Re: What is the state of blktap2?

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 01/21/2010 11:14 PM, Pasi Kärkkäinen wrote:
> On Thu, Jan 21, 2010 at 06:13:46PM -0500, David P. Quigley wrote:
>    
>> On Fri, 2010-01-22 at 00:59 +0200, Pasi Kärkkäinen wrote:
>>      
>>> On Fri, Jan 22, 2010 at 12:55:52AM +0200, Pasi Kärkkäinen wrote:
>>>        
>>>> On Thu, Jan 21, 2010 at 05:46:05PM -0500, David P. Quigley wrote:
>>>>          
>>>>> On Fri, 2010-01-22 at 00:38 +0200, Pasi Kärkkäinen wrote:
>>>>>            
>>>>>> On Thu, Jan 21, 2010 at 05:27:45PM -0500, David P. Quigley wrote:
>>>>>>              
>>>>>>> I'm currently working on moving storage services into their own domain
>>>>>>> and I've been looking at blktap2. I've been trying to get an image
>>>>>>> mounted with blktap2 and for some odd reason and tapdisk2 keeps hanging
>>>>>>> instead of quitting at the end. I haven't removed any of the storage
>>>>>>> startup code at this point so everything should be as it normally is in
>>>>>>> xen-unstable. Is this a known bug? Are there some requirements on
>>>>>>> blktap2 that I'm possibly not meeting? Is there anything in particular
>>>>>>> that I should be looking at to try to debug the problem?
>>>>>>>
>>>>>>>                
>>>>>> What kernel are you using? pv_ops dom0 kernel doesn't have working blktap2 yet..
>>>>>> linux-2.6.18-xen has working blktap2 support.
>>>>>>
>>>>>> -- Pasi
>>>>>>              
>>>>> I'm using the patches maintained by Andrew Lyon that are applied to
>>>>> 2.6.31.10. These are supposedly based on the OpenSUSE patches and can be
>>>>> found at http://code.google.com/p/gentoo-xen-kernel/downloads/list. I
>>>>> need a more recent kernel version so the 2.6.18 dom0 kernel isn't an
>>>>> option for me.
>>>>>
>>>>>            
>>>> Ok. I'm not sure if those OpenSUSE patches have blktap2 support included?
>>>> I know that at least Citrix XenServer, XCP and XCI 2.6.27 kernels do have blktap2.
>>>>
>>>> See:
>>>> http://wiki.xensource.com/xenwiki/XenDom0Kernels
>>>>
>>>>          
>>> More details about the pv_ops dom0 kernel (2.6.31.6 currently): It has initial version
>>> of blktap2 patches, but they'd need some debugging, because they're not yet working.
>>>
>>> -- Pasi
>>>        
>>
>> Looking under drivers through a make menuconfig on the pvops kernel I
>> don't see an entry for blktap2. I just see the entry for blktap. I know
>> that blktap2 was supposed to replace blktap but in the Novell patches
>> they are two separate config options and I don't seem to be seeing the
>> second on in the pvops kernel. Do I just enable blktap under drivers and
>> use tap:tapdisk:<type>  in the domU config to use blktap2?
>>
>>      
> See:
> http://git.kernel.org/?p=linux/kernel/git/jeremy/xen.git;a=shortlog;h=xen/master
>
> Commits like:
>
> 2009-12-10 	Jeremy Fitzhardinge	Merge branch 'xen/dom0/backend/blktap2' into xen/master
> 2009-12-10 	Jeremy Fitzhardinge	xen/blktap2: don't init on non-Xen system
> 2009-12-04 	Ian Campbell	blktap: cleanup usage of sysfs
> 2009-12-04 	Ian Campbell	blktap: wean off of use of the BlkBack pageflag.
> 2009-12-04 	Ian Campbell	Port blktap2 from 2.6.18 to tip.
> 2009-12-04 	Ian Campbell	Add build infrastrucuture for blktap2.
> 2009-12-04 	Ian Campbell	patch 03-blktap2-patch
> 2009-12-04 	Ian Campbell	patch 02-blkback-pagemap-patch
> 2009-12-04 	Ian Campbell	patch 01-blktap-patch
>
> I haven't tried it myself yet..
>    

It is pretty broken at present, and I'll probably commit a change to 
disable it for now.  Fortunately it looks like Daniel Stodden is going 
to have a crack at fixing it up.

     J