Answering questions that may arise related to the meaning of portions of an IEEE standard concerning specific applications.

IEEE Standards Interpretations for IEEE Std 1003.1b™-1993 IEEE Standard for Information Technology - Portable Operating System Interfaces (POSIX(R)) - Part 1: System Application Program Interface (API) - Amendment 1: Realtime Extension [C language]

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Interpretation Request #11
Topic: _POSIX_PRIORITIZED_IO part 3 Relevant Sections:, Page 153, Lines 733-734 Classification: (to be assigned)

The statement says "If {_POSIX_PRIORITIZED_IO} is defined, the implementation shall define for which files I/O prioritization is supported". The statement, as written, creates an untestable situation. Is an implementation which defines _POSIX_PRIORITIZED_IO, but defines no files for which I/O prioritization is supported (i.e. says it is supported for no files), a conforming implementation? It appears that if this were allowed, there would be no way to test conformance to the optional capabilities. Assuming that the interpretation answers "no" to the above question, I suggest that the sentence be clarified by also stating that "at least one implementation-defined file shall support I/O prioritization if this option is defined".

Interpretation Response
The standard is clear that it is implementation defined as to which, if any, files support the prioritized I/O option. This is testable by reading the conformance documentation which shall be provided by a conforming implementation. It is expected that any strictly conforming application will be cognizant of the implementation limitations and use that knowledge in the selection of systems to use.

Rationale for Interpretation