Re: [Qemu-discuss] TCP options ipv4 and ipv6 have no effect

[Sair, Umair]

If I am understanding correct, you are saying that we should set addr->has_ipv6 
and addr->has_ipv4 to true in any case, then in my opinion we should simply 
ignore the value of addr->has_ipv* while evaluating the value of ipv4 and ipv6 
variables in inet_addr_to_opts (bool ipv4 = addr->ipv4; bool ipv6 = 
addr->ipv6). And the "if (!ipv4 || !ipv6)" condition seems really strange to me.

Regards,
Umair Sair

-----Original Message-----
From: Peter Maydell [mailto:address@hidden 
Sent: Friday, October 02, 2015 10:57 PM
To: Sair, Umair
Cc: address@hidden; Paolo Bonzini; QEMU Developers
Subject: Re: [Qemu-discuss] TCP options ipv4 and ipv6 have no effect

(looping in qemu-devel and Paolo)

On 2 October 2015 at 17:54, Sair, Umair <address@hidden> wrote:
> I am working with qemu-2.4.0. I built it using mingw on Windows. I am 
> having a problem while connecting it to gdb. I figured out that qemu 
> gdb server is running on IPv6 whereas gdb tries to connect on IPv4. 
> This problem is already reported here: 
> https://bugs.launchpad.net/qemu/+bug/562107.
>
> gdd server runs on IPv6 even if I provide ipv4 tcp option (-S -gdb 
> tcp::10000,ipv4). In other words, providing ipv4 or ipv6 option have 
> no effect on both windows and linux. On linux it always runs on IPv4 
> and on Windows, it always runs on IPv6. Can you please help me out in 
> resolving this problem?
>
> I debugged qemu a bit and it seems to me that the problem is in 
> ‘inet_addr_to_opts()’ function of ‘qemu-sockets.c’. Following is the 
> excerpt from this function:
>
> static void inet_addr_to_opts(QemuOpts *opts, const InetSocketAddress 
> *addr) {
>
>     bool ipv4 = addr->ipv4 || !addr->has_ipv4;
>     bool ipv6 = addr->ipv6 || !addr->has_ipv6;
>
>     if (!ipv4 || !ipv6) {
>         qemu_opt_set_bool(opts, "ipv4", ipv4);
>         qemu_opt_set_bool(opts, "ipv6", ipv6);
>     }
>
> The ipv4 and ipv6 variables of this function are always true (because 
> we set
> addr->ipv4 = addr->has_ipv4 and addr->ipv6 = addr->has_ipv6), hence 
> addr->ipv4 and
> ipv6 option is never set in the if condition. The consequence is that 
> the socket is created with PF_UNSPEC and then for windows IPv6 and for 
> linux
> IPv4 socket is created (see inet_listen_opts() in qemu-sockets.c). Is 
> there a particular reason for the logic of inet_addr_to_opts()?

I'm not sure, but something definitely seems weird here; either inet_parse or 
inet_addr_to_opts is wrong, I think.

Paolo, you wrote this code I think; any idea?

My guess is that inet_parse should be setting addr->has_ipv6 to true (leaving 
addr->ipv6 false) if it decides it should be using IPv4 (and vice-versa for 
IPv6).

inet_addr_to_opts I think is correct where it does:
    bool ipv4 = addr->ipv4 || !addr->has_ipv4; because this is saying "try ipv4 
if specifically asked, or if the caller didn't specify either way".

I don't know why we have the "if (!ipv4 || !ipv6)" condition on the setting of 
the opts, though.

thanks
-- PMM