This change is completely contrary to real world behaviour. No modern filesystem I know of implements this behaviour as the default, and performance with the coresponding mount options (usually -o dirsync on Linux) is terrible as it forces a write out of the log (or corresponding action on non-log based filesystems) and in the common case of volatile write caches a cache flush. Retrospectively claiming this as standards behaviour in a "clarification" is utterly wrong. On Mon, Apr 22, 2013 at 11:15:38AM +0200, Xavier Roche wrote: > 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." ---end quoted text--- -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
