[Libguestfs] [nbdkit PATCH 2/2] server/sockets: get rid of AI_ADDRCONFIG

[Richard W.M. Jones]

On Wed, Jan 19, 2022 at 04:14:02PM +0100, Laszlo Ersek wrote:
> On 01/19/22 14:47, Richard W.M. Jones wrote:
> > On Wed, Jan 19, 2022 at 01:46:08PM +0000, Richard W.M. Jones wrote:
> >> On Tue, Jan 18, 2022 at 11:19:18AM -0600, Eric Blake wrote:
> >>> On Tue, Jan 18, 2022 at 02:48:33PM +0100, Laszlo Ersek wrote:
> >>>> +    case '4':
> >>>> +      tcpip_sock_af = AF_INET;
> >>>> +      break;
> >>>> +
> >>>> +    case '6':
> >>>> +      tcpip_sock_af = AF_INET6;
> >>>> +      break;
> >>>
> >>> Thus, if the user uses nbdkit -46 (or -64), the last one specified
> >>> silently overrides the earlier one, rather than being diagnosed as
> >>> conflicting or explicitly permitting both.  The override effect
> >>> matches the long-option naming --ipv4-only, so I can live with it,
> >>> but I'm also open to the idea of explicitly adding code to diagnose
> >>> both options at the same time as an error, if we think that's
> >>> friendlier than silent override.
> >>
> >> Is that actually an error?  -4 -6 says you want to listen on IPv4 and
> >> IPv6 which is redundant but not wrong.
> >
> > Oh wait, actually it doesn't work like I expected.
> >
> > Is it easy to make -4 -6 listen on both IPv4 & IPv6?
> 
> That's the default; in that case, just don't specify either.
> 
> -4 and -6 make AF_INET and AF_INET6 (respectively) the exclusive address
> family within which the argument of option "-i" is resolved. IOW, -4 and
> -6 are (intentionally) a very thin wrapper around hints.ai_family.
> 
> Here's some examples (with the "netstat -anp | grep nbdkit" output
> pasted after the command line):
> 
> # most generic use: no -i, no -4, no -6: binds the wildcard address for
> # both IPv4 and IPv6
> $ nbdkit -f null
> ->
> tcp        0      0 0.0.0.0:10809           0.0.0.0:*               LISTEN      219346/nbdkit
> tcp6       0      0 :::10809                :::*                    LISTEN      219346/nbdkit
> 
> # no "-i", so bind the wildcard address, but restricted to IPv4 with
> # "-4"
> $ nbdkit -4 -f null
> ->
> tcp        0      0 0.0.0.0:10809           0.0.0.0:*               LISTEN      219393/nbdkit
> 
> # no "-i", so bind the wildcard address, but restricted to IPv6 with
> # "-6"
> $ nbdkit -6 -f null
> ->
> tcp6       0      0 :::10809                :::*                    LISTEN      219397/nbdkit
> 
> # "-i localhost" causes getaddrinfo() to find both the IPv4 and IPv6
> # addresses (127.0.0.1 and ::1, respectively) in /etc/hosts
> $ nbdkit -f -i localhost null
> ->
> tcp        0      0 127.0.0.1:10809         0.0.0.0:*               LISTEN      219386/nbdkit
> tcp6       0      0 ::1:10809               :::*                    LISTEN      219386/nbdkit
> 
> # same as above, but "-4" restricts the resolution to IPv4
> $ nbdkit -i localhost -4 -f null
> ->
> tcp        0      0 127.0.0.1:10809         0.0.0.0:*               LISTEN      219402/nbdkit
> 
> # same as above, but "-6" restricts the resolution to IPv6
> $ nbdkit -i localhost -6 -f null
> ->
> tcp6       0      0 ::1:10809               :::*                    LISTEN      219405/nbdkit
> 
> # "-i" is passed a numeric address, so the address family is inherent
> $ nbdkit -i 127.0.0.1 -f null
> ->
> tcp        0      0 127.0.0.1:10809         0.0.0.0:*               LISTEN      219411/nbdkit
> 
> # same, but an IPv6 address is used
> $ nbdkit -i ::1 -f null
> ->
> tcp6       0      0 ::1:10809               :::*                    LISTEN      219414/nbdkit
> 
> # repeat the above two, with -4 / -6 restrictions, which are no-ops in
> # this case
> $ nbdkit -i 127.0.0.1 -4 -f null
> -> tcp        0      0 127.0.0.1:10809         0.0.0.0:*               LISTEN      219421/nbdkit
> 
> $ nbdkit -i ::1 -6 -f null
> ->
> tcp6       0      0 ::1:10809               :::*                    LISTEN      219424/nbdkit
> 
> # We can even attempt resolving the numeric addresses for the *wrong*
> # address family:
> 
> $ nbdkit -f -i 127.0.0.1 -6 null
> nbdkit: getaddrinfo: 127.0.0.1: 10809: Address family for hostname not supported
> 
> $ nbdkit -f -i ::1 -4 null
> nbdkit: getaddrinfo: ::1: 10809: Address family for hostname not supported
> 
> These too are correct, because the numeric address 127.0.0.1 is
> unresolvable in AF_INET6, and the numeric adress ::1 is unresolvable in
> AF_INET.

I think it's fine as it is, thanks!

Rich.

-- 
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