RE: Libvirt NVME support

On Mon, Nov 23, 2020 at 09:47:23 +0000, Thanos Makatos wrote: > > On Thu, Nov 19, 2020 at 10:17:56 +0000, Thanos Makatos wrote: > > > > As a starting point a trivial way to model this in the XML will be: > > > > > > > > <controller type='nvme' index='1' model='nvme'> > > > > > > > > And then add the storage into it as: > > > > > > > > <disk type='file' device='disk'> > > > > <source dev='/Host/QEMUGuest1.qcow2'/> > > > > <target dev='sda' bus='nvme'/> > > > > > > 'target dev' is how the device appears in the guest, right? It should be > > > something like 'nvme0n1'. I'm not sure though this is something that we > > can > > > put here anyway, I think the guest driver can number controllers arbitrarily. > > > > Well, it was supposed to be like that but really is not. Even with other > > buses the kernel can name the device arbitrarily, so it doesn't really > > matter. > > > > > Maybe we should specify something like BDF? Or is this something QEMU > > will > > > have to figure out how to do? > > > > > > > <address type='drive' controller='1' bus='0' target='0' unit='0'/> > > > > </disk> > > > > > > > > <disk type='file' device='disk'> > > > > <source dev='/Host/QEMUGuest2.qcow2'/> > > > > <target dev='sdb' bus='nvme'/> > > > > <address type='drive' controller='1' bus='0' target='0' unit='1'/> > > > > </disk> > > Revistiting your initial suggestion, it should be something like this > (s/sdb/nvme0): > > <disk type='file' device='disk'> > <source dev='/Host/QEMUGuest2.qcow2'/> > <target dev='nvme0' bus='nvme'/> > <address type='drive' controller='1' bus='0' target='0' unit='1'/> > </disk> Note that the parser for 'dev' is a bit quirky, old, and used in many places besides the qemu driver. It's also used with numbers in non-qemu cases. Extending that to parse numbers for nvme but not for sda might become ugly very quickly. Sticking with a letter at the end ('nvmea' might be a more straightforward approach.

> > > > > > > > > The 'drive' address here maps the disk to the controller. This example > > IIUC we need a way to associate storage (this XML snippet) with the controller > you defined earlier (<controller type='nvme' index='1' model='nvme'>). So > shouldn't we only require associating this piece of storage with the controller > based on the index? No. The common approach is to do it via what's specified as <address> > > > > > uses unit= as the way to specify the namespace ID. Both 'bus' and 'target' > > > > must be 0. > > I think 'namespace' or 'ns' would be more suitable instead of 'unit'. > What are 'bus' and 'target' here? And why do they have to be 0? > Do we really need dev='nvme0' in <target ...>? Specifying the controller index > should be enough, no? You certainly can add <address type='nvme' controller='1' ns='2'/> > Wouldn't this contain the minimum amount of information to unambiguously map > this piece of storage to the controller? > > <disk type='file' device='disk'> > <source dev='/Host/QEMUGuest2.qcow2'/> > <target dev='sdb' bus='nvme'/> > <address controller='1' ns='1'/> > </disk> That certainly is correct if you include the "type='nvme'" attribute.