Add cimfs differ and snapshotter

Details about CimFs project are discussed in #8346

Signed-off-by: Amit Barve <ambarve@microsoft.com>

vendor/github.com/Microsoft/hcsshim/pkg/cimfs/common.go

@@ -0,0 +1,134 @@
+//go:build windows
+// +build windows
+
+package cimfs
+
+import (
+	"bytes"
+	"context"
+	"encoding/binary"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/Microsoft/hcsshim/internal/log"
+	"github.com/Microsoft/hcsshim/pkg/cimfs/format"
+)
+
+var (
+	// Equivalent to SDDL of "D:NO_ACCESS_CONTROL".
+	nullSd = []byte{1, 0, 4, 128, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+)
+
+type OpError struct {
+	Cim string
+	Op  string
+	Err error
+}
+
+func (e *OpError) Error() string {
+	s := "cim " + e.Op + " " + e.Cim
+	s += ": " + e.Err.Error()
+	return s
+}
+
+// PathError is the error type returned by most functions in this package.
+type PathError struct {
+	Cim  string
+	Op   string
+	Path string
+	Err  error
+}
+
+func (e *PathError) Error() string {
+	s := "cim " + e.Op + " " + e.Cim
+	s += ":" + e.Path
+	s += ": " + e.Err.Error()
+	return s
+}
+
+type LinkError struct {
+	Cim string
+	Op  string
+	Old string
+	New string
+	Err error
+}
+
+func (e *LinkError) Error() string {
+	return "cim " + e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error()
+}
+
+func validateHeader(h *format.CommonHeader) error {
+	if !bytes.Equal(h.Magic[:], format.MagicValue[:]) {
+		return fmt.Errorf("not a cim file")
+	}
+	if h.Version.Major > format.CurrentVersion.Major || h.Version.Major < format.MinSupportedVersion.Major {
+		return fmt.Errorf("unsupported cim version. cim version %v must be between %v & %v", h.Version, format.MinSupportedVersion, format.CurrentVersion)
+	}
+	return nil
+}
+
+func readFilesystemHeader(f *os.File) (format.FilesystemHeader, error) {
+	var fsh format.FilesystemHeader
+
+	if err := binary.Read(f, binary.LittleEndian, &fsh); err != nil {
+		return fsh, fmt.Errorf("reading filesystem header: %w", err)
+	}
+
+	if err := validateHeader(&fsh.Common); err != nil {
+		return fsh, fmt.Errorf("validating filesystem header: %w", err)
+	}
+	return fsh, nil
+}
+
+// Returns the paths of all the objectID files associated with the cim at `cimPath`.
+func getObjectIDFilePaths(ctx context.Context, cimPath string) ([]string, error) {
+	f, err := os.Open(cimPath)
+	if err != nil {
+		return []string{}, fmt.Errorf("open cim file %s: %w", cimPath, err)
+	}
+	defer f.Close()
+
+	fsh, err := readFilesystemHeader(f)
+	if err != nil {
+		return []string{}, fmt.Errorf("readingp cim header: %w", err)
+	}
+
+	paths := []string{}
+	for i := 0; i < int(fsh.Regions.Count); i++ {
+		path := filepath.Join(filepath.Dir(cimPath), fmt.Sprintf("%s_%v_%d", format.ObjectIDFileName, fsh.Regions.ID, i))
+		if _, err := os.Stat(path); err == nil {
+			paths = append(paths, path)
+		} else {
+			log.G(ctx).WithError(err).Warnf("stat for object file %s", path)
+		}
+
+	}
+	return paths, nil
+}
+
+// Returns the paths of all the region files associated with the cim at `cimPath`.
+func getRegionFilePaths(ctx context.Context, cimPath string) ([]string, error) {
+	f, err := os.Open(cimPath)
+	if err != nil {
+		return []string{}, fmt.Errorf("open cim file %s: %w", cimPath, err)
+	}
+	defer f.Close()
+
+	fsh, err := readFilesystemHeader(f)
+	if err != nil {
+		return []string{}, fmt.Errorf("reading cim header: %w", err)
+	}
+
+	paths := []string{}
+	for i := 0; i < int(fsh.Regions.Count); i++ {
+		path := filepath.Join(filepath.Dir(cimPath), fmt.Sprintf("%s_%v_%d", format.RegionFileName, fsh.Regions.ID, i))
+		if _, err := os.Stat(path); err == nil {
+			paths = append(paths, path)
+		} else {
+			log.G(ctx).WithError(err).Warnf("stat for region file %s", path)
+		}
+	}
+	return paths, nil
+}