File System Extensibility and Reliability Using an in-Kernel Database
Aditya Kashyap · 2004
File systems are responsible for storing data efficiently and reliably. Databases also have similar tasks, but generally have more concern for reliability than file systems. We have developed a file system, KBDBFS, on top of an in-kernel database. KBDBFS supports standard file system operations, as well as other useful extensions such as extended attributes, ACLs, and a new operation to retrieve all the names of a file with hardlinks. To implement KBDBFS, we have ported the Berkeley DB software into the Linux kernel. Berkeley DB provides efficient and persistent storage of key-value pairs using hash tables and Btrees with full ACID semantics. Berkeley DB is a stable, high-quality, fully-featured, and widelyused embedded database. KBDBFS’s fundamental operations manipulate a database schema, rather than low-level objects like bitmaps and allocation tables, so it is easily extensible. KBDBFS uses BDB transactions around its file system operations; this ensures that KBDBFS operations are reliable. KBDBFS also exports the transaction API to user-level processes, allowing them to perform several file system operations atomically. Our performance evaluation shows that KBDBFS has acceptable overheads for user-like workloads.