parachain_system

Branch/Release: release-polkadot-v1.10.0

Source Code

Purpose

This pallet is a core element of each parachain. It will:

  • Aggregate information about built blocks

  • Process binary code upgrades

  • Process incoming messages from both relay chain and other parachains (if a channel is established between them)

  • Send outgoing messages to relay chain and other parachains

  • Build collation info when requested by collator

Config

  • Pallet-specific configs:

    • OnSystemEvent — a handler that will be called when new validation data will be set (once each block). New validation data will also be passed to it. Look to trait OnSystemEvent for more details.

    • SelfParaId — getter for a parachain id of this chain

    • OutboundXcmpMessageSource — source of outgoing XCMP messages. It is queried in finalize_block and later included into collation information

    • DmpQueue — a handler for the incoming downward messages from relay chain

    • ReservedDmpWeight — weight reserved for DMP message processing. This config seems to be is not used as the function that processes these messages (enqueue_inbound_downward_messages) returns used weight.

    • XcmpMessageHandler — a handler for the incoming horizontal messages from other parachains

    • ReservedXcmpWeight — default weight limit for the for the XCMP message processing. May be overriden by storage ReservedXcmpWeightOverride . If incoming messages in block will exceed the weight limit, they won’t be processed.

    • CheckAssociatedRelayNumber — type that implements trait CheckAssociatedRelayNumber . Currently there are three implementations: no check (AnyRelayNumber), strict increase (RelayNumberStrictlyIncreases), monotonic increase (RelayNumberMonotonicallyIncreases). It is needed to maintain some order between blocks in relay chain and parachain.

    • ConsensusHook — this is a feature-enabled config ( for the management of the unincluded segment. Requires the implementation of trait ConsensusHook. There are several implementations of it, in parachain-system crate (FixedCapacityUnincludedSegment) and in aura-ext crate (FixedVelocityConsensusHook). It is needed to maintain the logic of segment length handling.

  • Common parameters for all pallets:

    • RuntimeEvent

    • WeightInfo

Dispatchables

set_validation_data

pub fn set_validation_data(
    data: ParachainInherentData,
)

This call is an inherent, you can’t call this from another dispatchable or from client side. This call sets up validation data for collation, processes code upgrades and updates unincluded segments.

sudo_send_upward_message

pub fn sudo_send_upward_message(
    message: UpwardMessage,
)

Send a message to relay as a sudo.

Params:

  • message — a vec of bytes that represents a message that you send to the relay

Errors:

  • BadOrigin — call was made not from a sudo

authorize_upgrade

pub fn authorize_upgrade(
    code_hash: T::Hash,
    check_version: bool,
)

Authorize the upgrade. This call will put the hash and flag to the storage AuthorizedUpgrade. This call must be made as a sudo.

Params:

  • code_hash — hash of the authorized runtime binary

  • check_version — flag that indicates that the code should be checked for the possibility to upgrade. It will happen during the upgrade process itself.

Errors:

  • BadOrigin — call was made not from a sudo

Events:

  • UpgradeAuthorized(code_hash)

enact_authorized_upgrade

pub fn enact_authorized_upgrade(
    code: Vec<u8>,
)

Validate and perform the authorized upgrade.

Params:

  • code — runtime binary for the upgrade

Errors:

  • NothingAuthorized — there is no authorized upgrade, call authorize_upgrade in advance

  • Unauthorized — there is another upgrade authorized

Important Mentions and FAQ’s

Pallet’s workflow

  • Block Initialization

    • Remove already processed validation code

    • Update UnincludedSegment with latest parent hash

    • Cleans up ValidationData and other functions.

    • Calculate weights for everything that was done in on_finalize hook

  • Inherents — set_validation_data call

    • Clean the included segments from UnincludedSegment and update the AggregatedUnincludedSegment

    • Update ValidationData, RelayStateProof and other configs from relay.

    • Process the ValidationCode upgrade

  • Block Finalization

    • Enqueue all received messages from relay chain and other parachains

    • Update UnincludedSegment and AggregatedUnincludedSegment with the latest block data

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