On Fri, Mar 02, 2012 at 02:25:36PM +0400, Michael Tokarev wrote: > 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. Yes, I think you are correct - QEMU should take care to ensure that DNS resolution can not block the QEMU event loop thread. There is the GLib extension (getaddrinfo_a) which does async DNS resolution, but for sake of portability it is probably better to use a thread to do it. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
