From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53021) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V6f0S-0006q9-5G for qemu-devel@nongnu.org; Tue, 06 Aug 2013 07:00:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V6f0L-0005tq-Fw for qemu-devel@nongnu.org; Tue, 06 Aug 2013 07:00:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15222) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V6f0K-0005tR-Ss for qemu-devel@nongnu.org; Tue, 06 Aug 2013 07:00:41 -0400 Date: Tue, 6 Aug 2013 14:00:35 +0300 From: Gleb Natapov Message-ID: <20130806110035.GS8218@redhat.com> References: <1970367422.9695773.1375718517492.JavaMail.root@redhat.com> <20130805161833.GA4244@redhat.com> <51FFD6CE.5090302@redhat.com> <20130805182628.GC4244@redhat.com> <20130806072152.GK10891@redhat.com> <20130806083309.GA11051@redhat.com> <20130806083625.GF8218@redhat.com> <20130806092148.GC11051@redhat.com> <20130806093247.GL8218@redhat.com> <5200D15E.4030102@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <5200D15E.4030102@suse.de> Subject: Re: [Qemu-devel] [SeaBIOS] [PATCH] don't expose pvpanic device in the UI List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andreas =?utf-8?Q?F=C3=A4rber?= Cc: minyard@acm.org, Marcel Apfelbaum , seabios@seabios.org, qemu-devel@nongnu.org, "Michael S. Tsirkin" , Gerd Hoffmann , Paolo Bonzini On Tue, Aug 06, 2013 at 12:35:10PM +0200, Andreas F=C3=A4rber wrote: > Am 06.08.2013 11:32, schrieb Gleb Natapov: > > On Tue, Aug 06, 2013 at 12:21:48PM +0300, Michael S. Tsirkin wrote: > >> On Tue, Aug 06, 2013 at 11:36:25AM +0300, Gleb Natapov wrote: > >>> 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: > >>>>>> 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=3D0 > >>>> > >>>> Doesn't work for me. > >>> Bug that should be fixed. With this command line _STA should return > >>> zero. > >> > >> It doesn't have anything to do with _STA: device still appears in QOM. > > You said disabled, not removed. So does -global pvpanic,ioport=3D0 > > disables the device for you? > >=20 > >> It's a QEMU issue, devices that are added with -device are > >> documented in -device help and removed by dropping them from > >> command line. Devices added by default have no way to > >> be dropped from QOM except -nodefaults. > >> > > Are you saying that because pvpanic is added automatically QEMU -device > > help does not print help about it? Why not fix that? What QEMU --help > > issues has to do with deciding which devices should or should not be > > present by default? >=20 > You misunderstand: -device pvpanic,? will document that there is a > numeric port property, which as such is self-documenting. But there's no Yes, this is how I found it. > way for us to document there that port=3D0 has special meaning of "disable > this device in ACPI". >=20 Adding capability to describe a property should solve that and is a good idea regardless, no? "pvpanic.ioport=3Duint16" is not very descriptive. > Disabling a device usually requires to not include that device (or in > the future to "unrealize" it), which would require some way to suppress > having the device created internally by default. As done for floppy, > serial, etc. devices in x86 IIUC, which are in the same PIO situation as > the pvpanic device, except that they represent physical devices. > Adding some -no-pvpanic switch might be an alternative. And if not done > already, disabling the pvpanic device should definitely be documented > for the man page. We should not add -no-pvpanic! If there is a legitimate use for -no-pvpanic we should go with MST suggestion and do not create it by default. The question is why would anyone use -no-pvpanic? Legit reason, not just "to remove pvpanic". >=20 > To me this is less a concrete problem with Windows guests but a > conceptual question of how we go about enabling/disabling QEMU devices > in a hopefully consistent way. Agree. Now I see that some devises always present (even with -nodefualts) and some do not. The logic is not clear, but seams to be: if there is not legit reason to disable device or for stable topology device placemen need to be controlled, disable it with -nodefualts. In that case I do not see why pvpanic would not be always present. The reason this whole thread started with is non issue. >=20 > Writing a driver does not solve it fully, you'd still need to actively > install that driver, same issue as with virtio. virtio is opt-in, so for > customers not using our VM Driver Pack we offer AHCI as driver-less > alternative. There is no functionality loss without a driver. User is not required to install drivers. >=20 > I wonder if IPMI might be such an alternative in the future, in which > case we should come up with some way to fully disable pvpanic device > creation. CC'ing Corey. >=20 IPMI was considered, to complicated for what was needed. -- Gleb.