Move Linux client & common packages into a public repo.

logtail/filch/filch_unix.go

@@ -0,0 +1,30 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//+build !windows
+
+package filch
+
+import (
+	"os"
+	"syscall"
+)
+
+func saveStderr() (*os.File, error) {
+	fd, err := syscall.Dup(stderrFD)
+	if err != nil {
+		return nil, err
+	}
+	return os.NewFile(uintptr(fd), "stderr"), nil
+}
+
+func unsaveStderr(f *os.File) error {
+	err := dup2Stderr(f)
+	f.Close()
+	return err
+}
+
+func dup2Stderr(f *os.File) error {
+	return syscall.Dup2(int(f.Fd()), stderrFD)
+}