102 lines
3.3 KiB
Go
102 lines
3.3 KiB
Go
// +build linux
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package overlay2
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import (
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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/docker/docker/pkg/system"
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"github.com/pkg/errors"
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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 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"), "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, "work"))
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if err := unix.Mount("overlay", filepath.Join(td, "merged"), "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, "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 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, "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 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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