babe: support online configuration upgrades

client/consensus/babe/src/authorship.rs

@@ -19,7 +19,7 @@
 use merlin::Transcript;
 use sp_consensus_babe::{
 	AuthorityId, BabeAuthorityWeight, BABE_ENGINE_ID, BABE_VRF_PREFIX,
-	SlotNumber, AuthorityPair, BabeConfiguration
+	SlotNumber, AuthorityPair,
 };
 use sp_consensus_babe::digests::{PreDigest, PrimaryPreDigest, SecondaryPreDigest};
 use sp_consensus_vrf::schnorrkel::{VRFOutput, VRFProof};
@@ -147,12 +147,11 @@ fn claim_secondary_slot(
 pub fn claim_slot(
 	slot_number: SlotNumber,
 	epoch: &Epoch,
-	config: &BabeConfiguration,
 	keystore: &KeyStorePtr,
 ) -> Option<(PreDigest, AuthorityPair)> {
-	claim_primary_slot(slot_number, epoch, config.c, keystore)
+	claim_primary_slot(slot_number, epoch, epoch.config.c, keystore)
 		.or_else(|| {
-			if config.secondary_slots {
+			if epoch.config.secondary_slots {
 				claim_secondary_slot(
 					slot_number,
 					&epoch.authorities,

client/consensus/babe/src/lib.rs

@@ -59,7 +59,8 @@
 #![forbid(unsafe_code)]
 #![warn(missing_docs)]
 pub use sp_consensus_babe::{
-	BabeApi, ConsensusLog, BABE_ENGINE_ID, SlotNumber, BabeConfiguration,
+	BabeApi, ConsensusLog, BABE_ENGINE_ID, SlotNumber,
+	BabeEpochConfiguration, BabeGenesisConfiguration,
 	AuthorityId, AuthorityPair, AuthoritySignature,
 	BabeAuthorityWeight, VRF_OUTPUT_LENGTH,
 	digests::{
@@ -123,31 +124,37 @@ pub mod authorship;
 mod tests;
 
 /// BABE epoch information
-#[derive(Decode, Encode, Default, PartialEq, Eq, Clone, Debug)]
+#[derive(Decode, Encode, PartialEq, Eq, Clone, Debug)]
 pub struct Epoch {
-	/// The epoch index
+	/// The epoch index.
 	pub epoch_index: u64,
-	/// The starting slot of the epoch,
+	/// The starting slot of the epoch.
 	pub start_slot: SlotNumber,
-	/// The duration of this epoch
+	/// The duration of this epoch.
 	pub duration: SlotNumber,
-	/// The authorities and their weights
+	/// The authorities and their weights.
 	pub authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
-	/// Randomness for this epoch
+	/// Randomness for this epoch.
 	pub randomness: [u8; VRF_OUTPUT_LENGTH],
+	/// Configuration of the epoch.
+	pub config: BabeEpochConfiguration,
 }
 
 impl EpochT for Epoch {
-	type NextEpochDescriptor = NextEpochDescriptor;
+	type NextEpochDescriptor = (NextEpochDescriptor, BabeEpochConfiguration);
 	type SlotNumber = SlotNumber;
 
-	fn increment(&self, descriptor: NextEpochDescriptor) -> Epoch {
+	fn increment(
+		&self,
+		(descriptor, config): (NextEpochDescriptor, BabeEpochConfiguration)
+	) -> Epoch {
 		Epoch {
 			epoch_index: self.epoch_index + 1,
 			start_slot: self.start_slot + self.duration,
 			duration: self.duration,
 			authorities: descriptor.authorities,
 			randomness: descriptor.randomness,
+			config,
 		}
 	}
 
