Re: [libvirt] [PATCH 02/12] Introduce new domain create API virDomainCreateWithParams

On Wed, May 09, 2018 at 05:40 PM +0200, "Daniel P. Berrangé" <berrange(a)redhat.com&gt; wrote: > On Wed, May 09, 2018 at 04:56:12PM +0200, Marc Hartmayer wrote: >> Introduce new libvirt API virDomainCreateWithParams that allows to >> temporarily boot from another boot device, to use another kernel, >> initrd, and cmdline than defined in the persistent domain >> definition. All typed parameters are optional. >> >> The design of the API was chosen to ease future extensions. > > I don't really see the point in doing this. We already have the ability > to temporary boot with a different configuration than is stored in > the persistent XML. Just call virDomainCreateXML() passing in the > alternative XML doc. This allows changing *any* aspect of the guest > configuration, so we're not restricted to just bot device, kernel > initrd and cmdline, and thus won't need to write more code anytime > someone asks to be able to override something else too. I know there is the API virDomainCreateXML for creating a transient domain and that it’s possible to temporarily replace parts of the persistent XML with it. But my idea is _not_ to add a functionality to override parts of the persistent XML. My idea is to provide support allowing an easy one-time switch of the boot device in a persistently defined domain. For s390 it’s essential to have an easy way to change the boot configuration since it “knows” only one boot device at a time and it has no support for interactively changing the boot device during the boot/IPL process.

I started out with a fixed API (as it was done for example with virDomanCreateWithFiles) but than I liked the approach of providing an more extensible and flexible API better. This is also the reason why I used typed parameters for passing the arguments. This type of API is also not restricted to boot order changes since it could be freely expanded (e.g. passing file descriptors). I can certainly revert back to the static API.