net: update SOCK_CLOEXEC comment

For #45964
For #59359

Change-Id: I7fd295a096e5776102e057789d157da681df9073
Reviewed-on: https://go-review.googlesource.com/c/go/+/501939
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: ianlancetaylor

src/net/sock_cloexec.go

@@ -19,11 +19,9 @@ import (
 // descriptor as nonblocking and close-on-exec.
 func sysSocket(family, sotype, proto int) (int, error) {
 	s, err := socketFunc(family, sotype|syscall.SOCK_NONBLOCK|syscall.SOCK_CLOEXEC, proto)
-	// On Linux the SOCK_NONBLOCK and SOCK_CLOEXEC flags were
-	// introduced in 2.6.27 kernel and on FreeBSD both flags were
-	// introduced in 10 kernel. If we get an EINVAL error on Linux
-	// or EPROTONOSUPPORT error on FreeBSD, fall back to using
-	// socket without them.
+	// TODO: We can remove the fallback on Linux and *BSD,
+	// as currently supported versions all support accept4
+	// with SOCK_CLOEXEC, but Solaris does not. See issue #59359.
 	switch err {
 	case nil:
 		return s, nil