@@ -160,6 +167,25 @@ impl EpochT for Epoch {
 	}
 }
 
+impl Epoch {
+	/// Create the genesis epoch (epoch #0). This is defined to start at the slot of
+	/// the first block, so that has to be provided.
+	pub fn genesis(
+		genesis_config: &BabeGenesisConfiguration,
+		epoch_config: &BabeEpochConfiguration,
+		slot_number: SlotNumber
+	) -> Epoch {
+		Epoch {
+			epoch_index: 0,
+			start_slot: slot_number,
+			duration: epoch_config.epoch_length,
+			authorities: genesis_config.genesis_authorities.clone(),
+			randomness: genesis_config.randomness.clone(),
+			config: epoch_config.clone(),
+		}
+	}
+}
+
 #[derive(derive_more::Display, Debug)]
 enum Error<B: BlockT> {
 	#[display(fmt = "Multiple BABE pre-runtime digests, rejecting!")]
@@ -168,6 +194,8 @@ enum Error<B: BlockT> {
 	NoPreRuntimeDigest,
 	#[display(fmt = "Multiple BABE epoch change digests, rejecting!")]
 	MultipleEpochChangeDigests,
+	#[display(fmt = "Fetch new epoch configuration failed")]
+	FetchEpochConfig(B::Hash),
 	#[display(fmt = "Could not extract timestamp and slot: {:?}", _0)]
 	Extraction(sp_consensus::Error),
 	#[display(fmt = "Could not fetch epoch at {:?}", _0)]
@@ -246,7 +274,7 @@ pub static INTERMEDIATE_KEY: &[u8] = b"babe1";
 // and `super::babe::Config` can be eliminated.
 // https://github.com/paritytech/substrate/issues/2434
 #[derive(Clone)]
-pub struct Config(sc_consensus_slots::SlotDuration<BabeConfiguration>);
+pub struct Config(sc_consensus_slots::SlotDuration<BabeGenesisConfiguration>);
 
 impl Config {
 	/// Either fetch the slot duration from disk or compute it from the genesis
@@ -255,32 +283,22 @@ impl Config {
 		C: AuxStore + ProvideRuntimeApi<B>, C::Api: BabeApi<B, Error = sp_blockchain::Error>,
 	{
 		trace!(target: "babe", "Getting slot duration");
-		match sc_consensus_slots::SlotDuration::get_or_compute(client, |a, b| a.configuration(b)).map(Self) {
+		match sc_consensus_slots::SlotDuration::get_or_compute(client, |a, b| {
+			a.genesis_configuration(b)
+		}).map(Self) {
 			Ok(s) => Ok(s),
 			Err(s) => {
 				warn!(target: "babe", "Failed to get slot duration");
 				Err(s)
 			}
 		}
 	}
-
-	/// Create the genesis epoch (epoch #0). This is defined to start at the slot of
-	/// the first block, so that has to be provided.
-	pub fn genesis_epoch(&self, slot_number: SlotNumber) -> Epoch {
-		Epoch {
-			epoch_index: 0,
-			start_slot: slot_number,
-			duration: self.epoch_length,
-			authorities: self.genesis_authorities.clone(),
-			randomness: self.randomness.clone(),
-		}
-	}
 }
 
 impl std::ops::Deref for Config {
-	type Target = BabeConfiguration;
+	type Target = BabeGenesisConfiguration;
 
-	fn deref(&self) -> &BabeConfiguration {
+	fn deref(&self) -> &BabeGenesisConfiguration {
 		&*self.0
 	}
 }
@@ -438,7 +456,12 @@ impl<B, C, E, I, Error, SO> sc_consensus_slots::SimpleSlotWorker<B> for BabeWork
 
 	fn authorities_len(&self, epoch_descriptor: &Self::EpochData) -> Option<usize> {
 		self.epoch_changes.lock()
-			.viable_epoch(&epoch_descriptor, |slot| self.config.genesis_epoch(slot))
+			.viable_epoch(&epoch_descriptor, |slot| {
+				let epoch_config = self.client.runtime_api()
+					.epoch_configuration(&BlockId::number(Zero::zero()))
+					.ok()?;
+				Some(Epoch::genesis(&self.config, &epoch_config, slot))
+			})
 			.map(|epoch| epoch.as_ref().authorities.len())
 	}
 
