Add linuxkit metadata command

Only subcommand is currently `create` which is a thin wrapper to create an iso
file in the format expected by `pkg/metadata`.

Currently very basic and just takes the content on the command line but could
be extended to read from a file etc.

Signed-off-by: Ian Campbell <ian.campbell@docker.com>

docs/metadata.md

@@ -51,6 +51,15 @@ This hierarchy can then be used by individual containers, who can bind
 mount the config sub-directory into their namespace where it is
 needed.
 
+# Metadata image creation
+
+Run `linuxkit run` backends accept a `--data=STRING` option which will
+cause the given string to be passed to the VM in a platform specific
+manner to be picked up by the `pkg/metadata` component.
+
+Alternatively `linuxkit metadata create meta.iso STRING` will produce
+a correctly formatted ISO image which can be passed to a VM as a CDROM
+device for consumption by the `pkg/metadata` component.
 
 # Providers
 

src/cmd/linuxkit/main.go

@@ -41,6 +41,7 @@ func main() {
 	flag.Usage = func() {
 		fmt.Printf("USAGE: %s [options] COMMAND\n\n", filepath.Base(os.Args[0]))
 		fmt.Printf("Commands:\n")
+		fmt.Printf("  metadata    Metadata utilities\n")
 		fmt.Printf("  push        Push a VM image to a cloud or image store\n")
 		fmt.Printf("  run         Run a VM image on a local hypervisor or remote cloud\n")
 		fmt.Printf("  version     Print version information\n")
@@ -79,6 +80,8 @@ func main() {
 	}
 
 	switch args[0] {
+	case "metadata":
+		metadata(args[1:])
 	case "push":
 		push(args[1:])
 	case "run":

src/cmd/linuxkit/metadata.go

@@ -0,0 +1,73 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	log "github.com/Sirupsen/logrus"
+	"github.com/rneugeba/iso9660wrap"
+)
+
+func metadataCreateUsage() {
+	invoked := filepath.Base(os.Args[0])
+	fmt.Printf("USAGE: %s metadata create [file.iso] [metadata]\n\n", invoked)
+
+	fmt.Printf("'file.iso' is the file to create.\n")
+	fmt.Printf("'metadata' will be written to '/config' in the ISO.\n")
+	fmt.Printf("This is compatible with the linuxkit/metadata package\n")
+}
+
+func metadataCreate(args []string) {
+	if len(args) != 2 {
+		metadataCreateUsage()
+		os.Exit(1)
+	}
+	switch args[0] {
+	case "help", "-h", "-help", "--help":
+		metadataCreateUsage()
+		os.Exit(0)
+	}
+
+	isoImage := args[0]
+	metadata := args[1]
+
+	outfh, err := os.OpenFile(isoImage, os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		log.Fatal("Cannot create user data ISOs", "err", err)
+	}
+	defer outfh.Close()
+
+	err = iso9660wrap.WriteBuffer(outfh, []byte(metadata), "config")
+	if err != nil {
+		log.Fatal("Cannot write user data ISO", "err", err)
+	}
+}
+
+func metadataUsage() {
+	invoked := filepath.Base(os.Args[0])
+	fmt.Printf("USAGE: %s metadata COMMAND [options]\n\n", invoked)
+	fmt.Printf("Commands:\n")
+	fmt.Printf("  create      Create a metadata ISO\n")
+}
+
+func metadata(args []string) {
+	if len(args) < 1 {
+		metadataUsage()
+		os.Exit(1)
+	}
+	switch args[0] {
+	case "help", "-h", "-help", "--help":
+		metadataUsage()
+		os.Exit(0)
+	}
+
+	switch args[0] {
+	case "create":
+		metadataCreate(args[1:])
+	default:
+		fmt.Printf("%q is not a valid metadata command.\n\n", args[0])
+		metadataUsage()
+		os.Exit(1)
+	}
+}