Add nsenter command

cmd/nsenter/nsenter.go

@@ -0,0 +1,50 @@
+package nsenter
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"os/exec"
+	"strconv"
+	"syscall"
+
+	"github.com/USTC-vlab/vct/pkg/cgroup"
+	"github.com/spf13/cobra"
+)
+
+func nsenter(id string) error {
+	f, err := cgroup.OpenLXC(id, "ns/init.scope/cgroup.procs")
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	s := bufio.NewScanner(f)
+	if !s.Scan() {
+		return fmt.Errorf("empty cgroup file %s", f.Name())
+	}
+	args := []string{"nsenter", "-a", "-t", s.Text()}
+	path, err := exec.LookPath(args[0])
+	if err != nil {
+		return err
+	}
+	return syscall.Exec(path, args, os.Environ())
+}
+
+func runE(cmd *cobra.Command, args []string) error {
+	idStr := args[0]
+	_, err := strconv.Atoi(idStr)
+	if err != nil {
+		return err
+	}
+	return nsenter(idStr)
+}
+
+func MakeCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "nsenter PID...",
+		Short: "Enter container by ID",
+		Args:  cobra.ExactArgs(1),
+		RunE:  runE,
+	}
+	return cmd
+}

cmd/root.go

@@ -6,6 +6,7 @@ import (
 	"github.com/USTC-vlab/vct/cmd/iolimit"
 	"github.com/USTC-vlab/vct/cmd/iostat"
 	"github.com/USTC-vlab/vct/cmd/killall"
+	"github.com/USTC-vlab/vct/cmd/nsenter"
 	"github.com/USTC-vlab/vct/cmd/pressure"
 	"github.com/spf13/cobra"
 )
@@ -33,6 +34,7 @@ func MakeCmd() *cobra.Command {
 		iostat.MakeCmd(),
 		iolimit.MakeCmd(),
 		killall.MakeCmd(),
+		nsenter.MakeCmd(),
 		pressure.MakeCmd(),
 		versionCmd,
 	)