kernel: Add flushError method to notifications

This is done in addition with the following commit. Both have the goal
of getting rid of direct calls to AbortNode from kernel code. This extra
flushError method is added to notify specifically about errors that
arrise when flushing (syncing) block data to disk. Unlike other
instances, the current calls to AbortNode in the blockstorage flush
functions do not report an error to their callers.

This commit is part of the libbitcoinkernel project and further removes
the shutdown's and, more generally, the kernel library's dependency on
interface_ui with a kernel notification method. By removing interface_ui
from the kernel library, its dependency on boost is reduced to just
boost::multi_index. At the same time it also takes a step towards
de-globalising the interrupt infrastructure.

src/bitcoin-chainstate.cpp

@@ -97,6 +97,11 @@ int main(int argc, char* argv[])
         {
             std::cout << "Warning: " << warning.original << std::endl;
         }
+        void flushError(const std::string& debug_message) override
+        {
+            std::cerr << "Error flushing block data to disk: " << debug_message << std::endl;
+        }
+
     };
     auto notifications = std::make_unique<KernelNotifications>();
 
@@ -112,6 +117,7 @@ int main(int argc, char* argv[])
     const node::BlockManager::Options blockman_opts{
         .chainparams = chainman_opts.chainparams,
         .blocks_dir = abs_datadir / "blocks",
+        .notifications = chainman_opts.notifications,
     };
     ChainstateManager chainman{kernel_context.interrupt, chainman_opts, blockman_opts};
 

src/init.cpp

@@ -999,6 +999,7 @@ bool AppInitParameterInteraction(const ArgsManager& args)
         BlockManager::Options blockman_opts_dummy{
             .chainparams = chainman_opts_dummy.chainparams,
             .blocks_dir = args.GetBlocksDirPath(),
+            .notifications = chainman_opts_dummy.notifications,
         };
         auto blockman_result{ApplyArgsManOptions(args, blockman_opts_dummy)};
         if (!blockman_result) {
@@ -1423,6 +1424,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     BlockManager::Options blockman_opts{
         .chainparams = chainman_opts.chainparams,
         .blocks_dir = args.GetBlocksDirPath(),
+        .notifications = chainman_opts.notifications,
     };
     Assert(ApplyArgsManOptions(args, blockman_opts)); // no error can happen, already checked in AppInitParameterInteraction
 

src/kernel/blockmanager_opts.h

@@ -5,6 +5,7 @@
 #ifndef BITCOIN_KERNEL_BLOCKMANAGER_OPTS_H
 #define BITCOIN_KERNEL_BLOCKMANAGER_OPTS_H
 
+#include <kernel/notifications_interface.h>
 #include <util/fs.h>
 
 #include <cstdint>
@@ -25,6 +26,7 @@ struct BlockManagerOpts {
     bool fast_prune{false};
     bool stop_after_block_import{DEFAULT_STOPAFTERBLOCKIMPORT};
     const fs::path blocks_dir;
+    Notifications& notifications;
 };
 
 } // namespace kernel

src/kernel/notifications_interface.h

@@ -27,6 +27,14 @@ public:
     virtual void headerTip(SynchronizationState state, int64_t height, int64_t timestamp, bool presync) {}
     virtual void progress(const bilingual_str& title, int progress_percent, bool resume_possible) {}
     virtual void warning(const bilingual_str& warning) {}
+
+    //! The flush error notification is sent to notify the user that an error
+    //! occurred while flushing block data to disk. Kernel code may ignore flush
+    //! errors that don't affect the immediate operation it is trying to
+    //! perform. Applications can choose to handle the flush error notification
+    //! by logging the error, or notifying the user, or triggering an early
+    //! shutdown as a precaution against causing more errors.
+    virtual void flushError(const std::string& debug_message) {}
 };
 } // namespace kernel
 

src/node/blockstorage.cpp

@@ -528,7 +528,7 @@ void BlockManager::FlushUndoFile(int block_file, bool finalize)
 {
     FlatFilePos undo_pos_old(block_file, m_blockfile_info[block_file].nUndoSize);
     if (!UndoFileSeq().Flush(undo_pos_old, finalize)) {
-        AbortNode("Flushing undo file to disk failed. This is likely the result of an I/O error.");
+        m_opts.notifications.flushError("Flushing undo file to disk failed. This is likely the result of an I/O error.");
     }
 }
 
