Re: ext2 + -osync: not as easy as it seems

[Theodore Tso <tytso@MIT.EDU>]

On Wed, Jan 14, 2009 at 03:37:56PM +0100, Jan Kara wrote:
> > Um, we have that already; the sync_inode() followed by
> > blkdev_issue_flush() is the path taken by fdatasync(), I do believe.
>
>   Maybe ext4-patch-queue changes that area but in Linus's tree I see:
> 
>   if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
>          goto out;
> 
>   So if we just overwrite some data, we send them to disk via fdatawrite()
> and then we quickly bail out from ext4_sync_file() without doing
> blkdev_issue_flush().

So you're thinking about fdatawrite() being called by some code path
other than ext4_sync_file() before we call fsync()?  Yeah, that could
happen....  I think that will only happen if the file is opened
O_SYNC, but that raises another issue, which is that we're not forcing
a flush for writes when the file is opened O_SYNC.

							- Ted