blockstorage: Return on fatal block file flush error

By returning an error code if `FlushBlockFile` fails, the caller now has
to explicitly handle block file flushing errors. Before this change
such errors were non-explicitly ignored without a clear rationale.

Prior to this patch `FlushBlockFile` may have failed silently in
`Chainstate::FlushStateToDisk`. Improve this with a log line. Also add a
TODO comment to flesh out whether returning early in the case of an
error is appropriate or not. Returning early might be appropriate to
prohibit `WriteBlockIndexDB` from writing a block index entry that does
not refer to a fully flushed block.

Besides `Chainstate::FlushStateToDisk`, `FlushBlockFile` is also called
by `FindBlockPos`. Don't change the abort behavior there, since we don't
want to fail the function if the flushing of already written blocks
fails. Instead, just document it.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/node/blockstorage.h b/src/node/blockstorage.h
index 0e8b9abce9..3e0962386f 100644
--- a/src/node/blockstorage.h
+++ b/src/node/blockstorage.h
@@ -91,7 +91,10 @@ private:
      */
     bool LoadBlockIndex()
         EXCLUSIVE_LOCKS_REQUIRED(cs_main);
-    void FlushBlockFile(bool fFinalize = false, bool finalize_undo = false);
+
+    /** Return false if block file flushing fails. */
+    [[nodiscard]] bool FlushBlockFile(bool fFinalize = false, bool finalize_undo = false);
+
     void FlushUndoFile(int block_file, bool finalize = false);
     [[nodiscard]] bool FindBlockPos(FlatFilePos& pos, unsigned int nAddSize, unsigned int nHeight, uint64_t nTime, bool fKnown);
     bool FindUndoPos(BlockValidationState& state, int nFile, FlatFilePos& pos, unsigned int nAddSize);