Re: [libvirt] [PATCH] qemu: enable direct migration over IPv6

On 02/19/13 17:36, John Ferlan wrote: > On 02/15/2013 05:13 AM, Peter Krempa wrote: >> On 02/15/13 11:00, Ján Tomko wrote: >>> } >>> } >>> >>> + if (getaddrinfo(hostname, NULL, NULL, &info)) { >>> + virReportError(VIR_ERR_INTERNAL_ERROR, >>> + _("unable to get address info for %s"), >>> hostname); >>> + goto cleanup; >> >> Isn't there a possibility to fall back on IPv4 if this fails to minimize >> the chance of regressing? >> > > Yeah - this is tricky for some of the reasons I listed above. It seems > we need a way to tell or force the target qemu to use one family style > over the other because that's what the source resolved to using. Qemu does support ipv4 or ipv6 flags for hostnames. From a quick glance at the git history it seems it always has. Maybe we could always add the address family option to the migration URI to force this?

> > Assuming I'm reading things correctly we are about to tell the target > qemu how to start and to listen over the "first" style of address we > found in the source hosts' list. The source connect will use that > uri_out to perform the migration. The issue I can see becomes what if > the target (for some reason) doesn't support/have/use the family that > the host found first? When it goes to start up a localhost port, it > will fail right? Then what? > No, the perform phase happens on the destination, but the result is

still the same. If the families do not match (or they do match but they can't connect to each other via that family), migration will fail. Then the user either has to change the network configuration or specify the IP address directly.

>>> + } else { >>> + snprintf(migrateFrom, sizeof(migrateFrom), >>> + "tcp:0.0.0.0:%d", this_port); >> >> I thing this would be doable. Just do IPv4 by default if the resolution >> fails. >> > > Hmm... which resolution fails do you mean? Perhaps the "feature" needs > to be set/check some field that says the target qemu wants/desires IPv6; > otherwise, always fall back to use IPv4. > If the hostname specified by the user can only be resolved on the source, migration still works, but erroring out on getaddrinfo failure would break it. We can definitely tell qemu to listen on v4/v6 if we received an IP address. As for hostnames, we can either guess it from how it resolves on the source, destination or get the input from the user. Maybe we could add a migration flag for this and add ipv4 or ipv6 option to the migration URI for qemu based on the presence/absence of this flag. Or only do IPv6 migration if a URI with a v6 address or tcp6: scheme was present?