Am 06.08.2013 11:20, schrieb Gleb Natapov: > On Tue, Aug 06, 2013 at 10:45:01AM +0200, Andreas Färber wrote: >> Am 06.08.2013 10:36, schrieb Gleb Natapov: >>> On Tue, Aug 06, 2013 at 11:33:10AM +0300, Michael S. Tsirkin wrote: >>>> On Tue, Aug 06, 2013 at 10:21:52AM +0300, Gleb Natapov wrote: >>>>>> If you see a mouse in a room, how likely is it that there's >>>>>> a single mouse there? >>>>>> >>>>>> This is a PV technology which to me looks like it was >>>>>> rushed through and not only set on by default, but >>>>>> without a way to disable it - apparently on the assumption >>>>>> there's 0 chance it can cause any damage. Now that >>>>>> we do know the chance it's not there, why not go back >>>>>> to the standard interface, and why not give >>>>>> users a chance to enable/disable it? >>>>> You should be able to disable it with: -device pvpanic,ioport=0 >>>> >>>> Doesn't work for me. >>> Bug that should be fixed. With this command line _STA should return >>> zero. >>> >>>> Besides, both -device pvpanic and use of ioport=0 to disable it >>>> are completely undocumented. >>>> >>> Not the only undocumented thing in QEMU command line :) >> [snip] >> >> I disagree: -device adds a device, not removes one. It will still be >> present. >> > I assume you are answering to the quote about ioport=0, not > documentation here.
Answering to all of i) additional -device pvpanic,ioport=0 to disable another one, ii) ioport=0 to disable a certain device and iii) either being an undocumented feature to disable devices. ;) "Disabled" here referring both to not in PIO/ACPI/etc. and to not present in the QOM composition tree. In the end with pvpanic being an ISADevice, this goes back to my large series for Hervé's i87312 Super I/O chipset, where we discussed what would be involved in having a reconfigurable ISADevice not listen on some port/IRQ. We haven't decided on a solution yet (reconfiguring the i87312 from guest will assert or be ignored), and I strongly disagree to the solution of ioport=0 magic as general solution - either we should use realized=false (which then drops any VMStateDescription from migration) or revive my earlier attempts to add an explicit boolean ISADevice::enabled state, which would correspond to EEPROM-based reconfiguration of the plugged-in ISA card. Which of course would only help ISADevices but not MMIO-based SysBusDevices... Andreas -- SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
