On 05/04/10 18:23, Anthony Liguori wrote:
On 05/04/2010 08:49 AM, Reinhard Max wrote:
Hi,
I am maintaining the tightvnc package for openSUSE and was recently
confronted with an alleged vnc problem with QWMU that turned out to be
a shortcoming in QEMU's code for handling TCP server sockets, which is
used by the vnc and char modules.
The problem occurs when the address to listen on is given as a name
which resolves to multiple IP addresses the most prominent example
being "localhost" resolving to 127.0.0.1 and ::1 .
My tigervnc (tightvnc successor) has IPv6 support and handles this
just fine. There is also the option to force qemu to listen on ipv4
(or ipv6) only.
The existing code stopped walking the list of addresses returned by
getaddrinfo() as soon as one socket was successfully opened and bound.
The result was that a qemu instance started with "-vnc localhost:42"
only listened on ::1, wasn't reachable through 127.0.0.1. The fact
that the code set the IPV6_V6ONLY socket option didn't help, because
that option only works when the socket gets bound to the IPv6 wildcard
address (::), but is useless for explicit address bindings.
Indeed.
But that said, I'm not sure we're doing the wrong thing right now. Gerd,
what do you think about this behavior?
Reinhard is correct. If a hostname resolves to multiple addresses
like this ...
zweiblum kraxel ~# host zweiblum
zweiblum.home.kraxel.org has address 192.168.2.101
zweiblum.home.kraxel.org has IPv6 address
2001:6f8:1cb3:2:216:41ff:fee1:3d40
... qemu should listen on all addresses returned. Which in turn
requires multiple listening sockets.
Changing this is a big deal though, thats why I've taken the somewhat
unclean shortcut to listen on the first match only when implementing
this. Clients are supposed to try to connect to all addresses
returned by the lookup (and they do if they got IPv6 support), thus
this usually doesn't cause trouble in practice.
When going for multiple listening sockets in qemu we have to figure
how we'll handle this in a number of places as there is no single
listening address any more. Reporting the vnc server address in QMP
is one. I'm sure there are more.