Add a runtime config

This adds support for a runtime configuration file that can do:
- `mkdir` to make a directory at runtime, eg in `/var` or `/tmp`, to avoid workarounds
- `interface` that can create network interfaces in a container or move them
- `bindNS` that can bind mount namespaces of an `onboot` container to a file so a service can be started in that namespace.

It merges the `service` and `onboot` tools (in `init`) to avoid duplication. This also saves some size for
eg LCOW which did not use the `onboot` code in `runc`.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

pkg/init/cmd/service/main.go

@@ -0,0 +1,96 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	defaultSocket     = "/run/containerd/containerd.sock"
+	defaultPath       = "/containers/services"
+	defaultContainerd = "/usr/bin/containerd"
+	installPath       = "/usr/bin/service"
+	onbootPath        = "/containers/onboot"
+	shutdownPath      = "/containers/onshutdown"
+)
+
+var (
+	defaultLogFormatter = &log.TextFormatter{}
+)
+
+// infoFormatter overrides the default format for Info() log events to
+// provide an easier to read output
+type infoFormatter struct {
+}
+
+func (f *infoFormatter) Format(entry *log.Entry) ([]byte, error) {
+	if entry.Level == log.InfoLevel {
+		return append([]byte(entry.Message), '\n'), nil
+	}
+	return defaultLogFormatter.Format(entry)
+}
+
+func main() {
+	flag.Usage = func() {
+		fmt.Printf("USAGE: %s [options] COMMAND\n\n", filepath.Base(os.Args[0]))
+		fmt.Printf("Commands:\n")
+		fmt.Printf("  system-init Prepare the system at start of day\n")
+		fmt.Printf("  start       Start a service\n")
+		fmt.Printf("  help        Print this message\n")
+		fmt.Printf("\n")
+		fmt.Printf("Run '%s COMMAND --help' for more information on the command\n", filepath.Base(os.Args[0]))
+		fmt.Printf("\n")
+		fmt.Printf("Options:\n")
+		flag.PrintDefaults()
+	}
+	flagQuiet := flag.Bool("q", false, "Quiet execution")
+	flagVerbose := flag.Bool("v", false, "Verbose execution")
+
+	// Set up logging
+	log.SetFormatter(new(infoFormatter))
+	log.SetLevel(log.InfoLevel)
+	flag.Parse()
+	if *flagQuiet && *flagVerbose {
+		fmt.Printf("Can't set quiet and verbose flag at the same time\n")
+		os.Exit(1)
+	}
+	if *flagQuiet {
+		log.SetLevel(log.ErrorLevel)
+	}
+	if *flagVerbose {
+		// Switch back to the standard formatter
+		log.SetFormatter(defaultLogFormatter)
+		log.SetLevel(log.DebugLevel)
+	}
+
+	args := flag.Args()
+	if len(args) < 1 {
+		// check if called form startup scripts
+		command := os.Args[0]
+		switch {
+		case strings.Contains(command, "onboot"):
+			os.Exit(runcInit(onbootPath))
+		case strings.Contains(command, "onshutdown"):
+			os.Exit(runcInit(shutdownPath))
+		case strings.Contains(command, "containerd"):
+			systemInitCmd([]string{})
+			os.Exit(0)
+		}
+	}
+
+	switch args[0] {
+	case "start":
+		startCmd(args[1:])
+	case "system-init":
+		systemInitCmd(args[1:])
+	default:
+		fmt.Printf("%q is not valid command.\n\n", args[0])
+		flag.Usage()
+		os.Exit(1)
+	}
+}