Fix some LoadChainTip-related init-order bugs.

* Move the writing of fTxIndex to LoadBlockIndex - this fixes a
  bug introduced in d6af06d68aae985436cbc942f0d11078041d121b where
  InitBlockIndex was writing to fTxIndex which had not yet been
  checked (because LoadChainTip hadn't yet initialized the
  chainActive, which would otherwise have resulted in
  InitBlockIndex being a NOP), allowing you to modify -txindex
  without reindex, potentially corrupting your chainstate!

* Rename InitBlockIndex to LoadGenesisBlock, which is now a more
  natural name for it. Also check mapBlockIndex instead of
  chainActive, fixing a bug where we'd write the genesis block out
  on every start.

4 files changed, 47 insertions, 33 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 1e85642019..b1fe8e7d3c 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -646,7 +646,7 @@ void ThreadImport(std::vector<fs::path> vImportFiles)
         fReindex = false;
         LogPrintf("Reindexing finished\n");
         // To avoid ending up in a situation without genesis block, re-try initializing (no-op if reindexing worked):
-        InitBlockIndex(chainparams);
+        LoadGenesisBlock(chainparams);
     }
 
     // hardcoded $DATADIR/bootstrap.dat
@@ -1419,7 +1419,7 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
                     return InitError(_("Incorrect or no genesis block found. Wrong datadir for network?"));
 
                 // Initialize the block index (no-op if non-empty database was already loaded)
-                if (!InitBlockIndex(chainparams)) {
+                if (!fReindex && !LoadGenesisBlock(chainparams)) {
                     strLoadError = _("Error initializing block database");
                     break;
                 }
diff --git a/src/test/test_bitcoin.cpp b/src/test/test_bitcoin.cpp
index 3ba81ed17b..8ad955e7a2 100644
--- a/src/test/test_bitcoin.cpp
+++ b/src/test/test_bitcoin.cpp
@@ -72,7 +72,7 @@ TestingSetup::TestingSetup(const std::string& chainName) : BasicTestingSetup(cha
         pblocktree = new CBlockTreeDB(1 << 20, true);
         pcoinsdbview = new CCoinsViewDB(1 << 23, true);
         pcoinsTip = new CCoinsViewCache(pcoinsdbview);
-        if (!InitBlockIndex(chainparams)) {
+        if (!LoadGenesisBlock(chainparams)) {
             throw std::runtime_error("InitBlockIndex failed.");
         }
         {
diff --git a/src/validation.cpp b/src/validation.cpp
index d7d880d24f..ebbdb7e651 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3864,42 +3864,55 @@ void UnloadBlockIndex()
 bool LoadBlockIndex(const CChainParams& chainparams)
 {
     // Load block index from databases
-    if (!fReindex && !LoadBlockIndexDB(chainparams))
-        return false;
+    bool needs_init = fReindex;
+    if (!fReindex) {
+        bool ret = LoadBlockIndexDB(chainparams);
+        if (!ret) return false;
+        needs_init = mapBlockIndex.empty();
+    }
+
+    if (needs_init) {
+        // Everything here is for *new* reindex/DBs. Thus, though
+        // LoadBlockIndexDB may have set fReindex if we shut down
+        // mid-reindex previously, we don't check fReindex and
+        // instead only check it prior to LoadBlockIndexDB to set
+        // needs_init.
+
+        LogPrintf("Initializing databases...\n");
+        // Use the provided setting for -txindex in the new database
+        fTxIndex = GetBoolArg("-txindex", DEFAULT_TXINDEX);
+        pblocktree->WriteFlag("txindex", fTxIndex);
+    }
     return true;
 }
 
-bool InitBlockIndex(const CChainParams& chainparams)
+bool LoadGenesisBlock(const CChainParams& chainparams)
 {
     LOCK(cs_main);
 
-    // Check whether we're already initialized
-    if (chainActive.Genesis() != NULL)
+    // Check whether we're already initialized by checking for genesis in
+    // mapBlockIndex. Note that we can't use chainActive here, since it is
+    // set based on the coins db, not the block index db, which is the only
+    // thing loaded at this point.
+    if (mapBlockIndex.count(chainparams.GenesisBlock().GetHash()))
         return true;
 
-    // Use the provided setting for -txindex in the new database
-    fTxIndex = GetBoolArg("-txindex", DEFAULT_TXINDEX);
-    pblocktree->WriteFlag("txindex", fTxIndex);
-    LogPrintf("Initializing databases...\n");
-
     // Only add the genesis block if not reindexing (in which case we reuse the one already on disk)
-    if (!fReindex) {
-        try {
-            CBlock &block = const_cast<CBlock&>(chainparams.GenesisBlock());
-            // Start new block file
-            unsigned int nBlockSize = ::GetSerializeSize(block, SER_DISK, CLIENT_VERSION);
-            CDiskBlockPos blockPos;
-            CValidationState state;
-            if (!FindBlockPos(state, blockPos, nBlockSize+8, 0, block.GetBlockTime()))
-                return error("LoadBlockIndex(): FindBlockPos failed");
-            if (!WriteBlockToDisk(block, blockPos, chainparams.MessageStart()))
-                return error("LoadBlockIndex(): writing genesis block to disk failed");
-            CBlockIndex *pindex = AddToBlockIndex(block);
-            if (!ReceivedBlockTransactions(block, state, pindex, blockPos, chainparams.GetConsensus()))
-                return error("LoadBlockIndex(): genesis block not accepted");
-        } catch (const std::runtime_error& e) {
-            return error("LoadBlockIndex(): failed to initialize block database: %s", e.what());
-        }
+    try {
+        CBlock &block = const_cast<CBlock&>(chainparams.GenesisBlock());
+        // Start new block file
+        unsigned int nBlockSize = ::GetSerializeSize(block, SER_DISK, CLIENT_VERSION);
+        CDiskBlockPos blockPos;
+        CValidationState state;
+        if (!FindBlockPos(state, blockPos, nBlockSize+8, 0, block.GetBlockTime()))
+            return error("%s: FindBlockPos failed", __func__);
+        if (!WriteBlockToDisk(block, blockPos, chainparams.MessageStart()))
+            return error("%s: writing genesis block to disk failed", __func__);
+        CBlockIndex *pindex = AddToBlockIndex(block);
+        if (!ReceivedBlockTransactions(block, state, pindex, blockPos, chainparams.GetConsensus()))
+            return error("%s: genesis block not accepted", __func__);
+    } catch (const std::runtime_error& e) {
+        return error("%s: failed to write genesis block: %s", __func__, e.what());
     }
 
     return true;
diff --git a/src/validation.h b/src/validation.h
index a9f995abb8..3ce5023f0a 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -256,9 +256,10 @@ FILE* OpenBlockFile(const CDiskBlockPos &pos, bool fReadOnly = false);
 fs::path GetBlockPosFilename(const CDiskBlockPos &pos, const char *prefix);
 /** Import blocks from an external file */
 bool LoadExternalBlockFile(const CChainParams& chainparams, FILE* fileIn, CDiskBlockPos *dbp = NULL);
-/** Initialize a new block tree database + block data on disk */
-bool InitBlockIndex(const CChainParams& chainparams);
-/** Load the block tree and coins database from disk */
+/** Ensures we have a genesis block in the block tree, possibly writing one to disk. */
+bool LoadGenesisBlock(const CChainParams& chainparams);
+/** Load the block tree and coins database from disk,
+ * initializing state if we're running with -reindex. */
 bool LoadBlockIndex(const CChainParams& chainparams);
 /** Update the chain tip based on database information. */
 void LoadChainTip(const CChainParams& chainparams);