github.com/rish1988/moby@v25.0.2+incompatible/pkg/archive/archive_linux.go (about)

     1  package archive // import "github.com/docker/docker/pkg/archive"
     2  
     3  import (
     4  	"archive/tar"
     5  	"os"
     6  	"path/filepath"
     7  	"strings"
     8  
     9  	"github.com/docker/docker/pkg/system"
    10  	"github.com/pkg/errors"
    11  	"golang.org/x/sys/unix"
    12  )
    13  
    14  func getWhiteoutConverter(format WhiteoutFormat, inUserNS bool) (tarWhiteoutConverter, error) {
    15  	if format == OverlayWhiteoutFormat {
    16  		if inUserNS {
    17  			return nil, errors.New("specifying OverlayWhiteoutFormat is not allowed in userns")
    18  		}
    19  		return overlayWhiteoutConverter{}, nil
    20  	}
    21  	return nil, nil
    22  }
    23  
    24  type overlayWhiteoutConverter struct{}
    25  
    26  func (overlayWhiteoutConverter) ConvertWrite(hdr *tar.Header, path string, fi os.FileInfo) (wo *tar.Header, err error) {
    27  	// convert whiteouts to AUFS format
    28  	if fi.Mode()&os.ModeCharDevice != 0 && hdr.Devmajor == 0 && hdr.Devminor == 0 {
    29  		// we just rename the file and make it normal
    30  		dir, filename := filepath.Split(hdr.Name)
    31  		hdr.Name = filepath.Join(dir, WhiteoutPrefix+filename)
    32  		hdr.Mode = 0o600
    33  		hdr.Typeflag = tar.TypeReg
    34  		hdr.Size = 0
    35  	}
    36  
    37  	if fi.Mode()&os.ModeDir != 0 {
    38  		// convert opaque dirs to AUFS format by writing an empty file with the prefix
    39  		opaque, err := system.Lgetxattr(path, "trusted.overlay.opaque")
    40  		if err != nil {
    41  			return nil, err
    42  		}
    43  		if len(opaque) == 1 && opaque[0] == 'y' {
    44  			delete(hdr.PAXRecords, paxSchilyXattr+"trusted.overlay.opaque")
    45  
    46  			// create a header for the whiteout file
    47  			// it should inherit some properties from the parent, but be a regular file
    48  			wo = &tar.Header{
    49  				Typeflag:   tar.TypeReg,
    50  				Mode:       hdr.Mode & int64(os.ModePerm),
    51  				Name:       filepath.Join(hdr.Name, WhiteoutOpaqueDir),
    52  				Size:       0,
    53  				Uid:        hdr.Uid,
    54  				Uname:      hdr.Uname,
    55  				Gid:        hdr.Gid,
    56  				Gname:      hdr.Gname,
    57  				AccessTime: hdr.AccessTime,
    58  				ChangeTime: hdr.ChangeTime,
    59  			} //#nosec G305 -- An archive is being created, not extracted.
    60  		}
    61  	}
    62  
    63  	return
    64  }
    65  
    66  func (c overlayWhiteoutConverter) ConvertRead(hdr *tar.Header, path string) (bool, error) {
    67  	base := filepath.Base(path)
    68  	dir := filepath.Dir(path)
    69  
    70  	// if a directory is marked as opaque by the AUFS special file, we need to translate that to overlay
    71  	if base == WhiteoutOpaqueDir {
    72  		err := unix.Setxattr(dir, "trusted.overlay.opaque", []byte{'y'}, 0)
    73  		if err != nil {
    74  			return false, errors.Wrapf(err, "setxattr(%q, trusted.overlay.opaque=y)", dir)
    75  		}
    76  		// don't write the file itself
    77  		return false, err
    78  	}
    79  
    80  	// if a file was deleted and we are using overlay, we need to create a character device
    81  	if strings.HasPrefix(base, WhiteoutPrefix) {
    82  		originalBase := base[len(WhiteoutPrefix):]
    83  		originalPath := filepath.Join(dir, originalBase)
    84  
    85  		if err := unix.Mknod(originalPath, unix.S_IFCHR, 0); err != nil {
    86  			return false, errors.Wrapf(err, "failed to mknod(%q, S_IFCHR, 0)", originalPath)
    87  		}
    88  		if err := os.Chown(originalPath, hdr.Uid, hdr.Gid); err != nil {
    89  			return false, err
    90  		}
    91  
    92  		// don't write the file itself
    93  		return false, nil
    94  	}
    95  
    96  	return true, nil
    97  }