From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: passt.top; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=I8lffaPM; dkim-atps=neutral Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by passt.top (Postfix) with ESMTPS id 75C145A0772 for ; Mon, 05 Jan 2026 09:54:07 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1767603246; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NAECtCRwUs2fnQz6LgO1E2zMRmbmKRQ6SQBAffCH63s=; b=I8lffaPM1j739L1eeDMvrQ1s0b2TOfjLHf8PudgnyitIjUPNVdXXe8i6BUUKZ7akQcryek zoyANwHJimw+rBBaW1K9Mm+xwMPI8d4A/Wnzh9gbV0wbeK1w+S3vHCgdPR0W+ilLiyh1K7 A8CWa8DG7gzDAR8ylXL6A2J8yXWfKEA= Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-649-q2dfwJN_PY-9rlVWtwsfEQ-1; Mon, 05 Jan 2026 03:54:04 -0500 X-MC-Unique: q2dfwJN_PY-9rlVWtwsfEQ-1 X-Mimecast-MFC-AGG-ID: q2dfwJN_PY-9rlVWtwsfEQ_1767603243 Received: by mail-ed1-f70.google.com with SMTP id 4fb4d7f45d1cf-64b830ab6baso1624499a12.1 for ; Mon, 05 Jan 2026 00:54:04 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1767603243; x=1768208043; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=NAECtCRwUs2fnQz6LgO1E2zMRmbmKRQ6SQBAffCH63s=; b=GxgWvvmeEM2kmuRhe/egVv7snv+YHWpp0hfIncafw3dd7n1zEzuCLxvkHWPaL+GfYU +KHvwCASRqB9KFjKZ21Xc1ER2ZDHR+FBk6x7AxCFviEE7WGrQEILNd9HK1rLqmFeOrI/ 1YtL/pFZW8fqXQPty0+mFvuYrn+7QxjlY9n2/RhgdHEjvlEQNZEF2ucJ71A69QMoDQPB N3UgwnsdZ1uDHY704h09aEmhbfUFZHlsv0H3pYUsaCfkI88k4LAKssQqdSxxJESo7i3k dk86bqRSsdl3OCh/l8NQNVvh4v2SeX2oHrs2GF1cekp6NuQQ5lA3SznIwkHi05oaJrz7 CKwA== X-Gm-Message-State: AOJu0YyHTEvYrWcKj+MuqGseJZGUct1NppfJr89nW0d/CMmAsLJgjTVm 1vvRV0OZKxd8VRbSaV8ACsS42BDFZPGsiH/zZEPFWoCDbPXIlY9//C1sXxDd8EsQorUI1eMkwfg GDEu10Ff8OKtts8x+mq8SNMs3Z2lqv8mOgY0E1xHlc3jJI+trKAewbdjuF02/yzfnwchG0obn51 xNQvUaphIIt1GfoLQqSiIPURuWHYo1 X-Gm-Gg: AY/fxX7O3c5KNKCSFRnW7LKL8KbhQl57ZeqcFXKrqMgKHkvX46KkeQHTRccjTxHMbQw wXoBW00DhVbaERmDf6xJAbgCBAGvtrC5RMItdpCS7QcqOFqPs24GI9VN1xJ9QW1BakJD2AiMhAY EBN8UdpPAjvs4FKtBUCUJYohVjd14b3bUQ15eJ7ZY5Mu238mnLOhYNl4uHvhJH+oKapSRBMFXC9 t0TsnYM+vM9+/EkrOyVHpFgUZYX7MwjftyKXUDkrsrJ2Itg6EDN1amRnJudr6W5dCzvuGyKIiJk 3lnavhVPmFBt X-Received: by 2002:a05:6402:234a:b0:64d:1ea3:f205 with SMTP id 4fb4d7f45d1cf-64fd4929c19mr6888966a12.3.1767603242996; Mon, 05 Jan 2026 00:54:02 -0800 (PST) X-Google-Smtp-Source: AGHT+IEWefAPRHY77ne7p76Atvbye2cmaVVLO1/N7fAFNvs6Lk/+b7INEDrv2D+qqjYkdDQpj+nY4armSZK/ObIiD8A= X-Received: by 2002:a05:6402:234a:b0:64d:1ea3:f205 with SMTP id 4fb4d7f45d1cf-64fd4929c19mr6888942a12.3.1767603242412; Mon, 05 Jan 2026 00:54:02 -0800 (PST) MIME-Version: 1.0 References: <20251229095558.918055-1-yuhuang@redhat.com> In-Reply-To: From: Yumei Huang Date: Mon, 5 Jan 2026 16:53:49 +0800 X-Gm-Features: AQt7F2oz5_4-ghIiFz8y6tQ1aErtGD8maC9m60wmORO7DfHWFVy6wHMy998_WpA Message-ID: Subject: Re: [PATCH] conf, pasta: Add --no-tap option To: David Gibson X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: MszEBkJa7JM5SwWuDlREwkKH2yrfV5h-aRjZPz_P-oU_1767603243 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Message-ID-Hash: CL7SH3VQQFQL7QVQVFANFXNJQD7Y6R44 X-Message-ID-Hash: CL7SH3VQQFQL7QVQVFANFXNJQD7Y6R44 X-MailFrom: yuhuang@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: passt-dev@passt.top, sbrivio@redhat.com 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, Jan 5, 2026 at 12:18=E2=80=AFPM David Gibson wrote: > > On