On Thu, Dec 12, 2019 at 11:13:02 +0000, Daniel Berrange wrote:
On Wed, Dec 11, 2019 at 09:45:07AM -0500, Cole Robinson wrote:
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* 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.
Alternatively we can make it more clear by properly using the <driver name=''> attribute. If qemu is driving the backend we put 'qemu' in it, but other values can apply. This will also make sense e.g. when the qemu storage daemon will become a thing to configure that interface without confusion.