Re: [Qemu-devel] Use getaddrinfo for migration

[Michael Tokarev]

Not a reply to the patch but a general observation.

I noticed that the tcp migration uses gethostname
(or getaddrinfo after this patch) from the main
thread - is it really the way to go?  Note that
DNS query which is done may block for a large amount
of time.  Is it really safe in this context?  Should
it resolve the name in a separate thread, allowing
guest to run while it is doing that?

This question is important for me because right now
I'm evaluating a network-connected block device driver
which should do failover, so it will have to resolve
alternative name(s) at runtime (especially since list
of available targets is dynamic).

>From one point, _usually_, the delay there is very
small since it is unlikely you'll do migration or
failover overseas, so most likely you'll have the
answer from DNS handy.  But from another point, if
the DNS is malfunctioning right at that time (eg,
one of the two DNS resolvers is being rebooted),
the delay even from local DNS may be noticeable.

Thanks,

/mjt