Expose some functions of frame-executive for building a custom executive easier

[liuchengxu]

A custom executive is required in Subspace, specifically, we would like to have a hook right after initialize_block and apply_extrinsic to collect the intermediate storage root during the entire block execution.

One idea is to create a wrapped pallet-executive on frame-executive, only copy a few functions(basically execute_block because it ties the initialize_block and extrinsic execution tightly) and make some modifications there, delegating all the other functions to frame-executive directly to minimize the maintenance of this custom pallet-executive. These functions just need to be made public in that way:

substrate/frame/executive/src/lib.rs

Line 336 in 48e0b41

fn initial_checks(block: &Block) {

substrate/frame/executive/src/lib.rs

Line 411 in 48e0b41

fn idle_and_finalize_hook(block_number: NumberFor<Block>) {

substrate/frame/executive/src/lib.rs

Line 468 in 48e0b41

fn final_checks(header: &System::Header) {

The another way could be some generic solution that is able to make the executive naturally more flexible to these custom needs, I haven't got a pretty clear idea though :P.

[liuchengxu]

@bkchr Any thoughts on this feature request?

[bkchr]

to collect the intermediate storage root during the entire block execution.

Collect and then? What you want to do with that?

What happens at block production?

[nazar-pc]

Normally state root is collected after block execution, we also collect additional state roots after each transaction to make fraud proofs more efficient in our protocol.

[bkchr]

And you store them in the state?

[nazar-pc]

Currently yes

[bkchr]

I just have skimmed your code and the only change you made is the storage root calculation after apply_extrinsic. Is that true?

If yes, adding some callback there should be enough for you?

[liuchengxu]

I just have skimmed your code and the only change you made is the storage root calculation after apply_extrinsic. Is that true?

Nope. Not only after apply_extrinsic, but also after initialize_block https://github.com/subspace/subspace/blob/438c569b38/cumulus/pallets/executive/src/lib.rs#L238.

adding some callback there should be enough for you?

Yeah, that should be enough, I need two hooks to run right after initialize_block and apply_extrinsic.

[bkchr]

Ahh okay, yeah than adding some callback to these both and maybe after calling on_finalize should be okay?

[bkchr]

WDYT @shawntabrizi

[liuchengxu]

Ping @shawntabrizi