Re: [libvirt] how to know if PCI device has SR-IOV PF capability

On 11/23/2015 05:05 AM, Daniel P. Berrange wrote: >On Sun, Nov 22, 2015 at 11:04:28AM +0000, Moshe Levi wrote: >>Hi, >> >>I was looking on the output of virsh nodedev-dumpxml on a PCI to see if it has SR-IOV PF capability. >>It seem that if the virtual functions are enables the xml look like [1] but if the PCI has no VFs enabled the >>output is like in [2]. >>As you can see for PCI which has no VFs the <capability type='virt_functions'> tag doen't exist. >>Is this by design? >>I would except that <capability type='virt_functions'/> tag with empty elements will also be include in that case. >That is an bug. The capability should be reported regardless of whether >any are VFs currently enabled, so we should fix this. Prior to libvirt 1.0.4, "<capability type='virt_functions'>" was there for every PCI device regardless of whether or not it had the ability to have virtual functions. It looks like commit 9a3ff01d changed it to only emit that element when there was at least one VF. So it used to be wrong, and now it is wrong in a different way :-)

If we're going to switch to emiting virt_functions whenever a device has the potential to provide VFs, we may as well make it worthwhile and also emit the maximum possible VFs for the device, maybe simply: <capability type='virt_functions' maxCount='7'> (the current count is implicit in the number of entries in the list that follows. I don't have an opinion on whether it is better to also include explicitly with, e.g. "count='7'", or just leave it implicit).