WG15 Defect Report Ref: 9945-1-52
Topic: timestamps on read-only filesystems

This is an approved interpretation of 9945-1:1990.


Last update: 1997-05-20

                                                                9945-1-90 #52

        Classification: No Change.


	Topic:			timestamps on read-only filesystems
	Relevant Sections:, 2.3.5

Defect Report:
    ISO/IEC 9945-1:1990 Section defines "read only file system":

	A file system that has implementation defined characteristics
	restricting modifications.

    ISO/IEC 9945-1:1990 Section 2.3.5 "file times update" states:

	Updates are not done for files on read-only file systems.

    Is it permissible for an implementation to update the st_atime
    attribute held in-core but yet prevent the update of that attribute for
    the file on the read-only filesystem?

WG15 response for ISO/IEC 9945-1:1990 (IEEE Std 1003.1-1990)

    No, such an implementation is not conforming.

Rationale for Interpretation:

    The statement that a read-only filesystem has implementation-defined
    restrictions on modification does not prevent the standard itself from
    specifying restrictions.  Subclause 2.3.5 states that st_atime shall
    not be updated for a file on a read-only file system.   Subclause says that there are implementation-defined restrictions
    restricting modification, but these are in addition to any restrictions
    imposed by the standard.

    Note that read() marks the file for update, even on a read-only
    filesystem, but the update is never done.  This distinction is not
    particularly relevant to an application, since there is no way to
    find out that a time is "marked" but not "updated."

Editorial note for future revision of standard (not part of the interpretation)
It would improve readability if these two subclauses referenced
each other, but the fact that they don't doesn't change what is