* iou;
-
-  /* For the moment, if iovcnt is greater than IOV_MAX, fallback to the
-   * threadpool. In the future we might take advantage of IOSQE_IO_LINK. */
-  if (req->nbufs > IOV_MAX)
-    return 0;
-
-  iou = &uv__get_internal_fields(loop)->iou;
-
-  sqe = uv__iou_get_sqe(iou, loop, req);
-  if (sqe == NULL)
-    return 0;
-
-  sqe->addr = (uintptr_t) req->bufs;
-  sqe->fd = req->file;
-  sqe->len = req->nbufs;
-  sqe->off = req->off < 0 ? -1 : req->off;
-  sqe->opcode = is_read ? UV__IORING_OP_READV : UV__IORING_OP_WRITEV;
-
-  uv__iou_submit(iou);
-
-  return 1;
-}
-
-
-int uv__iou_fs_statx(uv_loop_t* loop,
-                     uv_fs_t* req,
-                     int is_fstat,
-                     int is_lstat) {
-  struct uv__io_uring_sqe* sqe;
-  struct uv__statx* statxbuf;
-  struct uv__iou* iou;
-
-  statxbuf = uv__malloc(sizeof(*statxbuf));
-  if (statxbuf == NULL)
-    return 0;
-
-  iou = &uv__get_internal_fields(loop)->iou;
-
-  sqe = uv__iou_get_sqe(iou, loop, req);
-  if (sqe == NULL) {
-    uv__free(statxbuf);
-    return 0;
-  }
-
-  req->ptr = statxbuf;
-
-  sqe->addr = (uintptr_t) req->path;
-  sqe->addr2 = (uintptr_t) statxbuf;
-  sqe->fd = AT_FDCWD;
-  sqe->len = 0xFFF; /* STATX_BASIC_STATS + STATX_BTIME */
-  sqe->opcode = UV__IORING_OP_STATX;
-
-  if (is_fstat) {
-    sqe->addr = (uintptr_t) "";
-    sqe->fd = req->file;
-    sqe->statx_flags |= 0x1000; /* AT_EMPTY_PATH */
-  }
-
-  if (is_lstat)
-    sqe->statx_flags |= AT_SYMLINK_NOFOLLOW;
-
-  uv__iou_submit(iou);
-
-  return 1;
-}
-
-
-void uv__statx_to_stat(const struct uv__statx* statxbuf, uv_stat_t* buf) {
-  buf->st_dev = makedev(statxbuf->stx_dev_major, statxbuf->stx_dev_minor);
-  buf->st_mode = statxbuf->stx_mode;
-  buf->st_nlink = statxbuf->stx_nlink;
-  buf->st_uid = statxbuf->stx_uid;
-  buf->st_gid = statxbuf->stx_gid;
-  buf->st_rdev = makedev(statxbuf->stx_rdev_major, statxbuf->stx_rdev_minor);
-  buf->st_ino = statxbuf->stx_ino;
-  buf->st_size = statxbuf->stx_size;
-  buf->st_blksize = statxbuf->stx_blksize;
-  buf->st_blocks = statxbuf->stx_blocks;
-  buf->st_atim.tv_sec = statxbuf->stx_atime.tv_sec;
-  buf->st_atim.tv_nsec = statxbuf->stx_atime.tv_nsec;
-  buf->st_mtim.tv_sec = statxbuf->stx_mtime.tv_sec;
-  buf->st_mtim.tv_nsec = statxbuf->stx_mtime.tv_nsec;
-  buf->st_ctim.tv_sec = statxbuf->stx_ctime.tv_sec;
-  buf->st_ctim.tv_nsec = statxbuf->stx_ctime.tv_nsec;
-  buf->st_birthtim.tv_sec = statxbuf->stx_btime.tv_sec;
-  buf->st_birthtim.tv_nsec = statxbuf->stx_btime.tv_nsec;
-  buf->st_flags = 0;
-  buf->st_gen = 0;
-}
-
-
-static void uv__iou_fs_statx_post(uv_fs_t* req) {
-  struct uv__statx* statxbuf;
-  uv_stat_t* buf;
-
-  buf = &req->statbuf;
-  statxbuf = req->ptr;
-  req->ptr = NULL;
-
-  if (req->result == 0) {
-    uv__msan_unpoison(statxbuf, sizeof(*statxbuf));
-    uv__statx_to_stat(statxbuf, buf);
-    req->ptr = buf;
-  }
-
-  uv__free(statxbuf);
-}
-
-
-static void uv__poll_io_uring(uv_loop_t* loop, struct uv__iou* iou) {
-  struct uv__io_uring_cqe* cqe;
-  struct uv__io_uring_cqe* e;
-  uv_fs_t* req;
-  uint32_t head;
-  uint32_t tail;
-  uint32_t mask;
-  uint32_t i;
-  uint32_t flags;
-  int nevents;
-  int rc;
-
-  head = *iou->cqhead;
-  tail = atomic_load_explicit((_Atomic uint32_t*) iou->cqtail,
-                              memory_order_acquire);
-  mask = iou->cqmask;
-  cqe = iou->cqe;
-  nevents = 0;
-
-  for (i = head; i != tail; i++) {
-    e = &cqe[i & mask];
-
-    req = (uv_fs_t*) (uintptr_t) e->user_data;
-    assert(req->type == UV_FS);
-
-    uv__req_unregister(loop, req);
-    iou->in_flight--;
-
-    /* io_uring stores error codes as negative numbers, same as libuv. */
-    req->result = e->res;
-
-    switch (req->fs_type) {
-      case UV_FS_FSTAT:
-      case UV_FS_LSTAT:
-      case UV_FS_STAT:
-        uv__iou_fs_statx_post(req);
-        break;
-      default:  /* Squelch -Wswitch warnings. */
-        break;
-    }
-
-    uv__metrics_update_idle_time(loop);
-    req->cb(req);
-    nevents++;
-  }
-
-  atomic_store_explicit((_Atomic uint32_t*) iou->cqhead,
-                        tail,
-                        memory_order_release);
-
-  /* Check whether CQE's overflowed, if so enter the kernel to make them
-   * available. Don't grab them immediately but in the next loop iteration to
-   * avoid loop starvation. */
-  flags = atomic_load_explicit((_Atomic uint32_t*) iou->sqflags,
-                               memory_order_acquire);
-
-  if (flags & UV__IORING_SQ_CQ_OVERFLOW) {
-    do
-      rc = uv__io_uring_enter(iou->ringfd, 0, 0, UV__IORING_ENTER_GETEVENTS);
