is cache-only-prefixes an nnpfs limitation?

[Tomas Olsson]

Adam Megacz <megacz at cs.berkeley.edu> writes:
> I understand that, currently, Arla must retrieve bytes 0..n of a file
> in order to access byte n+1.  Is this a limitation imposed by nnpfs,
> or simply the way arlad currently works?
> 
It's a limitation imposed by nnpfs. You probably want to take a look at the
protocol (arla/nnpfs/include/nnpfs/nnpfs_message.h) and arla/doc/nnpfs.txt
(may need an update). If you're adventurous, take a look at the protocol
version in block_branch in CVS, too. It's not exactly final.

> Specifically, I'm wondering about the possibilities of writing other
> filesystems that run on top of nnpfs (including the Win32 nnpfs), and
> I wanted to know if this limitation would be inherited.
>
Yup, the nnpfs implementation and protocol does limit things. It will get
less limiting, but I don't see us implementing completely free byte range
fetching. Apart from that, it should work. We've mentioned a few other
projects that use xfs/nnpfs here before. I guess arlad is the most complete
reference on how it is supposed to work, but it's not a very clear design.
If you happen to write up a little libnnpfs or so, I'm _very_ interested.

AFAIK, w2k nnpfs works very well for demos and benchmarks, but it does have
threading issues. Needs some work to be fit for production use.

What do you have in mind?

/t