buildkit/vendor/github.com/Microsoft/hcsshim/exportlayer.go

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package hcsshim
import (
"io"
"io/ioutil"
"os"
"syscall"
"github.com/Microsoft/go-winio"
"github.com/sirupsen/logrus"
)
// ExportLayer will create a folder at exportFolderPath and fill that folder with
// the transport format version of the layer identified by layerId. This transport
// format includes any metadata required for later importing the layer (using
// ImportLayer), and requires the full list of parent layer paths in order to
// perform the export.
func ExportLayer(info DriverInfo, layerId string, exportFolderPath string, parentLayerPaths []string) error {
title := "hcsshim::ExportLayer "
logrus.Debugf(title+"flavour %d layerId %s folder %s", info.Flavour, layerId, exportFolderPath)
// Generate layer descriptors
layers, err := layerPathsToDescriptors(parentLayerPaths)
if err != nil {
return err
}
// Convert info to API calling convention
infop, err := convertDriverInfo(info)
if err != nil {
logrus.Error(err)
return err
}
err = exportLayer(&infop, layerId, exportFolderPath, layers)
if err != nil {
err = makeErrorf(err, title, "layerId=%s flavour=%d folder=%s", layerId, info.Flavour, exportFolderPath)
logrus.Error(err)
return err
}
logrus.Debugf(title+"succeeded flavour=%d layerId=%s folder=%s", info.Flavour, layerId, exportFolderPath)
return nil
}
type LayerReader interface {
Next() (string, int64, *winio.FileBasicInfo, error)
Read(b []byte) (int, error)
Close() error
}
// FilterLayerReader provides an interface for extracting the contents of an on-disk layer.
type FilterLayerReader struct {
context uintptr
}
// Next reads the next available file from a layer, ensuring that parent directories are always read
// before child files and directories.
//
// Next returns the file's relative path, size, and basic file metadata. Read() should be used to
// extract a Win32 backup stream with the remainder of the metadata and the data.
func (r *FilterLayerReader) Next() (string, int64, *winio.FileBasicInfo, error) {
var fileNamep *uint16
fileInfo := &winio.FileBasicInfo{}
var deleted uint32
var fileSize int64
err := exportLayerNext(r.context, &fileNamep, fileInfo, &fileSize, &deleted)
if err != nil {
if err == syscall.ERROR_NO_MORE_FILES {
err = io.EOF
} else {
err = makeError(err, "ExportLayerNext", "")
}
return "", 0, nil, err
}
fileName := convertAndFreeCoTaskMemString(fileNamep)
if deleted != 0 {
fileInfo = nil
}
if fileName[0] == '\\' {
fileName = fileName[1:]
}
return fileName, fileSize, fileInfo, nil
}
// Read reads from the current file's Win32 backup stream.
func (r *FilterLayerReader) Read(b []byte) (int, error) {
var bytesRead uint32
err := exportLayerRead(r.context, b, &bytesRead)
if err != nil {
return 0, makeError(err, "ExportLayerRead", "")
}
if bytesRead == 0 {
return 0, io.EOF
}
return int(bytesRead), nil
}
// Close frees resources associated with the layer reader. It will return an
// error if there was an error while reading the layer or of the layer was not
// completely read.
func (r *FilterLayerReader) Close() (err error) {
if r.context != 0 {
err = exportLayerEnd(r.context)
if err != nil {
err = makeError(err, "ExportLayerEnd", "")
}
r.context = 0
}
return
}
// NewLayerReader returns a new layer reader for reading the contents of an on-disk layer.
// The caller must have taken the SeBackupPrivilege privilege
// to call this and any methods on the resulting LayerReader.
func NewLayerReader(info DriverInfo, layerID string, parentLayerPaths []string) (LayerReader, error) {
if procExportLayerBegin.Find() != nil {
// The new layer reader is not available on this Windows build. Fall back to the
// legacy export code path.
path, err := ioutil.TempDir("", "hcs")
if err != nil {
return nil, err
}
err = ExportLayer(info, layerID, path, parentLayerPaths)
if err != nil {
os.RemoveAll(path)
return nil, err
}
return &legacyLayerReaderWrapper{newLegacyLayerReader(path)}, nil
}
layers, err := layerPathsToDescriptors(parentLayerPaths)
if err != nil {
return nil, err
}
infop, err := convertDriverInfo(info)
if err != nil {
return nil, err
}
r := &FilterLayerReader{}
err = exportLayerBegin(&infop, layerID, layers, &r.context)
if err != nil {
return nil, makeError(err, "ExportLayerBegin", "")
}
return r, err
}
type legacyLayerReaderWrapper struct {
*legacyLayerReader
}
func (r *legacyLayerReaderWrapper) Close() error {
err := r.legacyLayerReader.Close()
os.RemoveAll(r.root)
return err
}