Re: [PATCH v2 06/15] fwd: Store forwarding tables indexed by (origin) pif

On Fri, Mar 20, 2026 at 09:58:34PM +0100, Stefano Brivio wrote:

On Thu, 19 Mar 2026 17:11:48 +1100 David Gibson wrote:

...

Currently we store the inbound (PIF_HOST) and outbound (PIF_SPLICE) forwarding tables in separate fields of struct ctx. In a number of places this requires somewhat awkward if or switch constructs to select the right table for updates. Conceptually simplify that by using an index of forwarding tables by pif, which as a bonus keeps track generically which pifs have implemented forwarding tables so far.

For now this doesn't simplify a lot textually, because many places that need this also have other special cases to apply by pif. It does simplify a few crucial places though, and we expect it will become more useful as the flexibility of the forwarding table is improved.

Signed-off-by: David Gibson --- conf.c | 53 +++++++++++++++++++++++++++------------------- flow.c | 22 +++++++------------ fwd.c | 65 ++++++++++++++++++++++++++++++--------------------------- fwd.h | 4 ++-- passt.h | 3 +-- 5 files changed, 77 insertions(+), 70 deletions(-)

diff --git a/conf.c b/conf.c index 940fb9e9..6af3c8a5 100644 --- a/conf.c +++ b/conf.c @@ -1252,11 +1252,12 @@ dns6: } }

- info("Inbound forwarding:"); - fwd_rules_print(&c->fwd_in); - if (c->mode == MODE_PASTA) { - info("Outbound forwarding:"); - fwd_rules_print(&c->fwd_out); + for (i = 0; i < PIF_NUM_TYPES; i++) { + if (!c->fwd[i]) + continue; + + info("Forwarding from %s:", pif_name(i));

I don't have a good solution to propose but it's slightly annoying that we're changing very clear "Inbound forwarding" and "Outbound forwarding" indications to "Forwarding from: " HOST | TAP | SPLICE.

Should we perhaps introduce a PIF_INBOUND_MAX value that's the same as HOST, and then:

if (i <= PIF_INBOUND_MAX) info("Inbound forwarding:"); else info("Outbound forwarding:");

?

That will become ambiguous as soon as we add tables for TAP.

I'm fine keeping it as it is, I would just have a slight preference to make it as clear as it was before. This is something users can now look at to double check things and I have the feeling we're avoid a bunch of bug reports as a result.

For now I've gone with: {Inbound|Outbound} forwarding rules (<pif name>):

...

diff --git a/passt.h b/passt.h index b614bdf0..5fc4e07f 100644 --- a/passt.h +++ b/passt.h @@ -264,8 +264,7 @@ struct ctx { unsigned int pasta_ifi; int pasta_conf_ns;

- struct fwd_table fwd_in; - struct fwd_table fwd_out; + struct fwd_table *fwd[PIF_NUM_TYPES];

Nit: the struct documentation should be updated accordingly.

Fixed. -- 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