Snap enable failure

vtinelli · July 9, 2018, 3:28pm

It looks like that doing a disable/enable on a snap with gpio plugs fails on enable: gpio are not exported before security profiles update.

If gpio is exported manually before snap enable, issue is not seen: sudo echo 192 > /sys/class/gpio/export

vtinelli@fe014e5031585858581367183b0483df:~$ snap disable private-snap
private-snap disabled

vtinelli@fe014e5031585858581367183b0483df:~$ snap enable private-snap
error: cannot perform the following tasks:

Setup snap “private-snap” (x1) security profiles (cannot setup apparmor for snap “private-snap”: cannot obtain apparmor specification for snap “private-snap”: lstat /sys/class/gpio/gpio192: no such file o
r directory)
Setup snap “private-snap” (x1) security profiles (cannot obtain apparmor specification for snap “private-snap”: lstat /sys/class/gpio/gpio192: no such file or directory)

kyleN · July 9, 2018, 3:50pm

I had the same result when disabling then enabling a snap that uses gpio interface (pi3).

@ogra?

ogra · July 9, 2018, 3:55pm

As i understand it the gpio interface should do that call itself from a line in the snaps systemd unit:

github.com

snapcore/snapd/blob/master/interfaces/builtin/gpio.go#L115


	return nil
}
func (iface *gpioInterface) SystemdConnectedSlot(spec *systemd.Specification, plug *interfaces.ConnectedPlug, slot *interfaces.ConnectedSlot) error {
	var gpioNum int64
	if err := slot.Attr("number", &gpioNum); err != nil {
		return err
	}
	serviceName := interfaces.InterfaceServiceName(slot.Snap().InstanceName(), fmt.Sprintf("gpio-%d", gpioNum))
	service := &systemd.Service{
		Type:            "oneshot",
		RemainAfterExit: true,
		ExecStart:       fmt.Sprintf("/bin/sh -c 'test -e /sys/class/gpio/gpio%d || echo %d > /sys/class/gpio/export'", gpioNum, gpioNum),
		ExecStop:        fmt.Sprintf("/bin/sh -c 'test ! -e /sys/class/gpio/gpio%d || echo %d > /sys/class/gpio/unexport'", gpioNum, gpioNum),
	}
	return spec.AddService(serviceName, service)
}
func (iface *gpioInterface) AutoConnect(*snap.PlugInfo, *snap.SlotInfo) bool {
	// allow what declarations allowed

sounds like an issue with that interface or the ordering of bits that are executed during dis/enable … @jdstrand any ideas ?

zyga-snapd · August 24, 2018, 12:44pm

I think I grok the issue now. Let me think about a possible fix.

EDIT: I sent a proposed fix to https://github.com/snapcore/snapd/pull/5721