Intended semantics for syscalls function _read?

["s dot achterop at rug dot nl" <s dot achterop at rug dot nl>]

   Hello list,

The documentation of this function does not describe how this function is to behave.
Is it blocking, or can it also be non-blocking.
What is the meaning of the return value? Or is it intentionally left ambiguous?
My guess would be:
   >=0  number of characters actually read
         zero meaning: zero characters read.
   < 0  error code (including eof?)

I want to use this function to read from serial/usb ports, using (man 2) read and scanf.
But also to test for the availability of a character on a port: a character_ready function.

Can I use (man 2) read in a non-blocking way? Or is there an other way?
Or should I directly use the _read function to make the character_ready function?

   Thanks in advance,
       Sietse Achterop


PS. I am using newlib as part of the GNU Embedded toolchain for a number of arm systems (stm32f4 based).

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