Re: [PATCH 2/4] fs: remove the never implemented aio_fsync file operation

[Christoph Hellwig <hch@lst.de>]

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.