internal/uevent: enumerate objects via sysfs

This is not a great way to implement cold boot, but I already have the implementation lying around.

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

internal/uevent/action.go

@@ -19,6 +19,10 @@ const (
 	KOBJ_OFFLINE
 	KOBJ_BIND
 	KOBJ_UNBIND
+
+	// Synthetic denotes a [Message] that originates from outside the kernel. It
+	// is not valid in the wire format and is only meaningful within this package.
+	Synthetic KobjectAction = 0xfeed
 )
 
 // lib/kobject_uevent.c
@@ -38,6 +42,10 @@ 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 == Synthetic {
+		return "synthetic"
+	}
+
 	if !act.Valid() {
 		return "unsupported kobject_action " + strconv.Itoa(int(act))
 	}
@@ -45,7 +53,7 @@ func (act KobjectAction) String() string {
 }
 
 func (act KobjectAction) AppendText(b []byte) ([]byte, error) {
-	if !act.Valid() {
+	if !act.Valid() && act != Synthetic {
 		return b, syscall.EINVAL
 	}
 	return append(b, act.String()...), nil