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

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Thu, Jul 22, 2010 at 01:46:35PM -0700, Dante Cinco wrote:
> 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.
> 

Uhm.. is this change intentional? 

-- Pasi


> 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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