Re: [PATCH v7 02/13] passt, pasta: Introduce unified multi-address data structures

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 14 May 2026 16:30:16 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Sun, Apr 12, 2026 at 08:53:08PM -0400, Jon Maloy wrote:
>
> > [...]
> >
> > +/** inany_prefix_len() - Convert prefix length to native format
> > + * @addr:	IPv4 or IPv6 address
> > + * @prefix_len:	prefix length (any format, auto-detected)  
> 
> If it's pertaining to an inany, it should always be IPv6 format.
> Auto-detecting just masks bugs elsewhere.
> 
> > + *
> > + * Return: prefix length in native format (0-32 for IPv4, 0-128 for IPv6)
> > + */
> > +static inline int inany_prefix_len(const union inany_addr *addr,
> > +				   int prefix_len)
> > +{
> > +	if (inany_v4(addr) && prefix_len >= 96)  
> 
> Yikes.  Even ignoring the fact I don't like this function at all

Can you then please suggest / sketch another solution? We went back and
forth on this topic quite a bit but we couldn't come up with anything
more elegant so far.

> this
> isn't good.  If we somehow get a IPv4-mapped inany with a prefix_len
> that's < 96, something has already gone wrong.  This, however, will
> just fall back to the IPv6 case.  So if prefix_len is 33..96 it will
> return something entirely nonsensical, and if it's 0..32 it will
> return something that looks ok, but ignores the fact that something is
> already wrong.
> 
> > +		return prefix_len - 96;
> > +
> > +	return prefix_len;
> > +}
> > +
> > +/** inany_prefix_len6() - Convert prefix length to generic format
> > + * @addr:	IPv4 or IPv6 address
> > + * @prefix_len:	prefix length (any format, auto-detected)
> > + *
> > + * Return: prefix length in generic format (96-128 for IPv4, 0-128 for IPv6)
> > + */
> > +static inline int inany_prefix_len6(const union inany_addr *addr,
> > +				    int prefix_len)  
> 
> This function should not be necessary.  If the prefix_len is attached
> to an inany, it should already be in IPv6 format.
> 
> > +{
> > +	if (inany_v4(addr) && prefix_len && prefix_len <= 32)
> > +		return prefix_len + 96;  
> 
> Similar comments here.  Also a 0.0.0.0/0 is a valid prefix which
> should be translated to ::ffff:0:0/96, not to ::ffff:0:0/0 as this
> function will.
> 
> > [...]

-- 
Stefano