On 08/03/2013 01:32 PM, Laine Stump wrote: >>> >>> 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. > > > It sounds like it's a safe bet to assume that -vga will put the device > on slot 2 for pc machinetypes and slot 1 for q35, no matter what other > devices there are, since -vga is always initialized first. Correct? Do > you see any chance that might change in the future? (e.g. due to some > other new device that needs to be initialized even before vga) Any future qemu will be new enough to not require the use of -vga, so we only have to worry about the behavior of 1.5 and earlier with regards to placement of -vga. > > >> >>> 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 ;) > > Are you saying that it's still required to use -vga instead of -device > qxl-vga for pc machinetype? Or that it was needed at one time, but that > is no longer the case? If the latter, is there a reliable way to make > the decision whether or not we need to use -vga? Regarding the decision on whether to use -device or -vga, our hands are tied. With qemu 1.5 or earlier, we HAVE to use -vga, where spice initialization had a bug such that use of -device would not display the mouse. That bug has been fixed for qemu 1.6, so for qemu 1.6, we prefer to use -device. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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