genesis 是創世區塊的意思. 一個區塊鏈就是從同一個創世區塊開始,通過規則形成的.不同的網路有不同的創世區塊, 主網路和測試網路的創世區塊是不同的.

這個模組根據傳入的genesis的初始值和database，來設定genesis的狀態，如果不存在創世區塊，那麼在database裡面建立它。

資料結構

// 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的欄位，起始塊的狀態。 它還通過配置來定義硬叉切換塊。
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 指定了最開始的區塊的初始狀態.
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.
// 如果儲存的區塊鏈配置不相容那麼會被更新(). 為了避免發生衝突,會返回一個錯誤,並且新的配置和原來的配置會返回.
// The returned chain configuration is never nil.

// genesis 如果是 testnet dev 或者是 rinkeby 模式， 那麼不為nil。如果是mainnet或者是私有連結。那麼為空
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) //獲取genesis對應的區塊
    if (stored == common.Hash{}) { //如果沒有區塊 最開始啟動geth會進入這裡。
        if genesis == nil { 
            //如果genesis是nil 而且stored也是nil 那麼使用主網路
            // 如果是test  dev  rinkeby 那麼genesis不為空 會設定為各自的genesis
            log.Info("Writing default main-net genesis block")
            genesis = DefaultGenesisBlock()
        } else { // 否則使用配置的區塊
            log.Info("Writing custom genesis block")
        }
        // 寫入資料庫
        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存在而且區塊也存在 那麼對比這兩個區塊是否相同
        block, _ := genesis.ToBlock()
        hash := block.Hash()
        if hash != stored {
            return genesis.Config, block.Hash(), &GenesisMismatchError{stored, hash}
        }
    }

    // Get the existing chain configuration.
    // 獲取當前存在的區塊鏈的genesis配置
    newcfg := genesis.configOrDefault(stored)
    // 獲取當前的區塊鏈的配置
    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.
    // 特殊情況：如果沒有提供新的配置，請不要更改非主網鏈的現有配置。 
    // 如果我們繼續這裡，這些鏈會得到AllProtocolChanges（和compat錯誤）。
    if genesis == nil && stored != params.MainnetGenesisHash {
        return storedcfg, stored, nil   // 如果是私有連結會從這裡退出。
    }

    // Check config compatibility and write the config. Compatibility errors
    // are returned to the caller unless we're already at block zero.
    // 檢查配置的相容性,除非我們在區塊0,否則返回相容性錯誤.
    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)
    // 如果區塊已經寫入資料了,那麼就不能更改genesis配置了
    if compatErr != nil && height != 0 && compatErr.RewindTo != 0 {
        return newcfg, stored, compatErr
    }
    // 如果是主網路會從這裡退出。
    return newcfg, stored, WriteChainConfig(db, stored, newcfg)
}
 

ToBlock, 這個方法使用genesis的資料，使用基於記憶體的資料庫，然後建立了一個block並返回。

// 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方法把給定的genesis的block和state寫入資料庫， 這個block被認為是規範的區塊鏈頭。

// 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)
    }
    // 寫入總難度
    if err := WriteTd(db, block.Hash(), block.NumberU64(), g.Difficulty); err != nil {
        return nil, err
    }
    // 寫入區塊
    if err := WriteBlock(db, block); err != nil {
        return nil, err
    }
    // 寫入區塊收據
    if err := WriteBlockReceipts(db, block.Hash(), block.NumberU64(), nil); err != nil {
        return nil, err
    }
    // 寫入   headerPrefix + num (uint64 big endian) + numSuffix -> hash
    if err := WriteCanonicalHash(db, block.Hash(), block.NumberU64()); err != nil {
        return nil, err
    }
    // 寫入  "LastBlock" -> hash
    if err := WriteHeadBlockHash(db, block.Hash()); err != nil {
        return nil, err
    }
    // 寫入 "LastHeader" -> hash
    if err := WriteHeadHeaderHash(db, block.Hash()); err != nil {
        return nil, err
    }
    config := g.Config
    if config == nil {
        config = params.AllProtocolChanges
    }
    // 寫入 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
}

返回各種模式的預設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),
    }
}