-    while (rc == -1 && errno == EINTR);
-
-    if (rc < 0)
-      perror("libuv: io_uring_enter(getevents)");  /* Can't happen. */
-  }
-
-  uv__metrics_inc_events(loop, nevents);
-  if (uv__get_internal_fields(loop)->current_timeout == 0)
-    uv__metrics_inc_events_waiting(loop, nevents);
-}
-
-
-static void uv__epoll_ctl_prep(int epollfd,
-                               struct uv__iou* ctl,
-                               struct epoll_event (*events)[256],
-                               int op,
-                               int fd,
-                               struct epoll_event* e) {
-  struct uv__io_uring_sqe* sqe;
-  struct epoll_event* pe;
-  uint32_t mask;
-  uint32_t slot;
-
-  if (ctl->ringfd == -1) {
-    if (!epoll_ctl(epollfd, op, fd, e))
-      return;
-
-    if (op == EPOLL_CTL_DEL)
-      return;  /* Ignore errors, may be racing with another thread. */
-
-    if (op != EPOLL_CTL_ADD)
-      abort();
-
-    if (errno != EEXIST)
-      abort();
-
-    /* File descriptor that's been watched before, update event mask. */
-    if (!epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, e))
-      return;
-
-    abort();
-  } else {
-    mask = ctl->sqmask;
-    slot = (*ctl->sqtail)++ & mask;
-
-    pe = &(*events)[slot];
-    *pe = *e;
-
-    sqe = ctl->sqe;
-    sqe = &sqe[slot];
-
-    memset(sqe, 0, sizeof(*sqe));
-    sqe->addr = (uintptr_t) pe;
-    sqe->fd = epollfd;
-    sqe->len = op;
-    sqe->off = fd;
-    sqe->opcode = UV__IORING_OP_EPOLL_CTL;
-    sqe->user_data = op | slot << 2 | (int64_t) fd << 32;
-
-    if ((*ctl->sqhead & mask) == (*ctl->sqtail & mask))
-      uv__epoll_ctl_flush(epollfd, ctl, events);
-  }
-}
-
-
-static void uv__epoll_ctl_flush(int epollfd,
-                                struct uv__iou* ctl,
-                                struct epoll_event (*events)[256]) {
-  struct epoll_event oldevents[256];
-  struct uv__io_uring_cqe* cqe;
-  uint32_t oldslot;
-  uint32_t slot;
-  uint32_t n;
-  int fd;
-  int op;
-  int rc;
-
-  STATIC_ASSERT(sizeof(oldevents) == sizeof(*events));
-  assert(ctl->ringfd != -1);
-  assert(*ctl->sqhead != *ctl->sqtail);
-
-  n = *ctl->sqtail - *ctl->sqhead;
-  do
-    rc = uv__io_uring_enter(ctl->ringfd, n, n, UV__IORING_ENTER_GETEVENTS);
-  while (rc == -1 && errno == EINTR);
-
-  if (rc < 0)
-    perror("libuv: io_uring_enter(getevents)");  /* Can't happen. */
-
-  if (rc != (int) n)
-    abort();
-
-  assert(*ctl->sqhead == *ctl->sqtail);
-
-  memcpy(oldevents, *events, sizeof(*events));
-
-  /* Failed submissions are either EPOLL_CTL_DEL commands for file descriptors
-   * that have been closed, or EPOLL_CTL_ADD commands for file descriptors
-   * that we are already watching. Ignore the former and retry the latter
-   * with EPOLL_CTL_MOD.
-   */
-  while (*ctl->cqhead != *ctl->cqtail) {
-    slot = (*ctl->cqhead)++ & ctl->cqmask;
-
-    cqe = ctl->cqe;
-    cqe = &cqe[slot];
-
-    if (cqe->res == 0)
-      continue;
-
-    fd = cqe->user_data >> 32;
-    op = 3 & cqe->user_data;
-    oldslot = 255 & (cqe->user_data >> 2);
-
-    if (op == EPOLL_CTL_DEL)
-      continue;
-
-    if (op != EPOLL_CTL_ADD)
-      abort();
-
-    if (cqe->res != -EEXIST)
-      abort();
-
-    uv__epoll_ctl_prep(epollfd,
-                       ctl,
-                       events,
-                       EPOLL_CTL_MOD,
-                       fd,
-                       &oldevents[oldslot]);
-  }
-}
-
-
 void uv__io_poll(uv_loop_t* loop, int timeout) {
-  uv__loop_internal_fields_t* lfields;
+  /* A bug in kernels < 2.6.37 makes timeouts larger than ~30 minutes
+   * effectively infinite on 32 bits architectures.  To avoid blocking
+   * indefinitely, we cap the timeout and poll again if necessary.
+   *
+   * Note that "30 minutes" is a simplification because it depends on
+   * the value of CONFIG_HZ.  The magic constant assumes CONFIG_HZ=1200,
+   * that being the largest value I have seen in the wild (and only once.)
+   */
+  static const int max_safe_timeout = 1789569;
   struct epoll_event events[1024];
-  struct epoll_event prep[256];
-  struct uv__invalidate inv;
   struct epoll_event* pe;
   struct epoll_event e;
-  struct uv__iou* ctl;
-  struct uv__iou* iou;
   int real_timeout;
   QUEUE* q;
   uv__io_t* w;
   sigset_t* sigmask;
   sigset_t sigset;
   uint64_t base;
-  int have_iou_events;
   int have_signals;
   int nevents;
-  int epollfd;
   int count;
   int nfds;
   int fd;
@@ -1109,9 +327,47 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
   int user_timeout;
   int reset_timeout;
 
