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Problem Report 0281 Details

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    Problem Report Number 0281
    Submitter's Classification Test Suite problem
    State Resolved
    Resolution Test Suite Deficiency (TSD)
    Problem Resolution ID TSD.X.0281
    Raised 2002-10-01 08:00
    Updated 2003-03-13 08:00
    Published 2002-10-08 08:00
    Product Standard Network File System
    Certification Program The Open Brand certification program
    Test Suite VSX4+XNFS version 4.4.5
    Test Identification POSIX.os/ioprim/write 16
    Problem Summary TSD4.281 For this test, the relevant part of the write(2) definition, taken from http://www.opengroup.org/onlinepubs/007904975/functions/write.html is this: " When attempting to write to a file descriptor (oth...
    Problem Text
    For this test, the relevant part of the write(2) definition,
    taken from

    http://www.opengroup.org/onlinepubs/007904975/functions/write.html

    is this:
    "
    When attempting to write to a file descriptor (other than a pipe
    or FIFO) that supports non-blocking writes and cannot accept the
    data immediately:

    * If the O_NONBLOCK flag is clear, write() shall block the
    calling thread until the data can be accepted.

    * If the O_NONBLOCK flag is set, write() shall not block the
    thread. If some data can be written without blocking the thread,
    write() shall write what it can and return the number of bytes
    written. Otherwise, it shall return -1 and set errno to [EAGAIN].
    "

    In the case of the IRIX NFS client:

    * we support non-blocking writes; and

    * the file descriptor *can* accept all the data
    due to client side file buffering.

    Hence, the write() call returns immediately with the indication
    that all the data has been written to the file descriptor.
    This is allowable behaviour because the file descriptor has not
    been opened with synchronous file semantics specified (O_SYNC).
    Irix will then write the data out to the server asynchronously.

    The Irix NFS server does generate an ENOSPC error, and it will
    be returned to the client test application on subsequent write()
    or close() calls to the file descriptor.

    Because the test does not do a second write() call, and
    specifically ignores the error from close, the error cannot be
    reported back to the test application.

    The test is attempting to achieve a return from write(2)
    that is >=0 and < the size of the write. That is, a partially
    successful write. We believe the test is incorrect in two ways.

    Firstly, in order to fullfil the requirements in the above quoted
    section, the test should open the file with O_NONBLOCK, which it fails
    to do.

    Secondly, this test assumes that the amount of data written to
    the file descriptor relates directly to the amount of data written
    to stable storage. This requires synchronous operation of the write()
    call. The relevant quote from the write(2) page is:

    "
    If the O_SYNC bit has been set, write I/O operations on the file
    descriptor shall complete as defined by synchronized I/O file
    integrity completion.
    "

    If we want to ensure that the above assumed semantics are used,
    according to the above quote, the file must be opened with the
    O_SYNC flag set. This has not been specified by the open() call
    in the test.

    The Irix NFS client returns the correct results if the file is
    opened with the O_SYNC and O_NONBLOCK flags set. We believe that
    the test file must be opened with these flags to ensure that the
    write() call to behave as the test requires.

    --
    Test Output
    /tset/POSIX.os/ioprim/write/T.write 16 Failed

    Test Description:
    If there is not enough space in the output device, then only as many
    bytes as there are room for will be written.
    Posix Ref: Component WRITE Assertion 6.4.2.2-11(B)

    Test Strategy:
    CREATE a new process and exec a subprogram
    SUBPROGRAM:
    SETUP the file system given by VSX_NOSPC_DEV to be almost full with
    setupnospc()
    DETERMINE size of one of the temporary files (fill.tmp1)
    WRITE a buffer to this file that is twenty times as large as its
    current size
    VERIFY that write() returned a value greater than zero and less than
    the buffer size
    CLEAN up file system with tidynospc()

    Test Information:
    write() returned 199800, expected < 199800

    Review Information

    Review Type TSMA Review
    Start Date null
    Completed null
    Status Complete
    Review Recommendation No Resolution Given
    Review Response
    This is accepted as a fault in the test suite.

    It is worth noting that the submitter's comments about O_NONBLOCK
    are incorrect, and the text quoted from the XSH specification
    related to O_NONBLOCK is irrelevant.

    The fault should be fixed by changing the test to open the file
    with O_SYNC set (when testing XNFS).

    Review Type SA Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution Test Suite Deficiency (TSD)
    Review Conclusion
    This is an agreed Test Suite Deficiency.

    Problem Reporting System Options:

     

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