This header file attempts to abstract the underlying operating system for the SQLite library to work on both POSIX and Windows systems. The file includes macros necessary for the SQLite library to work, such as the maximum pathname length and the default size of a disk sector. It also contains information on file locking in both Windows and Unix systems, including byte ranges and default locations. The file also includes functions for accessing SQLite file methods and SQLite VFS methods. Additionally, convenience functions for opening and closing files using sqlite3_malloc() are provided.
https://github.com/mackyle/sqlite/blob/18cf47156abe94255ae1495ba2da84517dce6081/src/os.h