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[176.103.220.4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f464a974csm15928303f8f.18.2026.07.15.00.11.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jul 2026 00:11:30 -0700 (PDT) From: Stefano Brivio To: David Gibson Subject: Re: [PATCH v2 1/5] fwd: Clarify semantics of --host-lo-to-ns-lo Message-ID: <20260715091129.282bbbf9@elisabeth> In-Reply-To: <20260713053856.1329271-2-david@gibson.dropbear.id.au> References: <20260713053856.1329271-1-david@gibson.dropbear.id.au> <20260713053856.1329271-2-david@gibson.dropbear.id.au> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.49; x86_64-pc-linux-gnu) MIME-Version: 1.0 Date: Wed, 15 Jul 2026 09:11:30 +0200 (CEST) X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: xGhz_9n7NLbrPGi_Yv9sqVXU-OP5ouf6eTELkoffV74_1784099493 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: I7L47KTUHXLDL76ULOIMC4VCEDX2HTFD X-Message-ID-Hash: I7L47KTUHXLDL76ULOIMC4VCEDX2HTFD 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: 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, 13 Jul 2026 15:38:52 +1000 David Gibson wrote: > The semantics of --host-lo-to-ns-lo as described in the man page don't > quite make sense: It says without the option forwarded packets will appear > to come _from_ the guest's public address, which is not usually true. > Instead the packets will arrive *to* the guest's public address. The exact > semantics are also a bit confusing in general. > > Rewrite both the man page and code to clarify this. The new rule is that > it redirects connections addressed to a host loopback address to the same > loopback address in the guest. This is notionally different from what we > had in two ways: > * We can now deliver to nonstandard loopback addresses within the guest, > not just the default one. This is technically a behavioural change, > but I think will be less surprising behaviour. > * The decision is now made on the original _destination_ address, rather > than source address. That's different theoretically, but not in > practice, since loopback packets must have loopback addresses for both > source and destination. > > We make it explicitly incompatible with --no-splice - previously it > was allowed, but would have no effect in that case. > > As well as being more precise right now, these semantics will intersect > better with other upcoming changes to the forwarding logic. > > Signed-off-by: David Gibson I added: Link: https://bugs.passt.top/show_bug.cgi?id=212 -- Stefano