-  lfields = uv__get_internal_fields(loop);
-  ctl = &lfields->ctl;
-  iou = &lfields->iou;
+  if (loop->nfds == 0) {
+    assert(QUEUE_EMPTY(&loop->watcher_queue));
+    return;
+  }
+
+  memset(&e, 0, sizeof(e));
+
+  while (!QUEUE_EMPTY(&loop->watcher_queue)) {
+    q = QUEUE_HEAD(&loop->watcher_queue);
+    QUEUE_REMOVE(q);
+    QUEUE_INIT(q);
+
+    w = QUEUE_DATA(q, uv__io_t, watcher_queue);
+    assert(w->pevents != 0);
+    assert(w->fd >= 0);
+    assert(w->fd < (int) loop->nwatchers);
+
+    e.events = w->pevents;
+    e.data.fd = w->fd;
+
+    if (w->events == 0)
+      op = EPOLL_CTL_ADD;
+    else
+      op = EPOLL_CTL_MOD;
+
+    /* XXX Future optimization: do EPOLL_CTL_MOD lazily if we stop watching
+     * events, skip the syscall and squelch the events after epoll_wait().
+     */
+    if (epoll_ctl(loop->backend_fd, op, w->fd, &e)) {
+      if (errno != EEXIST)
+        abort();
+
+      assert(op == EPOLL_CTL_ADD);
+
+      /* We've reactivated a file descriptor that's been watched before. */
+      if (epoll_ctl(loop->backend_fd, EPOLL_CTL_MOD, w->fd, &e))
+        abort();
+    }
+
+    w->events = w->pevents;
+  }
 
