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* Add markdown linting - add linter default rules - adapt rules to current code - fix the code for linting to pass - add CI check fix #1243 * Fix markdown for Substrate * Fix tooling install * Fix workflow * Add documentation * Remove trailing spaces * Update .github/.markdownlint.yaml Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io> * Fix mangled markdown/lists * Fix captalization issues on known words
90 lines
3.5 KiB
Markdown
90 lines
3.5 KiB
Markdown
# Shared Pallet
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This module is responsible for managing shared storage and configuration for other modules.
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It is important that other pallets are able to use the Shared Module, so it should not have a dependency on any other
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modules in the Parachains Runtime.
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For the moment, it is used exclusively to track the current session index across the Parachains Runtime system, and when
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it should be allowed to schedule future changes to Paras or Configurations.
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## Constants
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```rust
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// `SESSION_DELAY` is used to delay any changes to Paras registration or configurations.
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// Wait until the session index is 2 larger then the current index to apply any changes,
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// which guarantees that at least one full session has passed before any changes are applied.
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pub(crate) const SESSION_DELAY: SessionIndex = 2;
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```
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## Storage
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Helper structs:
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```rust
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struct AllowedRelayParentsTracker<Hash, BlockNumber> {
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// The past relay parents, paired with state roots, that are viable to build upon.
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//
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// They are in ascending chronologic order, so the newest relay parents are at
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// the back of the deque.
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//
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// (relay_parent, state_root)
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//
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// NOTE: the size limit of look-back is currently defined as a constant in Runtime.
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buffer: VecDeque<(Hash, Hash)>,
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// The number of the most recent relay-parent, if any.
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latest_number: BlockNumber,
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}
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```
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Storage Layout:
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```rust
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/// The current session index within the Parachains Runtime system.
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CurrentSessionIndex: SessionIndex;
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/// All the validators actively participating in parachain consensus.
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/// Indices are into the broader validator set.
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ActiveValidatorIndices: Vec<ValidatorIndex>,
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/// The parachain attestation keys of the validators actively participating in parachain consensus.
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/// This should be the same length as `ActiveValidatorIndices`.
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ActiveValidatorKeys: Vec<ValidatorId>
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/// Relay-parents allowed to build candidates upon.
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AllowedRelayParents: AllowedRelayParentsTracker<T::Hash, T::BlockNumber>,
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```
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## Initialization
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The Shared Module currently has no initialization routines.
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The Shared Module is initialized directly after the Configuration module, but before all other modules. It is important
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to update the Shared Module before any other module since its state may be used within the logic of other modules, and
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it is important that the state is consistent across them.
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## Session Change
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During a session change, the Shared Module receives and stores the current Session Index directly from the initializer
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module, along with the broader validator set, and it returns the new list of validators.
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The list of validators should be first shuffled according to the chain's random seed and then truncated. The indices of
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these validators should be set to `ActiveValidatorIndices` and then returned back to the initializer.
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`ActiveValidatorKeys` should be set accordingly.
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This information is used in the:
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* Configuration Module: For delaying updates to configurations until at lease one full session has passed.
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* Paras Module: For delaying updates to paras until at least one full session has passed.
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Allowed relay parents buffer, which is maintained by [ParaInherent](./parainherent.md) module, is cleared on every
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session change.
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## Finalization
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The Shared Module currently has no finalization routines.
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## Functions
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* `scheduled_sessions() -> SessionIndex`: Return the next session index where updates to the Parachains Runtime system
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would be safe to apply.
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* `set_session_index(SessionIndex)`: For tests. Set the current session index in the Shared Module.
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