internal/poll, net, syscall: use accept4 on illumos

Illumos supports the accept4 syscall, use it in internal/poll.accept
like on other platforms.

Add Accept4 to package syscall despite the package being frozen. The
other option would have been to add this to internal/syscall/unix, but
adding it to syscall avoids duplicating a lot of code in internal/poll
and net/internal/socktest. Also, all other platforms supporting the
accept4 syscall already export Accept4.

Follow CL 97196, CL 40895 and CL 94295

Change-Id: I13b32f0163a683840c02b16722730d9dfdb98f56
Reviewed-on: https://go-review.googlesource.com/c/go/+/256101
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/internal/poll/hook_cloexec.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build dragonfly freebsd linux netbsd openbsd
+// +build dragonfly freebsd illumos linux netbsd openbsd
 
 package poll
 

src/internal/poll/sock_cloexec.go

@@ -5,7 +5,7 @@
 // This file implements sysSocket and accept for platforms that
 // provide a fast path for setting SetNonblock and CloseOnExec.
 
-// +build dragonfly freebsd linux netbsd openbsd
+// +build dragonfly freebsd illumos linux netbsd openbsd
 
 package poll
 

src/internal/poll/sys_cloexec.go

@@ -5,7 +5,7 @@
 // This file implements sysSocket and accept for platforms that do not
 // provide a fast path for setting SetNonblock and CloseOnExec.
 
-// +build aix darwin js,wasm solaris
+// +build aix darwin js,wasm solaris,!illumos
 
 package poll
 

src/net/internal/socktest/sys_cloexec.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build dragonfly freebsd linux netbsd openbsd
+// +build dragonfly freebsd illumos linux netbsd openbsd
 
 package socktest
 

src/net/main_cloexec_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build dragonfly freebsd linux netbsd openbsd
+// +build dragonfly freebsd illumos linux netbsd openbsd
 
 package net
 

src/net/sock_cloexec.go

@@ -5,7 +5,7 @@
 // This file implements sysSocket and accept for platforms that
 // provide a fast path for setting SetNonblock and CloseOnExec.
 
-// +build dragonfly freebsd linux netbsd openbsd
+// +build dragonfly freebsd illumos linux netbsd openbsd
 
 package net
 

src/net/sys_cloexec.go

@@ -5,7 +5,7 @@
 // This file implements sysSocket and accept for platforms that do not
 // provide a fast path for setting SetNonblock and CloseOnExec.
 
-// +build aix darwin solaris
+// +build aix darwin solaris,!illumos
 
 package net
 

src/runtime/cgo/cgo.go

@@ -21,6 +21,7 @@ package cgo
 #cgo openbsd LDFLAGS: -lpthread
 #cgo aix LDFLAGS: -Wl,-berok
 #cgo solaris LDFLAGS: -lxnet
+#cgo illumos LDFLAGS: -lsocket
 
 // Issue 35247.
 #cgo darwin CFLAGS: -Wno-nullability-completeness

src/syscall/syscall_illumos.go

@@ -10,11 +10,34 @@ package syscall
 
 import "unsafe"
 
+//go:cgo_import_dynamic libc_accept4 accept4 "libsocket.so"
 //go:cgo_import_dynamic libc_flock flock "libc.so"
 
+//go:linkname procAccept4 libc_accept4
 //go:linkname procFlock libc_flock
 
-var procFlock libcFunc
+var (
+	procAccept4,
+	procFlock libcFunc
+)
+
+func Accept4(fd int, flags int) (int, Sockaddr, error) {
+	var rsa RawSockaddrAny
+	var addrlen _Socklen = SizeofSockaddrAny
+	nfd, _, errno := sysvicall6(uintptr(unsafe.Pointer(&procAccept4)), 4, uintptr(fd), uintptr(unsafe.Pointer(&rsa)), uintptr(unsafe.Pointer(&addrlen)), uintptr(flags), 0, 0)
+	if errno != 0 {
+		return 0, nil, errno
+	}
+	if addrlen > SizeofSockaddrAny {
+		panic("RawSockaddrAny too small")
+	}
+	sa, err := anyToSockaddr(&rsa)
+	if err != nil {
+		Close(int(nfd))
+		return 0, nil, err
+	}
+	return int(nfd), sa, nil
+}
 
 func Flock(fd int, how int) error {
 	_, _, errno := sysvicall6(uintptr(unsafe.Pointer(&procFlock)), 2, uintptr(fd), uintptr(how), 0, 0, 0, 0)