Re: [Qemu-devel] [PATCH v6 2/7] hw/misc: add vmcoreinfo device

[Marc-André Lureau]

Hi

On Tue, Oct 10, 2017 at 10:31 AM, Daniel P. Berrange
<address@hidden> wrote:
> On Tue, Oct 10, 2017 at 12:44:26AM +0300, Michael S. Tsirkin wrote:
>> On Mon, Oct 09, 2017 at 02:02:18PM +0100, Daniel P. Berrange wrote:
>> > On Mon, Oct 09, 2017 at 02:43:44PM +0200, Igor Mammedov wrote:
>> > > On Mon, 9 Oct 2017 12:03:36 +0100
>> > > "Daniel P. Berrange" <address@hidden> wrote:
>> > >
>> > > > On Mon, Sep 11, 2017 at 06:59:24PM +0200, Marc-André Lureau wrote:
>> > > > > See docs/specs/vmcoreinfo.txt for details.
>> > > > >
>> > > > > "etc/vmcoreinfo" fw_cfg entry is added when using "-device 
>> > > > > vmcoreinfo".
>> > > >
>> > > > I'm wondering if you considered just adding the entry to fw_cfg by
>> > > > default, without requiring any -device arg ? Unless I'm 
>> > > > misunderstanding,
>> > > > this doesn't feel like a device to me - its just a well known bucket
>> > > > in fw_cfg IIUC ?  Obviously its existance would need to be tied to
>> > > > the latest machine type for ABI reasons though. The benefit of this
>> > > > is that it would "just work" without us having to plumb it through to
>> > > > all the downstream applications that use QEMU for mgmt guest 
>> > > > (OpenStack,
>> > > > oVirt, GNOME Boxes, virt-manager, and countless other mgmt apps).
>> > > it follows model set by pvpanic device, it's easier to manage from 
>> > > migration
>> > > POV, one could use it even for old machine types with new qemu (just by 
>> > > adding
>> > > device, it makes instance not backwards migratable to old qemu but 
>> > > should work
>> > > for forward migration) and if user doesn't need it, device could be just 
>> > > omitted
>> > > from CLI.
>> >
>> > Sure but it means that in effect no one will have this functionality 
>> > enabled
>> > for several years. pvpanic has been around a long time and I rarely see it
>> > present in configured guests :-(
>> >
>> >
>> > Regards,
>> > Daniel
>>
>> libvirt runs with -nodefaults, right? I'd argue pretty strongly -nodefaults
>> shouldn't add optional devices anyway.
>
> This isn't really adding a device though is it - it is just a well known
> location in fw_cfg to receive data.

Enabling the device on some configurations by default can be done as a
follow-up patch. Can we get this series reviewed & merged?

thanks

-- 
Marc-André Lureau