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Re: [Qemu-devel] [PATCH 00/14] qdev: assign unique names to all devices

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH 00/14] qdev: assign unique names to all devices (part 1)
Date: Fri, 16 Sep 2011 19:11:36 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2

Am 16.09.2011 18:54, schrieb Anthony Liguori:
> On 09/16/2011 11:48 AM, Jan Kiszka wrote:
>> On 2011-09-16 18:00, Anthony Liguori wrote:
>>> This series introduces an infrastructure to remove anonymous devices from 
>>> qdev.
>>> Anonymous devices are one of the big gaps between qdev and QOM so removing 
>>> is
>>> a prerequisite to incrementally merging QOM.
>>> Besides the infrastructure, I also converted almost all of the possible PC
>>> devices to have unique names.  Please not that naming is not a property of
>>> devices but rather of the thing that creates the devices (usually machines).
>>> The names are ugly but this is because of the alternating device/bus 
>>> hierarchy
>>> in qdev.  For now, the names use '::' as deliminators but I think Jan has
>>> convinced me that down the road, we should use '/' as a deliminator such 
>>> that
>>> the resulting names are actually valid paths (using a canonical path 
>>> format).
>> I still don't see why we need to store strings as device references.
>> Everyone that lacks a reference (QEMU-external users) can pass in a path
>> - which can be a device name in the simple case. That path is resolved
>> to an object reference before proceeding with the requested service. If
>> an object should be serialized in whatever way and we need a stable
>> name, a central service could return this by walking up the composition
>> tree until a user-assigned name is found.
>> So there is really no need to bother device model developers with the
>> topics "How do I define a unique name?"
> This series just asks the device model developer to come up with a unique 
> *when* 
> they're doing device composition.  Even with a totally path based interface, 
> this is always going to be a firm requirement.
> I think it may be possible to eliminate required device names by having a 
> formal 
> notion of composition and have the devices store the names of the composed 
> devices as part of the reference to that device.  You could then have user 
> created devices use a separate hash table to track the names of those devices.
> But, we can't easily do this today.  Having either a fully qualified name or 
> a 
> composition name as part of qdev_create() is the Right Thing IMHO so I think 
> this is the stepping stone to something more sophisticated.

Actually, as I said, I think this naming scheme is already by far too
sophisticated. Jan is completely right, there is no point in duplicating
paths in a name. Either we assign names only if the user specified one,
or we auto-generate a really simple name that doesn't resemble a path,
can be easily typed and is actually useful to have in addition to paths
(my "#foo-1" suggestion).


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