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Re: [Qemu-devel] [PATCH v2 1/5] sockets: ensure we can bind to both ipv4
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [PATCH v2 1/5] sockets: ensure we can bind to both ipv4 & ipv6 separately |
Date: |
Mon, 22 May 2017 16:33:00 +0100 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Mon, May 22, 2017 at 10:26:09AM -0500, Eric Blake wrote:
> 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.
Also bear in mind the running time of this method is going to be
dominated by the getaddrinfo() call most of the time, so I don't
think there's any measurable perf difference to moving the label.
> > + 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
>
Regards,
Daniel
--
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- [Qemu-devel] [PATCH v2 0/5] Fix handling of IPv4/IPv6 dual stack, Daniel P. Berrange, 2017/05/19
- [Qemu-devel] [PATCH v2 1/5] sockets: ensure we can bind to both ipv4 & ipv6 separately, Daniel P. Berrange, 2017/05/19
- [Qemu-devel] [PATCH v2 2/5] sockets: don't block IPv4 clients when listening on "::", Daniel P. Berrange, 2017/05/19
- [Qemu-devel] [PATCH v2 3/5] sockets: ensure we don't accept IPv4 clients when IPv4 is disabled, Daniel P. Berrange, 2017/05/19
- [Qemu-devel] [PATCH v2 4/5] io: preserve ipv4/ipv6 flags when resolving InetSocketAddress, Daniel P. Berrange, 2017/05/19
- [Qemu-devel] [PATCH v2 5/5] tests: add functional test validating ipv4/ipv6 address flag handling, Daniel P. Berrange, 2017/05/19