After some thought I managed to simplify the original uaversionbits proposal
introducing a simple boolean flag to guarantee lock-in of a BIP9 deployment by
the timeout. This seems to be the simplest form combining optional flag day
activation with BIP9. This brings the best of both worlds allowing user
activated soft forks that can be activated early by the hash power.
Specification:
https://github.com/shaolinfry/bips/blob/bip-uavb/bip-uaversionbits.mediawiki
Previous discussion:
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-February/013643.html
<pre>
BIP: ?
Title: Version bits extension with guaranteed lock-in
Author: Shaolin Fry <shaolin...@protonmail.ch>
Comments-Summary: No comments yet.
Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-????
Status: Draft
Type: Informational
Created: 2017-02-01
License: BSD-3-Clause
CC0-1.0
</pre>
==Abstract==
This document specifies an extension to BIP9 that introduces an additional
activation parameter to guarantee activation of backward-compatible changes
(further called "soft forks").
==Motivation==
BIP9 introduced a mechanism for doing parallel soft forking deployments based
on repurposing the block nVersion field. Activation is dependent on near
unanimous hashrate signalling which may be impractical and is also subject to
veto by a small minority of non-signalling hashrate.
This specification provides a way to optionally guarantee lock-in at the end of
the BIP9 timeout, and therefore activation.
==Specification==
This specification adds a new per-chain deployment parameter to the existing
BIP9 specification as follows:
# The '''lockinontimeout''' boolean if set to true, will transition state to
LOCKED_IN at timeout if not already ACTIVE.
===State transitions===
<img src="bip-uaversionbits/states.png" align="middle"></img>
The state transition workflow is exactly the same as in BIP9 with an additional
rule: During the STARTED state if the '''lockinontimeout''' is set to true, the
state will transition to LOCKED_IN when '''timeout''' is reached.
case STARTED:
// BIP9 specification follows
if (GetMedianTimePast(block.parent) >= timeout) {
return (fLockInOnTimeout == true) ? THRESHOLD_LOCKED_IN : THRESHOLD_FAILED
}
int count = 0;
walk = block;
for (i = 0; i < 2016; i++) {
walk = walk.parent;
if (walk.nVersion & 0xE0000000 == 0x20000000 && (walk.nVersion >> bit) & 1 ==
1) {
count++;
}
}
if (count >= threshold) {
return LOCKED_IN;
}
return STARTED;
=== Reference implementation ===
https://github.com/bitcoin/bitcoin/compare/master...shaolinfry:bip-uaversionbits
==Deployments==
A living list of deployment proposals can be found
[[bip-0009/assignments.mediawiki|here]].
==Copyright==
This document is dual licensed as BSD 3-clause, and Creative Commons CC0 1.0
Universal._______________________________________________
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