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Depends on what system you have. On Linux-i386, we have

#define EWOULDBLOCK     EAGAIN

so it is necessarily the same thing. Can you report on what
system EAGAIN happens even if the file descriptor is
non-blocking?

As for documentation changes: The documentation currently says

   Read at most size bytes from the file (less if the read
hits EOF before obtaining size bytes)

I believe this statement is no longer true: with your
changes, it will return less data even without hitting EOF.