   sigmask = NULL;
   if (loop->flags & UV_LOOP_BLOCK_SIGPROF) {
@@ -1125,7 +381,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
   count = 48; /* Benchmarks suggest this gives the best throughput. */
   real_timeout = timeout;
 
-  if (lfields->flags & UV_METRICS_IDLE_TIME) {
+  if (uv__get_internal_fields(loop)->flags & UV_METRICS_IDLE_TIME) {
     reset_timeout = 1;
     user_timeout = timeout;
     timeout = 0;
@@ -1134,56 +390,24 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     user_timeout = 0;
   }
 
-  epollfd = loop->backend_fd;
-
-  memset(&e, 0, sizeof(e));
-
-  while (!QUEUE_EMPTY(&loop->watcher_queue)) {
-    q = QUEUE_HEAD(&loop->watcher_queue);
-    w = QUEUE_DATA(q, uv__io_t, watcher_queue);
-    QUEUE_REMOVE(q);
-    QUEUE_INIT(q);
-
-    op = EPOLL_CTL_MOD;
-    if (w->events == 0)
-      op = EPOLL_CTL_ADD;
-
-    w->events = w->pevents;
-    e.events = w->pevents;
-    e.data.fd = w->fd;
-
-    uv__epoll_ctl_prep(epollfd, ctl, &prep, op, w->fd, &e);
-  }
-
-  inv.events = events;
-  inv.prep = &prep;
-  inv.nfds = -1;
-
   for (;;) {
-    if (loop->nfds == 0)
-      if (iou->in_flight == 0)
-        break;
-
-    /* All event mask mutations should be visible to the kernel before
-     * we enter epoll_pwait().
-     */
-    if (ctl->ringfd != -1)
-      while (*ctl->sqhead != *ctl->sqtail)
-        uv__epoll_ctl_flush(epollfd, ctl, &prep);
-
     /* Only need to set the provider_entry_time if timeout != 0. The function
      * will return early if the loop isn't configured with UV_METRICS_IDLE_TIME.
      */
     if (timeout != 0)
       uv__metrics_set_provider_entry_time(loop);
 
-    /* Store the current timeout in a location that's globally accessible so
-     * other locations like uv__work_done() can determine whether the queue
-     * of events in the callback were waiting when poll was called.
+    /* See the comment for max_safe_timeout for an explanation of why
+     * this is necessary.  Executive summary: kernel bug workaround.
      */
-    lfields->current_timeout = timeout;
+    if (sizeof(int32_t) == sizeof(long) && timeout >= max_safe_timeout)
+      timeout = max_safe_timeout;
 
-    nfds = epoll_pwait(epollfd, events, ARRAY_SIZE(events), timeout, sigmask);
+    nfds = epoll_pwait(loop->backend_fd,
+                       events,
+                       ARRAY_SIZE(events),
+                       timeout,
+                       sigmask);
 
     /* Update loop->time unconditionally. It's tempting to skip the update when
      * timeout == 0 (i.e. non-blocking poll) but there is no guarantee that the
@@ -1203,7 +427,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
         continue;
 
       if (timeout == 0)
-        break;
+        return;
 
       /* We may have been inside the system call for longer than |timeout|
        * milliseconds so we need to update the timestamp to avoid drift.
@@ -1224,18 +448,27 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
         continue;
 
       if (timeout == 0)
-        break;
+        return;
 
