Re: [Qemu-devel] [PATCH 6/6] qdev: Generate IDs for anonymous devices

[Gleb Natapov <gleb@redhat.com>]

On Wed, Sep 07, 2011 at 12:27:23PM +0200, Jan Kiszka wrote:
> On 2011-09-07 11:50, Gleb Natapov wrote:
> > On Wed, Aug 31, 2011 at 08:31:26PM +0200, Jan Kiszka wrote:
> >> On 2011-08-29 23:19, Anthony Liguori wrote:
> >>> On 08/29/2011 03:56 PM, Jan Kiszka wrote:
> >>>> On 2011-08-29 21:23, Anthony Liguori wrote:
> >>>>> On 08/26/2011 09:48 AM, Jan Kiszka wrote:
> >>>>>> In order to address devices for that the user forgot or is even unable
> >>>>>> (no_user) to provide an ID, assign an automatically generated one. Such
> >>>>>> IDs have the format #<number>, thus are outside the name space availing
> >>>>>> to users. Don't use them for bus naming to avoid any other user-visible
> >>>>>> change.
> >>>>>
> >>>>> I don't think this is a very nice approach.  Why not eliminate anonymous
> >>>>> devices entirely and use a parent derived name for devices that are not
> >>>>> created by the user?
> >>>>
> >>>> This eliminates anonymous devices completely. So I guess you are asking
> >>>> for a different naming scheme, something like<parent-id>.child#<no>
> >>>> e.g.? Well, we would end up with fairly long names when a complete
> >>>> hierarchy is anonymous. What would be the benefit?
> >>>
> >>> No, I'm saying that whenever a device is created, it should be given a
> >>> non-random name.  IOW, the names of these devices should be stable.
> >>>
> >>>> I'm really just looking for some simple, temporary workaround without
> >>>> touching the existing fragile naming scheme. What we really need is full
> >>>> path addressing, but that without preserving all the legacy.
> >>>
> >>> Yeah, I understand, and I hesitated making any grander suggestions here,
> >>> but I'm not sure how much work it would be to just remove any caller
> >>> that passes NULL for ID and replace it with something more meaningful. I
> >>> think that's a helpful clean up long term no matter what.
> >>
> >> That won't solve the problem of finding a unique device name. If we want
> >> to derive it from stable device properties (bus addresses etc.), we
> >> first of all have to define them for all types of devices. And that's
> >> basically were the discussion exploded last year IIRC.
> >>
> > Why not use the OpenFirmware naming that we already have for some
> > devices instead of inventing something new?
> 
> Because I do not want to establish any path names before QOM conversion
> (including potential device reorganization) has been started.
In theory device paths are dictated by HW topology, not today's flavor of
QEMU object model.

> Specifically as I do not need naming for "some" devices, but for all.
> 
It can be extended. We already have three types of device naming. One is
used in qdev, another is used for migration and yet another one for
passing device names to firmware. We should converge to a single one :)

--
			Gleb.