Re: [libvirt] libvirt API/design questions

On Wed, Dec 11, 2019 at 09:45:07AM -0500, Cole Robinson wrote:

> * vhost-user-scsi and vhost-user-blk XML schema > https://www.redhat.com/archives/libvirt-users/2019-October/msg00018.html > > Last proposal was using <hostdev> for this, which revisiting it now > makes more sense than <disk>, because it vhost-user-X doesn't seem to > use qemu's block layer at all. So vhost-user-scsi would be: > > <hostdev mode='subsystem' type='scsi_host'> > <source protocol='vhostuser' type='unix' > path='/path/to/vhost-user-scsi.sock' mode='client'/> > </hostdev> > > vhost-user-blk maybe requires a new type='block' ? Otherwise it's > unclear how to differentiate between the two. Regardless it would be > nice to give the original patch author guidance here, they seemed > motivated to get this working This is a really tricky question in general. It is basically saying whether we consider <disk> to refer to the guest visible device type or the QEMU visible backend type. Originally these were always the same thing, but offloading to vhostuser has blurred the boundaries. I think in non-QEMU hypervisors where you don't have a split of frontend&backend in the config, you'd just have disks no matter what. With network we've continued to use <interface> with vhost-user. This makes me biased towards <disk>, at least for vhost-user-blk.