Patch to add support for advertising FULLSYNC to Mac OSX Clients

[Jeremy Allison]

On Sun, Feb 19, 2017 at 11:41:13AM -0800, Christoph Hellwig wrote:
> On Sun, Feb 19, 2017 at 08:44:47PM +0200, Alexander Bokovoy wrote:
> > On su, 19 helmi 2017, Christoph Hellwig wrote:
> > > Coming in late here, but I would suggest that the Samba team
> > > reconsiders implementing the flush commands properly, as in not
> > > being a no-op.  Except for the Apple world with it's odd FULLSYNC
> > > fcntl fsync/fdatasync is _the_ primitive to guarantee data integrity,
> > > and a major file sever that simply ignores it is a major disaster for
> > > the full storage stack.
> > Samba already has vfs_commit module which implements fsync/fdatasync
> > use. It can be stacked with other modules to achieve what you just
> > described.
> 
> I'm worried about doing the right thing out of the box and by default.

So really all you're asking for is 'strict sync = yes'
by default. That's doable.

FYI, for paranoid use cases we also have 'sync always'
as well, which makes every write followed by an fsync().