@@ -453,9 +476,13 @@ impl<B, C, E, I, Error, SO> sc_consensus_slots::SimpleSlotWorker<B> for BabeWork
 			slot_number,
 			self.epoch_changes.lock().viable_epoch(
 				&epoch_descriptor,
-				|slot| self.config.genesis_epoch(slot)
+				|slot| {
+					let epoch_config = self.client.runtime_api()
+						.epoch_configuration(&BlockId::number(Zero::zero()))
+						.ok()?;
+					Some(Epoch::genesis(&self.config, &epoch_config, slot))
+				}
 			)?.as_ref(),
-			&*self.config,
 			&self.keystore,
 		);
 
@@ -746,7 +773,12 @@ impl<Block, Client> Verifier<Block> for BabeVerifier<Block, Client> where
 			.ok_or_else(|| Error::<Block>::FetchEpoch(parent_hash))?;
 		let viable_epoch = epoch_changes.viable_epoch(
 			&epoch_descriptor,
-			|slot| self.config.genesis_epoch(slot)
+			|slot| {
+				let epoch_config = self.client.runtime_api()
+					.epoch_configuration(&BlockId::number(Zero::zero()))
+					.ok()?;
+				Some(Epoch::genesis(&self.config, &epoch_config, slot))
+			}
 		).ok_or_else(|| Error::<Block>::FetchEpoch(parent_hash))?;
 
 		// We add one to the current slot to allow for some small drift.
@@ -756,7 +788,6 @@ impl<Block, Client> Verifier<Block> for BabeVerifier<Block, Client> where
 			pre_digest: Some(pre_digest.clone()),
 			slot_now: slot_now + 1,
 			epoch: viable_epoch.as_ref(),
-			config: &self.config,
 		};
 
 		match verification::check_header::<Block>(v_params)? {
@@ -1005,18 +1036,29 @@ impl<Block, Client, Inner> BlockImport<Block> for BabeBlockImport<Block, Client,
 
 			let viable_epoch = epoch_changes.viable_epoch(
 				&epoch_descriptor,
-				|slot| self.config.genesis_epoch(slot),
+				|slot| {
+					let epoch_config = self.client.runtime_api()
+						.epoch_configuration(&BlockId::number(Zero::zero()))
+						.ok()?;
+					Some(Epoch::genesis(&self.config, &epoch_config, slot))
+				}
 			).ok_or_else(|| {
 				ConsensusError::ClientImport(Error::<Block>::FetchEpoch(parent_hash).into())
 			})?;
 
+			let epoch_config = self.client.runtime_api()
+				.epoch_configuration(&BlockId::hash(parent_hash))
+				.map_err(|_| ConsensusError::ClientImport(
+					Error::<Block>::FetchEpochConfig(parent_hash).into()
+				))?;
+
 			babe_info!("👶 New epoch {} launching at block {} (block slot {} >= start slot {}).",
 					   viable_epoch.as_ref().epoch_index,
 					   hash,
 					   slot_number,
 					   viable_epoch.as_ref().start_slot);
 
-			let next_epoch = viable_epoch.increment(next_epoch_descriptor);
+			let next_epoch = viable_epoch.increment((next_epoch_descriptor, epoch_config));
 
 			babe_info!("👶 Next epoch starts at slot {}", next_epoch.as_ref().start_slot);
 

client/consensus/babe/src/verification.rs

@@ -38,8 +38,6 @@ pub(super) struct VerificationParams<'a, B: 'a + BlockT> {
 	pub(super) slot_now: SlotNumber,
 	/// epoch descriptor of the epoch this block _should_ be under, if it's valid.
 	pub(super) epoch: &'a Epoch,
-	/// genesis config of this BABE chain.
-	pub(super) config: &'a super::Config,
 }
 
