Re: [libvirt] [PATCH v4 1/1] migration: add support for migrateURI configuration

On Thu, May 15, 2014 at 11:50:54AM +0200, Jiri Denemark wrote: > On Wed, May 14, 2014 at 15:18:09 +0800, Chen Fan wrote: > > For now, we set the migration URI via command line '--migrate_uri' or > > construct the URI by looking up the dest host's hostname which could be > > solved by DNS automatically. > > > > But in cases the dest host have two or more NICs to reach, we may need to > > send the migration data over a specific NIC which is different from the > > automatically resloved one for some reason like performance, security, etc. > > thus we must explicitly specify the migrateuri in command line everytime, > > but it is too troublesome if there are many such hosts(and don't forget > > virt-manager). > > > > This patches add a configuration file option on dest host to save the > > default migrate uri which explicitly specify which of this host's > > addresses is used for transferring data, thus user doesn't boring > > to specify it in command line everytime. > > > > Signed-off-by: Chen Fan <chen.fan.fnst(a)cn.fujitsu.com&gt; > > --- > > > > v3-v4: move up the default uri_in setting to > > qemuDomainMigratePrepare3Params() > > > > src/qemu/qemu.conf | 6 +++++- > > src/qemu/qemu_conf.c | 1 + > > src/qemu/qemu_conf.h | 1 + > > src/qemu/qemu_driver.c | 2 +- > > 4 files changed, 8 insertions(+), 2 deletions(-) > > > > diff --git a/src/qemu/qemu.conf b/src/qemu/qemu.conf > > index f0e802f..6b443d0 100644 > > --- a/src/qemu/qemu.conf > > +++ b/src/qemu/qemu.conf > > @@ -449,7 +449,11 @@ > > # > > #seccomp_sandbox = 1 > > > > - > > +# Override the migration URI for specifying one of host's IP addresses > > +# to transfer the migration data stream. > > +# Defaults to hostname, both IPv4 and IPv6 addresses are accepted. > > +# > > +#migrate_uri = "tcp://192.168.0.1" > > > > # Override the listen address for all incoming migrations. Defaults to > > # 0.0.0.0, or :: if both host and qemu are capable of IPv6. > > The more I think about this the more I incline to a slightly different > approach. Rather than providing a way to override migration URI, we > could just provide an option in libvirtd.conf to override what > virGetHostname returns. That is, the option (naturally called hostname) > would tell libvirt to use the configured hostname (which might even be > just an IP address) instead of trying to detect it. I'm not sure this is a good idea. The hostname is used in a number of places in libvirt, and we don't neccessarily want them all to use the same interface as the migration data. eg if you have a NIC that is dedicated just for migration traffic, you won't want to force other parts of libvirt to use that. So having the migration hostname specified separately is a good idea IMHO. Perhaps we could simplify though by having 'migrate_host' rather than 'migrate_uri' ?

And perhaps we do want a hostname override globally anyway, for other reasons. Regards, Daniel