Non-blocking I/O and EWOULDBLOCK vs. EAGAIN

[John Quarterman]

as essentially adopted 4.2BSD-style
non-blocking I/O, rather than System V-style non-blocking I/O.  The System V
Interface Definition says that System V will be changed to match the
/usr/group standard.

However,

	1) as the S5ID states, this may break existing code as it isn't
	   compatible with existing System V implementations.

and

	2) it's not compatible with 4.2BSD, either, because they return
	   EAGAIN if a non-blocking operation would have blocked had the
	   descriptor been in non-blocking mode, rather than EWOULDBLOCK.

Is there a good reason for constructing a new specification, incompatible
with *all* existing systems, rather than adopting the existing 4.2BSD
facility which provides the same functionality and merely uses a different
error code?  "The committee didn't want to add a new error code" is an
extremely bad reason, as they have already added new error codes for the
benefit of file locking.  UNIX error codes are far too overloaded already;
the problem should not be compounded.

	Guy Harris