       /* Interrupted by a signal. Update timeout and poll again. */
       goto update_timeout;
     }
 
-    have_iou_events = 0;
     have_signals = 0;
     nevents = 0;
 
-    inv.nfds = nfds;
-    lfields->inv = &inv;
+    {
+      /* Squelch a -Waddress-of-packed-member warning with gcc >= 9. */
+      union {
+        struct epoll_event* events;
+        uv__io_t* watchers;
+      } x;
+
+      x.events = events;
+      assert(loop->watchers != NULL);
+      loop->watchers[loop->nwatchers] = x.watchers;
+      loop->watchers[loop->nwatchers + 1] = (void*) (uintptr_t) nfds;
+    }
 
     for (i = 0; i < nfds; i++) {
       pe = events + i;
@@ -1245,12 +478,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
       if (fd == -1)
         continue;
 
-      if (fd == iou->ringfd) {
-        uv__poll_io_uring(loop, iou);
-        have_iou_events = 1;
-        continue;
-      }
-
       assert(fd >= 0);
       assert((unsigned) fd < loop->nwatchers);
 
@@ -1262,7 +489,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
          * Ignore all errors because we may be racing with another thread
          * when the file descriptor is closed.
          */
-        uv__epoll_ctl_prep(epollfd, ctl, &prep, EPOLL_CTL_DEL, fd, pe);
+        epoll_ctl(loop->backend_fd, EPOLL_CTL_DEL, fd, pe);
         continue;
       }
 
@@ -1319,13 +546,11 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
       loop->signal_io_watcher.cb(loop, &loop->signal_io_watcher, POLLIN);
     }
 
-    lfields->inv = NULL;
-
-    if (have_iou_events != 0)
-      break;  /* Event loop should cycle now so don't poll again. */
+    loop->watchers[loop->nwatchers] = NULL;
+    loop->watchers[loop->nwatchers + 1] = NULL;
 
     if (have_signals != 0)
-      break;  /* Event loop should cycle now so don't poll again. */
+      return;  /* Event loop should cycle now so don't poll again. */
 
     if (nevents != 0) {
       if (nfds == ARRAY_SIZE(events) && --count != 0) {
@@ -1333,11 +558,11 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
         timeout = 0;
         continue;
       }
-      break;
+      return;
     }
 
     if (timeout == 0)
-      break;
+      return;
 
     if (timeout == -1)
       continue;
@@ -1347,14 +572,10 @@ update_timeout:
 
     real_timeout -= (loop->time - base);
     if (real_timeout <= 0)
-      break;
+      return;
 
     timeout = real_timeout;
   }
-
-  if (ctl->ringfd != -1)
-    while (*ctl->sqhead != *ctl->sqtail)
-      uv__epoll_ctl_flush(epollfd, ctl, &prep);
 }
 
 uint64_t uv__hrtime(uv_clocktype_t type) {
@@ -1867,7 +1088,7 @@ static uint64_t uv__read_uint64(const char* filename) {
   if (0 == uv__slurp(filename, buf, sizeof(buf)))
     if (1 != sscanf(buf, "%" PRIu64, &rc))
       if (0 == strcmp(buf, "max\n"))
-        rc = UINT64_MAX;
+        rc = ~0ull;
 
   return rc;
 }
@@ -1903,7 +1124,6 @@ static void uv__get_cgroup1_memory_limits(char buf[static 1024], uint64_t* high,
   char filename[4097];
   char* p;
   int n;
-  uint64_t cgroup1_max;
 
   /* Find out where the controller is mounted. */
   p = uv__cgroup1_find_memory_controller(buf, &n);
@@ -1920,22 +1140,12 @@ static void uv__get_cgroup1_memory_limits(char buf[static 1024], uint64_t* high,
      * as indicated by uv__read_uint64 returning 0.
      */
      if (*high != 0 && *max != 0)
-       goto update_limits;
+       return;
   }
 
