Re: [PATCH 06/18] fwd: Better split forwarding rule specification from associated sockets

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Apr 08, 2026 at 11:39:55PM +0200, Stefano Brivio wrote:
> On Wed, 8 Apr 2026 11:30:29 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > On Wed, Apr 08, 2026 at 01:14:46AM +0200, Stefano Brivio wrote:
> > > On Tue,  7 Apr 2026 13:16:18 +1000
> > > David Gibson <david@gibson.dropbear.id.au> wrote:
> > >   
> > > > 6dad076df037 ("fwd: Split forwarding rule specification from its
> > > > implementation state") created struct fwd_rule_state with a forwarding rule
> > > > plus the table of sockets used for its implementation.  It turns out this
> > > > is quite awkward for sharing rule parsing code between passt and the
> > > > upcoming configuration client.  
> > > 
> > > Indeed, I hated it, in that short moment I had to fiddle with it. Thanks
> > > for coming up with a cleaner solution.  
> > 
> > Yeah, mea culpa.  Seemed like a good idea at the time, but it wasn't.
> > 
> > [snip]
> > > >  /**
> > > > - * struct fwd_table - Table of forwarding rules (per initiating pif)
> > > > + * struct fwd_table - Forwarding state (per initiating pif)
> > > >   * @count:	Number of forwarding rules
> > > >   * @rules:	Array of forwarding rules
> > > > + * @rulesocks:	Pointers to socket arrays per-rule  
> > > 
> > > I don't see this as particularly descriptive (which sockets? What's
> > > the array size?). I'm thinking of something like:
> > > 
> > >  @socks_ref:	Per-rule pointers to associated @socks, @sock_count of them  
> > 
> > There are @count of them, not @sock_count...
> 
> Oops, "of course"...
> 
> > which I guess just
> > emphasises the need for a better description.  How's this:
> > 
> >  * struct fwd_table - Forwarding state (per initiating pif)
> >  * @count:	Number of forwarding rules
> >  * @rules:	Array of forwarding rules
> >  * @rulesocks:	Array of @count pointers within @socks giving the start of the
> >  *		corresponding rule's listening sockets within the larger array
> 
> "Array of @count pointers" is ambiguous in English as it might refer to
> pointers to @count. It obviously doesn't, but it might take a couple of
> readings to realise that. Simple fix: "Array of pointers (@count of
> them) ...".

Good point.

> For the rest, yes, it's better, but I started wondering if we could
> simplify the representation a bit by, either:
> 
> 1. storing indices instead of int *, or

We could do that, but it makes lookups of a rule's sockets more
awkward for minimal benefit

> 2. storing start and end. I'm not sure if it's usable, but it would
>    actually look easier to describe

We could do that, but it means maintaining redundant information that
we never actually have a reason to consult

> if neither of these applies (I didn't really think it through), maybe
> this is slightly more intuitive:
> 
>  * Pointers to entry in @socks (@count of them) with first socket for each rule
> 
> ? If not, I think the version you just proposed is better than the
> original and sufficiently clear anyway.

I have this version now:

/**
 * struct fwd_table - Forwarding state (per initiating pif)
 * @count:	Number of forwarding rules
 * @rules:	Array of forwarding rules
 * @rulesocks:	Parallel array ro @rules (@count valid entries) of pointers to
 *		@socks entries giving the start of the corresponding rule's
 *		sockets within the larger array
 * @sock_count:	Number of entries used in @socks (for all rules combined)
 * @socks:	Listening sockets for forwarding
 */

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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