validation: Refactor file flush logic into FlatFileSeq.

src/flatfile.cpp

@@ -72,3 +72,22 @@ size_t FlatFileSeq::Allocate(const CDiskBlockPos& pos, size_t add_size, bool& ou
     }
     return 0;
 }
+
+bool FlatFileSeq::Flush(const CDiskBlockPos& pos, bool finalize)
+{
+    FILE* file = Open(FlatFilePos(pos.nFile, 0)); // Avoid fseek to nPos
+    if (!file) {
+        return error("%s: failed to open file %d", __func__, pos.nFile);
+    }
+    if (finalize && !TruncateFile(file, pos.nPos)) {
+        fclose(file);
+        return error("%s: failed to truncate file %d", __func__, pos.nFile);
+    }
+    if (!FileCommit(file)) {
+        fclose(file);
+        return error("%s: failed to commit file %d", __func__, pos.nFile);
+    }
+
+    fclose(file);
+    return true;
+}

src/flatfile.h

@@ -45,6 +45,15 @@ public:
      * @return The number of bytes successfully allocated.
      */
     size_t Allocate(const CDiskBlockPos& pos, size_t add_size, bool& out_of_space);
+
+    /**
+     * Commit a file to disk, and optionally truncate off extra pre-allocated bytes if final.
+     *
+     * @param[in] pos The first unwritten position in the file to be flushed.
+     * @param[in] finalize True if no more data will be written to this file.
+     * @return true on success, false on failure.
+     */
+    bool Flush(const CDiskBlockPos& pos, bool finalize = false);
 };
 
 #endif // BITCOIN_FLATFILE_H

src/validation.cpp

@@ -1630,25 +1630,12 @@ void static FlushBlockFile(bool fFinalize = false)
 {
     LOCK(cs_LastBlockFile);
 
-    CDiskBlockPos posOld(nLastBlockFile, 0);
+    CDiskBlockPos block_pos_old(nLastBlockFile, vinfoBlockFile[nLastBlockFile].nSize);
+    CDiskBlockPos undo_pos_old(nLastBlockFile, vinfoBlockFile[nLastBlockFile].nUndoSize);
+
     bool status = true;
-
+    status &= BlockFileSeq().Flush(block_pos_old, fFinalize);
-    FILE *fileOld = OpenBlockFile(posOld);
+    status &= UndoFileSeq().Flush(undo_pos_old, fFinalize);
-    if (fileOld) {
-        if (fFinalize)
-            status &= TruncateFile(fileOld, vinfoBlockFile[nLastBlockFile].nSize);
-        status &= FileCommit(fileOld);
-        fclose(fileOld);
-    }
-
-    fileOld = OpenUndoFile(posOld);
-    if (fileOld) {
-        if (fFinalize)
-            status &= TruncateFile(fileOld, vinfoBlockFile[nLastBlockFile].nUndoSize);
-        status &= FileCommit(fileOld);
-        fclose(fileOld);
-    }
-
     if (!status) {
         AbortNode("Flushing block file to disk failed. This is likely the result of an I/O error.");
     }