Re: [rfc] fsync_range?

[Jamie Lokier <jamie@shareable.org>]

Theodore Tso wrote:
> On Wed, Jan 21, 2009 at 07:23:06AM +0100, Nick Piggin wrote:
> > > 
> > > But sync_file_range() has a bug, which you've pointed out - the
> > > missing _data-retrieval_ metadata isn't synced.  In other words, it's
> > > completely useless.
> > 
> > I don't know. I don't think this is a newly discovered problem.
> > I think it's been known for a while, so I don't know what's
> > going on.
> 
> We should ask if anyone is actually using sync_file_range (cough,
> <Oracle>, cough, cough).  But if I had to guess, for those people who
> are using it, they don't much care, because 99% of the time they are
> overwriting data blocks within a file which isn't changing in size, so
> there is no data-retrieval metadata to sync.

What about btrfs with data checksums?  Doesn't that count among
data-retrieval metadata?  What about nilfs, which always writes data
to a new place?  Etc.

I'm wondering what exactly sync_file_range() definitely writes, and
what it doesn't write.

If it's just in use by Oracle, and nobody's sure what it does, that
smacks of those secret APIs in Windows that made Word run a bit faster
than everyone else's word processer...  sort of. :-)

-- Jamie