[sytelus]

The abstraction is not really file but stream of bytes. It turns of any object with stream of bytes will need similar set of operations: open, create, read, write, close, seek etc. This is fairly generic and powerful abstraction.

[cyphar]

The abstraction is a file descriptor. Not all things represented by file descriptors support read(2) or _llseek(2), but by representing them as file descriptors you can reuse other things like af_unix file descriptor passing.