Merge branch 'master' into ao-past-session-slashing-runtime

* master:
  Companion: wasm-builder support stable Rust (#6967)
  Fix feature (#6966)
  configuration: backport async backing parameters from the feature branch (#6961)
  Histogram support in runtime metrics (#6935)
  Bump openssl from 0.10.38 to 0.10.48 (#6955)
  Proxy for Nomination Pools (#6846)
  Nomination Pools migration v5: RewardPool fix (#6957)
  bump timestamp script to v0.2 (#6954)
  Subsystem channel tweaks (#6905)
  Companion for #13683 (#6944)
  inherent disputes: remove per block initializer and disputes timeout event (#6937)

primitives/src/vstaging/mod.rs

@@ -17,5 +17,26 @@
 //! Staging Primitives.
 
 // Put any primitives used by staging APIs functions here
+pub use crate::v4::*;
+use sp_std::prelude::*;
 
-pub mod slashing;
+use parity_scale_codec::{Decode, Encode};
+use primitives::RuntimeDebug;
+use scale_info::TypeInfo;
+
+/// Candidate's acceptance limitations for asynchronous backing per relay parent.
+#[derive(RuntimeDebug, Copy, Clone, PartialEq, Encode, Decode, TypeInfo)]
+#[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+pub struct AsyncBackingParams {
+	/// The maximum number of para blocks between the para head in a relay parent
+	/// and a new candidate. Restricts nodes from building arbitrary long chains
+	/// and spamming other validators.
+	///
+	/// When async backing is disabled, the only valid value is 0.
+	pub max_candidate_depth: u32,
+	/// How many ancestors of a relay parent are allowed to build candidates on top
+	/// of.
+	///
+	/// When async backing is disabled, the only valid value is 0.
+	pub allowed_ancestry_len: u32,
+}