genesis 是创世区块的意思. 一个区块链就是从同一个创世区块开始,通过规则形成的.不同的网络有不同的创世区块, 主网络和测试网路的创世区块是不同的.

这个模块根据传入的genesis的初始值和database，来设置genesis的状态，如果不存在创世区块，那么在database里面创建它。

数据结构

// Genesis specifies the header fields, state of a genesis block. It also defines hard
// fork switch-over blocks through the chain configuration.
// Genesis指定header的字段，起始块的状态。它还通过配置来定义硬叉切换块。
type Genesis struct {
Config *params.ChainConfig `json:"config"`
Nonce uint64 `json:"nonce"`
Timestamp uint64 `json:"timestamp"`
ExtraData []byte `json:"extraData"`
GasLimit uint64 `json:"gasLimit" gencodec:"required"`
Difficulty *big.Int `json:"difficulty" gencodec:"required"`
Mixhash common.Hash `json:"mixHash"`
Coinbase common.Address `json:"coinbase"`
Alloc GenesisAlloc `json:"alloc" gencodec:"required"`
// These fields are used for consensus tests. Please don't use them
// in actual genesis blocks.
Number uint64 `json:"number"`
GasUsed uint64 `json:"gasUsed"`
ParentHash common.Hash `json:"parentHash"`
}
// GenesisAlloc specifies the initial state that is part of the genesis block.
// GenesisAlloc 指定了最开始的区块的初始状态.
type GenesisAlloc map[common.Address]GenesisAccount

SetupGenesisBlock,

// SetupGenesisBlock writes or updates the genesis block in db.
//
// The block that will be used is:
//
// genesis == nil genesis != nil
// +------------------------------------------
// db has no genesis | main-net default | genesis
// db has genesis | from DB | genesis (if compatible)
//
// The stored chain configuration will be updated if it is compatible (i.e. does not
// specify a fork block below the local head block). In case of a conflict, the
// error is a *params.ConfigCompatError and the new, unwritten config is returned.
// 如果存储的区块链配置不兼容那么会被更新(). 为了避免发生冲突,会返回一个错误,并且新的配置和原来的配置会返回.
// The returned chain configuration is never nil.
// genesis 如果是 testnet dev 或者是 rinkeby 模式，那么不为nil。如果是mainnet或者是私有链接。那么为空
func SetupGenesisBlock(db ethdb.Database, genesis *Genesis) (*params.ChainConfig, common.Hash, error) {
if genesis != nil && genesis.Config == nil {
return params.AllProtocolChanges, common.Hash{}, errGenesisNoConfig
}
// Just commit the new block if there is no stored genesis block.
stored := GetCanonicalHash(db, 0) //获取genesis对应的区块
if (stored == common.Hash{}) { //如果没有区块最开始启动geth会进入这里。
if genesis == nil {
//如果genesis是nil 而且stored也是nil 那么使用主网络
// 如果是test dev rinkeby 那么genesis不为空会设置为各自的genesis
log.Info("Writing default main-net genesis block")
genesis = DefaultGenesisBlock()
} else { // 否则使用配置的区块
log.Info("Writing custom genesis block")
}
// 写入数据库
block, err := genesis.Commit(db)
return genesis.Config, block.Hash(), err
}
// Check whether the genesis block is already written.
if genesis != nil { //如果genesis存在而且区块也存在那么对比这两个区块是否相同
block, _ := genesis.ToBlock()
hash := block.Hash()
if hash != stored {
return genesis.Config, block.Hash(), &GenesisMismatchError{stored, hash}
}
}
// Get the existing chain configuration.
// 获取当前存在的区块链的genesis配置
newcfg := genesis.configOrDefault(stored)
// 获取当前的区块链的配置
storedcfg, err := GetChainConfig(db, stored)
if err != nil {
if err == ErrChainConfigNotFound {
// This case happens if a genesis write was interrupted.
log.Warn("Found genesis block without chain config")
err = WriteChainConfig(db, stored, newcfg)
}
return newcfg, stored, err
}
// Special case: don't change the existing config of a non-mainnet chain if no new
// config is supplied. These chains would get AllProtocolChanges (and a compat error)
// if we just continued here.
// 特殊情况：如果没有提供新的配置，请不要更改非主网链的现有配置。
// 如果我们继续这里，这些链会得到AllProtocolChanges（和compat错误）。
if genesis == nil && stored != params.MainnetGenesisHash {
return storedcfg, stored, nil // 如果是私有链接会从这里退出。
}
// Check config compatibility and write the config. Compatibility errors
// are returned to the caller unless we're already at block zero.
// 检查配置的兼容性,除非我们在区块0,否则返回兼容性错误.
height := GetBlockNumber(db, GetHeadHeaderHash(db))
if height == missingNumber {
return newcfg, stored, fmt.Errorf("missing block number for head header hash")
}
compatErr := storedcfg.CheckCompatible(newcfg, height)
// 如果区块已经写入数据了,那么就不能更改genesis配置了
if compatErr != nil && height != 0 && compatErr.RewindTo != 0 {
return newcfg, stored, compatErr
}
// 如果是主网络会从这里退出。
return newcfg, stored, WriteChainConfig(db, stored, newcfg)
}

