[TUHS] Unix APIs: elegant or not?

I was just reading this book review: http://www.pathsensitive.com/2018/10/book-review-philosophy-of-software.html and came across these paragraphs: <book quote> The mechanism for file IO provided by the Unix operating system and its descendants, such as Linux, is a beautiful example of a deep interface. There are only five basic system calls for I/O, with simple signatures: int open(const char* path, int flags, mode_t permissions); ssize_t read(int fd, void* buffer, size_t count); ssize_t write(int fd, const void* buffer, size_t count); off_t lseek(int fd, off_t offset, int referencePosition); int close(int fd); </book quote> The POSIX file API is a great example, but not of a deep interface. Rather, it’s a great example of how code with a very complicated interface may look deceptively simple when reduced to C-style function signatures. It’s a stateful API with interesting orderings and interactions between calls. The flags and permissions parameters of open hide an enormous amount of complexity, with hidden requirements like “exactly one of these five bits should be specified.” open may return 20 different error codes, each with their own meaning, and many with references to specific implementations. The authors of SibylIFS tried to write down an exact description of the open interface. Their annotated version[1] of the POSIX standard is over 3000 words. Not counting basic machinery, it took them over 200 lines[2] to write down the properties of open in higher-order logic, and another 70 to give the interactions between open and close. [1]: https://github.com/sibylfs/sibylfs_src/blob/8a7f53ba58654249b0ec0725ce38878… [2]: https://github.com/sibylfs/sibylfs_src/blob/8a7f53ba58654249b0ec0725ce38878… I just thought it was a thought-provoking comment on the apparent elegance of the Unix file API that actually has some subtle complexity. Cheers, Warren