some initial spans for approval voting (#2525)

* some initial spans for approval voting

* add stage earlier

polkadot/node/jaeger/src/lib.rs

@@ -45,7 +45,8 @@
 //! ```
 
 use sp_core::traits::SpawnNamed;
-use polkadot_primitives::v1::{CandidateHash, Hash, PoV, ValidatorIndex};
+use polkadot_primitives::v1::{CandidateHash, Hash, PoV, ValidatorIndex, BlakeTwo256, HashT};
+use parity_scale_codec::Encode;
 use sc_network::PeerId;
 
 use parking_lot::RwLock;
@@ -176,6 +177,7 @@ pub enum Stage {
 	AvailabilityDistribution = 5,
 	AvailabilityRecovery = 6,
 	BitfieldDistribution = 7,
+	ApprovalChecking = 8,
 	// Expand as needed, numbers should be ascending according to the stage
 	// through the inclusion pipeline, or according to the descriptions
 	// in [the path of a para chain block]
@@ -381,6 +383,15 @@ pub fn hash_span(hash: &Hash, span_name: &'static str) -> Span {
 	span
 }
 
+/// Creates a `Span` referring to the given descriptor, which should be unique.
+#[inline(always)]
+pub fn descriptor_span(descriptor: impl Encode, span_name: &'static str) -> Span {
+	INSTANCE.read_recursive().span(
+		|| { BlakeTwo256::hash_of(&descriptor) },
+		span_name,
+	).into()
+}
+
 /// Stateful convenience wrapper around [`mick_jaeger`].
 pub enum Jaeger {
 	/// Launched and operational state.