Re: [Xen-devel] BLKTAPCTRL[2375]: blktapctrl_linux.c:86: blktap0 open failed

[Dante Cinco <dantecinco@xxxxxxxxx>]

Daniel,

You got it right with tap2 (instead of tap). That's the key.

So with Xen 4.0.0 and 2.6.32.14 it's: disk = [
'tap:tapdisk:vhd:/mnt/win2008sp2.vhd,xvda:sda1,w' ]

and with Xen 4.0.1-rc4 and 2.6.32.16 it's: disk = [
'tap2:tapdisk:vhd:/mnt/win2008sp2.vhd,xvda:sda1,w' ]

Very subtle change but makes a world of difference. My Windows 2008
domU is now booting from a VHD file.

Here's what I see in /sys/devices/virtual/blktap2/blktap0/debug:
vhd:/mnt/win2008sp2.vhd (253:0), refcnt: 0, dev_inuse: 0x0000001e
capacity: 0x3200000, sector size: 0x200, device users: 2
pending requests: 0

And in /var/log/xen/ qemu-dm-svm.log:
Using xvda for guest's hda
Using file /dev/xen/blktap-2/tapdev0 in read-write mode

Thanks a lot for your help.

Dante


On Thu, Jul 22, 2010 at 1:11 PM, Daniel Stodden
<daniel.stodden@xxxxxxxxxx> wrote:
> On Thu, 2010-07-22 at 12:59 -0400, Dante Cinco wrote:
>> Daniel,
>>
>> My cfg has this: disk = [ 'tap:tapdisk:vhd:/mnt/win2008sp2.vhd,xvda:sda1,w' ]
>>
>> If I remove tapdisk, I get this error:
>>
>> Error: need more than 1 value to unpack
>>
>> Here's a more basic question: How do I check if my dom0 kernel has
>> blktap2? Is the presence of /dev/xen/blktap-2 (such as below) a
>> necessary indicator?
>> kaan-20:~# ls -l /dev/xen/blktap-2
>> crw------- 1 root root 253,  0 Jul 21 20:29 blktap0
>> crw------- 1 root root  10, 59 Jul 21 20:29 control
>> brw------- 1 root root 253,  0 Jul 21 20:29 tapdev0
>
> No. These will be generated by udev in the future, in which case this
> would be indication, too. But right now the toolstack mknods them if
> they don't exist.
>
> You should see a /sys/class/blktap2 directory and 'tapdev' and 'blktap2'
> device entries in /proc/devices.
>
>> The system with Xen 4.0.1-rc4 and 2.6.32.16 where VHD does not work
>> does not have any blktap in /dev/xen:
>> kaan-11:~# ls -l /dev/xen
>> crw-rw---- 1 root root 10, 54 Jul 22 01:57 evtchn
>> crw-rw---- 1 root root 10, 61 Jul 22 01:57 gntdev
>> Does this mean this dom0 kernel does not have the blktap driver?
>>
>> The kernel config file for the system where VHD does not work contains
>> the following. Is this correct?
>> CONFIG_XEN_BLKDEV_FRONTEND=m
>> CONFIG_XEN_BLKDEV_BACKEND=y
>> CONFIG_XEN_BLKDEV_TAP=y
>> CONFIG_XEN_BLKBACK_PAGEMAP=y
>
> Yep.
>
> Problem is I'm not very good with xen-stable, as you might have already
> guessed.
>
> There's a lot of 'tap' vs. 'tap2' stuff in the python sources.
>
> How about tap2:tapdisk:...?
>
> :>
>
> Daniel
>
>

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