Re: [Qemu-devel] [PATCH 0/5] PCI hotplug fixes/cleanup

[Marcelo Tosatti]

On Wed, Apr 04, 2012 at 11:51:00PM -0600, Alex Williamson wrote:
> We've been batting this one back and forth.  This series includes
> several of the cleanups and specification clarifications from my
> series awhile back.  Patch 5 is my proposed alternative to
> Michael's PCI hotplug race fix.  Since that version I added slot
> present tracking so we can be a little more strategic about which
> slots we ask the guest to check.  The approach for that path is
> described in the commit log.  I tested hotplug on both Linux an
> Windows guests (XP + 2k8), intentionally trying to do back to back
> device_add and device_del to get a race, but couldn't (I did
> however get a glibc double free that seems unrelated to this
> series).
> 
> Long term I'd like to deprecate the up/down PCI hotplug interface
> and move to a new model.  I think perhaps we should define 3 new
> registers:
> 
> 1) Device present in slot bitmap (foundation already in 5/5 here)
> 2) Virtual slot power state bitmap
> 3) Requested slot date bitmap
> 
> With these we should be able to do proper _STA, _PS0, and _PS3.
> We'd maintain the eject register for _EJ0, but deprecate up/down.

What problem are you trying to address by doing so?

What is the need for power control? Clearly there is no advantage in    
powering down a virtual device.