A file API is not the same thing as a filesystem API. The holy grail is still a universal but high(-enough)-level filesystem API.

mmap is not a C feature, but POSIX. There are C platforms that don't provide mmap, and on those that do you can use mmap from other languages (there's mmap module in the Python's standard library, for example).

"best file API" and the man page for the O_ flags disagree.

> However, in other most languages, you have to read() in tiny chunks, parse, process, serialize and finally write() back to the disk. This works, but is verbose and needlessly limited

C has those too and am glad that they do. This is what allows one to do other things while the buffer gets filled, without the need for multithreading.

Yes easier standardized async interfaces would have been nice, not sure how well supported they are.