PoV Reclaim (Clawback) Node Side (#1462)

This PR provides the infrastructure for the pov-reclaim mechanism
discussed in #209. The goal is to provide the current proof size to the
runtime so it can be used to reclaim storage weight.

## New Host Function
- A new host function is provided
[here](https://github.com/skunert/polkadot-sdk/blob/5b317fda3be205f4136f10d4490387ccd4f9765d/cumulus/primitives/pov-reclaim/src/lib.rs#L23).
It returns the size of the current proof size to the runtime. If
recording is not enabled, it returns 0.

## Implementation Overview
- Implement option to enable proof recording during import in the
client. This is currently enabled for `polkadot-parachain`,
`parachain-template` and the cumulus test node.
- Make the proof recorder ready for no-std. It was previously only
enabled for std environments, but we need to record the proof size in
`validate_block` too.
- Provide a recorder implementation that only the records the size of
incoming nodes and does not store the nodes itself.
- Fix benchmarks that were broken by async backing changes
- Provide new externalities extension that is registered by default if
proof recording is enabled.
- I think we should discuss the naming, pov-reclaim was more intuitive
to me, but we could also go with clawback like in the issue.

## Impact of proof recording during import
With proof recording: 6.3058 Kelem/s
Without proof recording: 6.3427 Kelem/s

The measured impact on the importing performance is quite low on my
machine using the block import benchmark. With proof recording I am
seeing a performance hit of 0.585%.

---------

Co-authored-by: command-bot <>
Co-authored-by: Davide Galassi <davxy@datawok.net>
Co-authored-by: Bastian Köcher <git@kchr.de>

cumulus/primitives/proof-size-hostfunction/src/lib.rs

@@ -0,0 +1,107 @@
+// Copyright (C) Parity Technologies (UK) Ltd.
+// This file is part of Cumulus.
+
+// Cumulus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Cumulus.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Tools for reclaiming PoV weight in parachain runtimes.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use sp_externalities::ExternalitiesExt;
+
+use sp_runtime_interface::runtime_interface;
+
+#[cfg(feature = "std")]
+use sp_trie::proof_size_extension::ProofSizeExt;
+
+pub const PROOF_RECORDING_DISABLED: u64 = u64::MAX;
+
+/// Interface that provides access to the current storage proof size.
+///
+/// Should return the current storage proof size if [`ProofSizeExt`] is registered. Otherwise, needs
+/// to return u64::MAX.
+#[runtime_interface]
+pub trait StorageProofSize {
+	/// Returns the current storage proof size.
+	fn storage_proof_size(&mut self) -> u64 {
+		self.extension::<ProofSizeExt>().map_or(u64::MAX, |e| e.storage_proof_size())
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use sp_core::Blake2Hasher;
+	use sp_state_machine::TestExternalities;
+	use sp_trie::{
+		proof_size_extension::ProofSizeExt, recorder::Recorder, LayoutV1, PrefixedMemoryDB,
+		TrieDBMutBuilder, TrieMut,
+	};
+
+	use crate::{storage_proof_size, PROOF_RECORDING_DISABLED};
+
+	const TEST_DATA: &[(&[u8], &[u8])] = &[(b"key1", &[1; 64]), (b"key2", &[2; 64])];
+
+	type TestLayout = LayoutV1<sp_core::Blake2Hasher>;
+
+	fn get_prepared_test_externalities() -> (TestExternalities<Blake2Hasher>, Recorder<Blake2Hasher>)
+	{
+		let mut db = PrefixedMemoryDB::default();
+		let mut root = Default::default();
+
+		{
+			let mut trie = TrieDBMutBuilder::<TestLayout>::new(&mut db, &mut root).build();
+			for (k, v) in TEST_DATA {
+				trie.insert(k, v).expect("Inserts data");
+			}
+		}
+
+		let recorder: sp_trie::recorder::Recorder<Blake2Hasher> = Default::default();
+		let trie_backend = sp_state_machine::TrieBackendBuilder::new(db, root)
+			.with_recorder(recorder.clone())
+			.build();
+
+		let mut ext: TestExternalities<Blake2Hasher> = TestExternalities::default();
+		ext.backend = trie_backend;
+		(ext, recorder)
+	}
+
+	#[test]
+	fn host_function_returns_size_from_recorder() {
+		let (mut ext, recorder) = get_prepared_test_externalities();
+		ext.register_extension(ProofSizeExt::new(recorder));
+
+		ext.execute_with(|| {
+			assert_eq!(storage_proof_size::storage_proof_size(), 0);
+			sp_io::storage::get(b"key1");
+			assert_eq!(storage_proof_size::storage_proof_size(), 175);
+			sp_io::storage::get(b"key2");
+			assert_eq!(storage_proof_size::storage_proof_size(), 275);
+			sp_io::storage::get(b"key2");
+			assert_eq!(storage_proof_size::storage_proof_size(), 275);
+		});
+	}
+
+	#[test]
+	fn host_function_returns_max_without_extension() {
+		let (mut ext, _) = get_prepared_test_externalities();
+
+		ext.execute_with(|| {
+			assert_eq!(storage_proof_size::storage_proof_size(), PROOF_RECORDING_DISABLED);
+			sp_io::storage::get(b"key1");
+			assert_eq!(storage_proof_size::storage_proof_size(), PROOF_RECORDING_DISABLED);
+			sp_io::storage::get(b"key2");
+			assert_eq!(storage_proof_size::storage_proof_size(), PROOF_RECORDING_DISABLED);
+		});
+	}
+}