beefy: add support to configure BEEFY genesis

client/beefy/src/lib.rs

@@ -53,7 +53,7 @@ use sp_keystore::SyncCryptoStorePtr;
 use sp_mmr_primitives::MmrApi;
 use sp_runtime::{
 	generic::BlockId,
-	traits::{Block, One, Zero},
+	traits::{Block, Zero},
 };
 use std::{collections::VecDeque, marker::PhantomData, sync::Arc};
 
@@ -344,6 +344,12 @@ where
 	R: ProvideRuntimeApi<B>,
 	R::Api: BeefyApi<B>,
 {
+	let beefy_genesis = runtime
+		.runtime_api()
+		.beefy_genesis(&BlockId::hash(best_grandpa.hash()))
+		.ok()
+		.flatten()
+		.ok_or_else(|| ClientError::Backend("BEEFY pallet expected to be active.".into()))?;
 	// Walk back the imported blocks and initialize voter either, at the last block with
 	// a BEEFY justification, or at pallet genesis block; voter will resume from there.
 	let blockchain = backend.blockchain();
@@ -376,19 +382,18 @@ where
 			break state
 		}
 
-		if *header.number() == One::one() {
-			// We've reached chain genesis, initialize voter here.
-			let genesis_num = *header.number();
+		if *header.number() == beefy_genesis {
+			// We've reached BEEFY genesis, initialize voter here.
 			let genesis_set = expect_validator_set(runtime, BlockId::hash(header.hash()))
 				.and_then(genesis_set_sanity_check)?;
 			info!(
 				target: "beefy",
 				"🥩 Loading BEEFY voter state from genesis on what appears to be first startup. \
 				Starting voting rounds at block {:?}, genesis validator set {:?}.",
-				genesis_num, genesis_set,
+				beefy_genesis, genesis_set,
 			);
 
-			sessions.push_front(Rounds::new(genesis_num, genesis_set));
+			sessions.push_front(Rounds::new(beefy_genesis, genesis_set));
 			break PersistedState::checked_new(best_grandpa, Zero::zero(), sessions, min_block_delta)
 				.ok_or_else(|| ClientError::Backend("Invalid BEEFY chain".into()))?
 		}
@@ -441,13 +446,16 @@ where
 					None => break
 				};
 				let at = BlockId::hash(notif.header.hash());
-				if let Some(active) = runtime.runtime_api().validator_set(&at).ok().flatten() {
-					// Beefy pallet available, return best grandpa at the time.
-					info!(
-						target: "beefy", "🥩 BEEFY pallet available: block {:?} validator set {:?}",
-						notif.header.number(), active
-					);
-					return Ok(notif.header)
+				if let Some(start) = runtime.runtime_api().beefy_genesis(&at).ok().flatten() {
+					if *notif.header.number() >= start {
+						// Beefy pallet available, return header for best grandpa at the time.
+						info!(
+							target: "beefy",
+							"🥩 BEEFY pallet available: block {:?} beefy genesis {:?}",
+							notif.header.number(), start
+						);
+						return Ok(notif.header)
+					}
 				}
 			},
 			_ = gossip_engine => {

client/beefy/src/tests.rs

@@ -252,6 +252,10 @@ macro_rules! create_test_api {
 			}
 			sp_api::mock_impl_runtime_apis! {
 				impl BeefyApi<Block> for RuntimeApi {
+					fn beefy_genesis() -> Option<NumberFor<Block>> {
+						Some(sp_runtime::traits::One::one())
+					}
+
 					fn validator_set() -> Option<BeefyValidatorSet> {
 						BeefyValidatorSet::new(make_beefy_ids(&[$($inits),+]), 0)
 					}

frame/beefy/src/lib.rs

@@ -49,6 +49,7 @@ pub use pallet::*;
 pub mod pallet {
 	use super::*;
 	use frame_support::pallet_prelude::*;
+	use frame_system::pallet_prelude::BlockNumberFor;
 
 	#[pallet::config]
 	pub trait Config: frame_system::Config {
@@ -91,15 +92,27 @@ pub mod pallet {
 	pub(super) type NextAuthorities<T: Config> =
 		StorageValue<_, BoundedVec<T::BeefyId, T::MaxAuthorities>, ValueQuery>;
 
+	/// Block number where BEEFY consensus is enabled/started
+	#[pallet::storage]
+	#[pallet::getter(fn genesis_block)]
+	pub(super) type GenesisBlock<T: Config> =
+		StorageValue<_, Option<BlockNumberFor<T>>, ValueQuery>;
+
 	#[pallet::genesis_config]
 	pub struct GenesisConfig<T: Config> {
+		/// Initial set of BEEFY authorities.
 		pub authorities: Vec<T::BeefyId>,
+		/// Block number where BEEFY consensus should start.
+		/// Should match the session where initial authorities are active.
+		/// *Note:* Ideally use block number where GRANDPA authorities are changed,
+		/// to guarantee the client gets a finality notification for exactly this block.
+		pub genesis_block: Option<BlockNumberFor<T>>,
 	}
 
 	#[cfg(feature = "std")]
 	impl<T: Config> Default for GenesisConfig<T> {
 		fn default() -> Self {
-			Self { authorities: Vec::new() }
+			Self { authorities: Vec::new(), genesis_block: None }
 		}
 	}
 
@@ -110,6 +123,7 @@ pub mod pallet {
 				// we panic here as runtime maintainers can simply reconfigure genesis and restart
 				// the chain easily
 				.expect("Authorities vec too big");
+			<GenesisBlock<T>>::put(&self.genesis_block);
 		}
 	}
 }

primitives/beefy/src/lib.rs

@@ -43,7 +43,7 @@ use codec::{Codec, Decode, Encode};
 use scale_info::TypeInfo;
 use sp_application_crypto::RuntimeAppPublic;
 use sp_core::H256;
-use sp_runtime::traits::Hash;
+use sp_runtime::traits::{Hash, NumberFor};
 use sp_std::prelude::*;
 
 /// Key type for BEEFY module.
@@ -201,6 +201,9 @@ sp_api::decl_runtime_apis! {
 	/// API necessary for BEEFY voters.
 	pub trait BeefyApi
 	{
+		/// Return the block number where BEEFY consensus is enabled/started
+		fn beefy_genesis() -> Option<NumberFor<Block>>;
+
 		/// Return the current active BEEFY validator set
 		fn validator_set() -> Option<ValidatorSet<crypto::AuthorityId>>;
 	}

test-utils/runtime/src/lib.rs

@@ -973,6 +973,10 @@ cfg_if! {
 			}
 
 			impl beefy_primitives::BeefyApi<Block> for Runtime {
+				fn beefy_genesis() -> Option<BlockNumber> {
+					None
+				}
+
 				fn validator_set() -> Option<beefy_primitives::ValidatorSet<beefy_primitives::crypto::AuthorityId>> {
 					None
 				}