sockets: ensure we can bind to both ipv4 & ipv6 separately
When binding to an IPv6 socket we currently force the IPV6_V6ONLY flag to off. This means that the IPv6 socket will accept both IPv4 & IPv6 sockets when QEMU is launched with something like -vnc :::1 While this is good for that case, it is bad for other cases. For example if an empty hostname is given, getaddrinfo resolves it to 2 addresses 0.0.0.0 and ::, in that order. We will thus bind to 0.0.0.0 first, and then fail to bind to :: on the same port. The same problem can happen if any other hostname lookup causes the IPv4 address to be reported before the IPv6 address. When we get an IPv6 bind failure, we should re-try the same port, but with IPV6_V6ONLY turned on again, to avoid clash with any IPv4 listener. This ensures that -vnc :1 will bind successfully to both 0.0.0.0 and ::, and also avoid -vnc :1,to=2 from mistakenly using a 2nd port for the :: listener. This is a regression due to commit 396f935a "ui: add ability to specify multiple VNC listen addresses". Acked-by: NGerd Hoffmann <kraxel@gmail.com> Reviewed-by: NEric Blake <eblake@redhat.com> Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org> Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
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