Re: [Qemu-devel] Should we auto-generate IDs?

[Programmingkid]

On Aug 26, 2015, at 6:01 PM, Jeff Cody wrote:

> On Wed, Aug 26, 2015 at 02:17:17PM -0400, Programmingkid wrote:
>> 
>> On Aug 26, 2015, at 2:08 PM, Jeff Cody wrote:
>> 
>>> On Wed, Aug 26, 2015 at 01:29:04PM -0400, Programmingkid wrote:
>>>> 
>>>> On Aug 26, 2015, at 1:25 PM, Jeff Cody wrote:
>>>> 
>>>>> On Wed, Aug 26, 2015 at 06:31:57PM +0200, Markus Armbruster wrote:
>>>>>> Did you drop cc's intentionally?  I put them right back.
>>>>>> 
>>>>>> Programmingkid <address@hidden> writes:
>>>>>> 
>>>>>>> On Aug 25, 2015, at 8:38 AM, Markus Armbruster wrote:
>>>>>>> 
>>>>>>>> You're proposing to revise a qdev design decision, namely the purpose 
>>>>>>>> of
>>>>>>>> IDs.  This has been discussed before, and IDs remained unchanged.
>>>>>>>> Perhaps it's time to revisit this issue.  Cc'ing a few more people.
>>>>>>>> 
>>>>>>>> Relevant prior threads:
>>>>>>>> * [PATCH] qdev: Reject duplicate and anti-social device IDs
>>>>>>>> http://thread.gmane.org/gmane.comp.emulators.qemu/71230/focus=72272
>>>>>>>> * [PATCH 6/6] qdev: Generate IDs for anonymous devices
>>>>>>>> http://thread.gmane.org/gmane.comp.emulators.qemu/114853/focus=114858
>>>>>>>> * [PATCH] qdev: Assign a default device ID when none is provided.
>>>>>>>> http://thread.gmane.org/gmane.comp.emulators.qemu/249702
>>>>>>>> * IDs in QOM (was: [PATCH] util: Emancipate id_wellformed() from 
>>>>>>>> QemuOpt
>>>>>>>> http://thread.gmane.org/gmane.comp.emulators.qemu/299945/focus=300381
>>>>>>>> 
>>>>>>> 
>>>>>>> After reading all the threads, I realize why all the attempts to
>>>>>>> accept a device ID patch failed.
>>>>>>> It is because it was assumed everyone would agree on one patch to
>>>>>>> accept. This is
>>>>>>> very unlikely. It would take someone in a leadership position to
>>>>>>> decide which patch
>>>>>>> should be accepted. From one of the threads above, I saw Anthony
>>>>>>> Liguori participate.
>>>>>>> He was in the perfect position to make the choice. The person who is
>>>>>>> in his position now
>>>>>>> is Peter Maydell. Maybe we should just ask him to look at all the
>>>>>>> candidate patches and
>>>>>>> have him pick one to use. 
>>>>>> 
>>>>>> Yes, when no consensus emerges, problems tend to go unsolved.
>>>>>> 
>>>>>> Before we appeal to authority to break the deadlock, we should make
>>>>>> another attempt at finding consensus.
>>>>>> 
>>>>>> I know that we've entertained the idea of automatically generated IDs
>>>>>> for block layer objects (that's why I cc'ed some block guys).
>>>>> 
>>>>> Yeah, I was one of the ones that proposed some auto-generated IDs for
>>>>> the block layer, specifically for BlockDriverState, making use of the
>>>>> node-name field that Benoit introduced a while ago.  Here is my patch
>>>>> (not sure if this is the latest version, but it is sufficient for this
>>>>> discussion):
>>>>> 
>>>>> http://patchwork.ozlabs.org/patch/355990/
>>>>> 
>>>>> I'm not sure about the requirements needed by device ID names, and
>>>>> they may of course differ from what I was thinking for BDS entries.
>>>>> 
>>>>> Here is what I was after with my patch for node-name auto-generation:
>>>>> 
>>>>> * Identifiable as QEMU generated / reserved namespace
>>>>> 
>>>>> * Guaranteed uniqueness
>>>>> 
>>>>> * Non-predictable (don't want users trying to guess / assume
>>>>> generated node-names)
>>>>> 
>>>>> My approach was overkill in some ways (24 characters!).  But for
>>>>> better or worse, what I had was:
>>>>> 
>>>>>              __qemu##00000000IAIYNXXR
>>>>>              ^^^^^^^^
>>>>> QEMU namespace ----|    ^^^^^^^^
>>>>>                        |     ^^^^^^^^^
>>>>> Increment counter, unique |         |
>>>>>                                  |
>>>>> Random string, to spoil prediction  |
>>>> 
>>>> Yikes! 24 characters long. That is a bit much to type. Thank you very much
>>>> for your effort.
>>> 
>>> IMO, the number of characters to type is pretty low on the list of
>>> requirements, although it can still be addressed secondary to other
>>> concerns.
>>> 
>>> I should have made this in reply to Markus' other email, because the
>>> important part of this is try and address his point #2:
>>> 
>>> (from Markus' other email):
>>>> 2. The ID must be well-formed.
>>> 
>>> To have a well-formed ID, we need to have know requirements of the ID
>>> structure (i.e. the why and what of it all)
>>> 
>>> I don't know if the three requirements I had above apply to all areas
>>> in QEMU, but I expect they do, in varying degrees of importance.  The
>>> length itself can be tweaked.
>>> 
>>> Talking with John Snow over IRC (added to the CC), one thing he
>>> suggested was adding in sub-domain spaces; e.g.:
>>> 
>>> __qemu#bn#00000000#IAIYNXXR
>>> 
>>> Where the 'bn' in this case would be for Block Nodes, etc..
>>> 
>>> This may make the scheme extensible through QEMU, where auto-generated
>>> IDs are desired.
>>> 
>>> (sorry to say, this lengthens things, rather than shortening them!)
>>> 
>>> We can, of course, make the string shorter - if the random characters
>>> are just there for spoiling predictability, then 2-3 should be
>>> sufficient. We could then end up with something like this:
>>> 
>>> __qemu#bn#00000000#XR
>>> 
>>> The "__qemu" part of the namespace could be shortened as well, but it
>>> would be nice if it was easy recognizable as being from QEMU.
>> 
>> If this ID format was supported, I'm thinking being able to copy and paste 
>> from
>> the monitor is a necessary feature. 
>> 
>> Any way it could be shorted? I was hoping no more than three characters 
>> long. 
>> 
> 
> Likely could be shorter, but something in the realm of three
> characters doesn't seem very realistic.

Sure it is. Just set device id's like this: 0, 1, 2, 3, 4, 5, 6....