Re: [PATCH v3] treewide: Introduce 'local mode' for disconnected setups

On 26/11/2024 06:54, Stefano Brivio wrote:

There are setups where no host interface is available or configured at all, intentionally or not, temporarily or not, but users expect (Podman) containers to run in any case as they did with slirp4netns, and we're now getting reports that we broke such setups at a rather alarming rate.

To this end, if we don't find any usable host interface, instead of exiting:

- for IPv4, use 169.254.2.1 as guest/container address and 169.254.2.2 as default gateway

- for IPv6, don't assign any address (forcibly disable DHCPv6), and use the *first* link-local address we observe to represent the guest/container. Advertise fe80::1 as default gateway

- use 'tap0' as default interface name for pasta

Change ifi4 and ifi6 in struct ctx to int and accept a special -1 value meaning that no host interface was selected, but the IP family is enabled. The fact that the kernel uses unsigned int values for those is not an issue as 1. one can't create so many interfaces anyway and 2. we otherwise handle those values transparently.

Fix a botched conditional in conf_print() to actually skip printing DHCPv6 information if DHCPv6 is disabled (and skip printing NDP information if NDP is disabled).

Link: https://github.com/containers/podman/issues/24614 Signed-off-by: Stefano Brivio Tested-by: Paul Holzinger

As mentioned on IRC I noticed a problem in Podman with this as we ignore link local addresses when adding host entries but that is a Podman bug and must be fixed there. -- Paul Holzinger