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From: jsq@ut-sally.UUCP (John Quarterman)
Newsgroups: mod.std.unix
Subject: Non-blocking I/O and EWOULDBLOCK vs. EAGAIN
Message-ID: <2424@ut-sally.UUCP>
Date: Sun, 21-Jul-85 14:06:36 EDT
Article-I.D.: ut-sally.2424
Posted: Sun Jul 21 14:06:36 1985
Date-Received: Mon, 22-Jul-85 15:13:31 EDT
Reply-To: std-unix@ut-sally.UUCP
Organization: U. Texas CS Dept., Austin, Texas
Lines: 30
Approved: jsq@ut-sally.UUCP
Discussions-Of: UNIX standards, particularly the IEEE P1003 draft standard.

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