linux-kernel - Re: [Xen-devel] Re: [PATCH 11/11] Unplug emulated disks and nics

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Date:	Thu, 27 May 2010 10:51:25 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ian Jackson <Ian.Jackson@...citrix.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Don Dutile <ddutile@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] Re: [PATCH 11/11] Unplug emulated disks and nics

On 05/27/2010 07:49 AM, Ian Jackson wrote:
> Stefano Stabellini writes ("[Xen-devel] Re: [PATCH 11/11] Unplug emulated disks and nics"):
>   
>> On Wed, 26 May 2010, Jeremy Fitzhardinge wrote:
>>     
>>> Wow, this interface is perverse.  It reuses the same IO port but changes
>>> function depending on the size of the IO?  Again, wow.
>>>       
>>  
>> Yeah, before you ask, I didn't write it :)
>>     
> Yes, neither did I :-).  However, I did document it and now I also
> maintain the "product number" registry.  Did you find the interface
> spec ?  Enclosed below in case not.
>   

Thanks.  We should probably start a Documentation/xen/ and put this in
there as part of the patch.

> I hereby allocate you ("pvops PV-on-HVM Linux, upstream") product
> number 3.  Does the kernel have a way to distinguish between upstream
> and other versions ?  Eg, there's the kernel version name suffix
> thingy if I remember rightly.  Perhaps we should allocate a different
> number for "some pvops pv-on-hvm Linux with a nonempty kernel version
> name suffix".  Please advise.
>
> You are welcome to use whatever you like for the "build number".
> Perhaps the best thing would a two-byte encoding of the kernel version
> number if that is possible.  As the purpose is logging and
> blacklisting, it's not that critical although it's better to reuse the
> same number for excessively similar builds than to use a random scheme
> which might generate accidental clashes between unrelated versions.
>   

We could include 2 bytes of the HEAD changeset or something, with some
risk of collision.  Or just choose a constant and stick with it until
some interesting qualitative driver change makes it worthwhile bumping
the version.

I guess I can see some value in this info for recording in a log to do
some diagnostics, but the whole blacklist concept seems highly dubious
to me.  Some kind of feature negotiation makes a lot more sense to me...

    J
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