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275 lines
9.1 KiB
Go
275 lines
9.1 KiB
Go
//go:build linux
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// +build linux
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package overlay
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import (
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"errors"
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"fmt"
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"io/ioutil"
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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/containers/storage/pkg/archive"
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"github.com/containers/storage/pkg/idtools"
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"github.com/containers/storage/pkg/ioutils"
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"github.com/containers/storage/pkg/mount"
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"github.com/containers/storage/pkg/system"
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"github.com/containers/storage/pkg/unshare"
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"github.com/sirupsen/logrus"
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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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func doesSupportNativeDiff(d, mountOpts string) error {
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td, err := ioutil.TempDir(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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logrus.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, "work"), 0755); err != nil {
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return err
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}
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if err := os.Mkdir(filepath.Join(td, "merged"), 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"), archive.GetOverlayXattrName("opaque"), []byte("y"), 0); err != nil {
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return fmt.Errorf("failed to set opaque flag on middle layer: %w", err)
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}
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mountFlags := "lowerdir=%s:%s,upperdir=%s,workdir=%s"
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if unshare.IsRootless() {
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mountFlags = mountFlags + ",userxattr"
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}
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opts := fmt.Sprintf(mountFlags, path.Join(td, "l2"), path.Join(td, "l1"), path.Join(td, "l3"), path.Join(td, "work"))
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flags, data := mount.ParseOptions(mountOpts)
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if data != "" {
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opts = fmt.Sprintf("%s,%s", opts, data)
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}
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if err := unix.Mount("overlay", filepath.Join(td, "merged"), "overlay", uintptr(flags), opts); err != nil {
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return fmt.Errorf("failed to mount overlay: %w", err)
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}
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defer func() {
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if err := unix.Unmount(filepath.Join(td, "merged"), 0); err != nil {
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logrus.Warnf("Failed to unmount check directory %v: %v", filepath.Join(td, "merged"), 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 := ioutil.WriteFile(filepath.Join(td, "merged", "d", "f"), []byte{}, 0644); err != nil {
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return fmt.Errorf("failed to write to merged directory: %w", err)
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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"), archive.GetOverlayXattrName("opaque"))
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if err != nil {
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return fmt.Errorf("failed to read opaque flag on upper layer: %w", err)
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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, "merged", "d1"), filepath.Join(td, "merged", "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 fmt.Errorf("failed to rename dir in merged directory: %w", err)
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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"), archive.GetOverlayXattrName("redirect"))
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if err != nil {
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return fmt.Errorf("failed to read redirect flag on upper layer: %w", err)
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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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// doesMetacopy checks if the filesystem is going to optimize changes to
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// metadata by using nodes marked with an "overlay.metacopy" attribute to avoid
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// copying up a file from a lower layer unless/until its contents are being
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// modified
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func doesMetacopy(d, mountOpts string) (bool, error) {
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td, err := ioutil.TempDir(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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logrus.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, l2, work, merged
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if err := os.MkdirAll(filepath.Join(td, "l1"), 0755); err != nil {
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return false, err
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}
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if err := ioutils.AtomicWriteFile(filepath.Join(td, "l1", "f"), []byte{0xff}, 0700); err != nil {
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return false, err
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}
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if err := os.MkdirAll(filepath.Join(td, "l2"), 0755); err != nil {
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return false, err
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}
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if err := os.Mkdir(filepath.Join(td, "work"), 0755); err != nil {
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return false, err
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}
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if err := os.Mkdir(filepath.Join(td, "merged"), 0755); err != nil {
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return false, err
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}
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// Mount using the mandatory options and configured options
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opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", path.Join(td, "l1"), path.Join(td, "l2"), path.Join(td, "work"))
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if unshare.IsRootless() {
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opts = fmt.Sprintf("%s,userxattr", opts)
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}
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flags, data := mount.ParseOptions(mountOpts)
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if data != "" {
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opts = fmt.Sprintf("%s,%s", opts, data)
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}
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if err := unix.Mount("overlay", filepath.Join(td, "merged"), "overlay", uintptr(flags), opts); err != nil {
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if errors.Is(err, unix.EINVAL) {
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logrus.Info("metacopy option not supported on this kernel", mountOpts)
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return false, nil
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}
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return false, fmt.Errorf("failed to mount overlay for metacopy check with %q options: %w", mountOpts, err)
