Re: [libvirt] [Qemu-devel] default slot used for vga device on q35 machines

Hi, > qemu-kvm -M q35 -nodefaults -nodefconfig -qmp unix:/tmp/qemu,server > -vnc :15 -vga std -usb > > Then ran "query-pci" in the qmp monitor and found that the vga device is > put at slot 1 instead of slot 2. > > My questions: > > 1) Is this difference intentional, or a bug? The vga simply goes into the first free slot. That happens to be #2 with i440fx and #1 with q35.

> 2) If it's intentional, will the device always be at slot 1 (and trigger > an error if something else is also placed at slot 1), or is it just > picking the first unused slot? (that would *not* be good, because we > must be able to predict what device is in which slot and prevent them > from changing from run to run). The vga is the very first (pci) device being created (when selecting via -vga), so it gets the slots mentioned above no matter what, even though simply picking the first unused slot. > 3) Does the qxl multihead support really require that the device be at > slot 2 (as stated in the above bugzilla commend)? Or is that just a > misunderstanding/overstatement? It's not required at all. The problem is that on older qemu versions (pre-memory-api basically) it was impossible to create functional vga devices via -device due to an initialization order issue. Which implies you have to use -vga instead, which in turn implies the vga ends up in slot #2. On i440fx, but q35 didn't exist yet back then ;)