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

On Tue, Jan 13, 2026 at 01:12:09AM +0100, Stefano Brivio wrote:

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

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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).

Ok.

But we implicitly break any outbound forwarding because our listening sockets will be unreachable (bind() succeeds though).

Networking doesn't work until you configure networking, that's the normal state for !--config-net. I don't see why that should be different for outbound forwards than anything else.

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.

I mean.. probably? Almost certainly when pasta is creating the ns - but in that case there's very little reason not to use --config-net anyway. The case I'm concerned about is attaching this to an existing netns: this can alter the existing network config there. -- 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