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}
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defer func() {
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if err := unix.Unmount(filepath.Join(td, "merged"), 0); err != nil {
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logrus.Warnf("Failed to unmount check directory %v: %v", filepath.Join(td, "merged"), err)
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}
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}()
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// Make a change that only impacts the inode, and check if the pulled-up copy is marked
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// as a metadata-only copy
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if err := os.Chmod(filepath.Join(td, "merged", "f"), 0600); err != nil {
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return false, fmt.Errorf("changing permissions on file for metacopy check: %w", err)
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}
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metacopy, err := system.Lgetxattr(filepath.Join(td, "l2", "f"), archive.GetOverlayXattrName("metacopy"))
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if err != nil {
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if errors.Is(err, unix.ENOTSUP) {
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logrus.Info("metacopy option not supported")
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return false, nil
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}
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return false, fmt.Errorf("metacopy flag was not set on file in upper layer: %w", err)
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}
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return metacopy != nil, nil
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}
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// doesVolatile checks if the filesystem supports the "volatile" mount option
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func doesVolatile(d string) (bool, error) {
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td, err := ioutil.TempDir(d, "volatile-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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logrus.Warnf("Failed to remove check directory %v: %v", td, err)
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}
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}()
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if err := os.MkdirAll(filepath.Join(td, "lower"), 0755); err != nil {
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return false, err
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}
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if err := os.MkdirAll(filepath.Join(td, "upper"), 0755); err != nil {
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return false, err
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}
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if err := os.Mkdir(filepath.Join(td, "work"), 0755); err != nil {
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return false, err
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}
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if err := os.Mkdir(filepath.Join(td, "merged"), 0755); err != nil {
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return false, err
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}
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// Mount using the mandatory options and configured options
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opts := fmt.Sprintf("volatile,lowerdir=%s,upperdir=%s,workdir=%s", path.Join(td, "lower"), path.Join(td, "upper"), path.Join(td, "work"))
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if err := unix.Mount("overlay", filepath.Join(td, "merged"), "overlay", 0, opts); err != nil {
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return false, fmt.Errorf("failed to mount overlay for volatile check: %w", err)
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}
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defer func() {
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if err := unix.Unmount(filepath.Join(td, "merged"), 0); err != nil {
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logrus.Warnf("Failed to unmount check directory %v: %v", filepath.Join(td, "merged"), err)
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}
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}()
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return true, nil
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}
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// supportsIdmappedLowerLayers checks if the kernel supports mounting overlay on top of
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// a idmapped lower layer.
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func supportsIdmappedLowerLayers(home string) (bool, error) {
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layerDir, err := ioutil.TempDir(home, "compat")
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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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_ = os.RemoveAll(layerDir)
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}()
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mergedDir := filepath.Join(layerDir, "merged")
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lowerDir := filepath.Join(layerDir, "lower")
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lowerMappedDir := filepath.Join(layerDir, "lower-mapped")
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upperDir := filepath.Join(layerDir, "upper")
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workDir := filepath.Join(layerDir, "work")
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_ = idtools.MkdirAs(mergedDir, 0700, 0, 0)
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_ = idtools.MkdirAs(lowerDir, 0700, 0, 0)
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_ = idtools.MkdirAs(lowerMappedDir, 0700, 0, 0)
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_ = idtools.MkdirAs(upperDir, 0700, 0, 0)
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_ = idtools.MkdirAs(workDir, 0700, 0, 0)
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idmap := []idtools.IDMap{
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{
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ContainerID: 0,
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HostID: 0,
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Size: 1,
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},
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}
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pid, cleanupFunc, err := createUsernsProcess(idmap, idmap)
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if err != nil {
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return false, err
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}
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defer cleanupFunc()
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if err := createIDMappedMount(lowerDir, lowerMappedDir, int(pid)); err != nil {
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return false, fmt.Errorf("create mapped mount: %w", err)
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}
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defer unix.Unmount(lowerMappedDir, unix.MNT_DETACH)
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opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerMappedDir, upperDir, workDir)
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flags := uintptr(0)
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if err := unix.Mount("overlay", mergedDir, "overlay", flags, opts); err != nil {
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return false, err
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}
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defer func() {
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_ = unix.Unmount(mergedDir, unix.MNT_DETACH)
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}()
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return true, nil
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}
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