Xen devel - Sep 2005 - When is "physical-device" created in xenstore?

Saw a strange problem. When blkfront writes event channel number and
ring-ref to xenstore, the watch registered by blkback is notified.
However immediately watch handler in blkback found there''s no
"physical-device" under xenstore which should refer to major/minor
number of device for domU. Then failed to create vbd and finally the
connection can''t be setup.

So my puzzle is, when should physical-device be created? And who creates
this item? I searched for name string in whole tools directory to only
find instance in block-file/block-phy/block-endb. I configured disk
image by /dev/loop0, so ideally block-phy should be used. However I
still failed to find where block-phy is invoked.

Any clues?

Thanks,
Kevin

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If making following temp hack in XendDomainInfo.py:

             back = { ''type'' : type,
                      ''params'' : params,
                      ''frontend'' : frontpath,
-                     ''frontend-id'' : "%i" %
self.domid }
+                     ''frontend-id'' : "%i" %
self.domid,
+                    ''physical-device'' : "%li" %
blkdev_name_to_number(params) }
             xstransact.Write(backpath, back)

Then physical-device is created under backend and the communication can be
setup. However this hard code definitely breaks existing logical behind. Should
I do any specific configuration? From the Blkctl.py, it said that
"phy" type doesn''t require bind/unbind script, but I
didn''t find the place to add that item specifically. ;-(

Thanks,
Kevin
>-----Original Message-----
>From: xen-devel-bounces@lists.xensource.com
>[mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Tian, Kevin
>Sent: 2005年9月20日 16:37
>To: xen-devel@lists.xensource.com
>Subject: [Xen-devel] When is "physical-device" created in
xenstore?
>
>Saw a strange problem. When blkfront writes event channel number and
>ring-ref to xenstore, the watch registered by blkback is notified.
>However immediately watch handler in blkback found there''s no
>"physical-device" under xenstore which should refer to major/minor
>number of device for domU. Then failed to create vbd and finally the
>connection can''t be setup.
>
>So my puzzle is, when should physical-device be created? And who creates
>this item? I searched for name string in whole tools directory to only
>find instance in block-file/block-phy/block-endb. I configured disk
>image by /dev/loop0, so ideally block-phy should be used. However I
>still failed to find where block-phy is invoked.
>
>Any clues?
>
>Thanks,
>Kevin
>
>_______________________________________________
>Xen-devel mailing list
>Xen-devel@lists.xensource.com
>http://lists.xensource.com/xen-devel
_______________________________________________
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On Tue, Sep 20, 2005 at 07:41:09PM +0800, Tian, Kevin wrote:
> If making following temp hack in XendDomainInfo.py:
> 
>              back = { ''type'' : type,
>                       ''params'' : params,
>                       ''frontend'' : frontpath,
> -                     ''frontend-id'' : "%i" %
self.domid }
> +                     ''frontend-id'' : "%i" %
self.domid,
> +                    ''physical-device'' : "%li"
% blkdev_name_to_number(params) }
>              xstransact.Write(backpath, back)
> 
> Then physical-device is created under backend and the communication can be
> setup. However this hard code definitely breaks existing logical
> behind. Should I do any specific configuration? From the Blkctl.py, it said
> that "phy" type doesn''t require bind/unbind script, but
I didn''t find the
> place to add that item specifically. ;-(
Hi Kevin,

The key physical-device is created inside the block-phy script, as I think you
found.  This is called by xen-backend.agent, which in turn is called by the
Linux hotplug system (keying off the name ''xen-backend'').  The
file Blkctl.py
is completely unused, AFAICT, and should be removed.

The problems that you are having starting your device are probably down to a
broken or nonexistent installation of the hotplug system.  You should check
that first.  If your hotplug system is working, then maybe you are failing to
find xenstore-write.

HTH,

Ewan.

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>From: Ewan Mellor [mailto:ewan@xensource.com]
>Sent: 2005年9月20日 21:12
>On Tue, Sep 20, 2005 at 07:41:09PM +0800, Tian, Kevin wrote:
>
>> If making following temp hack in XendDomainInfo.py:
>>
>>              back = { ''type'' : type,
>>                       ''params'' : params,
>>                       ''frontend'' : frontpath,
>> -                     ''frontend-id'' : "%i"
% self.domid }
>> +                     ''frontend-id'' : "%i"
% self.domid,
>> +                    ''physical-device'' :
"%li" %
>blkdev_name_to_number(params) }
>>              xstransact.Write(backpath, back)
>>
>> Then physical-device is created under backend and the communication can
be
>> setup. However this hard code definitely breaks existing logical
>> behind. Should I do any specific configuration? From the Blkctl.py, it
said
>> that "phy" type doesn''t require bind/unbind script,
but I didn''t find the
>> place to add that item specifically. ;-(
>
>Hi Kevin,
>
>The key physical-device is created inside the block-phy script, as I think
you
>found.  This is called by xen-backend.agent, which in turn is called by the
>Linux hotplug system (keying off the name ''xen-backend''). 
The file Blkctl.py
>is completely unused, AFAICT, and should be removed.
>
>The problems that you are having starting your device are probably down to a
>broken or nonexistent installation of the hotplug system.  You should check
>that first.  If your hotplug system is working, then maybe you are failing
to
>find xenstore-write.
>
>HTH,
>
>Ewan.
Hi, Ewan,
	Thanks for your description about the work flow. Actually I found the cause
from bad lines in xen-backend.script, which has already been fixed by Keir
several days ago. After removing the bad lines, the "physical-device"
can be created automatically.

Thanks,
Kevin

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