From 07ba3481e2624d85eaf5ff5808bd2d0280bcbb22 Mon Sep 17 00:00:00 2001
From: Bitflash <btf01@proton.me>
Date: Sat, 1 Aug 2026 14:29:28 -0300
Subject: mine: do not trust a stored generate flag with no mining mode beside
 it (#87)

fGenerateBitcoins and nMineMode only mean anything together, and a wallet.dat
can hold one without the other: Bitcoin 0.1.0 already wrote fGenerateBitcoins
when mining was toggled, years before this fork had a mode. #84 restored that
lone flag, which puts the node in the one state the miner cannot act on --
generate on, mode relay -- so every miner thread starts and returns at the relay
guard. The machine looks like it is mining and hashes nothing.

That happened to a 32-core node on its first 1.2.11 start: "Mining with 31
thread(s)" followed by 31 lines of "BitcoinMiner thread N returned true".

The flag is now believed only when the mode it belongs to was stored with it,
and the pair is made coherent either way.
---
 src/db.cpp | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

(limited to 'src/db.cpp')

diff --git a/src/db.cpp b/src/db.cpp
index 3af87fb..7763af8 100644
--- a/src/db.cpp
+++ b/src/db.cpp
@@ -551,6 +551,9 @@ bool CReviewDB::WriteReviews(uint256 hash, const vector<CReview>& vReviews)
 
 bool CWalletDB::LoadWallet(vector<unsigned char>& vchDefaultKeyRet)
 {
+    // Whether wallet.dat actually carried a mining mode, as opposed to just the
+    // ancient fGenerateBitcoins flag. See the reconciliation further down.
+    bool fHaveStoredMineMode = false;
     vchDefaultKeyRet.clear();
 
     // Satoshi's "todo: shouldn't we catch exceptions" sat here since 2009, and
@@ -669,7 +672,7 @@ bool CWalletDB::LoadWallet(vector<unsigned char>& vchDefaultKeyRet)
                 // participant cannot work without.
                 if (!fMineModeFromCommandLine)
                 {
-                    if (strKey == "nMineMode")          ssValue >> nMineMode;
+                    if (strKey == "nMineMode")          { ssValue >> nMineMode; fHaveStoredMineMode = true; }
                     if (strKey == "fGenerateBitcoins")  ssValue >> fGenerateBitcoins;
                     if (strKey == "strParticipantPool") ssValue >> strParticipantPool;
                 }
@@ -692,6 +695,32 @@ bool CWalletDB::LoadWallet(vector<unsigned char>& vchDefaultKeyRet)
         return false;
     }
 
+    // fGenerateBitcoins and nMineMode only mean anything together, and a
+    // wallet.dat can easily hold one without the other: Bitcoin 0.1.0 already
+    // wrote fGenerateBitcoins when mining was toggled, years before this fork
+    // had a mode at all. Restoring that lone flag put a node into the one state
+    // the miner cannot act on -- generate on, mode relay -- so every miner
+    // thread started and returned at the relay guard, and the machine sat there
+    // looking like it was mining while hashing nothing. That happened to a
+    // 32-core node on the first 1.2.11 start.
+    //
+    // So the flag is only believed when the mode it belongs to was stored with
+    // it, and the pair is made coherent either way.
+    if (!fMineModeFromCommandLine)
+    {
+        if (!fHaveStoredMineMode)
+        {
+            if (fGenerateBitcoins)
+                printf("LoadWallet: ignoring a stored fGenerateBitcoins with no mining mode "
+                       "beside it -- it predates this setting and cannot be read on its own\n");
+            fGenerateBitcoins = 0;
+        }
+        else
+        {
+            fGenerateBitcoins = (nMineMode != MINE_RELAY) ? 1 : 0;
+        }
+    }
+
     printf("nTransactionFee = %lld\n", nTransactionFee);
     printf("addrIncoming = %s\n", addrIncoming.ToString().c_str());
     printf("nMineMode = %d, strParticipantPool = %s, fGenerateBitcoins = %d (%s)\n",
-- 
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