Add findpid subcommand

cmd/findpid/findpid.go

@@ -0,0 +1,55 @@
+package findpid
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+func findLXCForPid(pid string) (string, error) {
+	filename := fmt.Sprintf("/proc/%s/cgroup", pid)
+	f, err := os.Open(filename)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+	s := bufio.NewScanner(f)
+	if !s.Scan() {
+		return "", fmt.Errorf("empty cgroup file %s", filename)
+	}
+	line := s.Text()
+	remainder, ok := strings.CutPrefix(line, "0::/lxc/")
+	if !ok {
+		return "", fmt.Errorf("invalid cgroup file %s (read %q)", filename, line)
+	}
+	parts := strings.SplitN(remainder, "/", 2)
+	if len(parts) != 2 {
+		return "", fmt.Errorf("invalid cgroup file %s (read %q)", filename, line)
+	}
+	return parts[0], nil
+}
+
+func runE(cmd *cobra.Command, args []string) error {
+	w := cmd.OutOrStdout()
+	for _, pid := range args {
+		id, err := findLXCForPid(pid)
+		if err != nil {
+			return err
+		}
+		fmt.Fprintf(w, "%s: %s\n", pid, id)
+	}
+	return nil
+}
+
+func MakeCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "findpid PID...",
+		Short: "Find container ID by PID",
+		Args:  cobra.MinimumNArgs(1),
+		RunE:  runE,
+	}
+	return cmd
+}

cmd/root.go

@@ -2,6 +2,7 @@ package cmd
 
 import (
 	"github.com/USTC-vlab/vct/cmd/df"
+	"github.com/USTC-vlab/vct/cmd/findpid"
 	"github.com/USTC-vlab/vct/cmd/iostat"
 	"github.com/USTC-vlab/vct/cmd/pressure"
 	"github.com/spf13/cobra"
@@ -21,6 +22,7 @@ func MakeCmd() *cobra.Command {
 	}
 	cmd.CompletionOptions.HiddenDefaultCmd = true
 	cmd.AddCommand(df.MakeCmd())
+	cmd.AddCommand(findpid.MakeCmd())
 	cmd.AddCommand(iostat.MakeCmd())
 	cmd.AddCommand(pressure.MakeCmd())
 	return cmd