   /* Fall back to the limits of the global memory controller. */
   *high = uv__read_uint64("/sys/fs/cgroup/memory/memory.soft_limit_in_bytes");
   *max = uv__read_uint64("/sys/fs/cgroup/memory/memory.limit_in_bytes");
-
-  /* uv__read_uint64 detects cgroup2's "max", so we need to separately detect
-   * cgroup1's maximum value (which is derived from LONG_MAX and PAGE_SIZE).
-   */
-update_limits:
-  cgroup1_max = LONG_MAX & ~(sysconf(_SC_PAGESIZE) - 1);
-  if (*high == cgroup1_max)
-    *high = UINT64_MAX;
-  if (*max == cgroup1_max)
-    *max = UINT64_MAX;
 }
 
 static void uv__get_cgroup2_memory_limits(char buf[static 1024], uint64_t* high,
diff --git a/deps/uv/src/unix/os390.c b/deps/uv/src/unix/os390.c
index a87c2d77faf..3954b2c2753 100644
--- a/deps/uv/src/unix/os390.c
+++ b/deps/uv/src/unix/os390.c
@@ -808,7 +808,6 @@ static int os390_message_queue_handler(uv__os390_epoll* ep) {
 
 void uv__io_poll(uv_loop_t* loop, int timeout) {
   static const int max_safe_timeout = 1789569;
-  uv__loop_internal_fields_t* lfields;
   struct epoll_event events[1024];
   struct epoll_event* pe;
   struct epoll_event e;
@@ -831,8 +830,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     return;
   }
 
-  lfields = uv__get_internal_fields(loop);
-
   while (!QUEUE_EMPTY(&loop->watcher_queue)) {
     uv_stream_t* stream;
 
@@ -880,7 +877,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
   int nevents = 0;
   have_signals = 0;
 
-  if (lfields->flags & UV_METRICS_IDLE_TIME) {
+  if (uv__get_internal_fields(loop)->flags & UV_METRICS_IDLE_TIME) {
     reset_timeout = 1;
     user_timeout = timeout;
     timeout = 0;
@@ -899,12 +896,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     if (sizeof(int32_t) == sizeof(long) && timeout >= max_safe_timeout)
       timeout = max_safe_timeout;
 
-    /* Store the current timeout in a location that's globally accessible so
-     * other locations like uv__work_done() can determine whether the queue
-     * of events in the callback were waiting when poll was called.
-     */
-    lfields->current_timeout = timeout;
-
     nfds = epoll_wait(loop->ep, events,
                       ARRAY_SIZE(events), timeout);
 
diff --git a/deps/uv/src/unix/posix-poll.c b/deps/uv/src/unix/posix-poll.c
index 7e7de86845d..711780ece8d 100644
--- a/deps/uv/src/unix/posix-poll.c
+++ b/deps/uv/src/unix/posix-poll.c
@@ -132,7 +132,6 @@ static void uv__pollfds_del(uv_loop_t* loop, int fd) {
 
 
 void uv__io_poll(uv_loop_t* loop, int timeout) {
-  uv__loop_internal_fields_t* lfields;
   sigset_t* pset;
   sigset_t set;
   uint64_t time_base;
@@ -153,8 +152,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     return;
   }
 
-  lfields = uv__get_internal_fields(loop);
-
   /* Take queued watchers and add their fds to our poll fds array.  */
   while (!QUEUE_EMPTY(&loop->watcher_queue)) {
     q = QUEUE_HEAD(&loop->watcher_queue);
@@ -182,7 +179,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
   assert(timeout >= -1);
   time_base = loop->time;
 
-  if (lfields->flags & UV_METRICS_IDLE_TIME) {
+  if (uv__get_internal_fields(loop)->flags & UV_METRICS_IDLE_TIME) {
     reset_timeout = 1;
     user_timeout = timeout;
     timeout = 0;
@@ -201,12 +198,6 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     if (timeout != 0)
       uv__metrics_set_provider_entry_time(loop);
 
-    /* Store the current timeout in a location that's globally accessible so
-     * other locations like uv__work_done() can determine whether the queue
-     * of events in the callback were waiting when poll was called.
-     */
-    lfields->current_timeout = timeout;
-
     if (pset != NULL)
       if (pthread_sigmask(SIG_BLOCK, pset, NULL))
         abort();
diff --git a/deps/uv/src/uv-common.h b/deps/uv/src/uv-common.h
index decde5362c8..2720121addc 100644
--- a/deps/uv/src/uv-common.h
+++ b/deps/uv/src/uv-common.h
@@ -396,37 +396,9 @@ struct uv__loop_metrics_s {
 void uv__metrics_update_idle_time(uv_loop_t* loop);
 void uv__metrics_set_provider_entry_time(uv_loop_t* loop);
 
