Re: silent semantic changes with reiser4

Jamie Lokier
2004-08-26T16:53:51Z

Rik van Riel wrote:
> And if an unaware application reads the compound file
> and then writes it out again, does the filesystem
> interpret the contents and create the other streams ?

Yes, exactly that. The streams are created on demand of course, and
by userspace helpers when that's appropriate which I suspect it almost
always is.

> Unless I overlook something (please tell me what), the
> scheme just proposed requires filesystems to look at
> the content of files that is being written out, in
> order to make the streams work.

Yes. Hence the idea of coherent views between two files: writing to
one affects the content of the other, although the calcalation is only
done on demand (or when the fs wants to migrate the representation --
for example, creating the flat container prior to deleting the
regeneratable pieces in order to save space).

I haven't seen anything from Namesys that says they'll do that. I
have the impression the streams are just generated in memory on the
fly, not stored on disk with a cacheing policy, but that's just an
impression. (We've all seen the Namesys white papers, they're not
_that_ revealing). :)

I'm just pointing out how to do it _right_. I think it will turn out
like this eventually, either next year or some time over the next
decade after some iterations. Inevitable. Mark my words, etc. :)

-- Jamie