mv contrib/cmd tests/cmd (except memfd-bind)

The following commands are moved from `contrib/cmd` to `tests/cmd`:
- fs-idmap
- pidfd-kill
- recvtty
- remap-rootfs
- sd-helper
- seccompagent

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

tests/cmd/pidfd-kill/pidfd-kill.go

@@ -0,0 +1,114 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"os"
+	"os/signal"
+
+	"github.com/urfave/cli"
+	"golang.org/x/sys/unix"
+
+	"github.com/opencontainers/runc/libcontainer/utils"
+)
+
+const (
+	usage = `Open Container Initiative tests/cmd/pidfd-kill
+
+pidfd-kill is an implementation of a consumer of runC's --pidfd-socket API.
+After received SIGTERM, pidfd-kill sends the given signal to init process by
+pidfd received from --pidfd-socket.
+
+To use pidfd-kill, just specify a socket path at which you want to receive
+pidfd:
+
+    $ pidfd-kill [--signal KILL] socket.sock
+`
+)
+
+func main() {
+	app := cli.NewApp()
+	app.Name = "pidfd-kill"
+	app.Usage = usage
+
+	app.Flags = []cli.Flag{
+		cli.StringFlag{
+			Name:  "signal",
+			Value: "SIGKILL",
+			Usage: "Signal to send to the init process",
+		},
+		cli.StringFlag{
+			Name:  "pid-file",
+			Value: "",
+			Usage: "Path to write the pidfd-kill process ID to",
+		},
+	}
+
+	app.Action = func(ctx *cli.Context) error {
+		args := ctx.Args()
+		if len(args) != 1 {
+			return errors.New("required a single socket path")
+		}
+
+		socketFile := ctx.Args()[0]
+
+		pidFile := ctx.String("pid-file")
+		if pidFile != "" {
+			pid := fmt.Sprintf("%d\n", os.Getpid())
+			if err := os.WriteFile(pidFile, []byte(pid), 0o644); err != nil {
+				return err
+			}
+			defer os.Remove(pidFile)
+		}
+
+		sigStr := ctx.String("signal")
+		if sigStr == "" {
+			sigStr = "SIGKILL"
+		}
+		sig := unix.SignalNum(sigStr)
+
+		pidfdFile, err := recvPidfd(socketFile)
+		if err != nil {
+			return err
+		}
+		defer pidfdFile.Close()
+
+		signalCh := make(chan os.Signal, 16)
+		signal.Notify(signalCh, unix.SIGTERM)
+		<-signalCh
+
+		return unix.PidfdSendSignal(int(pidfdFile.Fd()), sig, nil, 0)
+	}
+	if err := app.Run(os.Args); err != nil {
+		fmt.Fprintln(os.Stderr, "fatal error:", err)
+		os.Exit(1)
+	}
+}
+
+func recvPidfd(socketFile string) (*os.File, error) {
+	ln, err := net.Listen("unix", socketFile)
+	if err != nil {
+		return nil, err
+	}
+	defer ln.Close()
+
+	conn, err := ln.Accept()
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+
+	unixconn, ok := conn.(*net.UnixConn)
+	if !ok {
+		return nil, errors.New("failed to cast to unixconn")
+	}
+
+	socket, err := unixconn.File()
+	if err != nil {
+		return nil, err
+	}
+	defer socket.Close()
+
+	return utils.RecvFile(socket)
+}