frame/beefy: add privileged call to reset BEEFY consensus (#1534)

We want to be able to (re)set BEEFY genesis in order to (re)start BEEFY
consensus on chains which didn't run it since genesis.

This commit adds privileged helper call to (re)set BEEFY genesis to some
block in the future.

Signed-off-by: Adrian Catangiu <adrian@parity.io>

substrate/frame/beefy/src/default_weights.rs

@@ -49,4 +49,8 @@ impl crate::WeightInfo for () {
 			// fetching set id -> session index mappings
 			.saturating_add(DbWeight::get().reads(2))
 	}
+
+	fn set_new_genesis() -> Weight {
+		DbWeight::get().writes(1)
+	}
 }

substrate/frame/beefy/src/lib.rs

@@ -33,7 +33,7 @@ use frame_system::{
 use log;
 use sp_runtime::{
 	generic::DigestItem,
-	traits::{IsMember, Member},
+	traits::{IsMember, Member, One},
 	RuntimeAppPublic,
 };
 use sp_session::{GetSessionNumber, GetValidatorCount};
@@ -62,7 +62,7 @@ const LOG_TARGET: &str = "runtime::beefy";
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
-	use frame_system::pallet_prelude::BlockNumberFor;
+	use frame_system::{ensure_root, pallet_prelude::BlockNumberFor};
 
 	#[pallet::config]
 	pub trait Config: frame_system::Config {
@@ -152,8 +152,8 @@ pub mod pallet {
 		StorageMap<_, Twox64Concat, sp_consensus_beefy::ValidatorSetId, SessionIndex>;
 
 	/// Block number where BEEFY consensus is enabled/started.
-	/// By changing this (through governance or sudo), BEEFY consensus is effectively
-	/// restarted from the new block number.
+	/// By changing this (through privileged `set_new_genesis()`), BEEFY consensus is effectively
+	/// restarted from the newly set block number.
 	#[pallet::storage]
 	#[pallet::getter(fn genesis_block)]
 	pub(super) type GenesisBlock<T: Config> =
@@ -174,7 +174,7 @@ pub mod pallet {
 		fn default() -> Self {
 			// BEEFY genesis will be first BEEFY-MANDATORY block,
 			// use block number one instead of chain-genesis.
-			let genesis_block = Some(sp_runtime::traits::One::one());
+			let genesis_block = Some(One::one());
 			Self { authorities: Vec::new(), genesis_block }
 		}
 	}
@@ -198,6 +198,8 @@ pub mod pallet {
 		InvalidEquivocationProof,
 		/// A given equivocation report is valid but already previously reported.
 		DuplicateOffenceReport,
+		/// Submitted configuration is invalid.
+		InvalidConfiguration,
 	}
 
 	#[pallet::call]
@@ -265,6 +267,23 @@ pub mod pallet {
 			)?;
 			Ok(Pays::No.into())
 		}
+
+		/// Reset BEEFY consensus by setting a new BEEFY genesis at `delay_in_blocks` blocks in the
+		/// future.
+		///
+		/// Note: `delay_in_blocks` has to be at least 1.
+		#[pallet::call_index(2)]
+		#[pallet::weight(<T as Config>::WeightInfo::set_new_genesis())]
+		pub fn set_new_genesis(
+			origin: OriginFor<T>,
+			delay_in_blocks: BlockNumberFor<T>,
+		) -> DispatchResult {
+			ensure_root(origin)?;
+			ensure!(delay_in_blocks >= One::one(), Error::<T>::InvalidConfiguration);
+			let genesis_block = frame_system::Pallet::<T>::block_number() + delay_in_blocks;
+			GenesisBlock::<T>::put(Some(genesis_block));
+			Ok(())
+		}
 	}
 
 	#[pallet::validate_unsigned]
@@ -452,4 +471,5 @@ impl<T: Config> IsMember<T::BeefyId> for Pallet<T> {
 
 pub trait WeightInfo {
 	fn report_equivocation(validator_count: u32, max_nominators_per_validator: u32) -> Weight;
+	fn set_new_genesis() -> Weight;
 }

substrate/frame/beefy/src/tests.rs

@@ -791,3 +791,25 @@ fn valid_equivocation_reports_dont_pay_fees() {
 		assert_eq!(post_info.pays_fee, Pays::Yes);
 	})
 }
+
+#[test]
+fn set_new_genesis_works() {
+	let authorities = test_authorities();
+
+	new_test_ext_raw_authorities(authorities).execute_with(|| {
+		start_era(1);
+
+		let new_genesis_delay = 10u64;
+		// the call for setting new genesis should work
+		assert_ok!(Beefy::set_new_genesis(RuntimeOrigin::root(), new_genesis_delay,));
+		let expected = System::block_number() + new_genesis_delay;
+		// verify new genesis was set
+		assert_eq!(Beefy::genesis_block(), Some(expected));
+
+		// setting delay < 1 should fail
+		assert_err!(
+			Beefy::set_new_genesis(RuntimeOrigin::root(), 0u64,),
+			Error::<Test>::InvalidConfiguration,
+		);
+	});
+}