File systems are a fundamental part of computer systems, which organize and protect the files and data on assorted devices, including computers, smartphones, and enterprise servers. Due to its crucial role, vulnerabilities and bugs in the file system can lead to severe consequences such as data loss and system crashes. After decades of development, file systems have become increasingly complex, yet bugs continue to emerge. Meanwhile, many new file systems are invented to support new hardware or features, often without undergoing comprehensive testing. To address these gaps, we develop a checking framework (Metis) that can thoroughly and efficiently test file …