Interpretations

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 #4
Topic: mmap Relevant Sections: 12.2.1 Classification: (to be assigned)

I would like to request a formal interpretation on IEEE Std 1003.1b-1993. IEEE Std 1003.1-1990 defines file times (access time and modification time), and specifies in detail how functions in that standard effect the file times. IEEE Std 1003.1b-1993 adds the mmap() function (12.2.1) as a completely new way to access a regular file. However, It does not seem to specify how accesses to a file via mmap() affect the file times. To be specific, when shall, and when may, the implementation mark st_atime and st_mtime for update in each of the following cases: (1) mmap() is called with PROT_READ. (2) mmap() is called with MAP_SHARED and PROT_WRITE. (3) Application modifies a page previous mapped with MAP_SHARED, PROT_WRITE. (4) Application references a page mapped MAP_PRIVATE that has not been modified by the process. (Keep in mind that the process might be seeing data that has changed since the mmap().) (5) Application modifies a page mapped MAP_PRIVATE, PROT_WRITE. (6) Application references a page mapped MAP_PRIVATE that was previously modified by the process. (7) msync() (12.2.4) is called on pages mapped with mmap().

Interpretation Response
The standard is silent on this matter. The committee notes that this is inconsistent with page 27 line 626 which states generally that it should specified and this matter is being referred to the sponsor for consideration.

Rationale for Interpretation
None.