linux-kernel - Re: [PATCH 2/4] fs: remove the never implemented aio

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Date:   Tue, 1 Nov 2016 15:30:08 +0100
From:   Christoph Hellwig <hch@....de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Dave Chinner <david@...morbit.com>, Christoph Hellwig <hch@....de>,
        Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
        Dmitry Monakhov <dmonakhov@...nvz.org>,
        Jeff Moyer <jmoyer@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-aio@...ck.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] fs: remove the never implemented aio_fsync file
        operation

On Mon, Oct 31, 2016 at 06:30:11PM -0700, Linus Torvalds wrote:
> I still suspect that if we want to do this, we should strive to expose
> all the other syncing flags from sync_file_range() too.

sync_file_range is entirely different from fsync -
sync_file_range allows you detailed control of data writeback, but it
does not allow to commit metadata at all, i.e. it's not a data integrity
operation. 

> Yeah, that's more of a "keep writes streaming" interface than a
> fsync() like interface, but I think the two really do fit together.
> It's kind of sad how we have this very fragmented interface to
> writeback, where  some operations take that "data vs metadata", some
> operations take a range of bytes, and some operations take that "start
> writeback vs wait for it", but nothing does all of the above. They are
> really just different faces of the same writeback coin.

sync_file_range at the moment actually doesn't involve the fs, which
has it's own set of problems.  So yes, maybe we need a full blown
sync method unifying fsync, sync_file_range and which enables ranged
data integrity fsync and asynchronous operations of all this.

But to go back to Dave's argument - none of that can archived with that
aio_fsync method added more than 10 years ago and never implemented.