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Last update: 1997-05-20
9945-1-90 #52
Classification: No Change.
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Topic: timestamps on read-only filesystems
Relevant Sections: 2.2.2.69, 2.3.5
Defect Report:
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ISO/IEC 9945-1:1990 Section 2.2.2.69 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)
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No, such an implementation is not conforming.
Rationale for Interpretation:
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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
2.2.2.69 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
required.
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