11:19 a.m.
On Tue, Jan 18, 2022 at 02:48:33PM +0100, Laszlo Ersek wrote:
The AI_ADDRCONFIG hint of getaddrinfo() is supposed to restrict the
name
resolution to such address families (IPv4 vs. IPv6) for which the
resolving host has publicly routable addresses assigned.
The main problem with AI_ADDRCONFIG can be shown with the following
command line:
$ nbdkit -f -p 32776 -P pidfile -i ::1 -exit-with-parent null
s/-exit/--exit/
On a host where ::1 is the only IPv6 address assigned (namely to the
loopback interface), the command fails with
> nbdkit: getaddrinfo: ::1: 32776: Address family for hostname not
> supported
due to the "publicly routable" requirement.
Remove AI_ADDRCONFIG from the getaddrinfo() hints, and as a replacement,
introduce the "-4" and "-6" options, similarly to netcat and ssh.
Hmm, I said in my earlier reply that it may not be worth the extra
effort, but now that you've done it, it would be a shame to rip it
out.
(1) This makes options of the form:
-i 127.0.0.1
-i ::1
work regardless of "public" IPv6 / IPv4 connectivity;
(2) options of the form
-i localhost
-i FQDN
will bind both IPv4 and IPv6 addresses of the desired interface(s);
(3) omitting the option "-i" will bind both IPv4 and IPv6 wildcard
addresses (0.0.0.0 and ::);
(4) the configurations in (2) and (3) can be restricted to IPv4 or IPv6
addresses by adding the "-4" or "-6" option, respectively.
Importantly, this change allows the "connect-tcp6" test case of libnbd to
pass on such hosts that have no IPv6 connectivity (i.e., where the only
assigned IPv6 address is ::1, namely on the loopback interface).
Ref: https://listman.redhat.com/archives/libguestfs/2022-January/msg00110.html
Signed-off-by: Laszlo Ersek <lersek(a)redhat.com>
---
+++ b/server/main.c
@@ -86,6 +86,7 @@ static void error_if_stdio_closed (void);
static void switch_stdio (void);
static void winsock_init (void);
+int tcpip_sock_af = AF_UNSPEC; /* -4, -6 */
struct debug_flag *debug_flags; /* -D */
bool exit_with_parent; /* --exit-with-parent */
const char *export_name; /* -e */
@@ -367,6 +368,14 @@ main (int argc, char *argv[])
exit (EXIT_FAILURE);
#endif
+ 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.
+++ b/docs/nbdkit.pod
@@ -173,6 +173,24 @@ Display information about nbdkit or a specific plugin:
Display brief command line usage information and exit.
+=item B<-4>
+
+=item B<--ipv4-only>
+
+=item B<-6>
+
+=item B<--ipv6-only>
+
+When a non-numeric argument is passed to the I<-i> option (such as a
+Fully Qualified Domain Name, or a host name from C</etc/hosts>),
+restrict the name resolution to IPv4 or IPv6 addresses.
+
+When the I<-i> option is omitted, listen on only the IPv4 or IPv6
+address of all interfaces (C<0.0.0.0> or C<::>, respectively).
This effect (when -i is not used) is good justification for having
-4/-6 support.
+
+When both I<-4> and I<-6> options are present on the command line, the
+last one takes effect.
Ah, so you documented the override as intentional. It is possible to
use a git orderfile to create patches with documentation changes
appearing first in the output (see scripts/git.orderfile), which can
make it easier to review related changes in logical (rather than
alphabetical filename) order.
So with that, you have my ACK for the series, after addressing the
minor typo I spotted.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org