[PATCH v3 04/11] xfs: update inode allocation/free transaction reservations for finobt

[Christoph Hellwig]

On Thu, Feb 20, 2014 at 01:49:10PM -0500, Brian Foster wrote:
> > Right, that can happen. But my question is this: how realistic is it
> > that we have someone who has ENOSPC because of enough zero length
> > files to trigger this? I've never seen an application or user try to
> > store any significant number of zero length files, so I suspect this
> > is a theoretical problem, not a practical one.
> > 
> 
> Probably not very realistic. ;) The only thing I know that does rely on
> some zero-length files is gluster distribution to represent "link files"
> when one a file that hashes to one server ends up stored on another.
> Even then, I don't see how we would ever have a situation where those
> link files exist in such massive numbers and are removed in bulk. So
> it's likely a pathological scenario.

Zero data blocks are the only case for device nodes or fifos, very
common for symlinks that can be stored inline, and not unusual for
directories.