Re: [PATCH] conf, pasta: Add --no-tap option

On Mon, 12 Jan 2026 15:26:14 +1100 David Gibson wrote:

On Sat, Jan 10, 2026 at 07:12:19PM +0100, Stefano Brivio wrote:

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On Mon, 5 Jan 2026 16:53:49 +0800 Yumei Huang wrote:

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On Mon, Jan 5, 2026 at 12:18 PM David Gibson wrote:

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On Mon, Dec 29, 2025 at 05:55:58PM +0800, Yumei Huang wrote:

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+ if (c->pasta_conf_ns) + die("--no-tap is incompatible with --config-net");

I don't think this is right. We still can and should bring up 'lo' in the --no-tap case.

I see your point, but seems c->pasta_conf_ns is only used for tap as https://passt.top/passt/tree/pasta.c#n328, 'lo' is configured before that line.

Right, and the reason is that there are basic bits of functionality (probing pipe sizes if I recall correctly, or anyway probing for some kind of capability) that need the loopback interface to be up.

Ah, right. Drat. In general I don't like us touching the guest netlink at all if we don't have --config-net. Hrm.. now what exactly needs this. It's not anything in sock_probe_features() - that runs in the host ns. Not pipe sizes, either - that also takes place in the host ns (and netns is irrelevant to pipes, anyway). There could well be something, but I'm not sure what it is.

Actually, I tried, and I don't get any trouble (but I think I had some error when I added that in 2021). But we implicitly break any outbound forwarding because our listening sockets will be unreachable (bind() succeeds though). So... I would be wary of changing that at this point. There might be users relying on it, and it's otherwise harmless I guess. -- Stefano