202 lines
6.8 KiB
Go
202 lines
6.8 KiB
Go
//go:build linux
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// +build linux
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package overlay2 // import "github.com/docker/docker/daemon/graphdriver/overlay2"
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import (
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"fmt"
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"os"
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"path"
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"path/filepath"
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"syscall"
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"github.com/containerd/containerd/mount"
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"github.com/containerd/containerd/pkg/userns"
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"github.com/docker/docker/daemon/graphdriver/overlayutils"
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"github.com/docker/docker/pkg/system"
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"github.com/pkg/errors"
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"golang.org/x/sys/unix"
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)
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// doesSupportNativeDiff checks whether the filesystem has a bug
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// which copies up the opaque flag when copying up an opaque
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// directory or the kernel enable CONFIG_OVERLAY_FS_REDIRECT_DIR.
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// When these exist naive diff should be used.
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//
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// When running in a user namespace, returns errRunningInUserNS
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// immediately.
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func doesSupportNativeDiff(d string) error {
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if userns.RunningInUserNS() {
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return errors.New("running in a user namespace")
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}
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td, err := os.MkdirTemp(d, "opaque-bug-check")
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if err != nil {
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return err
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}
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defer func() {
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if err := os.RemoveAll(td); err != nil {
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logger.Warnf("Failed to remove check directory %v: %v", td, err)
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}
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}()
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// Make directories l1/d, l1/d1, l2/d, l3, work, merged
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if err := os.MkdirAll(filepath.Join(td, "l1", "d"), 0755); err != nil {
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return err
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}
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if err := os.MkdirAll(filepath.Join(td, "l1", "d1"), 0755); err != nil {
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return err
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}
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if err := os.MkdirAll(filepath.Join(td, "l2", "d"), 0755); err != nil {
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return err
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}
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if err := os.Mkdir(filepath.Join(td, "l3"), 0755); err != nil {
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return err
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}
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if err := os.Mkdir(filepath.Join(td, workDirName), 0755); err != nil {
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return err
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}
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if err := os.Mkdir(filepath.Join(td, mergedDirName), 0755); err != nil {
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return err
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}
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// Mark l2/d as opaque
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if err := system.Lsetxattr(filepath.Join(td, "l2", "d"), "trusted.overlay.opaque", []byte("y"), 0); err != nil {
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return errors.Wrap(err, "failed to set opaque flag on middle layer")
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}
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opts := fmt.Sprintf("lowerdir=%s:%s,upperdir=%s,workdir=%s", path.Join(td, "l2"), path.Join(td, "l1"), path.Join(td, "l3"), path.Join(td, workDirName))
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if err := unix.Mount("overlay", filepath.Join(td, mergedDirName), "overlay", 0, opts); err != nil {
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return errors.Wrap(err, "failed to mount overlay")
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}
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defer func() {
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if err := unix.Unmount(filepath.Join(td, mergedDirName), 0); err != nil {
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logger.Warnf("Failed to unmount check directory %v: %v", filepath.Join(td, mergedDirName), err)
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}
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}()
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// Touch file in d to force copy up of opaque directory "d" from "l2" to "l3"
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if err := os.WriteFile(filepath.Join(td, mergedDirName, "d", "f"), []byte{}, 0644); err != nil {
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return errors.Wrap(err, "failed to write to merged directory")
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}
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// Check l3/d does not have opaque flag
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xattrOpaque, err := system.Lgetxattr(filepath.Join(td, "l3", "d"), "trusted.overlay.opaque")
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if err != nil {
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return errors.Wrap(err, "failed to read opaque flag on upper layer")
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}
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if string(xattrOpaque) == "y" {
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return errors.New("opaque flag erroneously copied up, consider update to kernel 4.8 or later to fix")
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}
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// rename "d1" to "d2"
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if err := os.Rename(filepath.Join(td, mergedDirName, "d1"), filepath.Join(td, mergedDirName, "d2")); err != nil {
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// if rename failed with syscall.EXDEV, the kernel doesn't have CONFIG_OVERLAY_FS_REDIRECT_DIR enabled
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if err.(*os.LinkError).Err == syscall.EXDEV {
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return nil
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}
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return errors.Wrap(err, "failed to rename dir in merged directory")
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}
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// get the xattr of "d2"
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xattrRedirect, err := system.Lgetxattr(filepath.Join(td, "l3", "d2"), "trusted.overlay.redirect")
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if err != nil {
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return errors.Wrap(err, "failed to read redirect flag on upper layer")
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}
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if string(xattrRedirect) == "d1" {
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return errors.New("kernel has CONFIG_OVERLAY_FS_REDIRECT_DIR enabled")
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}
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return nil
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}
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// Forked from https://github.com/containers/storage/blob/05c69f1b2a5871d170c07dc8d2eec69c681e143b/drivers/overlay/check.go
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//
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// usingMetacopy checks if overlayfs's metacopy feature is active. When active,
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// overlayfs will only copy up metadata (as opposed to the whole file) when a
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// metadata-only operation is performed. Affected inodes will be marked with
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// the "(trusted|user).overlay.metacopy" xattr.