@@ -547,7 +547,7 @@ void BlockManager::FlushBlockFile(bool fFinalize, bool finalize_undo)
 
     FlatFilePos block_pos_old(m_last_blockfile, m_blockfile_info[m_last_blockfile].nSize);
     if (!BlockFileSeq().Flush(block_pos_old, fFinalize)) {
-        AbortNode("Flushing block file to disk failed. This is likely the result of an I/O error.");
+        m_opts.notifications.flushError("Flushing block file to disk failed. This is likely the result of an I/O error.");
     }
     // we do not always flush the undo file, as the chain tip may be lagging behind the incoming blocks,
     // e.g. during IBD or a sync after a node going offline

src/node/kernel_notifications.cpp

@@ -11,6 +11,7 @@
 #include <common/args.h>
 #include <common/system.h>
 #include <node/interface_ui.h>
+#include <shutdown.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 #include <util/translation.h>
@@ -72,4 +73,9 @@ void KernelNotifications::warning(const bilingual_str& warning)
     DoWarning(warning);
 }
 
+void KernelNotifications::flushError(const std::string& debug_message)
+{
+    AbortNode(debug_message);
+}
+
 } // namespace node

src/node/kernel_notifications.h

@@ -25,6 +25,8 @@ public:
     void progress(const bilingual_str& title, int progress_percent, bool resume_possible) override;
 
     void warning(const bilingual_str& warning) override;
+
+    void flushError(const std::string& debug_message) override;
 };
 } // namespace node
 

src/test/blockmanager_tests.cpp

@@ -5,14 +5,16 @@
 #include <chainparams.h>
 #include <node/blockstorage.h>
 #include <node/context.h>
+#include <node/kernel_notifications.h>
 #include <util/chaintype.h>
 #include <validation.h>
 
 #include <boost/test/unit_test.hpp>
 #include <test/util/setup_common.h>
 
-using node::BlockManager;
 using node::BLOCK_SERIALIZATION_HEADER_SIZE;
+using node::BlockManager;
+using node::KernelNotifications;
 using node::MAX_BLOCKFILE_SIZE;
 
 // use BasicTestingSetup here for the data directory configuration, setup, and cleanup
@@ -21,9 +23,11 @@ BOOST_FIXTURE_TEST_SUITE(blockmanager_tests, BasicTestingSetup)
 BOOST_AUTO_TEST_CASE(blockmanager_find_block_pos)
 {
     const auto params {CreateChainParams(ArgsManager{}, ChainType::MAIN)};
+    KernelNotifications notifications{};
     const BlockManager::Options blockman_opts{
         .chainparams = *params,
         .blocks_dir = m_args.GetBlocksDirPath(),
+        .notifications = notifications,
     };
     BlockManager blockman{m_node.kernel->interrupt, blockman_opts};
     CChain chain {};

src/test/util/setup_common.cpp

@@ -196,6 +196,7 @@ ChainTestingSetup::ChainTestingSetup(const ChainType chainType, const std::vecto
     const BlockManager::Options blockman_opts{
         .chainparams = chainman_opts.chainparams,
         .blocks_dir = m_args.GetBlocksDirPath(),
+        .notifications = chainman_opts.notifications,
     };
     m_node.chainman = std::make_unique<ChainstateManager>(m_node.kernel->interrupt, chainman_opts, blockman_opts);
     m_node.chainman->m_blockman.m_block_tree_db = std::make_unique<CBlockTreeDB>(DBParams{

src/test/validation_chainstatemanager_tests.cpp

@@ -389,6 +389,7 @@ struct SnapshotTestSetup : TestChain100Setup {
             const BlockManager::Options blockman_opts{
                 .chainparams = chainman_opts.chainparams,
                 .blocks_dir = m_args.GetBlocksDirPath(),
+                .notifications = chainman_opts.notifications,
             };
             // For robustness, ensure the old manager is destroyed before creating a
             // new one.