Hard Forks

Monero makes use of hard-forks to update its protocol. Although it has never been used, Monero has a system in it's codebase to allow voting for activation of a hard-fork¹. It works by using the blocks minor version field as a voting field, when enough blocks vote for a hard fork the fork is activated.

Because Monero has never used hard fork voting, you don't need to implement it but as it's included in the codebase, an explanation is included here.

Blocks version and vote

Monero uses the block's major version field as an indicator of hard-fork and the minor version field as an indicator of the blocks vote. A minor version of 0 is treated as a vote for 1 as legacy blocks use to just set this field to 0².

The block's vote must be greater than or equal to the version, a vote higher than the maximum known hard-fork is interpreted as a vote for the latest hard-fork³. So if a block is at V2 then the vote must be V2 or higher.

Accepting a fork

When a hard-fork is added to Monero's protocol it must specify a threshold, a number between 0 and 100, this is the proportion of blocks in the window that must vote for this fork (or a later one) for it to activate. For all current forks the threshold is 0 meaning that no votes are needed for the fork to activate.

Monero keeps track of a week (10,080 blocks) worth of votes⁴, when a new block is added Monero works backwards through the list of hard-forks (latest to oldest) tallying the votes and checking if the number of votes is bigger than the amount needed⁵, votes for later hardforks are also votes for previous hard-forks. The amount needed is calculated:

\( amountNeeded = \frac{windowSize * threshold + 99}{100} \)

If the amount of votes is greater than or equal to the amount needed and the current blockchain height is greater than or equal to the hard-fork height the HF is activated⁵.

Mainnet Hard-Forks 6

Testnet Hard-Forks 8

Stagenet Hard-Forks 9