Migrate parachain swaps to Coretime (#3714)

This PR notifies broker pallet for any parachain slot swaps performed on
the relay chain. This is achieved by registering an `OnSwap` for the the
`coretime` pallet. The hook sends XCM message to the broker chain and
invokes a new extrinsic `swap_leases` which updates `Leases` storage
item (which keeps the legacy parachain leases).

I made two assumptions in this PR:
1.
[`Leases`](https://github.com/paritytech/polkadot-sdk/blob/4987d7982461e2e5ffe219cdf71ec697284cea7c/substrate/frame/broker/src/lib.rs#L120)
in `broker` pallet and
[`Leases`](https://github.com/paritytech/polkadot-sdk/blob/4987d7982461e2e5ffe219cdf71ec697284cea7c/polkadot/runtime/common/src/slots/mod.rs#L118)
in `slots` pallet are in sync.
2. `swap_leases` extrinsic from `broker` pallet can be triggered only by
root or by the XCM message from the relay chain. If not - the extrinsic
will generate an error and do nothing.

As a side effect from the changes `OnSwap` trait is moved from
runtime/common/traits.rs to runtime/parachains. Otherwise it is not
accessible from `broker` pallet.

Closes #3552

TODOs:

- [x] Weights
- [x] Tests

---------

Co-authored-by: command-bot <>
Co-authored-by: eskimor <eskimor@users.noreply.github.com>
Co-authored-by: Bastian Köcher <git@kchr.de>

polkadot/runtime/parachains/src/coretime/mod.rs

@@ -83,6 +83,8 @@ enum CoretimeCalls {
 	SetLease(pallet_broker::TaskId, pallet_broker::Timeslice),
 	#[codec(index = 19)]
 	NotifyCoreCount(u16),
+	#[codec(index = 99)]
+	SwapLeases(ParaId, ParaId),
 }
 
 #[frame_support::pallet]
@@ -233,6 +235,24 @@ impl<T: Config> Pallet<T> {
 			}
 		}
 	}
+
+	// Handle legacy swaps in coretime. Notifies broker parachain that a lease swap has occurred via
+	// XCM message. This function is meant to be used in an implementation of `OnSwap` trait.
+	pub fn on_legacy_lease_swap(one: ParaId, other: ParaId) {
+		let message = Xcm(vec![
+			Instruction::UnpaidExecution {
+				weight_limit: WeightLimit::Unlimited,
+				check_origin: None,
+			},
+			mk_coretime_call(crate::coretime::CoretimeCalls::SwapLeases(one, other)),
+		]);
+		if let Err(err) = send_xcm::<T::SendXcm>(
+			Location::new(0, [Junction::Parachain(T::BrokerId::get())]),
+			message,
+		) {
+			log::error!("Sending `SwapLeases` to coretime chain failed: {:?}", err);
+		}
+	}
 }
 
 impl<T: Config> OnNewSession<BlockNumberFor<T>> for Pallet<T> {

polkadot/runtime/rococo/src/lib.rs

@@ -38,7 +38,7 @@ use runtime_common::{
 		LocatableAssetConverter, ToAuthor, VersionedLocatableAsset, VersionedLocationConverter,
 	},
 	paras_registrar, paras_sudo_wrapper, prod_or_fast, slots,
-	traits::Leaser,
+	traits::{Leaser, OnSwap},
 	BlockHashCount, BlockLength, SlowAdjustingFeeUpdate,
 };
 use scale_info::TypeInfo;
@@ -1078,7 +1078,7 @@ impl paras_registrar::Config for Runtime {
 	type RuntimeOrigin = RuntimeOrigin;
 	type RuntimeEvent = RuntimeEvent;
 	type Currency = Balances;
-	type OnSwap = (Crowdloan, Slots);
+	type OnSwap = (Crowdloan, Slots, SwapLeases);
 	type ParaDeposit = ParaDeposit;
 	type DataDepositPerByte = DataDepositPerByte;
 	type WeightInfo = weights::runtime_common_paras_registrar::WeightInfo<Runtime>;
@@ -1306,6 +1306,14 @@ impl pallet_asset_rate::Config for Runtime {
 	type BenchmarkHelper = runtime_common::impls::benchmarks::AssetRateArguments;
 }
 
