Merge pull request #3512 from kolyshkin/fix-mntns-userns-II

Refactor mountFd code

libcontainer/console_linux.go

@@ -18,7 +18,7 @@ func mountConsole(slavePath string) error {
  if f != nil {
  f.Close()
  }
- return mount(slavePath, "/dev/console", "", "bind", unix.MS_BIND, "")
+ return mount(slavePath, "/dev/console", "bind", unix.MS_BIND, "")
 }
 
 // dupStdio opens the slavePath for the console and dups the fds to the current

libcontainer/container_linux.go

@@ -1277,9 +1277,8 @@ func (c *Container) makeCriuRestoreMountpoints(m *configs.Mount) error {
  case "bind":
  // The prepareBindMount() function checks if source
  // exists. So it cannot be used for other filesystem types.
- // TODO: pass something else than nil? Not sure if criu is
- // impacted by issue #2484
- if err := prepareBindMount(m, c.config.Rootfs, nil); err != nil {
+ // TODO: pass srcFD? Not sure if criu is impacted by issue #2484.
+ if err := prepareBindMount(mountEntry{Mount: m}, c.config.Rootfs); err != nil {
  return err
  }
  default:
@@ -1357,8 +1356,8 @@ func (c *Container) prepareCriuRestoreMounts(mounts []*configs.Mount) error {
  // because during initial container creation mounts are
  // set up in the order they are configured.
  if m.Device == "bind" {
- if err := utils.WithProcfd(c.config.Rootfs, m.Destination, func(procfd string) error {
- if err := mount(m.Source, m.Destination, procfd, "", unix.MS_BIND|unix.MS_REC, ""); err != nil {
+ if err := utils.WithProcfd(c.config.Rootfs, m.Destination, func(dstFD string) error {
+ if err := mountViaFDs(m.Source, "", m.Destination, dstFD, "", unix.MS_BIND|unix.MS_REC, ""); err != nil {
  return err
  }
  return nil
@@ -1411,7 +1410,7 @@ func (c *Container) Restore(process *Process, criuOpts *CriuOpts) error {
  if err != nil {
  return err
  }
- err = mount(c.config.Rootfs, root, "", "", unix.MS_BIND|unix.MS_REC, "")
+ err = mount(c.config.Rootfs, root, "", unix.MS_BIND|unix.MS_REC, "")
  if err != nil {
  return err
  }

libcontainer/mount_linux.go

@@ -10,8 +10,9 @@ import (
 type mountError struct {
  op string
  source string
+ srcFD string
  target string
- procfd string
+ dstFD  string
  flags uintptr
  data string
  err error
@@ -22,19 +23,21 @@ func (e *mountError) Error() string {
  out := e.op + " "
 
  if e.source != "" {
- out += e.source + ":" + e.target
- } else {
- out += e.target
+ out += "src=" + e.source + ", "
+ if e.srcFD != "" {
+ out += "srcFD=" + e.srcFD + ", "
+ }
  }
- if e.procfd != "" {
- out += " (via " + e.procfd + ")"
+ out += "dst=" + e.target
+ if e.dstFD != "" {
+ out += ", dstFD=" + e.dstFD
  }
 
  if e.flags != uintptr(0) {
- out += ", flags: 0x" + strconv.FormatUint(uint64(e.flags), 16)
+ out += ", flags=0x" + strconv.FormatUint(uint64(e.flags), 16)
  }
  if e.data != "" {
- out += ", data: " + e.data
+ out += ", data=" + e.data
  }
 
  out += ": " + e.err.Error()
@@ -47,19 +50,36 @@ func (e *mountError) Unwrap() error {
  return e.err
 }
 
-// mount is a simple unix.Mount wrapper. If procfd is not empty, it is used
-// instead of target (and the target is only used to add context to an error).
-func mount(source, target, procfd, fstype string, flags uintptr, data string) error {
+// mount is a simple unix.Mount wrapper, returning an error with more context
+// in case it failed.
+func mount(source, target, fstype string, flags uintptr, data string) error {
+ return mountViaFDs(source, "", target, "", fstype, flags, data)
+}
+
+// mountViaFDs is a unix.Mount wrapper which uses srcFD instead of source,
+// and dstFD instead of target, unless those are empty. The *FD arguments,
+// if non-empty, are expected to be in the form of a path to an opened file
+// descriptor on procfs (i.e. "/proc/self/fd/NN").
+//
+// If case an FD is used instead of a source or a target path, the
+// corresponding path is only used to add context to an error in case
+// the mount operation has failed.
+func mountViaFDs(source, srcFD, target, dstFD, fstype string, flags uintptr, data string) error {
+ src := source
+ if srcFD != "" {
+ src = srcFD
+ }
  dst := target
- if procfd != "" {
- dst = procfd
+ if dstFD != "" {
+ dst = dstFD
  }
- if err := unix.Mount(source, dst, fstype, flags, data); err != nil {
+ if err := unix.Mount(src, dst, fstype, flags, data); err != nil {
  return &mountError{
  op: "mount",
  source: source,
+ srcFD: srcFD,
  target: target,
- procfd: procfd,
+ dstFD: dstFD,
  flags: flags,
  data: data,
  err: err,