Re: fs-independent quotas

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Oct 20, 2011 at 03:08:16PM +0000, David Holland wrote:
> That's way more complicated than necessary. Think of it as like
> VOP_READDIR - you get passed a position, you send back some number of
> items, and update the position.

Depending on how the data are stored on disk, the notion of position
(which also implies some ordering) can be difficult to handle,
especially if the data we're reading can change between two calls,
causing the position do become invalid.

It's certainly less trouble to send back to userland the whole set of
data - especially if what userland wants is the whole set of data
(I can't see what a partial read of quota would be usefull for).

> 
> If you want to take the trouble to guarantee strict transactional
> consistency, you can easily enough by checking generation numbers and
> failing with a particular errno if things have changed; but I don't
> think there's any real need for that level of strict consistency for
> quotas. Much less so than for readdir, at least, and we manage to cope
> with readdir the way it is.

I agree with this.

> 
> The reason to wrap the position in a cursor abstraction is to allow
> flexibility about how the position is represented.

But then the cursor would still be stored in userland ?

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--