On Mon, 22 May 2023 18:42:01 +1000 David Gibson <david(a)gibson.dropbear.id.au> wrote:On Mon, May 22, 2023 at 01:42:17AM +0200, Stefano Brivio wrote:Yes, there's a way, but to keep things asynchronous in a simple way we process errors from nl_req() only at the next request. This part doesn't really need to be asynchronous, though: we could add a flag for nl_req() saying that we want to know about NLMSG_ERROR right away. This looks relatively straightforward, and already an improvement in the sense you mentioned. Actually parsing the error and finding out the offending route is a bit more complicated, though. -- StefanoInstead of just fetching the default gateway and configuring a single equivalent route in the target namespace, on 'pasta --config-net', it might be desirable in some cases to copy the whole set of routes corresponding to a given output interface. For instance, in: https://github.com/containers/podman/issues/18539 IPv4 Default Route Does Not Propagate to Pasta Containers on Hetzner VPSes configuring the default gateway won't work without a gateway-less route (specifying the output interface only), because the default gateway is, somewhat dubiously, not on the same subnet as the container. This is a similar case to the one covered by commit 7656a6f88882 ("conf: Adjust netmask on mismatch between IPv4 address/netmask and gateway"), and I'm not exactly proud of that workaround. We also have: https://bugs.passt.top/show_bug.cgi?id=49 pasta does not work with tap-style interface for which, eventually, we should be able to configure a gateway-less route in the target namespace. Introduce different operation modes for nl_route(), including a new NL_DUP one, not exposed yet, which simply parrots back to the kernel the route dump for a given interface from the outer namespace, fixing up flags and interface indices on the way, and requesting to add the same routes in the target namespace, on the interface we manage. For n routes we want to duplicate, send n identical netlink requests including the full dump: routes might depend on each other and the kernel processes RTM_NEWROUTE messages sequentially, not atomically, and repeating the full dump naturally resolves dependencies without the need to actually calculate them. I'm not kidding, it actually works pretty well.If there's a way to detect whether the kernel rejected some of the routes, it would be nice to cut that loop short as soon as all the routes are inserted. Obviously that could be a followup improvement, though.