Re: silent semantic changes with reiser4

Jamie Lokier
2004-08-26T16:00:53Z

Christophe Saout wrote:
> I'm just thinking about something. While you can't cut bytes out of unix
> iles a lot of filesystems can do this (holes). Most of them only on a
> block boundary, reiser4 on a byte boundary. If the filesystems could
> export this functionality using an enhanced API we could implement a
> compression plugin and other things on the VFS level that works with
> every filesystem supporting the required mechanisms, not only reiser4.
> And those features would take advantage of reiser4's storage mechanisms.
> I think Hans made the plugins reiser4-only because only reiser4 has a
> similar API at that time (and obviously because he didn't even think
> about doing it otherwise).

Yes. In some cases the compression or re-archiving algorithm would
choose different parameters, depending on the alignment capabilities
of the underlying filesystem. In some cases, that alignment is
"offset 0 is the only one you can have", which is a severe special
case where truncate and rewrite is required for changes.

> > By the way, can reiser4 share parts of files between different files?
>
> At the moment a file is exactly one object. But someone could write
> another file plugin that spans a file across multiple objects, then yes,
> multiple files could share parts.

Nice. That's useful for files which appear as themselves and also as
part of a container.

And also for revision managed filesystems :)

-- Jamie