github.com/michael-k/docker@v1.7.0-rc2/pkg/chrootarchive/archive.go (about)

     1  package chrootarchive
     2  
     3  import (
     4  	"bytes"
     5  	"encoding/json"
     6  	"flag"
     7  	"fmt"
     8  	"io"
     9  	"os"
    10  	"path/filepath"
    11  	"runtime"
    12  	"syscall"
    13  
    14  	"github.com/docker/docker/pkg/archive"
    15  	"github.com/docker/docker/pkg/reexec"
    16  )
    17  
    18  var chrootArchiver = &archive.Archiver{Untar: Untar}
    19  
    20  func chroot(path string) error {
    21  	if err := syscall.Chroot(path); err != nil {
    22  		return err
    23  	}
    24  	return syscall.Chdir("/")
    25  }
    26  
    27  func untar() {
    28  	runtime.LockOSThread()
    29  	flag.Parse()
    30  
    31  	var options *archive.TarOptions
    32  
    33  	//read the options from the pipe "ExtraFiles"
    34  	if err := json.NewDecoder(os.NewFile(3, "options")).Decode(&options); err != nil {
    35  		fatal(err)
    36  	}
    37  
    38  	if err := chroot(flag.Arg(0)); err != nil {
    39  		fatal(err)
    40  	}
    41  	if err := archive.Unpack(os.Stdin, "/", options); err != nil {
    42  		fatal(err)
    43  	}
    44  	// fully consume stdin in case it is zero padded
    45  	flush(os.Stdin)
    46  	os.Exit(0)
    47  }
    48  
    49  func Untar(tarArchive io.Reader, dest string, options *archive.TarOptions) error {
    50  	if tarArchive == nil {
    51  		return fmt.Errorf("Empty archive")
    52  	}
    53  	if options == nil {
    54  		options = &archive.TarOptions{}
    55  	}
    56  	if options.ExcludePatterns == nil {
    57  		options.ExcludePatterns = []string{}
    58  	}
    59  
    60  	dest = filepath.Clean(dest)
    61  	if _, err := os.Stat(dest); os.IsNotExist(err) {
    62  		if err := os.MkdirAll(dest, 0777); err != nil {
    63  			return err
    64  		}
    65  	}
    66  
    67  	decompressedArchive, err := archive.DecompressStream(tarArchive)
    68  	if err != nil {
    69  		return err
    70  	}
    71  	defer decompressedArchive.Close()
    72  
    73  	// We can't pass a potentially large exclude list directly via cmd line
    74  	// because we easily overrun the kernel's max argument/environment size
    75  	// when the full image list is passed (e.g. when this is used by
    76  	// `docker load`). We will marshall the options via a pipe to the
    77  	// child
    78  	r, w, err := os.Pipe()
    79  	if err != nil {
    80  		return fmt.Errorf("Untar pipe failure: %v", err)
    81  	}
    82  	cmd := reexec.Command("docker-untar", dest)
    83  	cmd.Stdin = decompressedArchive
    84  	cmd.ExtraFiles = append(cmd.ExtraFiles, r)
    85  	output := bytes.NewBuffer(nil)
    86  	cmd.Stdout = output
    87  	cmd.Stderr = output
    88  
    89  	if err := cmd.Start(); err != nil {
    90  		return fmt.Errorf("Untar error on re-exec cmd: %v", err)
    91  	}
    92  	//write the options to the pipe for the untar exec to read
    93  	if err := json.NewEncoder(w).Encode(options); err != nil {
    94  		return fmt.Errorf("Untar json encode to pipe failed: %v", err)
    95  	}
    96  	w.Close()
    97  
    98  	if err := cmd.Wait(); err != nil {
    99  		return fmt.Errorf("Untar re-exec error: %v: output: %s", err, output)
   100  	}
   101  	return nil
   102  }
   103  
   104  func TarUntar(src, dst string) error {
   105  	return chrootArchiver.TarUntar(src, dst)
   106  }
   107  
   108  // CopyWithTar creates a tar archive of filesystem path `src`, and
   109  // unpacks it at filesystem path `dst`.
   110  // The archive is streamed directly with fixed buffering and no
   111  // intermediary disk IO.
   112  func CopyWithTar(src, dst string) error {
   113  	return chrootArchiver.CopyWithTar(src, dst)
   114  }
   115  
   116  // CopyFileWithTar emulates the behavior of the 'cp' command-line
   117  // for a single file. It copies a regular file from path `src` to
   118  // path `dst`, and preserves all its metadata.
   119  //
   120  // If `dst` ends with a trailing slash '/', the final destination path
   121  // will be `dst/base(src)`.
   122  func CopyFileWithTar(src, dst string) (err error) {
   123  	return chrootArchiver.CopyFileWithTar(src, dst)
   124  }
   125  
   126  // UntarPath is a convenience function which looks for an archive
   127  // at filesystem path `src`, and unpacks it at `dst`.
   128  func UntarPath(src, dst string) error {
   129  	return chrootArchiver.UntarPath(src, dst)
   130  }