set gas price to external contract

contracts/DODOVendorMachine/impl/DVM.sol

@@ -10,6 +10,7 @@ pragma experimental ABIEncoderV2;
 
 import {IFeeRateModel} from "../../intf/IFeeRateModel.sol";
 import {IPermissionManager} from "../../lib/PermissionManager.sol";
+import {IGasPriceSource} from "../../lib/GasPriceSource.sol";
 import {DVMTrader} from "./DVMTrader.sol";
 import {DVMFunding} from "./DVMFunding.sol";
 import {DVMVault} from "./DVMVault.sol";
@@ -22,6 +23,7 @@ contract DVM is DVMTrader, DVMFunding {
         address lpFeeRateModel,
         address mtFeeRateModel,
         address tradePermissionManager,
+        address gasPriceSource,
         uint256 i,
         uint256 k
     ) external {
@@ -32,10 +34,10 @@ contract DVM is DVMTrader, DVMFunding {
         _LP_FEE_RATE_MODEL_ = IFeeRateModel(lpFeeRateModel);
         _MT_FEE_RATE_MODEL_ = IFeeRateModel(mtFeeRateModel);
         _TRADE_PERMISSION_ = IPermissionManager(tradePermissionManager);
+        _GAS_PRICE_LIMIT_ = IGasPriceSource(gasPriceSource);
         _MAINTAINER_ = maintainer;
         _I_ = i;
         _K_ = k;
-        _GAS_PRICE_LIMIT_ = uint256(-1);
     }
 
     // ============ Version Control ============

contracts/DODOVendorMachine/impl/DVMStorage.sol

@@ -14,6 +14,7 @@ import {SafeMath} from "../../lib/SafeMath.sol";
 import {DODOMath} from "../../lib/DODOMath.sol";
 import {DecimalMath} from "../../lib/DecimalMath.sol";
 import {IPermissionManager} from "../../lib/PermissionManager.sol";
+import {IGasPriceSource} from "../../lib/GasPriceSource.sol";
 import {IFeeRateModel} from "../../intf/IFeeRateModel.sol";
 import {DVMVault} from "./DVMVault.sol";
 
@@ -22,7 +23,7 @@ contract DVMStorage is InitializableOwnable, ReentrancyGuard {
 
     // ============ Variables for Control ============
 
-    uint256 public _GAS_PRICE_LIMIT_;
+    IGasPriceSource public _GAS_PRICE_LIMIT_;
 
     // ============ Advanced Controls ============
 
@@ -62,6 +63,11 @@ contract DVMStorage is InitializableOwnable, ReentrancyGuard {
         _;
     }
 
+    modifier limitGasPrice() {
+        require(tx.gasprice <= _GAS_PRICE_LIMIT_.getGasPrice(), "GAS_PRICE_EXCEED");
+        _;
+    }
+
     // ============ Helper Functions ============
 
     function calculateBase0(uint256 baseAmount, uint256 quoteAmount) public view returns (uint256) {
@@ -93,8 +99,8 @@ contract DVMStorage is InitializableOwnable, ReentrancyGuard {
         _MAINTAINER_ = newMaintainer;
     }
 
-    function setGasPriceLimit(uint256 newGasPriceLimit) external onlyOwner {
-        _GAS_PRICE_LIMIT_ = newGasPriceLimit;
+    function setGasPriceSource(address newGasPriceLimitSource) external onlyOwner {
+        _GAS_PRICE_LIMIT_ = IGasPriceSource(newGasPriceLimitSource);
     }
 
     function setBuy(bool open) external onlyOwner {

contracts/DODOVendorMachine/impl/DVMTrader.sol

@@ -20,6 +20,7 @@ contract DVMTrader is DVMStorage {
     function sellBase(address to)
         external
         preventReentrant
+        limitGasPrice
         isSellAllow(to)
         returns (uint256 receiveQuoteAmount)
     {
@@ -37,6 +38,7 @@ contract DVMTrader is DVMStorage {
     function sellQuote(address to)
         external
         preventReentrant
+        limitGasPrice
         isBuyAllow(to)
         returns (uint256 receiveBaseAmount)
     {