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Re: [libvirt] [PATCH] expose SR IOV physical/virtual function relationships



On Tue, Dec 01, 2009 at 12:03:49PM -0500, Dave Allan wrote:
> Daniel P. Berrange wrote:
> >On Tue, Dec 01, 2009 at 10:33:08AM -0500, Dave Allan wrote:
> >>Attached is a patch that exposes the relationships between physical and 
> >>virtual functions on SR IOV capable devices.
> >>
> >
> >
> >>+            if (data->pci_dev.physical_function) {
> >>+                virBufferEscapeString(&buf, "    
> >><physical_function>%s</physical_function>\n",
> >>+                                      data->pci_dev.physical_function);
> >>+            }
> >>+            if (data->pci_dev.num_virtual_functions > 0) {
> >>+                for (i = 0 ; i < data->pci_dev.num_virtual_functions ; 
> >>i++) {
> >>+                    virBufferEscapeString(&buf, "    
> >><virtual_function>%s</virtual_function>\n",
> >>+                                          
> >>data->pci_dev.virtual_functions[i]);
> >>+                }
> >>+            }
> >
> >
> >What is the actual content of those two new elements ?  Are they
> >the names of the corresponding device, suitble for a 
> >virNodeDevLooupByName() ?
> 
> They are the PCI device BDF or config address, e.g.:
> 
>     <virtual_function>0000:01:10.0</virtual_function>
> 
> so, no, they aren't suitable for lookup by name.  Using the names of the 
> corresponding devices was my first attempt, but there is a dependency 
> problem there.  At the time that we process one device, the others 
> aren't necessarily created in libvirt, so it's not possible to look them 
> up.  If we wanted to go that route, we'd have to do additional work at 
> the time of dumping the xml, which I think is a little kludgy.  I'd 
> rather we created an API to lookup a libvirt device by its BDF.

I don't much like including the raw BDF format, because it is effectively
adding a 3rd way of specifying PCI addresses in libvirt XML. We already
have 2 different ways, which is 1 too many

Node dev XML

  <capability type='pci'>
    <domain>0</domain>
    <bus>0</bus>
    <slot>31</slot>
    <function>1</function>
  </capability>


Domain XML for host devices & guest addresses

  <address domain='0x0000' bus='0x00' slot='0x1f' function='0x5'/>

Yes, my bad for screwing up the nodedev  XML format when I designed
it, stupidly choosing decimal instead of hex :-(

I think we should make the virtual/physical function follow the domain
XML style, with an <address/> element. Perhaps also use nested capabilities
in the way we did for NPIV host/vport stuff

  <capability type='physical_function'>
    <address domain='0x0000' bus='0x00' slot='0x1f' function='0x1'/>
  </capability>

  <capability type='virtual_functions'>
    <address domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
    <address domain='0x0000' bus='0x00' slot='0x1f' function='0x3'/>
    <address domain='0x0000' bus='0x00' slot='0x1f' function='0x4'/>
  </capability>


I'd even be inclined to retro-fit the existing <capability type='pci'>
XML to duplicate the address info in this saner format eg

  <capability type='pci'>
    <address domain='0x0000' bus='0x00' slot='0x1f' function='0x1' />
    <domain>0</domain>
    <bus>0</bus>
    <slot>31</slot>
    <function>1</function>
  </capability>


So, a PCI card with SR-IOV would end up looking like

  <capability type='pci'>
    <domain>0</domain>
    <bus>0</bus>
    <slot>31</slot>
    <function>1</function>
    <address domain='0x0000' bus='0x00' slot='0x1f' function='0x1' />

    <capability type='virtual_functions'>
      <address domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
      <address domain='0x0000' bus='0x00' slot='0x1f' function='0x3'/>
      <address domain='0x0000' bus='0x00' slot='0x1f' function='0x4'/>
    </capability>
  </capability>

The nice thing about this kind of nesting is that it would let us show
that a card is capable of exposing virtual functions, even if it does
not currently have any enabled


Regards,
Daniel
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