Re: Making an interface for alternative data streams

[Dave Chinner <david@fromorbit.com>]

On Tue, Mar 22, 2016 at 05:52:32PM -0400, J. Bruce Fields wrote:
> On Wed, Mar 23, 2016 at 08:29:31AM +1100, Dave Chinner wrote:
> > If you want additional seekable data streams, then come up with a
> > filesystem namespace method of addressing these alternate data
> > streams as *separate files containing data*. That's all an ADS is -
> > a namespace hack to address multiple data files through a single
> > file name. That's the problem that needs solving and it has nothing
> > to do with xattrs.
> 
> There was some thread about this years ago.  Looking... "silent semantic
> changes with reiser4" or "possible design issues for hybrids" look like
> the relevant threads.
>
> One good starting point might be:
> 
> 	http://mid.gmane.org/20040826212853.GA21964@parcelfarce.linux.theplanet.co.uk
> 
> Don't know how out of date that might be now.

Not sure it is the same issue - that looks like auto-bind-mount
stuff. There are some relevant questions though, like "directory
over file" semantics and implications...

But we have covered this ground before, and at LSF/MM summits, too.
historically it has been made pretty clear that xattrs are not
something that can be used for alternate data streams. I think ADS
is primarily a namespace and API problem - that needs to be sorted
out first, and then what filesytems need to implement will be
obvious.

Perhaps overlayfs is a good place to start prototyping such
functionality as there is an abstraction between the presented
namespace and the underlying storage of the data....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com