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Make sure gpio exported before apparmor setup #2

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Make sure gpio exported before apparmor setup #2

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12 changes: 6 additions & 6 deletions interfaces/builtin/gpio.go
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Original file line number Diff line number Diff line change
Expand Up @@ -104,21 +104,21 @@ func (iface *GpioInterface) ConnectedPlugSnippet(plug *interfaces.Plug, slot *in

// PermanentSlotSnippet - no slot snippets provided
func (iface *GpioInterface) PermanentSlotSnippet(slot *interfaces.Slot, securitySystem interfaces.SecuritySystem) ([]byte, error) {
return nil, nil
}

// ConnectedSlotSnippet - no slot snippets provided
func (iface *GpioInterface) ConnectedSlotSnippet(plug *interfaces.Plug, slot *interfaces.Slot, securitySystem interfaces.SecuritySystem) ([]byte, error) {
switch securitySystem {
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Moving to PermanentSlotSnippet is fine. It'll be the core or gadget snap that is the providing side, so no big deal moving the exports IMO.

case interfaces.SecurityUDev:
// NOTE: nothing unexports this GPIO when the slot is disconnected but
// AFAIK this doesn't hurt.
snippet := fmt.Sprintf(`ACTION=="add", SUBSYSTEM=="gpio", RUN+="/bin/echo %v > /syc/class/gpio/export"`, slot.Attrs["number"])
snippet := fmt.Sprintf(`SUBSYSTEM=="gpio", RUN+="/bin/sh -c '/bin/echo %v > /sys/class/gpio/export'"`, slot.Attrs["number"])
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Why was ACTION=="add" removed?

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I removed ACTION==add because:

  • the udev backend uses the command "udevadm trigger" (Note: no flags) to reload udev rules
  • the default ACTION sent by the trigger command is "change" so the command in the original rule would not be matched on install of the snap
  • we need to ensure the gpio is exported before any connection is made so the apparmor snippet can be created

By not specifying an action at all I think the rule is processed immediately as it only requires the device to be present. The guarantees that the gpio will be exported. The cost is that I don't believe it is actually possible to unexport a gpio with a rule like this in place. This may be a reasonable trade-off to guarantee the apparmor snippet can be created.

return []byte(snippet), nil
}
return nil, nil
}

// ConnectedSlotSnippet - no slot snippets provided
func (iface *GpioInterface) ConnectedSlotSnippet(plug *interfaces.Plug, slot *interfaces.Slot, securitySystem interfaces.SecuritySystem) ([]byte, error) {
return nil, nil
}

// AutoConnect returns whether interface should be auto-connected by default
func (iface *GpioInterface) AutoConnect() bool {
return false
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5 changes: 2 additions & 3 deletions interfaces/builtin/gpio_test.go
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Expand Up @@ -135,9 +135,8 @@ func (s *GpioInterfaceSuite) TestSanitizePlug(c *C) {

func (s *GpioInterfaceSuite) TestUsedSnippet(c *C) {
slot := s.gadgetGpioSlot
plug := s.gadgetPlug
content, err := s.iface.ConnectedSlotSnippet(plug, slot, interfaces.SecurityUDev)
content, err := s.iface.PermanentSlotSnippet(slot, interfaces.SecurityUDev)
c.Assert(err, IsNil)
expected := `ACTION=="add", SUBSYSTEM=="gpio", RUN+="/bin/echo 100 > /syc/class/gpio/export"`
expected := `SUBSYSTEM=="gpio", RUN+="/bin/sh -c '/bin/echo 100 > /sys/class/gpio/export'"`
c.Assert(string(content), Equals, expected)
}