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


From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH 0/5] PCI hotplug fixes/cleanup
Date: Sun, 8 Apr 2012 10:15:26 +0300
User-agent: Mutt/1.5.21 (2010-09-15)

On Sun, Apr 08, 2012 at 02:13:00AM -0300, Marcelo Tosatti wrote:
> 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.

There probably are for an assigned device?

-- 
MST



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