Revert "Add support for mounts on Darwin"

This reverts commit 2799b28e61.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

mount/mount_linux.go

@@ -23,6 +23,7 @@ import (
 	"path"
 	"runtime"
 	"strings"
+	"time"
 
 	exec "golang.org/x/sys/execabs"
 	"golang.org/x/sys/unix"
@@ -119,6 +120,92 @@ func (m *Mount) mount(target string) (err error) {
 	return nil
 }
 
+// Unmount the provided mount path with the flags
+func Unmount(target string, flags int) error {
+	if err := unmount(target, flags); err != nil && err != unix.EINVAL {
+		return err
+	}
+	return nil
+}
+
+// fuseSuperMagic is defined in statfs(2)
+const fuseSuperMagic = 0x65735546
+
+func isFUSE(dir string) bool {
+	var st unix.Statfs_t
+	if err := unix.Statfs(dir, &st); err != nil {
+		return false
+	}
+	return st.Type == fuseSuperMagic
+}
+
+// unmountFUSE attempts to unmount using fusermount/fusermount3 helper binary.
+//
+// For FUSE mounts, using these helper binaries is preferred, see:
+// https://github.com/containerd/containerd/pull/3765#discussion_r342083514
+func unmountFUSE(target string) error {
+	var err error
+	for _, helperBinary := range []string{"fusermount3", "fusermount"} {
+		cmd := exec.Command(helperBinary, "-u", target)
+		err = cmd.Run()
+		if err == nil {
+			return nil
+		}
+	}
+	return err
+}
+
+func unmount(target string, flags int) error {
+	if isFUSE(target) {
+		if err := unmountFUSE(target); err == nil {
+			return nil
+		}
+	}
+	for i := 0; i < 50; i++ {
+		if err := unix.Unmount(target, flags); err != nil {
+			switch err {
+			case unix.EBUSY:
+				time.Sleep(50 * time.Millisecond)
+				continue
+			default:
+				return err
+			}
+		}
+		return nil
+	}
+	return fmt.Errorf("failed to unmount target %s: %w", target, unix.EBUSY)
+}
+
+// UnmountAll repeatedly unmounts the given mount point until there
+// are no mounts remaining (EINVAL is returned by mount), which is
+// useful for undoing a stack of mounts on the same mount point.
+// UnmountAll all is noop when the first argument is an empty string.
+// This is done when the containerd client did not specify any rootfs
+// mounts (e.g. because the rootfs is managed outside containerd)
+// UnmountAll is noop when the mount path does not exist.
+func UnmountAll(mount string, flags int) error {
+	if mount == "" {
+		return nil
+	}
+	if _, err := os.Stat(mount); os.IsNotExist(err) {
+		return nil
+	}
+
+	for {
+		if err := unmount(mount, flags); err != nil {
+			// EINVAL is returned if the target is not a
+			// mount point, indicating that we are
+			// done. It can also indicate a few other
+			// things (such as invalid flags) which we
+			// unfortunately end up squelching here too.
+			if err == unix.EINVAL {
+				return nil
+			}
+			return err
+		}
+	}
+}
+
 // parseMountOptions takes fstab style mount options and parses them for
 // use with a standard mount() syscall
 func parseMountOptions(options []string) (int, []string, bool) {