[xfs-masters] [Bug 418] New: unwritten extents remain unwritten after mmap() modifies them

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http://oss.sgi.com/bugzilla/show_bug.cgi?id=418

           Summary: unwritten extents remain unwritten after mmap() modifies
                    them
           Product: Linux XFS
           Version: Current
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: XFS kernel code
        AssignedTo: xfs-master@xxxxxxxxxxx
        ReportedBy: wsl-xfs-bugzilla@xxxxxxxx


If a file is allocated using XFS_IOC_RESVSP64 then mmap()ed with PROT_WRITE and
written to (by altering bytes in the mmap()ed memory region), the extents remain
marked as ?unwritten? even after the file is munmap()ed.
If the data is still cached it will appear to the application that all is well,
but as soon as data is actually read from disk the ?unwritten? flag will cause
reads to be all zero again.

Note that the file had to be truncated upwards to the same size as the resvsp to
prevent a bus error when writing to the mmap()ed region.

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