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Re: [Qemu-devel] [PATCH v2 1/5] sockets: ensure we can bind to both ipv4
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v2 1/5] sockets: ensure we can bind to both ipv4 & ipv6 separately |
Date: |
Mon, 22 May 2017 10:26:09 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 |
On 05/19/2017 01:03 PM, Daniel P. Berrange wrote:
> 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.
>
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
> util/qemu-sockets.c | 31 +++++++++++++++++++++++--------
> 1 file changed, 23 insertions(+), 8 deletions(-)
>
> for (p = port_min; p <= port_max; p++) {
> +#ifdef IPV6_V6ONLY
> + /* listen on both ipv4 and ipv6 */
> + int v6only = 0;
> +#endif
> inet_setport(e, p);
> +#ifdef IPV6_V6ONLY
> + rebind:
> + if (e->ai_family == PF_INET6) {
The rebind: label could go here with no change in semantics and one less
conditional when compiled without optimization. But hopefully the
compiler is smart enough to see that under -O2, so I don't see a reason
for you to change the code.
> + qemu_setsockopt(slisten, IPPROTO_IPV6, IPV6_V6ONLY, &v6only,
> + sizeof(v6only));
> + }
> +#endif
> if (bind(slisten, e->ai_addr, e->ai_addrlen) == 0) {
> goto listen;
> }
> +
> +#ifdef IPV6_V6ONLY
> + /* If we got EADDRINUSE from an IPv6 bind & V6ONLY is unset,
> + * it could be that the IPv4 port is already claimed, so retry
> + * with V6ONLY set
> + */
> + if (e->ai_family == PF_INET6 && errno == EADDRINUSE && !v6only) {
> + v6only = 1;
> + goto rebind;
> + }
> +#endif
> +
Reviewed-by: Eric Blake <address@hidden>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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