Mon, Dec 29, 2025 at 05:55:58PM +0800, Yumei Huang wrote: > > This patch introduces a mode where we only forward loopback connections > > and traffic between two namespaces (via the loopback interface, 'lo'), > > without a tap device. > > > > With this, podman can support forwarding ::1 in custom networks when us= ing > > rootlesskit for forwarding ports. > > > > In --no-tap mode, --host-lo-to-ns-lo, --no-icmp and --no-ra is automati= cally > > enabled. Options requiring a tap device (--ns-ifname, --ns-mac-addr, > > --config-net, --outbound-if4/6) are rejected. > > > > Link: https://bugs.passt.top/show_bug.cgi?id=3D149 > > Signed-off-by: Yumei Huang > > Nice work. There are some things that need polish, but overall this > looks pretty good to me. Like Stefano, I'm pleasantly surprised at > how simple it turned out to be. > > > --- > > conf.c | 56 +++++++++++++++++++++++++++++++++++++++++--------------- > > fwd.c | 3 +++ > > passt.1 | 5 +++++ > > passt.h | 2 ++ > > pasta.c | 3 +++ > > tap.c | 11 +++++++---- > > 6 files changed, 61 insertions(+), 19 deletions(-) > > > > diff --git a/conf.c b/conf.c > > index 84ae12b..353d0a5 100644 > > --- a/conf.c > > +++ b/conf.c > > @@ -1049,7 +1049,8 @@ pasta_opts: > > " --no-copy-addrs DEPRECATED:\n" > > " Don't copy all addresses to names= pace\n" > > " --ns-mac-addr ADDR Set MAC address on tap interface\= n" > > - " --no-splice Disable inbound socket splicing\n= "); > > + " --no-splice Disable inbound socket splicing\n= " > > + " --no-tap Don't create tap device\n"); > > I feel like this description can be improved, but I'm not exactly sure > how, yet. > > > > > passt_exit(status); > > } > > @@ -1451,6 +1452,7 @@ void conf(struct ctx *c, int argc, char **argv) > > {"no-ndp", no_argument, &c->no_ndp, 1= }, > > {"no-ra", no_argument, &c->no_ra, 1= }, > > {"no-splice", no_argument, &c->no_splice, 1= }, > > + {"no-tap", no_argument, &c->no_tap, 1= }, > > {"freebind", no_argument, &c->freebind, 1= }, > > {"no-map-gw", no_argument, &no_map_gw, 1= }, > > {"ipv4-only", no_argument, NULL, '= 4' }, > > @@ -1947,8 +1949,11 @@ void conf(struct ctx *c, int argc, char **argv) > > } > > } while (name !=3D -1); > > > > - if (c->mode !=3D MODE_PASTA) > > + if (c->mode !=3D MODE_PASTA) { > > c->no_splice =3D 1; > > + if (c->no_tap) > > + die("--no-tap is for pasta mode only"); > > + } > > > > if (c->mode =3D=3D MODE_PASTA && !c->pasta_conf_ns) { > > if (copy_routes_opt) > > @@ -1957,6 +1962,25 @@ void conf(struct ctx *c, int argc, char **argv) > > die("--no-copy-addrs needs --config-net"); > > } > > > > + if (c->mode =3D=3D MODE_PASTA && c->no_tap) { > > + if (c->no_splice) > > + die("--no-tap is incompatible with --no-splice"); > > + if (*c->ip4.ifname_out || *c->ip6.ifname_out) > > + die("--no-tap is incompatible with --outbound-if4= /6"); > > + if (*c->pasta_ifn) > > + die("--no-tap is incompatible with --ns-ifname"); > > + if (*c->guest_mac) > > + die("--no-tap is incompatible with --ns-mac-addr"= ); > > These all make sense. It might also make sense to exclude the -i > option - setting a template interface also makes no sense in --no-tap > mode. Sure, I can add an if condition with if4 (as if4=3Dif6 in that case). > > > + 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. > > > + c->host_lo_to_ns_lo =3D 