WG15 Defect Report Ref: 9945-1-amd1-10

This is an approved interpretation of 9945-1-amd1-1993.


Last update: 1997-05-20

                                                                9945-1-amd1-93 #10


	Defect Report Number: (to be assigned by WG15)
        Topic:                  _POSIX_PRIORITIZED_IO part 2
        Relevant Sections:
        Classification:         (to be assigned)

Defect Report:

From: "Frank Prindle" <prindle@voicenet.com>
Date: Tue, 28 May 1996 08:52:51 +0000

FOR ISO/IEC 9945-1-amd1-1993:

1b2. Subsection, Page 152-153, Lines 729-732:

	Regarding the option identified by {_POSIX_PRIORITIZED_IO}, the
	statement says "When prioritized asynchronous I/O requests to the same
	file are blocked waiting for a resource required for that I/O operation,
	the higher-priority I/O requests shall be granted the resource before
	lower-priority I/O requests are granted the resource."  The statement
	does not address a common situation involving multiple files and a
	single resource.

	If prioritized asynchronous I/O requests to DIFFERENT files are
	blocked waiting for the SAME resource, shall higher-priority I/O
	requests be granted that resource before lower-priority I/O requests,
	regardless of which file?  It only seems logical, given the effect which
	this option is intended to achieve - scheduling async I/O based on
	priority; it seems that the writers didn't consider the very obvious
	situation of a physical disk (resource) which implements several files.

	Assuming that the interpretation answers "yes" to the above question,
	I suggest that the semantics of the Prioritized I/O option be clarified
	to explicitly address the case of multiple files per device, indicating
	that the prioritization of granting the resource (device) is still
	priority based, and not undefined as it is now.

WG15 response for 9945-1-amd1-1993

The standard is silent on the question of the relative ordering of requests
to different devices.  A conforming system is not constrained by the
standard as to which order to handle the requests and a conforming
applications must be able to handle any ordering.  

The interpretations committee believes that this was the intent of the 
working and balloting group in this area in order to avoid additional 
complexity and problems with devices that the groups were not familar.   

Forwarded to Interp group chair: 5/28/96
Finalised: 6/25/96