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//
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// The CONFIG_OVERLAY_FS_METACOPY option, the overlay.metacopy parameter, or
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// the metacopy mount option can all enable metacopy mode. For more details on
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// this feature, see filesystems/overlayfs.txt in the kernel documentation
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// tree.
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//
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// Note that the mount option should never be relevant should never come up the
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// daemon has control over all of its own mounts and presently does not request
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// metacopy. Nonetheless, a user or kernel distributor may enable metacopy, so
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// we should report in the daemon whether or not we detect its use.
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func usingMetacopy(d string) (bool, error) {
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userxattr := false
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if userns.RunningInUserNS() {
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needed, err := overlayutils.NeedsUserXAttr(d)
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if err != nil {
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return false, err
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}
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if needed {
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userxattr = true
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}
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}
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td, err := os.MkdirTemp(d, "metacopy-check")
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if err != nil {
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return false, err
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}
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defer func() {
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if err := os.RemoveAll(td); err != nil {
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logger.WithError(err).Warnf("failed to remove check directory %v", td)
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}
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}()
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l1, l2, work, merged := filepath.Join(td, "l1"), filepath.Join(td, "l2"), filepath.Join(td, "work"), filepath.Join(td, "merged")
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for _, dir := range []string{l1, l2, work, merged} {
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if err := os.Mkdir(dir, 0755); err != nil {
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return false, err
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}
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}
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// Create empty file in l1 with 0700 permissions for metacopy test
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if err := os.WriteFile(filepath.Join(l1, "f"), []byte{}, 0700); err != nil {
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return false, err
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}
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opts := []string{fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", l1, l2, work)}
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if userxattr {
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opts = append(opts, "userxattr")
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}
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m := mount.Mount{
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Type: "overlay",
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Source: "overlay",
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Options: opts,
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}
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if err := m.Mount(merged); err != nil {
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return false, errors.Wrap(err, "failed to mount overlay for metacopy check")
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}
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defer func() {
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if err := mount.UnmountAll(merged, 0); err != nil {
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logger.WithError(err).Warnf("failed to unmount check directory %v", merged)
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}
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}()
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// Make a change that only impacts the inode, in the upperdir
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if err := os.Chmod(filepath.Join(merged, "f"), 0600); err != nil {
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return false, errors.Wrap(err, "error changing permissions on file for metacopy check")
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}
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// ...and check if the pulled-up copy is marked as metadata-only
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xattr, err := system.Lgetxattr(filepath.Join(l2, "f"), overlayutils.GetOverlayXattr("metacopy"))
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if err != nil {
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// ENOTSUP signifies the FS does not support either xattrs or metacopy. In either case,
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// it is not a fatal error, and we should report metacopy as unused.
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if errors.Is(err, unix.ENOTSUP) {
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return false, nil
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}
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return false, errors.Wrap(err, "metacopy flag was not set on file in the upperdir")
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}
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usingMetacopy := xattr != nil
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logger.WithField("usingMetacopy", usingMetacopy).Debug("successfully detected metacopy status")
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return usingMetacopy, nil
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}
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