1; > > + c->no_icmp =3D 1; > > + c->no_ra =3D 1; > > + c->no_dns =3D 1; > > + c->no_dns_search =3D 1; > > The reasoning for the last two items is a bit unclear to me. IIUC, > no_dns and no_dns_search aren't so much about "support" for DNS itself > but for advertising DNS settings via DHCP. Since DHCP will be > unsupported, so are these as a consequence. Is that right? Yeah, I think so. Actually I added c->no_dhcp, c->no_ndp here as well, then removed them as they are set in later changes(conditions about c->ifi4/c->ifi6), though they turn out to be not quite right :'\ > > > + } > > + > > if (!ifi4 && *c->ip4.ifname_out) > > ifi4 =3D if_nametoindex(c->ip4.ifname_out); > > > > @@ -1980,9 +2004,9 @@ void conf(struct ctx *c, int argc, char **argv) > > log_conf_parsed =3D true; /* Stop printing everything */ > > > > nl_sock_init(c, false); > > - if (!v6_only) > > + if (!v6_only && !c->no_tap) > > c->ifi4 =3D conf_ip4(ifi4, &c->ip4); > > - if (!v4_only) > > + if (!v4_only && !c->no_tap) > > c->ifi6 =3D conf_ip6(ifi6, &c->ip6); > > > > if (c->ifi4 && c->mtu < IPV4_MIN_MTU) { > > @@ -1998,30 +2022,32 @@ void conf(struct ctx *c, int argc, char **argv) > > (*c->ip6.ifname_out && !c->ifi6)) > > die("External interface not usable"); > > > > - if (!c->ifi4 && !c->ifi6 && !*c->pasta_ifn) { > > + if (!c->ifi4 && !c->ifi6 && !*c->pasta_ifn && !c->no_tap) { > > strncpy(c->pasta_ifn, pasta_default_ifn, > > sizeof(c->pasta_ifn) - 1); > > } > > > > if (!c->ifi4 && !v6_only) { > > - info("IPv4: no external interface as template, use local = mode"); > > - > > - conf_ip4_local(&c->ip4); > > + if (!c->no_tap) { > > + info("IPv4: no external interface as template, us= e local mode"); > > + conf_ip4_local(&c->ip4); > > + } > > c->ifi4 =3D -1; > > } > > > > if (!c->ifi6 && !v4_only) { > > - info("IPv6: no external interface as template, use local = mode"); > > - > > - conf_ip6_local(&c->ip6); > > + if (!c->no_tap) { > > + info("IPv6: no external interface as template, us= e local mode"); > > + conf_ip6_local(&c->ip6); > > + } > > c->ifi6 =3D -1; > > } > > > > - if (c->ifi4 && !no_map_gw && > > + if (c->ifi4 > 0 && !no_map_gw && > > This isn't quite right. ifi4 =3D=3D -1 now occurs in two cases: local > mode, and --no-tap mode. Not setting map_host_loopback makes sense > for --no-tap mode, but it's still needed for local mode. I'm a bit confused by map_host_loopback. I don't quite understand the use scenario. IIUC, either in --no-tap mode or local mode, guest can only communicate with host. Then why do we need to set map_host_loopback? What's the benefit? > > > IN4_IS_ADDR_UNSPECIFIED(&c->ip4.map_host_loopback)) > > c->ip4.map_host_loopback =3D c->ip4.guest_gw; > > > > - if (c->ifi6 && !no_map_gw && > > + if (c->ifi6 > 0 && !no_map_gw && > > Same here. > > > IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_host_loopback)) > > c->ip6.map_host_loopback =3D c->ip6.guest_gw; > > > > @@ -2116,10 +2142,10 @@ void conf(struct ctx *c, int argc, char **argv) > > conf_ports(c, name, optarg, &c->udp.fwd_out); > > } while (name !