create: add support for --bundle and --pid-file

Co-authored-by: Samuel Karp <me@samuelkarp.com>

cmd/runj/create.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strconv"
 
 	"go.sbk.wtf/runj/jail"
 	"go.sbk.wtf/runj/oci"
@@ -45,8 +46,14 @@ import (
 // integrations on top of runc expect this behavior, runj copies that at the
 // expense of more complication in the codebase.
 func createCommand() *cobra.Command {
+	var (
+		bundle        string
+		consoleSocket string
+		pidFile       string
+	)
+
 	create := &cobra.Command{
-		Use:   "create <container-id> <path-to-bundle>",
+		Use:   "create <container-id> [path-to-bundle]",
 		Short: "Create a new container with given ID and bundle",
 		Long: `Create a new container with given ID and bundle.  IDs must be unique.
 
@@ -57,9 +64,17 @@ filesystem.
 The specification file includes an args parameter. The args parameter is used
 to specify command(s) that get run when the container is started. To change the
 command(s) that get executed on start, edit the args parameter of the spec.`,
-		Args: cobra.ExactArgs(2),
+		Args: cobra.RangeArgs(1, 2),
 		PreRunE: func(cmd *cobra.Command, args []string) error {
-			bundle := args[1]
+			if len(args) == 2 {
+				if bundle != "" {
+					return fmt.Errorf("must specify bundle via argument (%q) or flag (%q), not both", args[1], bundle)
+				}
+				bundle = args[1]
+			}
+			if bundle == "" {
+				return errors.New("bundle is required, specify via argument or --bundle flag")
+			}
 			bundleConfig := filepath.Join(bundle, oci.ConfigFileName)
 			fInfo, err := os.Stat(bundleConfig)
 			if err != nil {
@@ -71,16 +86,29 @@ command(s) that get executed on start, edit the args parameter of the spec.`,
 			return nil
 		},
 	}
-	consoleSocket := create.Flags().String(
+	flags := create.Flags()
+	flags.StringVarP(
+		&bundle,
+		"bundle",
+		"b",
+		"",
+		"path to the root of the bundle directory")
+	flags.StringVar(
+		&consoleSocket,
 		"console-socket",
 		"",
 		`path to an AF_UNIX socket which will receive a
 file descriptor referencing the master end of
 the console's pseudoterminal`)
+	flags.StringVar(
+		&pidFile,
+		"pid-file",
+		"",
+		`specify a file where the process ID will be
+written`)
 	create.RunE = func(cmd *cobra.Command, args []string) (err error) {
 		disableUsage(cmd)
 		id := args[0]
-		bundle := args[1]
 		var s *state.State
 		s, err = state.Create(id, bundle)
 		if err != nil {
@@ -121,15 +149,15 @@ the console's pseudoterminal`)
 		}
 		// console socket validation
 		if ociConfig.Process.Terminal {
-			if *consoleSocket == "" {
+			if consoleSocket == "" {
 				return errors.New("console-socket is required when Process.Terminal is true")
 			}
-			if socketStat, err := os.Stat(*consoleSocket); err != nil {
-				return fmt.Errorf("failed to stat console socket %q: %w", *consoleSocket, err)
+			if socketStat, err := os.Stat(consoleSocket); err != nil {
+				return fmt.Errorf("failed to stat console socket %q: %w", consoleSocket, err)
 			} else if socketStat.Mode()&os.ModeSocket != os.ModeSocket {
-				return fmt.Errorf("console-socket %q is not a socket", *consoleSocket)
+				return fmt.Errorf("console-socket %q is not a socket", consoleSocket)
 			}
-		} else if *consoleSocket != "" {
+		} else if consoleSocket != "" {
 			return errors.New("console-socket provided but Process.Terminal is false")
 		}
 		var confPath string
@@ -154,13 +182,21 @@ the console's pseudoterminal`)
 		// Setup and start the "runj-entrypoint" helper program in order to
 		// get the container STDIO hooked up properly.
 		var entrypoint *exec.Cmd
-		entrypoint, err = jail.SetupEntrypoint(id, true, ociConfig.Process.Args, ociConfig.Process.Env, *consoleSocket)
+		entrypoint, err = jail.SetupEntrypoint(id, true, ociConfig.Process.Args, ociConfig.Process.Env, consoleSocket)
 		if err != nil {
 			return err
 		}
 		// the runj-entrypoint pid will become the container process's pid
 		// through a series of exec(2) calls
 		s.PID = entrypoint.Process.Pid
+		if pidFile != "" {
+			pidValue := strconv.Itoa(s.PID)
+			err = os.WriteFile(pidFile, []byte(pidValue), 0o666)
+			if err != nil {
+				return err
+			}
+		}
+
 		return nil
 	}
 	return create

docs/oci.md

@@ -7,8 +7,10 @@ spec](https://github.com/opencontainers/runtime-spec/blob/master/runtime.md#crea
 as requiring two positional arguments: `<container-id> <path-to-bundle>`.
 However, `runc` (the reference implementation of the spec) accepts only a single
 positional argument (`<container-id>`) and instead uses either the current
-working directory as the bundle or accepts it through the `-b`/`bundle` flag.
+working directory as the bundle or accepts it through the `-b`/`--bundle` flag.
 See [here](https://github.com/opencontainers/runc/blob/2cf8d240075dd322b9385100c9af4b149c973391/create.go#L12-L30).
+For compatibility with runc and other integrations, runj now supports the flag
+in addition to the positional argument form.
 
 ## Non-terminal STDIO