+// Notify `coretime` pallet when a lease swap occurs
+pub struct SwapLeases;
+impl OnSwap for SwapLeases {
+	fn on_swap(one: ParaId, other: ParaId) {
+		coretime::Pallet::<Runtime>::on_legacy_lease_swap(one, other);
+	}
+}
+
 construct_runtime! {
 	pub enum Runtime
 	{

polkadot/runtime/westend/src/lib.rs

@@ -62,7 +62,7 @@ use runtime_common::{
 		LocatableAssetConverter, ToAuthor, VersionedLocatableAsset, VersionedLocationConverter,
 	},
 	paras_registrar, paras_sudo_wrapper, prod_or_fast, slots,
-	traits::Leaser,
+	traits::{Leaser, OnSwap},
 	BalanceToU256, BlockHashCount, BlockLength, CurrencyToVote, SlowAdjustingFeeUpdate,
 	U256ToBalance,
 };
@@ -1302,7 +1302,7 @@ impl paras_registrar::Config for Runtime {
 	type RuntimeOrigin = RuntimeOrigin;
 	type RuntimeEvent = RuntimeEvent;
 	type Currency = Balances;
-	type OnSwap = (Crowdloan, Slots);
+	type OnSwap = (Crowdloan, Slots, SwapLeases);
 	type ParaDeposit = ParaDeposit;
 	type DataDepositPerByte = RegistrarDataDepositPerByte;
 	type WeightInfo = weights::runtime_common_paras_registrar::WeightInfo<Runtime>;
@@ -1414,6 +1414,14 @@ impl pallet_asset_rate::Config for Runtime {
 	type BenchmarkHelper = runtime_common::impls::benchmarks::AssetRateArguments;
 }
 
+// Notify `coretime` pallet when a lease swap occurs
+pub struct SwapLeases;
+impl OnSwap for SwapLeases {
+	fn on_swap(one: ParaId, other: ParaId) {
+		coretime::Pallet::<Runtime>::on_legacy_lease_swap(one, other);
+	}
+}
+
 #[frame_support::runtime(legacy_ordering)]
 mod runtime {
 	#[runtime::runtime]

prdoc/pr_3714.prdoc

@@ -0,0 +1,10 @@
+title: Handle legacy lease swaps on coretime
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      When a `registar::swap` extrinsic is executed it swaps two leases on the relay chain but the
+      broker chain never knows about this swap. This change notifies the broker chain via a XCM
+      message for a swap so that it can update its state.
+crates:
+  - name: pallet-broker

substrate/frame/broker/src/benchmarking.rs

@@ -918,6 +918,23 @@ mod benches {
 		Ok(())
 	}
 
+	#[benchmark]
+	fn swap_leases() -> Result<(), BenchmarkError> {
+		let admin_origin =
+			T::AdminOrigin::try_successful_origin().map_err(|_| BenchmarkError::Weightless)?;
+
+		// Add two leases in `Leases`
+		let n = (T::MaxLeasedCores::get() / 2) as usize;
+		let mut leases = vec![LeaseRecordItem { task: 1, until: 10u32.into() }; n];
+		leases.extend(vec![LeaseRecordItem { task: 2, until: 20u32.into() }; n]);
+		Leases::<T>::put(BoundedVec::try_from(leases).unwrap());
+
+		#[extrinsic_call]
+		_(admin_origin as T::RuntimeOrigin, 1, 2);
+
+		Ok(())
+	}
+
 	// Implements a test for each benchmark. Execute with:
 	// `cargo test -p pallet-broker --features runtime-benchmarks`.
 	impl_benchmark_test_suite!(Pallet, crate::mock::new_test_ext(), crate::mock::Test);

substrate/frame/broker/src/dispatchable_impls.rs

@@ -437,4 +437,22 @@ impl<T: Config> Pallet<T> {
 		Self::deposit_event(Event::AllowedRenewalDropped { core, when });
 		Ok(())
 	}
+
+	pub(crate) fn do_swap_leases(id: TaskId, other: TaskId) -> DispatchResult {
+		let mut id_leases_count = 0;
+		let mut other_leases_count = 0;
+		Leases::<T>::mutate(|leases| {
+			leases.iter_mut().for_each(|lease| {
+				if lease.task == id {
+					lease.task = other;
+					id_leases_count += 1;
+				} else if lease.task == other {
+					lease.task = id;
+					other_leases_count += 1;
+				}
+			})
+		});
+
+		Ok(())
+	}
 }

substrate/frame/broker/src/lib.rs

@@ -786,5 +786,13 @@ pub mod pallet {
 			Self::do_notify_core_count(core_count)?;
 			Ok(())
 		}
+
+		#[pallet::call_index(99)]
+		#[pallet::weight(T::WeightInfo::swap_leases())]
+		pub fn swap_leases(origin: OriginFor<T>, id: TaskId, other: TaskId) -> DispatchResult {
+			T::AdminOrigin::ensure_origin_or_root(origin)?;
+			Self::do_swap_leases(id, other)?;
+			Ok(())
+		}
 	}
 }