=3D -1); > > > > - if (!c->ifi4) > > + if (c->ifi4 <=3D 0) > > c->no_dhcp =3D 1; > > > > - if (!c->ifi6) { > > + if (c->ifi6 <=3D 0) { > > c->no_ndp =3D 1; > > c->no_dhcpv6 =3D 1; > > And here. Local mode can still use NDP and DHCP, even though --no-tap > mode can't. It might be simpler to force no_ndp, no_dhcp etc. along > with no_ra and the rest above. Sure, I will add them. > > > } else if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr)) { > > diff --git a/fwd.c b/fwd.c > > index 44a0e10..2f4a89a 100644 > > --- a/fwd.c > > +++ b/fwd.c > > @@ -780,6 +780,9 @@ uint8_t fwd_nat_from_host(const struct ctx *c, uint= 8_t proto, > > return PIF_SPLICE; > > } > > > > + if (c->no_tap) > > + return PIF_NONE; > > + > > if (!nat_inbound(c, &ini->eaddr, &tgt->oaddr)) { > > if (inany_v4(&ini->eaddr)) { > > if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.our_tap_addr)= ) > > diff --git a/passt.1 b/passt.1 > > index db0d662..2d643f7 100644 > > --- a/passt.1 > > +++ b/passt.1 > > @@ -755,6 +755,11 @@ Default is to let the tap driver build a pseudoran= dom hardware address. > > Disable the bypass path for inbound, local traffic. See the section \f= BHandling > > of local traffic in pasta\fR in the \fBNOTES\fR for more details. > > > > +.TP > > +.BR \-\-no-tap > > +Do not create a tap device in the namespace. In this mode, only local = loopback > > +traffic between namespaces is forwarded using splice. > > This probably wants some work, because I'm not sure "tap device" and > "splice" are sufficiently clear in this context. Yeah, I will think about that. Thanks. > > > > + > > .SH EXAMPLES > > > > .SS \fBpasta > > diff --git a/passt.h b/passt.h > > index 79d01dd..0c1ec4c 100644 > > --- a/passt.h > > +++ b/passt.h > > @@ -200,6 +200,7 @@ struct ip6_ctx { > > * @no_ndp: Disable NDP handler altogether > > * @no_ra: Disable router advertisements > > * @no_splice: Disable socket splicing for inbound traff= ic > > + * @no_tap: Do not create tap device > > * @host_lo_to_ns_lo: Map host loopback addresses to ns loopbac= k addresses > > * @freebind: Allow binding of non-local addresses for = forwarding > > * @low_wmem: Low probed net.core.wmem_max > > @@ -277,6 +278,7 @@ struct ctx { > > int no_ndp; > > int no_ra; > > int no_splice; > > + int no_tap; > > int host_lo_to_ns_lo; > > int freebind; > > > > diff --git a/pasta.c b/pasta.c > > index 0ddd6b0..3510ec5 100644 > > --- a/pasta.c > > +++ b/pasta.c > > @@ -316,6 +316,9 @@ void pasta_ns_conf(struct ctx *c) > > die("Couldn't bring up loopback interface in namespace: %= s", > > strerror_(-rc)); > > > > + if (c->no_tap) > > + return; > > + > > /* Get or set MAC in target namespace */ > > if (MAC_IS_ZERO(c->guest_mac)) > > nl_link_get_mac(nl_sock_ns, c->pasta_ifi, c->guest_mac); > > diff --git a/tap.c b/tap.c > > index 9d1344b..9b4eedc 100644 > > --- a/tap.c > > +++ b/tap.c > > @@ -1491,13 +1491,16 @@ static int tap_ns_tun(void *arg) > > */ > > static void tap_sock_tun_init(struct ctx *c) > > { > > - NS_CALL(tap_ns_tun, c); > > - if (c->fd_tap =3D=3D -1) > > - die("Failed to set up tap device in namespace"); > > + if (!c->no_tap) { > > + NS_CALL(tap_ns_tun, c); > > + if (c->fd_tap =3D=3D -1) > > + die("Failed to set up tap device in namespace"); > > + } > > > > pasta_ns_conf(c); > > > > - tap_start_connection(c); > > + if (!c->no_tap) > > + tap_start_connection(c); > > } > > > > /** > > -- > > 2.49.0 > > > > -- > 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 wa= y > | around. > http://www.ozlabs.org/~dgibson --=20 Thanks, Yumei Huang