Re: [Qemu-devel] [PATCH v3 0/3] nonblocking connect address handling cleanup

[Michael S. Tsirkin]

On Thu, Sep 20, 2012 at 05:55:14PM +0300, Orit Wasserman wrote:
> On 09/20/2012 04:19 PM, Markus Armbruster wrote:
> > Orit Wasserman <address@hidden> writes:
> > 
> >> Changes from v2:
> >>    - remove the use of getnameinfo
> >>    - remove errp for inet_connect_addr
> >>    - remove QemuOpt "block"
> >>    - fix errors in wait_for_connect 
> >>    - pass ConnectState as a parameter to allow concurrent connect ops
> >>
> >> getaddrinfo can give us a list of addresses, but we only try to
> >> connect to the first one. If that fails we never proceed to
> >> the next one.  This is common on desktop setups that often have ipv6
> >> configured but not actually working.
> >> A simple way to reproduce the problem is migration:
> >> for the destination use -incoming tcp:0:4444, run migrate -d 
> >> tcp:localhost:4444
> >> migration will fail on hosts that have both IPv4 and IPV6 address for 
> >> localhost.
> >>
> >> To fix this, refactor address resolution code and make 
> >> inet_nonblocking_connect
> >> retry connection with a different address.
> > 
> > Almost there for connect.
> > 
> > I'm afraid we have a similar problem with listen: we bind only on the
> > first address that works.  Shouldn't we bind all of them?
> > 
> > http://www.akkadia.org/drepper/userapi-ipv6.html
> > 
> yes listen should be fixed but lets do it in a separate patch set.
> 
> Orit

One useful hack is to set  AI_ADDRCONFIG hint, this way
you don't get ipv6 addresses if your system does not
have any configured, this results in faster connections
on some boxes.

http://linux.die.net/man/3/getaddrinfo

This probably should be a separate patch too,
if for no other reason than that it makes failures
in connect much harder to trigger and test.

-- 
MST