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[2a10:fc81:a806:d6a9::1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47eda463e92sm2274925e9.16.2026.01.12.16.12.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jan 2026 16:12:10 -0800 (PST) Date: Tue, 13 Jan 2026 01:12:09 +0100 From: Stefano Brivio To: David Gibson Subject: Re: [PATCH] conf, pasta: Add --no-tap option Message-ID: <20260113011209.3c5ed9f6@elisabeth> In-Reply-To: References: <20251229095558.918055-1-yuhuang@redhat.com> <20260110191219.29498050@elisabeth> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.49; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: O86iYm94jgHCL3iYgrn6qQ7FysOWpGzys8C6XI8O02A_1768263132 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Message-ID-Hash: VGNTIVLK7VIFKY6U37KPYTCBMVWTO7MB X-Message-ID-Hash: VGNTIVLK7VIFKY6U37KPYTCBMVWTO7MB X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: Yumei Huang , passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: 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: > > On Mon, 5 Jan 2026 16:53:49 +0800 > > Yumei Huang wrote: > > =20 > > > On Mon, Jan 5, 2026 at 12:18=E2=80=AFPM David Gibson > > > wrote: =20 > > > > > > > > On Mon, Dec 29, 2025 at 05:55:58PM +0800, Yumei Huang wrote: =20 > > > > > > > > > + if (c->pasta_conf_ns) > > > > > + die("--no-tap is incompatible with --config= -net"); =20 > > > > > > > > I don't think this is right. We still can and should bring up 'lo'= in > > > > the --no-tap case. =20 > > >=20 > > > 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. =20 > >=20 > > 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. =20 >=20 > 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. --=20 Stefano