On Tue, Aug 03, 2010 at 10:22:22PM +0300, Avi Kivity wrote: > On 08/03/2010 10:13 PM, Richard W.M. Jones wrote: > >On Tue, Aug 03, 2010 at 09:43:39PM +0300, Avi Kivity wrote: > >>libguestfs does not depend on an x86 architectural feature. > >>qemu-system-x86_64 emulates a PC, and PCs don't have -kernel. We > >>should discourage people from depending on this interface for > >>production use. > >I really don't get this whole thing where we must slavishly > >emulate an exact PC ... > > This has two motivations: > > - documented interfaces: we suck at documentation. We seldom > document. Even when we do document something, the documentation is > often inaccurate, misleading, and incomplete. While an "exact PC" > unfortunately doesn't exist, it's a lot closer to reality than, say, > an "exact Linux syscall interface". If we adopt an existing > interface, we already have the documentation, and if there's a > conflict between the documentation and our implementation, it's > clear who wins (well, not always). > > - preexisting guests: if we design a new interface, we get to update > all guests; and there are many of them. Whereas an "exact PC" will > be seen by the guest vendors as well who will then add whatever > support is necessary. On the other hand we end up with stuff like only being able to add 29 virtio-blk devices to a single guest. As best as I can tell, this comes from PCI, and this limit required a bunch of hacks when implementing virt-df. These are reasonable motivations, but I think they are partially about us: We could document things better and make things future-proof. I'm surprised by how lacking the doc requirements are for qemu (compared to, hmm, libguestfs for example). We could demand that OSes write device drivers for more qemu devices -- already OS vendors write thousands of device drivers for all sorts of obscure devices, so this isn't really much of a demand for them. In fact, they're already doing it. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://et.redhat.com/~rjones/virt-df/ -- 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
