runtime: utilize EVFILT_USER to wake up kevent for kqueue

Fixes #66760

Change-Id: I6ba5bc5b00506b66cb8dc3984a61f32a6358d9bc
Reviewed-on: https://go-review.googlesource.com/c/go/+/577895
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Andy Pan <panjf2000@gmail.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

1 files changed, 73 insertions, 0 deletions

diff --git a/src/runtime/netpoll_kqueue_pipe.go b/src/runtime/netpoll_kqueue_pipe.go
new file mode 100644
index 0000000000..98f73e84d2
--- /dev/null
+++ b/src/runtime/netpoll_kqueue_pipe.go
@@ -0,0 +1,73 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build netbsd || openbsd
+
+package runtime
+
+import "unsafe"
+
+// TODO(panjf2000): NetBSD didn't implement EVFILT_USER for user-established events
+// until NetBSD 10.0, check out https://www.netbsd.org/releases/formal-10/NetBSD-10.0.html
+// Therefore we use the pipe to wake up the kevent on NetBSD at this point. Get back here
+// and switch to EVFILT_USER when we bump up the minimal requirement of NetBSD to 10.0.
+// Alternatively, maybe we can use EVFILT_USER on the NetBSD by checking the kernel version
+// via uname(3) and fall back to the pipe if the kernel version is older than 10.0.
+
+var netpollBreakRd, netpollBreakWr uintptr // for netpollBreak
+
+func addWakeupEvent(kq int32) {
+	r, w, errno := nonblockingPipe()
+	if errno != 0 {
+		println("runtime: pipe failed with", -errno)
+		throw("runtime: pipe failed")
+	}
+	ev := keventt{
+		filter: _EVFILT_READ,
+		flags:  _EV_ADD,
+	}
+	*(*uintptr)(unsafe.Pointer(&ev.ident)) = uintptr(r)
+	n := kevent(kq, &ev, 1, nil, 0, nil)
+	if n < 0 {
+		println("runtime: kevent failed with", -n)
+		throw("runtime: kevent failed")
+	}
+	netpollBreakRd = uintptr(r)
+	netpollBreakWr = uintptr(w)
+}
+
+func wakeNetpoll(_ int32) {
+	for {
+		var b byte
+		n := write(netpollBreakWr, unsafe.Pointer(&b), 1)
+		if n == 1 || n == -_EAGAIN {
+			break
+		}
+		if n == -_EINTR {
+			continue
+		}
+		println("runtime: netpollBreak write failed with", -n)
+		throw("runtime: netpollBreak write failed")
+	}
+}
+
+func isWakeup(ev *keventt) bool {
+	if uintptr(ev.ident) == netpollBreakRd {
+		if ev.filter == _EVFILT_READ {
+			return true
+		}
+		println("runtime: netpoll: break fd ready for", ev.filter)
+		throw("runtime: netpoll: break fd ready for something unexpected")
+	}
+	return false
+}
+
+func drainWakeupEvent(_ int32) {
+	var buf [16]byte
+	read(int32(netpollBreakRd), noescape(unsafe.Pointer(&buf[0])), int32(len(buf)))
+}
+
+func netpollIsPollDescriptor(fd uintptr) bool {
+	return fd == uintptr(kq) || fd == netpollBreakRd || fd == netpollBreakWr
+}