Re: RFC: IPv6 hostfwd command line syntax [was Re: [PATCH v6 2/4] util/qemu-sockets.c: Split host:port parsing out of inet_parse]

From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Doug Evans <dje@google.com>
Cc: "Samuel Thibault" <samuel.thibault@ens-lyon.org>,
	"Marc-André Lureau" <marcandre.lureau@gmail.com>,
	QEMU <qemu-devel@nongnu.org>
Subject: Re: RFC: IPv6 hostfwd command line syntax [was Re: [PATCH v6 2/4] util/qemu-sockets.c: Split host:port parsing out of inet_parse]
Date: Wed, 26 May 2021 14:57:21 +0100	[thread overview]
Message-ID: <YK5TweOui5bwJ6vl@redhat.com> (raw)
In-Reply-To: <CADPb22TW5GkwcF_08R1KBr+NKBGLOHBwFqHPOJKVgiDa6w2VKA@mail.gmail.com>

On Tue, May 25, 2021 at 12:37:21PM -0700, Doug Evans wrote:
> Hi.
> 
> I want to confirm the command line syntax y'all want for ipv6 host
> forwarding.
> 
> IIUC, the command line syntax is required to be consistent with the use of
> "ipv6=on|off" elsewhere.
> Can you confirm that's correct?
> 
> If so, how does one apply "ipv6=on" to the "::60022-:22" hostfwd spec in
> the following example:
> 
> $ qemu-system-x86_64 [...] --nic user,id=n1,model=e1000,hostfwd=::60022-:22
> 
> ?

Probably easier if we start from the HMP  hostfwd_add command which takes

  hostfwd_add  ::60022-:22

With that, adding the flags is obvious

  hostfwd_add  ::60022-:22,ipv6=on|off,ipv4=on|off

IIUC, that can be handled in the slirp_hostfwd() method impl.

The question is then how this works on the CLI. IIUC ,the "hostfwd=XXX"
ARG value is passed to slirp_hostfwd() eventually, so the change for
the HMP parsing will "just work".

The complication is that the comma is ambiguous between the --net arg
parsing, and the hostfwd parsing. So you would end up having to escape
the commas (ie replace , with ,,):

 --nic user,id=n1,model=e1000,hostfwd=::60022-:22,,ipv6=on,,ipv4=on

If you forget to escape the commas, then the flag ends up applying
to the --nic instead, where ipv4/ipv6 are indeed value for other
reasons.

This kind of sucks, but that's where we are with the old fashioned
design of --nic parsing

Not sure if someone else has better ideas here ?

Regards,
Daniel
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