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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2016-2021 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package builtin
import (
"fmt"
"os"
"github.com/snapcore/snapd/interfaces"
"github.com/snapcore/snapd/interfaces/apparmor"
"github.com/snapcore/snapd/interfaces/systemd"
"github.com/snapcore/snapd/logger"
"github.com/snapcore/snapd/snap"
)
const gpioSummary = `allows access to specific GPIO pin`
const gpioBaseDeclarationSlots = `
gpio:
allow-installation:
slot-snap-type:
- core
- gadget
deny-auto-connection: true
`
var gpioSysfsGpioBase = "/sys/class/gpio/gpio"
// gpioInterface type
type gpioInterface struct{}
// String returns the same value as Name().
func (iface *gpioInterface) String() string {
return iface.Name()
}
// Name of the gpioInterface
func (iface *gpioInterface) Name() string {
return "gpio"
}
func (iface *gpioInterface) StaticInfo() interfaces.StaticInfo {
return interfaces.StaticInfo{
Summary: gpioSummary,
BaseDeclarationSlots: gpioBaseDeclarationSlots,
}
}
// BeforePrepareSlot checks the slot definition is valid
func (iface *gpioInterface) BeforePrepareSlot(slot *snap.SlotInfo) error {
// Must have a GPIO number
number, ok := slot.Attrs["number"]
if !ok {
return fmt.Errorf("gpio slot must have a number attribute")
}
// Valid values of number
if _, ok := number.(int64); !ok {
return fmt.Errorf("gpio slot number attribute must be an int")
}
// Slot is good
return nil
}
func (iface *gpioInterface) AppArmorConnectedPlug(spec *apparmor.Specification, plug *interfaces.ConnectedPlug, slot *interfaces.ConnectedSlot) error {
var number int64
if err := slot.Attr("number", &number); err != nil {
return err
}
path := fmt.Sprint(gpioSysfsGpioBase, number)
// Entries in /sys/class/gpio for single GPIO's are just symlinks
// to their correct device part in the sysfs tree. Given AppArmor
// requires symlinks to be dereferenced, evaluate the GPIO
// path and add the correct absolute path to the AppArmor snippet.
dereferencedPath, err := evalSymlinks(path)
if err != nil && os.IsNotExist(err) {
// If the specific gpio is not available there is no point
// exporting it, we should also not fail because this
// will block snapd updates (LP: 1866424)
logger.Noticef("cannot export not existing gpio %s", path)
return nil
}
if err != nil {
return err
}
spec.AddSnippet(fmt.Sprintf("%s/* rwk,", dereferencedPath))
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
}
serviceSuffix := 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(serviceSuffix, service)
}
func (iface *gpioInterface) AutoConnect(*snap.PlugInfo, *snap.SlotInfo) bool {
// allow what declarations allowed
return true
}
func init() {
registerIface(&gpioInterface{})
}
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