-#ifdef __linux__
-struct uv__iou {
-  uint32_t* sqhead;
-  uint32_t* sqtail;
-  uint32_t* sqarray;
-  uint32_t sqmask;
-  uint32_t* sqflags;
-  uint32_t* cqhead;
-  uint32_t* cqtail;
-  uint32_t cqmask;
-  void* sq;   /* pointer to munmap() on event loop teardown */
-  void* cqe;  /* pointer to array of struct uv__io_uring_cqe */
-  void* sqe;  /* pointer to array of struct uv__io_uring_sqe */
-  size_t sqlen;
-  size_t cqlen;
-  size_t maxlen;
-  size_t sqelen;
-  int ringfd;
-  uint32_t in_flight;
-};
-#endif  /* __linux__ */
-
 struct uv__loop_internal_fields_s {
   unsigned int flags;
   uv__loop_metrics_t loop_metrics;
-  int current_timeout;
-#ifdef __linux__
-  struct uv__iou ctl;
-  struct uv__iou iou;
-  void* inv;  /* used by uv__platform_invalidate_fd() */
-#endif  /* __linux__ */
 };
 
 #endif /* UV_COMMON_H_ */
diff --git a/deps/uv/src/win/core.c b/deps/uv/src/win/core.c
index 9a3be58849a..e4041ec86a6 100644
--- a/deps/uv/src/win/core.c
+++ b/deps/uv/src/win/core.c
@@ -424,7 +424,6 @@ int uv_backend_timeout(const uv_loop_t* loop) {
 
 
 static void uv__poll_wine(uv_loop_t* loop, DWORD timeout) {
-  uv__loop_internal_fields_t* lfields;
   DWORD bytes;
   ULONG_PTR key;
   OVERLAPPED* overlapped;
@@ -434,10 +433,9 @@ static void uv__poll_wine(uv_loop_t* loop, DWORD timeout) {
   uint64_t user_timeout;
   int reset_timeout;
 
-  lfields = uv__get_internal_fields(loop);
   timeout_time = loop->time + timeout;
 
-  if (lfields->flags & UV_METRICS_IDLE_TIME) {
+  if (uv__get_internal_fields(loop)->flags & UV_METRICS_IDLE_TIME) {
     reset_timeout = 1;
     user_timeout = timeout;
     timeout = 0;
@@ -452,12 +450,6 @@ static void uv__poll_wine(uv_loop_t* loop, DWORD timeout) {
     if (timeout != 0)
       uv__metrics_set_provider_entry_time(loop);
 
-    /* Store the current timeout in a location that's globally accessible so
-     * other locations like uv__work_done() can determine whether the queue
-     * of events in the callback were waiting when poll was called.
-     */
-    lfields->current_timeout = timeout;
-
     GetQueuedCompletionStatus(loop->iocp,
                               &bytes,
                               &key,
@@ -515,7 +507,6 @@ static void uv__poll_wine(uv_loop_t* loop, DWORD timeout) {
 
 
 static void uv__poll(uv_loop_t* loop, DWORD timeout) {
-  uv__loop_internal_fields_t* lfields;
   BOOL success;
   uv_req_t* req;
   OVERLAPPED_ENTRY overlappeds[128];
@@ -527,10 +518,9 @@ static void uv__poll(uv_loop_t* loop, DWORD timeout) {
   uint64_t actual_timeout;
   int reset_timeout;
 
-  lfields = uv__get_internal_fields(loop);
   timeout_time = loop->time + timeout;
 
-  if (lfields->flags & UV_METRICS_IDLE_TIME) {
+  if (uv__get_internal_fields(loop)->flags & UV_METRICS_IDLE_TIME) {
     reset_timeout = 1;
     user_timeout = timeout;
     timeout = 0;
@@ -547,12 +537,6 @@ static void uv__poll(uv_loop_t* loop, DWORD timeout) {
     if (timeout != 0)
       uv__metrics_set_provider_entry_time(loop);
 
-    /* Store the current timeout in a location that's globally accessible so
-     * other locations like uv__work_done() can determine whether the queue
-     * of events in the callback were waiting when poll was called.
-     */
-    lfields->current_timeout = timeout;
-
     success = pGetQueuedCompletionStatusEx(loop->iocp,
                                            overlappeds,
                                            ARRAY_SIZE(overlappeds),