forked from toolshed/abra
108 lines
3.0 KiB
Go
108 lines
3.0 KiB
Go
package archive
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import (
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"archive/tar"
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"fmt"
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"os"
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"path/filepath"
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"strings"
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"github.com/moby/sys/userns"
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"golang.org/x/sys/unix"
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)
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func getWhiteoutConverter(format WhiteoutFormat) tarWhiteoutConverter {
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if format == OverlayWhiteoutFormat {
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return overlayWhiteoutConverter{}
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}
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return nil
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}
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type overlayWhiteoutConverter struct{}
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func (overlayWhiteoutConverter) ConvertWrite(hdr *tar.Header, path string, fi os.FileInfo) (wo *tar.Header, _ error) {
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// convert whiteouts to AUFS format
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if fi.Mode()&os.ModeCharDevice != 0 && hdr.Devmajor == 0 && hdr.Devminor == 0 {
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// we just rename the file and make it normal
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dir, filename := filepath.Split(hdr.Name)
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hdr.Name = filepath.Join(dir, WhiteoutPrefix+filename)
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hdr.Mode = 0o600
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hdr.Typeflag = tar.TypeReg
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hdr.Size = 0
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}
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if fi.Mode()&os.ModeDir == 0 {
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// FIXME(thaJeztah): return a sentinel error instead of nil, nil
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return nil, nil
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}
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opaqueXattrName := "trusted.overlay.opaque"
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if userns.RunningInUserNS() {
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opaqueXattrName = "user.overlay.opaque"
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}
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// convert opaque dirs to AUFS format by writing an empty file with the prefix
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opaque, err := lgetxattr(path, opaqueXattrName)
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if err != nil {
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return nil, err
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}
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if len(opaque) != 1 || opaque[0] != 'y' {
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// FIXME(thaJeztah): return a sentinel error instead of nil, nil
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return nil, nil
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}
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delete(hdr.PAXRecords, paxSchilyXattr+opaqueXattrName)
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// create a header for the whiteout file
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// it should inherit some properties from the parent, but be a regular file
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return &tar.Header{
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Typeflag: tar.TypeReg,
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Mode: hdr.Mode & int64(os.ModePerm),
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Name: filepath.Join(hdr.Name, WhiteoutOpaqueDir), // #nosec G305 -- An archive is being created, not extracted.
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Size: 0,
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Uid: hdr.Uid,
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Uname: hdr.Uname,
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Gid: hdr.Gid,
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Gname: hdr.Gname,
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AccessTime: hdr.AccessTime,
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ChangeTime: hdr.ChangeTime,
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}, nil
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}
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func (c overlayWhiteoutConverter) ConvertRead(hdr *tar.Header, path string) (bool, error) {
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base := filepath.Base(path)
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dir := filepath.Dir(path)
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// if a directory is marked as opaque by the AUFS special file, we need to translate that to overlay
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if base == WhiteoutOpaqueDir {
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opaqueXattrName := "trusted.overlay.opaque"
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if userns.RunningInUserNS() {
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opaqueXattrName = "user.overlay.opaque"
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}
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err := unix.Setxattr(dir, opaqueXattrName, []byte{'y'}, 0)
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if err != nil {
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return false, fmt.Errorf("setxattr('%s', %s=y): %w", dir, opaqueXattrName, err)
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}
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// don't write the file itself
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return false, err
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}
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// if a file was deleted and we are using overlay, we need to create a character device
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if strings.HasPrefix(base, WhiteoutPrefix) {
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originalBase := base[len(WhiteoutPrefix):]
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originalPath := filepath.Join(dir, originalBase)
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if err := unix.Mknod(originalPath, unix.S_IFCHR, 0); err != nil {
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return false, fmt.Errorf("failed to mknod('%s', S_IFCHR, 0): %w", originalPath, err)
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}
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if err := os.Chown(originalPath, hdr.Uid, hdr.Gid); err != nil {
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return false, err
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}
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// don't write the file itself
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return false, nil
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}
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return true, nil
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}
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