Re: [PATCH 15/18] pif: Limit pif names to IFNAMSIZ (16) bytes

On Sun, Mar 29, 2026 at 02:02:27PM +0200, Stefano Brivio wrote:

On Fri, 27 Mar 2026 15:34:27 +1100 David Gibson wrote:

...

All current pif names are quite short, and we expect them to remain short when/if we allow arbitrary pifs. However, because of the structure of the current code we don't enforce any limit on the length.

This will become more important with dynamic configuration updates, so start enforcing a length limit. Specifically we allow pif names to be up to IFNAMSIZ bytes, including the terminating \0. This is semi-arbitrary - there's no particular reason we have to use the same length limit as kernel netif names. However, when we do allow arbitrary pifs, we expect that we might support a similar number to the number of kernel interfaces. It might make sense to use names matching kernel interface names in that future. So, re-use IFNAMSIZ to avoid surprise.

And what if... we used 128 instead, which is reasonably longer than UNIX_PATH_MAX (108, which despite the application usage in POSIX 2024.1: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/sys_un.h.html is still commonly used a path length limit, also by passt itself)?

Well, certainly we could make pif names longer...

At that point we could embed UNIX domain socket paths as PIF name (possibly with some additional specifier) which _might_ be useful to forward UNIX sockets in the https://bugs.passt.top/show_bug.cgi?id=200 sense.

...but I don't think that rationale is compelling. The unix socket path would be the equivalent of IP+port, not the pif. I don't see how embedding a unix path in the pif would be useful.

It's not the only way to implement it, but perhaps it's one possibility that might make sense for what we know now? What do you think?

It also has the advantage of being sufficiently longer than IFNAMSIZ, so that should we ever need to have stuff like "container_A:eth0" in a PIF name, we could have it as well.

That's a more convincing case. Ok, I'll expand the pif name size for the next spin. -- 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