Doug Evans, le ven. 05 mars 2021 16:05:05 -0800, a ecrit:
> Given that the code is not supposed to be able to know brackets were present
> (they're stripped off early on), what does the above mean w.r.t. the guest?
> For the host we can have "" mean listen on both IPv4 and IPv6
> (by default, absent extra options like ipv4=off).
> But what does a guest address of "" mean?
> IPv4? IPv6? Both?
It cannot really be "both" since it'd need to know.
The 0.0.0.0 address used to mean the dhcp-provided address, and we don't
have a way to know the ipv6 address used with the stateless selection,
so I would say that empty address would be just the dhcp-provided
address. Most probably the guest will pick it up anyway, and guests
usually listen the same on ipv4 and ipv6, so I'd say empty most probably
means the user wants to just connect to ipv4 (whatever protocol was used
to connect to the host).
I realize IPv6 obviates the need for a stateful DHCPv6 server.
Alas setting the hostfwd on the command line is *nice*, but it is currently
*impossible* for IPv6: many system's macaddrs are random,
and their IPv6 address is (at least often) derived from their macaddr.
Thus for those systems the hostfwds have to be set up after the guest has
booted enough to announce its address, and then the user can obtain the
address to pass to hostfwd_add either by logging in and running
ifconfig or some such (which can't be done
via ssh from the host with user-mode networking because the hostfwd
doesn't exist yet), or querying the NDP table and hope it's there.
[I'm probably missing a better alternative though, and just haven't come
up with it yet. Is it possible for QEMU to lazily determine the
guest's IPv6 address? I.e., postpone the ""->guest address mapping
until it's needed and then, say, take the first entry in the NDP table?
That feels a bit fragile: what if someone else gets the first entry in
the NDP table? But is that any more fragile than assuming the first
handed out DHCP address is to the guest? [<<-- Honest question,
can we assume the first handed out DHCP address will necessarily
be the guest?]
Anyways,
If we eventually want a way to say "take this place-holder address
and map it to the guest's IPv6 address" and follow the current spec,
the preferable syntax would be ",ipv4" or ",ipv6" (fortunately that works - using
",ipv6=off" or ",ipv4=off" is pretty clumsy). And then we'll have to of course
flag ",ipv4=off,ipv6=off" and ",ipv4=on,ipv6=on" as errors.
But that would mean the defaults for the guest would have to be
different than for the host. E.g.,
host: ",ipv4" means both, whereas
guest: ",ipv4" (ideally) means ipv4 (since both is meaningless)