* consensus/ethash: add maxEpoch constant
* consensus/ethash: improve cache/dataset handling
There are two fixes in this commit:
Unmap the memory through a finalizer like the libethash wrapper did. The
release logic was incorrect and freed the memory while it was being
used, leading to crashes like in #14495 or #14943.
Track caches and datasets using simplelru instead of reinventing LRU
logic. This should make it easier to see whether it's correct.
* consensus/ethash: restore 'future item' logic in lru
* consensus/ethash: use mmap even in test mode
This makes it possible to shorten the time taken for TestCacheFileEvict.
* consensus/ethash: shuffle func calc*Size comments around
* consensus/ethash: ensure future cache/dataset is in the lru cache
* consensus/ethash: add issue link to the new test
* consensus/ethash: fix vet
* consensus/ethash: fix test
* consensus: tiny issue + nitpick fixes
* cmd, consensus, eth: split ethash related config to it own
* eth, consensus: minor polish
* eth, consenus, console: compress pow testing config field to single one
* consensus, eth: document pow mode
`geth makedag <blocknumber> <path>` was creating DAGs for
`<blocknumber>/<epoch_length> + 1`, hence
it was impossible to create an epoch 0 DAG.
This fixes the calculations in `consensus/ethash/ethash.go` for
`MakeDataset` and `MakeCache`, and applies `gofmt`.
This commit adds pluggable consensus engines to go-ethereum. In short, it
introduces a generic consensus interface, and refactors the entire codebase to
use this interface.
