cmd/snap-gpio-helper: add skeleton with re-exec support

build-aux/snap/snapcraft.yaml

@@ -324,7 +324,8 @@ parts:
             lib/snapd/snap-seccomp
             lib/snapd/snap-update-ns
             lib/snapd/snapctl
-            lib/snapd/snapd-apparmor)
+            lib/snapd/snapd-apparmor
+            lib/snapd/snap-gpio-helper)
       for cmd in "${CMDS[@]}"; do
         case "${cmd}" in
            # FIXME: some binaries need to be run confined in apps. But

cmd/snap-gpio-helper/cmd_export.go

@@ -0,0 +1,35 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2025 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 main
+
+import (
+	"errors"
+)
+
+type cmdExportChardev struct {
+	ChipLabels string `long:"chip-labels" description:"comma-separated list of source chip label(s) to match" required:"yes"`
+	Lines      uint   `long:"line" description:"comma-separated list of gpio line(s) to export" required:"yes"`
+	Gadget     string `long:"gadget" description:"gadget snap name" required:"yes"`
+	Slot       string `long:"slot" description:"gpio-chardev slot name" required:"yes"`
+}
+
+func (c *cmdExportChardev) Execute(args []string) error {
+	return errors.New("not implemented")
+}

cmd/snap-gpio-helper/cmd_unexport.go

@@ -0,0 +1,31 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2025 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 main
+
+import "errors"
+
+type cmdUnexportChardev struct {
+	Gadget string `long:"gadget" description:"gadget snap name" required:"yes"`
+	Slot   string `long:"slot" description:"gpio-chardev slot name" required:"yes"`
+}
+
+func (c *cmdUnexportChardev) Execute(args []string) error {
+	return errors.New("not implemented")
+}

cmd/snap-gpio-helper/main.go

@@ -0,0 +1,53 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2025 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 main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/jessevdk/go-flags"
+
+	"github.com/snapcore/snapd/snapdtool"
+)
+
+type options struct {
+	CmdExportChardev   cmdExportChardev   `command:"export-chardev"`
+	CmdUnexportChardev cmdUnexportChardev `command:"unexport-chardev"`
+}
+
+func run(osArgs1 []string) error {
+	var opts options
+	p := flags.NewParser(&opts, flags.HelpFlag|flags.PassDoubleDash)
+
+	if _, err := p.ParseArgs(osArgs1); err != nil {
+		return err
+	}
+	return nil
+}
+
+func main() {
+	snapdtool.ExecInSnapdOrCoreSnap()
+
+	if err := run(os.Args[1:]); err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+		os.Exit(1)
+	}
+}

packaging/ubuntu-16.04/snapd.install.in

@@ -12,6 +12,7 @@ usr/bin/snap-preseed /usr/lib/snapd/
 usr/bin/snap-recovery-chooser /usr/lib/snapd/
 usr/bin/snap-fde-keymgr /usr/lib/snapd/
 usr/bin/snapd-apparmor /usr/lib/snapd/
+usr/bin/snap-gpio-helper /usr/lib/snapd/
 
 # bash completion
 data/completion/bash/snap /usr/share/bash-completion/completions

tests/main/snap-gpio-helper/task.yaml

@@ -0,0 +1,24 @@
+summary: Check that snap-helper-helper exists
+
+details: |
+  The test verifies that snap-gpio-helper exists
+
+systems: [ubuntu-*]
+
+execute: |
+    libexecdir=$(os.paths libexec-dir)
+    if tests.info is-snapd-from-archive; then
+        libexecdir="/snap/snapd/current$libexecdir"
+    fi
+
+    if [ ! -f "$libexecdir/snapd/snap-gpio-helper" ]; then
+      exit 1
+    fi
+
+    # Verify that snap-gpio-helper skeleton re-execs
+    echo "Ensure snap-gpio-helper re-execs"
+    set +e
+    SNAPD_DEBUG=1 "$libexecdir/snapd/snap-gpio-helper" 2>&1 | MATCH "DEBUG: restarting into"
+    set -e
+
+    # TODO: add more checks