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Merge bitcoin/bitcoin#31384: mining: bugfix: Fix duplicate coinbase tx weight reservation

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386eecff5f doc: add release notes (ismaelsadeeq)
3eaa0a3b66 miner: init: add `-blockreservedweight` startup option (ismaelsadeeq)
777434a2cd doc: rpc: improve `getmininginfo` help text (ismaelsadeeq)
c8acd4032d init: fail to start when `-blockmaxweight` exceeds `MAX_BLOCK_WEIGHT` (ismaelsadeeq)
5bb31633cc test: add `-blockmaxweight` startup option functional test (ismaelsadeeq)
2c7d90a6d6 miner: bugfix: fix duplicate weight reservation in block assembler (ismaelsadeeq)

Pull request description:

  * This PR attempts to fix the duplicate coinbase weight reservation issue we currently have.
  * Fixes #21950

  We reserve 4000 weight units for coinbase transaction in `DEFAULT_BLOCK_MAX_WEIGHT`

  7590e93bc7/src/policy/policy.h (L23)

  And also reserve additional `4000` weight units in the default `BlockCreationOptions` struct.

  7590e93bc7/src/node/types.h (L36-L40)

  **Motivation**

  - This issue was first noticed during a review here https://github.com/bitcoin/bitcoin/pull/11100#discussion_r136157411)
  - It was later reported in issue #21950.
  - I also came across the bug while writing a test for building the block template. I could not create a block template above `3,992,000` in the block assembler, and this was not documented anywhere. It took me a while to realize that we were reserving space for the coinbase transaction weight twice.

  ---
  This PR fixes this by consolidating the reservation to be in a single location in the codebase.

  This PR then adds a new startup option `-blockreservedweight` whose default is `8000` that can be used to lower or increase the block reserved weight for block header, txs count, coinbase tx.

ACKs for top commit:
  Sjors:
    ACK 386eecff5f
  fjahr:
    Code review ACK 386eecff5f
  glozow:
    utACK 386eecff5f, nonblocking nits. I do think the release notes should be clarified more
  pinheadmz:
    ACK 386eecff5f

Tree-SHA512: f27efa1da57947b7f4d42b9322b83d13afe73dd749dd9cac49360002824dd41c99a876a610554ac2d67bad7485020b9dcc423a8e6748fc79d6a10de6d4357d4c
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glozow
2025-02-10 08:14:50 -05:00
parent 6a46be75c4 386eecff5f
commit 6b165f5906
11 changed files with 202 additions and 19 deletions
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doc/release-notes-31384.md Normal file
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- Node and Mining
---
- **PR #31384** fixed an issue where block reserved weight for fixed-size block header, transactions count,
and coinbase transaction was done in two separate places.
Before this pull request, the policy default for the maximum block weight was `3,996,000` WU, calculated by
subtracting `4,000 WU` from the `4,000,000 WU` consensus limit to account for the fixed-size block header,
transactions count, and coinbase transaction. During block assembly, Bitcoin Core clamped custom `-blockmaxweight`
value to not be more than the policy default.
Additionally, the mining code added another `4,000 WU` to the initial reservation, reducing the effective block template
size to `3,992,000 WU`.
Due to this issue, the total reserved weight was always `8,000 WU`, meaning that even when specifying a `-blockmaxweight`
higher than the policy default, the actual block size never exceeded `3,992,000 WU`.
The fix consolidates the reservation into a single place and introduces a new startup option,
`-blockreservedweight` (default: `8,000 WU`). This startup option specifies the reserved weight for
the fixed-size block header, transactions count, and coinbase transaction.
The default value of `-blockreservedweight` was chosen to preserve the previous behavior.
**Upgrade Note:** The default `-blockreservedweight` ensures backward compatibility for users who relied on the previous behavior.
Users who manually set `-blockmaxweight` to its maximum value of `4,000,000 WU` should be aware that this
value previously had no effect since it was clamped to `3,996,000 WU`.
Users lowering `-blockreservedweight` should ensure that the total weight (for the block header, transaction count, and coinbase transaction)
does not exceed the reduced value.
As a safety check, Bitcoin core will **fail to start** when `-blockreservedweight` init parameter value is lower than `2000` weight units.
Bitcoin Core will also **fail to start** if the `-blockmaxweight` or `-blockreservedweight` init parameter exceeds
consensus limit of `4,000,000` weight units.