[PATCH] xfs: merge fsync and O_SYNC handling

[Felix Blyakher]

On Aug 26, 2009, at 10:11 PM, Christoph Hellwig wrote:

> The guarantees for O_SYNC are exactly the same as the ones we need to
> make for an fsync call (and given that Linux O_SYNC is O_DSYNC the
> equivalent is fdadatasync, but we treat both the same in XFS), except
> with a range data writeout.  Jan Kara has started unifying these two
> path for filesystems using the generic helpers, and I've started to
> look at XFS.
>
> The actual transaction commited by xfs_fsync and  
> xfs_write_sync_logforce
> has a different transaction number, but actually is exactly the same.
> We'll only use the fsync transaction going forward.  One major  
> difference
> is that xfs_write_sync_logforce never issues a cache flush unless we
> commit a transaction causing that as a side-effect, which is an  
> obvious
> bug in the O_SYNC handling.  Second all the locking and i_update_size
> vs i_update_core changes from 978b7237123d007b9fa983af6e0e2fa8f97f9934
> never made it to xfs_write_sync_logforce, so we add them back.
>
> To make xfs_fsync easily usable from the O_SYNC path, the  
> filemap_fdatawait
> call is moved up to xfs_file_fsync, so that we don't wait on the whole
> file after we already waited for our portion in xfs_write.
>
> We'll also use a plain call to filemap_write_and_wait_range instead
> of the previous sync_page_rang which did it in two steps including
> an half-hearted inode write out that doesn't help us.
>
> Once we're done with this also remove the now useless i_update_size
> tracking.
>
>
> Signed-off-by: Christoph Hellwig <hch at lst.de>

Reviewed-by: Felix Blyakher <felixb at sgi.com>