Re: aio_fsync() a directory ?

[Xavier Roche <roche+kml2 at exalead dot com>]

Just to close this thread, Geoff Clare has summarized the changes 
regarding aio_fsync() and relationship wrt. directory entry data.

<http://austingroupbugs.net/view.php?id=672>

"In the April 18 teleconference it was agreed that the standard
should mandate that directory operations are always synchronized
on conforming file systems, and should include warnings about
non-conforming configurations. The proposed changes are as follows.

Changes to XBD...

At page 94 line 2581-2588 section 3.376 change:

    For read, when the operation has been completed or diagnosed if
    unsuccessful. The read is complete only when an image of the data
    has been successfully transferred to the requesting process. If
    there were any pending write requests affecting the data to be
    read at the time that the synchronized read operation was
    requested, these write requests are successfully transferred prior
    to reading the data.

    For write, when the operation has been completed or diagnosed if
    unsuccessful. The write is complete only when the data specified
    in the write request is successfully transferred and all file
    system information required to retrieve the data is successfully
    transferred.

to:

    For read operations, when the operation has been completed or
    diagnosed if unsuccessful. The operation is complete only when an
    image of the data has been successfully transferred to the
    requesting process. If there were any pending write requests or
    (if the file is a directory) directory modifications affecting
    the data to be read at the time that the synchronized read
    operation was requested, these requests are successfully
    transferred prior to reading the data.

    For write operations and directory modification operations, when
    the operation has been completed or diagnosed if unsuccessful. The
    operation is complete only when the written data or (if the file
    is a directory) modified directory entries have been successfully
    transferred to storage and all file system information required
    to retrieve them is successfully transferred.

At page 107 line 2859 add a new XBD 4.2 section (and renumber the
current 4.2 and all later 4.x sections):

    4.2 Directory Operations

    All file system operations that read a directory or that modify
    the contents of a directory (for example creating, unlinking, or
    renaming a file) shall be completed as defined for synchronized
    I/O data integrity completion (see section 3.376).

    <small>Note: Although conforming file systems are required to
       perform all directory modifications as synchronized I/O
       operations, some file systems may support non-conforming
       configurations (for example via mount options) where
       directory modifications are not synchronized. Applications
       that rely on directory modifications being synchronized should
       only be used with such file systems in their conforming
       configuration(s).</small>

Changes to XSH...

At page 574 line 19833 section aio_fsync() change the APPLICATION
USAGE section from:

    None.

to:

    Refer to fdatasync() and fsync().

At page 815 line 27215 section fdatasync() append to the first
paragraph:

    If the file is a directory, an implicit fdatasync() is already
    performed on every I/O operation (see XBD 4.2) and consequently
    if fdatasync() is called explicitly it shall take no action and
    shall return the value 0.

At page 815 line 27232 section fdatasync() change the APPLICATION
USAGE section from:

    None.

to:

    Although conforming file systems are required to complete all
    directory modifications as defined for synchronized I/O data
    integrity completion, some file systems may support non-conforming
    configurations (for example via mount options) where directory
    modifications are not synchronized. When the file system is
    configured in this way, calls to fdatasync() on directories may
    cause I/O operations to be synchronized, rather than being a no-op.

At page 954 line 31987 section fsync() add a new paragraph to the
APPLICATION USAGE section:

    Since conforming file systems are required to complete all
    directory modifications as defined for synchronized I/O data
    integrity completion (see XBD 4.2), calling fsync() on a directory
    only synchronizes the file attributes such as timestamps. However,
    some file systems may support non-conforming configurations (for
    example via mount options) where modifications to directory
    contents are not synchronized. When the file system is configured
    in this way, calls to fsync() on directories may cause directory
    contents to be synchronized in addition to file attributes.

Changes to XRAT...

At page 3444 line 115531 add a new XRAT A.4.2 section (and renumber
the current A.4.2 and all later A.4.x sections):

    A.4.2 Directory Operations

    Earlier versions of this standard did not make clear that all directory
    modifications are performed as synchronized I/O operations, although
    that is the historical behavior and was always intended. Applications
    have no need to call fdatasync() or fsync() on a directory unless
    they want to synchronize the file attributes (using fsync()), provided
    the directory is on a conforming file system. However, since
    applications may wish to use fdatasync() or fsync() to synchronize
    directory modifications on non-conforming file systems, implementations
    are required to support fdatasync() on directories as a no-op on
    conforming file systems."