Open-source local file systems, such as Linux Ext4, XFS, and Btrfs, remain a critical component in the world of modern storage. For example, many recent distributed file systems, such as Google GFS and Hadoop DFS, replicate data objects (and associated metadata) across local file systems. The authors conduct a comprehensive study of file-system code evolution. By analyzing eight years of Linux filesystem changes across 5079 patches, they derive numerous new (and sometimes surprising) insights into the file-system development process; their results should be useful for both the development of file systems themselves as well as the improvement of bug-finding tools.