internal/uevent: kobject_action lookup

This is encoded as part of kobject uevent message headers.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/uevent/action.go

@@ -0,0 +1,74 @@
+package uevent
+
+import (
+	"strconv"
+	"syscall"
+)
+
+// KobjectAction represents enum kobject_action found in include/linux/kobject.h
+// and their corresponding string representations in lib/kobject_uevent.c.
+type KobjectAction uint32
+
+// include/linux/kobject.h
+const (
+	KOBJ_ADD KobjectAction = iota
+	KOBJ_REMOVE
+	KOBJ_CHANGE
+	KOBJ_MOVE
+	KOBJ_ONLINE
+	KOBJ_OFFLINE
+	KOBJ_BIND
+	KOBJ_UNBIND
+)
+
+// lib/kobject_uevent.c
+var kobject_actions = [...]string{
+	KOBJ_ADD:     "add",
+	KOBJ_REMOVE:  "remove",
+	KOBJ_CHANGE:  "change",
+	KOBJ_MOVE:    "move",
+	KOBJ_ONLINE:  "online",
+	KOBJ_OFFLINE: "offline",
+	KOBJ_BIND:    "bind",
+	KOBJ_UNBIND:  "unbind",
+}
+
+// Valid returns whether the value of act is defined.
+func (act KobjectAction) Valid() bool { return int(act) < len(kobject_actions) }
+
+// String returns the corresponding string sent over netlink.
+func (act KobjectAction) String() string {
+	if !act.Valid() {
+		return "unsupported kobject_action " + strconv.Itoa(int(act))
+	}
+	return kobject_actions[act]
+}
+
+func (act KobjectAction) AppendText(b []byte) ([]byte, error) {
+	if !act.Valid() {
+		return b, syscall.EINVAL
+	}
+	return append(b, act.String()...), nil
+}
+
+func (act KobjectAction) MarshalText() ([]byte, error) {
+	return act.AppendText(nil)
+}
+
+// An UnsupportedActionError describes a string representation of [KobjectAction]
+// not yet supported by this package.
+type UnsupportedActionError string
+
+func (e UnsupportedActionError) Error() string {
+	return "unsupported kobject_action " + strconv.Quote(string(e))
+}
+
+func (act *KobjectAction) UnmarshalText(data []byte) error {
+	for v, s := range kobject_actions {
+		if string(data) == s {
+			*act = KobjectAction(v)
+			return nil
+		}
+	}
+	return UnsupportedActionError(data)
+}