 /// Check a header has been signed by the right key. If the slot is too far in
@@ -63,7 +61,6 @@ pub(super) fn check_header<B: BlockT + Sized>(
 		pre_digest,
 		slot_now,
 		epoch,
-		config,
 	} = params;
 
 	let authorities = &epoch.authorities;
@@ -102,10 +99,10 @@ pub(super) fn check_header<B: BlockT + Sized>(
 				primary,
 				sig,
 				&epoch,
-				config.c,
+				epoch.config.c,
 			)?;
 		},
-		PreDigest::Secondary(secondary) if config.secondary_slots => {
+		PreDigest::Secondary(secondary) if epoch.config.secondary_slots => {
 			debug!(target: "babe", "Verifying Secondary block");
 
 			check_secondary_header::<B>(

client/consensus/epochs/src/lib.rs

@@ -394,11 +394,11 @@ impl<Hash, Number, E: Epoch> EpochChanges<Hash, Number, E> where
 		descriptor: &ViableEpochDescriptor<Hash, Number, E>,
 		make_genesis: G,
 	) -> Option<ViableEpoch<E, &E>> where
-		G: FnOnce(E::SlotNumber) -> E
+		G: FnOnce(E::SlotNumber) -> Option<E>
 	{
 		match descriptor {
 			ViableEpochDescriptor::UnimportedGenesis(slot_number) => {
-				Some(ViableEpoch::UnimportedGenesis(make_genesis(*slot_number)))
+				make_genesis(*slot_number).map(ViableEpoch::UnimportedGenesis)
 			},
 			ViableEpochDescriptor::Signaled(identifier, _) => {
 				self.epoch(&identifier).map(ViableEpoch::Signaled)

primitives/consensus/babe/src/lib.rs

@@ -89,15 +89,32 @@ pub enum ConsensusLog {
 	OnDisabled(AuthorityIndex),
 }
 
-/// Configuration data used by the BABE consensus engine.
+/// Genesis configuration data used by the BABE consensus engine.
 #[derive(Clone, PartialEq, Eq, Encode, Decode, RuntimeDebug)]
-pub struct BabeConfiguration {
+pub struct BabeGenesisConfiguration {
 	/// The slot duration in milliseconds for BABE. Currently, only
 	/// the value provided by this type at genesis will be used.
-	///
-	/// Dynamic slot duration may be supported in the future.
 	pub slot_duration: u64,
 
+	/// The authorities for the genesis epoch.
+	pub genesis_authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
+
+	/// The randomness for the genesis epoch.
+	pub randomness: Randomness,
+}
+
+#[cfg(feature = "std")]
+impl sp_consensus::SlotData for BabeGenesisConfiguration {
+	fn slot_duration(&self) -> u64 {
+		self.slot_duration
+	}
+
+	const SLOT_KEY: &'static [u8] = b"babe_configuration";
+}
+
+/// Configuration data used by the BABE consensus engine.
+#[derive(Clone, PartialEq, Eq, Encode, Decode, RuntimeDebug)]
+pub struct BabeEpochConfiguration {
 	/// The duration of epochs in slots.
 	pub epoch_length: SlotNumber,
 
@@ -109,34 +126,19 @@ pub struct BabeConfiguration {
 	/// of a slot being empty.
 	pub c: (u64, u64),
 
-	/// The authorities for the genesis epoch.
-	pub genesis_authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
-
-	/// The randomness for the genesis epoch.
-	pub randomness: Randomness,
-
 	/// Whether this chain should run with secondary slots, which are assigned
 	/// in round-robin manner.
 	pub secondary_slots: bool,
 }
 
-#[cfg(feature = "std")]
-impl sp_consensus::SlotData for BabeConfiguration {
-	fn slot_duration(&self) -> u64 {
-		self.slot_duration
-	}
-
-	const SLOT_KEY: &'static [u8] = b"babe_configuration";
-}
-
 sp_api::decl_runtime_apis! {
 	/// API necessary for block authorship with BABE.
 	pub trait BabeApi {
-		/// Return the configuration for BABE. Currently,
-		/// only the value provided by this type at genesis will be used.
-		///
-		/// Dynamic configuration may be supported in the future.
-		fn configuration() -> BabeConfiguration;
+		/// Return the epoch configuration for BABE. The configuration is read once every epoch.
+		fn epoch_configuration() -> BabeEpochConfiguration;
+
+		/// Return the genesis configuration for BABE. The configuration is only read on genesis.
+		fn genesis_configuration() -> BabeGenesisConfiguration;
 
 		/// Returns the slot number that started the current epoch.
 		fn current_epoch_start() -> SlotNumber;