LoadMempool: Pass in load_path, stop using gArgs

Also:
1. Have CChainState::LoadMempool and ::ThreadImport take in paths and
   pass it through untouched to LoadMempool.
2. Make LoadMempool exit early if the load_path is empty.
3. Adjust the call to ::ThreadImport in ::AppInitMain to correctly pass
   in an empty path if mempool persistence is disabled.

src/init.cpp

@@ -1673,7 +1673,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     }
 
     chainman.m_load_block = std::thread(&util::TraceThread, "loadblk", [=, &chainman, &args] {
-        ThreadImport(chainman, vImportFiles, args);
+        ThreadImport(chainman, vImportFiles, args, ShouldPersistMempool(args) ? MempoolPath(args) : fs::path{});
     });
 
     // Wait for genesis block to be processed

src/node/blockstorage.cpp

@@ -823,7 +823,7 @@ struct CImportingNow {
     }
 };
 
-void ThreadImport(ChainstateManager& chainman, std::vector<fs::path> vImportFiles, const ArgsManager& args)
+void ThreadImport(ChainstateManager& chainman, std::vector<fs::path> vImportFiles, const ArgsManager& args, const fs::path& mempool_path)
 {
     SetSyscallSandboxPolicy(SyscallSandboxPolicy::INITIALIZATION_LOAD_BLOCKS);
     ScheduleBatchPriority();
@@ -893,6 +893,6 @@ void ThreadImport(ChainstateManager& chainman, std::vector<fs::path> vImportFile
             return;
         }
     } // End scope of CImportingNow
-    chainman.ActiveChainstate().LoadMempool(args);
+    chainman.ActiveChainstate().LoadMempool(mempool_path);
 }
 } // namespace node

src/node/blockstorage.h

@@ -211,7 +211,7 @@ bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const FlatFilePos& pos, c
 
 bool UndoReadFromDisk(CBlockUndo& blockundo, const CBlockIndex* pindex);
 
-void ThreadImport(ChainstateManager& chainman, std::vector<fs::path> vImportFiles, const ArgsManager& args);
+void ThreadImport(ChainstateManager& chainman, std::vector<fs::path> vImportFiles, const ArgsManager& args, const fs::path& mempool_path);
 } // namespace node
 
 #endif // BITCOIN_NODE_BLOCKSTORAGE_H

src/test/fuzz/validation_load_mempool.cpp

@@ -43,6 +43,6 @@ FUZZ_TARGET_INIT(validation_load_mempool, initialize_validation_load_mempool)
     auto fuzzed_fopen = [&](const fs::path&, const char*) {
         return fuzzed_file_provider.open();
     };
-    (void)chainstate.LoadMempool(g_setup->m_args, fuzzed_fopen);
+    (void)chainstate.LoadMempool(MempoolPath(g_setup->m_args), fuzzed_fopen);
     (void)DumpMempool(pool, MempoolPath(g_setup->m_args), fuzzed_fopen, true);
 }

src/validation.cpp

@@ -3865,12 +3865,10 @@ void PruneBlockFilesManual(CChainState& active_chainstate, int nManualPruneHeigh
     }
 }
 
-void CChainState::LoadMempool(const ArgsManager& args, FopenFn mockable_fopen_function)
+void CChainState::LoadMempool(const fs::path& load_path, FopenFn mockable_fopen_function)
 {
     if (!m_mempool) return;
-    if (args.GetBoolArg("-persistmempool", DEFAULT_PERSIST_MEMPOOL)) {
+    ::LoadMempool(*m_mempool, load_path, *this, mockable_fopen_function);
-        ::LoadMempool(*m_mempool, *this, mockable_fopen_function);
-    }
     m_mempool->SetLoadTried(!ShutdownRequested());
 }
 
@@ -4644,9 +4642,11 @@ bool CChainState::ResizeCoinsCaches(size_t coinstip_size, size_t coinsdb_size)
 
 static const uint64_t MEMPOOL_DUMP_VERSION = 1;
 
-bool LoadMempool(CTxMemPool& pool, CChainState& active_chainstate, FopenFn mockable_fopen_function)
+bool LoadMempool(CTxMemPool& pool, const fs::path& load_path, CChainState& active_chainstate, FopenFn mockable_fopen_function)
 {
-    FILE* filestr{mockable_fopen_function(gArgs.GetDataDirNet() / "mempool.dat", "rb")};
+    if (load_path.empty()) return false;
+
+    FILE* filestr{mockable_fopen_function(load_path, "rb")};
     CAutoFile file(filestr, SER_DISK, CLIENT_VERSION);
     if (file.IsNull()) {
         LogPrintf("Failed to open mempool file from disk. Continuing anyway.\n");

src/validation.h

@@ -679,7 +679,7 @@ public:
     void CheckBlockIndex();
 
     /** Load the persisted mempool from disk */
-    void LoadMempool(const ArgsManager& args, fsbridge::FopenFn mockable_fopen_function = fsbridge::fopen);
+    void LoadMempool(const fs::path& load_path, fsbridge::FopenFn mockable_fopen_function = fsbridge::fopen);
 
     /** Update the chain tip based on database information, i.e. CoinsTip()'s best block. */
     bool LoadChainTip() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
@@ -1018,7 +1018,7 @@ bool DeploymentEnabled(const ChainstateManager& chainman, DEP dep)
 bool DumpMempool(const CTxMemPool& pool, const fs::path& dump_path, fsbridge::FopenFn mockable_fopen_function = fsbridge::fopen, bool skip_file_commit = false);
 
 /** Load the mempool from disk. */
-bool LoadMempool(CTxMemPool& pool, CChainState& active_chainstate, fsbridge::FopenFn mockable_fopen_function = fsbridge::fopen);
+bool LoadMempool(CTxMemPool& pool, const fs::path& load_path, CChainState& active_chainstate, fsbridge::FopenFn mockable_fopen_function = fsbridge::fopen);
 
 /**
  * Return the expected assumeutxo value for a given height, if one exists.