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|
package main
import (
"context"
"flag"
"fmt"
"io/ioutil"
"log"
"os/exec"
"path/filepath"
"github.com/containerd/containerd"
"github.com/containerd/containerd/content"
"github.com/containerd/containerd/images"
"github.com/containerd/containerd/namespaces"
"github.com/containerd/containerd/platforms"
"github.com/docker/docker/pkg/archive"
"github.com/google/renameio"
ocispec "github.com/opencontainers/image-spec/specs-go/v1"
)
const (
containerdSock = "/run/containerd/containerd.sock"
defaultNamespace = "c2vm"
)
var (
platform = platforms.Only(ocispec.Platform{
OS: "linux",
Architecture: "amd64",
})
)
func main() {
var (
containerName = flag.String("container", "", "Name of the container")
outFile = flag.String("out", "container.img", "firecracker output to create")
)
flag.Parse()
if *containerName == "" {
log.Fatal("a container is required")
}
client, err := containerd.New(containerdSock)
if err != nil {
log.Fatalf("failed to create a client for containerd: %v", err)
}
defer client.Close()
ctx := namespaces.WithNamespace(context.Background(), defaultNamespace)
ctx, done, err := client.WithLease(ctx)
if err != nil {
log.Fatalf("failed to get a lease: %v", err)
}
defer done(ctx)
image, err := client.Pull(ctx, *containerName, containerd.WithPlatformMatcher(platform))
if err != nil {
log.Fatalf("failed to pull the container %s: %v\n", *containerName, err)
}
imageSize, err := image.Usage(ctx, containerd.WithUsageManifestLimit(1))
if err != nil {
log.Fatalf("failed to get the size of the image: %v", err)
}
log.Printf("pulled %s (%d bytes)\n", image.Name(), imageSize)
mntDir, err := ioutil.TempDir("", "c2vm")
if err != nil {
log.Fatalf("Failed to create mount temp dir: %v\n", err)
}
if err := createLoopDevice(*outFile, mntDir); err != nil {
log.Fatalf("%v\n", err)
}
if err := extract(ctx, client, image, mntDir); err != nil {
log.Fatalf("failed to extract the container: %v\n", err)
}
if err = extraFiles(mntDir); err != nil {
log.Fatalf("failed to add extra files to the image: %v\n", err)
}
if err := detachLoopDevice(mntDir); err != nil {
log.Fatalf("failed to umount %s: %v\n", mntDir, err)
}
if err := resizeImage(*outFile); err != nil {
log.Fatalf("failed to resize the image %s: %s\n", *outFile, err)
}
}
func extract(ctx context.Context, client *containerd.Client, image containerd.Image, mntDir string) error {
manifest, err := images.Manifest(ctx, client.ContentStore(), image.Target(), platform)
if err != nil {
log.Fatalf("failed to get the manifest: %v\n", err)
}
for _, desc := range manifest.Layers {
log.Printf("extracting layer %s\n", desc.Digest.String())
layer, err := client.ContentStore().ReaderAt(ctx, desc)
if err != nil {
return err
}
if err := archive.Untar(content.NewReader(layer), mntDir, &archive.TarOptions{NoLchown: true}); err != nil {
return err
}
}
return nil
}
func createLoopDevice(rawFile, mntDir string) error {
f, err := renameio.TempFile("", rawFile)
if err != nil {
return err
}
defer f.Cleanup()
command := exec.Command("fallocate", "-l", "2G", f.Name())
if err := command.Run(); err != nil {
return fmt.Errorf("fallocate error: %s", err)
}
command = exec.Command("mkfs.ext4", "-F", f.Name())
if err := command.Run(); err != nil {
return fmt.Errorf("mkfs.ext4 error: %s", err)
}
f.CloseAtomicallyReplace()
command = exec.Command("mount", "-o", "loop", rawFile, mntDir)
if err := command.Run(); err != nil {
return fmt.Errorf("mount error: %s", err)
}
log.Printf("mounted %s on %s\n", rawFile, mntDir)
return nil
}
func detachLoopDevice(mntDir string) error {
log.Printf("umount %s\n", mntDir)
command := exec.Command("umount", mntDir)
return command.Run()
}
func resizeImage(rawFile string) error {
// let's bring the image to a more reasonable size. We do this by
// first running e2fsck on the image then we can resize the image.
command := exec.Command("/usr/bin/e2fsck", "-p", "-f", rawFile)
if err := command.Run(); err != nil {
return fmt.Errorf("e2fsck error: %s", err)
}
command = exec.Command("resize2fs", "-M", rawFile)
if err := command.Run(); err != nil {
return fmt.Errorf("resize2fs error: %s", err)
}
return nil
}
func extraFiles(mntDir string) error {
if err := writeToFile(filepath.Join(mntDir, "etc", "hosts"), "127.0.0.1\tlocalhost\n"); err != nil {
return err
}
if err := writeToFile(filepath.Join(mntDir, "etc", "resolv.conf"), "nameserver 192.168.0.1\n"); err != nil {
return err
}
return nil
}
func writeToFile(filepath string, content string) error {
if err := ioutil.WriteFile(filepath, []byte(content), 0644); err != nil {
return fmt.Errorf("writeToFile %s: %v", filepath, err)
}
return nil
}
|
