aio_fsync() a directory ?

[Xavier Roche]

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."