ToBlock, 这个方法使用genesis的数据，使用基于内存的数据库，然后创建了一个block并返回。

// ToBlock creates the block and state of a genesis specification.
func (g *Genesis) ToBlock() (*types.Block, *state.StateDB) {
db, _ := ethdb.NewMemDatabase()
statedb, _ := state.New(common.Hash{}, state.NewDatabase(db))
for addr, account := range g.Alloc {
statedb.AddBalance(addr, account.Balance)
statedb.SetCode(addr, account.Code)
statedb.SetNonce(addr, account.Nonce)
for key, value := range account.Storage {
statedb.SetState(addr, key, value)
}
}
root := statedb.IntermediateRoot(false)
head := &types.Header{
Number: new(big.Int).SetUint64(g.Number),
Nonce: types.EncodeNonce(g.Nonce),
Time: new(big.Int).SetUint64(g.Timestamp),
ParentHash: g.ParentHash,
Extra: g.ExtraData,
GasLimit: new(big.Int).SetUint64(g.GasLimit),
GasUsed: new(big.Int).SetUint64(g.GasUsed),
Difficulty: g.Difficulty,
MixDigest: g.Mixhash,
Coinbase: g.Coinbase,
Root: root,
}
if g.GasLimit == 0 {
head.GasLimit = params.GenesisGasLimit
}
if g.Difficulty == nil {
head.Difficulty = params.GenesisDifficulty
}
return types.NewBlock(head, nil, nil, nil), statedb
}

Commit方法和MustCommit方法, Commit方法把给定的genesis的block和state写入数据库，这个block被认为是规范的区块链头。

// Commit writes the block and state of a genesis specification to the database.
// The block is committed as the canonical head block.
func (g *Genesis) Commit(db ethdb.Database) (*types.Block, error) {
block, statedb := g.ToBlock()
if block.Number().Sign() != 0 {
return nil, fmt.Errorf("can't commit genesis block with number > 0")
}
if _, err := statedb.CommitTo(db, false); err != nil {
return nil, fmt.Errorf("cannot write state: %v", err)
}
// 写入总难度
if err := WriteTd(db, block.Hash(), block.NumberU64(), g.Difficulty); err != nil {
return nil, err
}
// 写入区块
if err := WriteBlock(db, block); err != nil {
return nil, err
}
// 写入区块收据
if err := WriteBlockReceipts(db, block.Hash(), block.NumberU64(), nil); err != nil {
return nil, err
}
// 写入 headerPrefix + num (uint64 big endian) + numSuffix -> hash
if err := WriteCanonicalHash(db, block.Hash(), block.NumberU64()); err != nil {
return nil, err
}
// 写入 "LastBlock" -> hash
if err := WriteHeadBlockHash(db, block.Hash()); err != nil {
return nil, err
}
// 写入 "LastHeader" -> hash
if err := WriteHeadHeaderHash(db, block.Hash()); err != nil {
return nil, err
}
config := g.Config
if config == nil {
config = params.AllProtocolChanges
}
// 写入 ethereum-config-hash -> config
return block, WriteChainConfig(db, block.Hash(), config)
}
// MustCommit writes the genesis block and state to db, panicking on error.
// The block is committed as the canonical head block.
func (g *Genesis) MustCommit(db ethdb.Database) *types.Block {
block, err := g.Commit(db)
if err != nil {
panic(err)
}
return block
}

返回各种模式的默认Genesis

// DefaultGenesisBlock returns the Ethereum main net genesis block.
func DefaultGenesisBlock() *Genesis {
return &Genesis{
Config: params.MainnetChainConfig,
Nonce: 66,
ExtraData: hexutil.MustDecode("0x11bbe8db4e347b4e8c937c1c8370e4b5ed33adb3db69cbdb7a38e1e50b1b82fa"),
GasLimit: 5000,
Difficulty: big.NewInt(17179869184),
Alloc: decodePrealloc(mainnetAllocData),
}
}
// DefaultTestnetGenesisBlock returns the Ropsten network genesis block.
func DefaultTestnetGenesisBlock() *Genesis {
return &Genesis{
Config: params.TestnetChainConfig,
Nonce: 66,
ExtraData: hexutil.MustDecode("0x3535353535353535353535353535353535353535353535353535353535353535"),
GasLimit: 16777216,
Difficulty: big.NewInt(1048576),
Alloc: decodePrealloc(testnetAllocData),
}
}
// DefaultRinkebyGenesisBlock returns the Rinkeby network genesis block.
func DefaultRinkebyGenesisBlock() *Genesis {
return &Genesis{
Config: params.RinkebyChainConfig,
Timestamp: 1492009146,
ExtraData: hexutil.MustDecode("0x52657370656374206d7920617574686f7269746168207e452e436172746d616e42eb768f2244c8811c63729a21a3569731535f067ffc57839b00206d1ad20c69a1981b489f772031b279182d99e65703f0076e4812653aab85fca0f00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"),
GasLimit: 4700000,
Difficulty: big.NewInt(1),
Alloc: decodePrealloc(rinkebyAllocData),
}
}
// DevGenesisBlock returns the 'geth --dev' genesis block.
func DevGenesisBlock() *Genesis {
return &Genesis{
Config: params.AllProtocolChanges,
Nonce: 42,
GasLimit: 4712388,
Difficulty: big.NewInt(131072),
Alloc: decodePrealloc(devAllocData),
}
}

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