blob: 5df8afd662055e09d8a58179f5500224b09599f4 [file] [log] [blame]
// +build !windows
package chrootarchive // import ""
import (
// untar is the entry-point for docker-untar on re-exec. This is not used on
// Windows as it does not support chroot, hence no point sandboxing through
// chroot and rexec.
func untar() {
var options *archive.TarOptions
//read the options from the pipe "ExtraFiles"
if err := json.NewDecoder(os.NewFile(3, "options")).Decode(&options); err != nil {
if err := chroot(flag.Arg(0)); err != nil {
if err := archive.Unpack(os.Stdin, "/", options); err != nil {
// fully consume stdin in case it is zero padded
if _, err := flush(os.Stdin); err != nil {
func invokeUnpack(decompressedArchive io.Reader, dest string, options *archive.TarOptions) error {
// We can't pass a potentially large exclude list directly via cmd line
// because we easily overrun the kernel's max argument/environment size
// when the full image list is passed (e.g. when this is used by
// `docker load`). We will marshall the options via a pipe to the
// child
r, w, err := os.Pipe()
if err != nil {
return fmt.Errorf("Untar pipe failure: %v", err)
cmd := reexec.Command("docker-untar", dest)
cmd.Stdin = decompressedArchive
cmd.ExtraFiles = append(cmd.ExtraFiles, r)
output := bytes.NewBuffer(nil)
cmd.Stdout = output
cmd.Stderr = output
if err := cmd.Start(); err != nil {
return fmt.Errorf("Untar error on re-exec cmd: %v", err)
//write the options to the pipe for the untar exec to read
if err := json.NewEncoder(w).Encode(options); err != nil {
return fmt.Errorf("Untar json encode to pipe failed: %v", err)
if err := cmd.Wait(); err != nil {
// when `xz -d -c -q | docker-untar ...` failed on docker-untar side,
// we need to exhaust `xz`'s output, otherwise the `xz` side will be
// pending on write pipe forever
io.Copy(ioutil.Discard, decompressedArchive)
return fmt.Errorf("Error processing tar file(%v): %s", err, output)
return nil