Should os.ModeCharDevice be taken into account?

[thaJeztah]

Relates to moby/moby#38758 / moby/moby#38404 (comment) / golang/go@a2a3dd0

Due to a change in Go 1.12, some file modes are no longer being returned as os. ModeDevice, but as os.ModeCharDevice. This caused pulling images to break on docker (moby/moby#38404 (comment)).

I'm not very familiar with this repository, but a quick search showed some similar uses in this package, so I suspect some of those will have to be updated accordingly.

continuity/fs/copy.go

Lines 137 to 140 in 004b464

	case (fi.Mode() & os.ModeDevice) == os.ModeDevice:
	if err := copyDevice(target, fi); err != nil {
	return errors.Wrapf(err, "failed to create device")
	}

continuity/resource.go

Lines 552 to 553 in c2ac4ec

	case base.Mode()&os.ModeDevice != 0:
	return newDevice(*base, b.Path, b.Major, b.Minor)

continuity/resource.go

Lines 434 to 437 in c2ac4ec

	func newDevice(base resource, paths []string, major, minor uint64) (Device, error) {
	if base.Mode()&os.ModeDevice == 0 {
	return nil, fmt.Errorf("not a device")
	}

continuity/context.go

Lines 501 to 502 in c2ac4ec

	} else if (fi.Mode() & os.ModeDevice) == 0 {
	return fmt.Errorf("%q should be a device, but is not", resource.Path())

continuity/context.go

Line 192 in c2ac4ec

if fi.Mode()&os.ModeDevice != 0 {

continuity/devices/devices_unix.go

Line 46 in c2ac4ec

if mode&os.ModeDevice != 0 {

[thaJeztah]

ping @cpuguy83 @AkihiroSuda @tonistiigi @dmcgowan PTAL

[thaJeztah]

Ok, so the approach here is more defensive than the variation in Moby; os.ModeCharDevice will always be set in combination with os.ModeDevice.

The code in this repository checks if os.ModeDevice (irregardless of it being a os.ModeCharDevice or not), whereas the Moby code checks for an exact match, expecting only os.ModeDevice to be set, therefore causing it to break with Go 1.12.