Re: [Xen-users] Install blktap2 kernel module on CentOS 6

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Oct 25, 2013 at 04:21:57PM +0000, Kim Larry wrote:
> Hi, 
> 
> I'm currently stuck with creating VM which cannot boot with disk using 
> blktap2 driver. I've been searching nearly a whole week and I couldn't get a 
> answer. When creating vm with blktap2, it keep shows a error: 
> 

Blktap2 is not upstreamed, and Xen on CentOS 6 uses upstream kernel so
you're not likely to find blktap2 anywhere.

Any reason to stick with blktap2? Can you not use QEMU / blkback
instead?

>  libxl: debug: libxl_device.c:200:disk_try_backend: Disk vdev=xvda, backend 
> tap unsuitable because blktap not available. 
> 
> VM configuration (XML):
> 
> <domain type='xen'>
>   <name>test</name>
>   <uuid>fed10f30-077d-4d2a-87aa-ccc76c290426</uuid>
>   <memory unit='KiB'>524288</memory>
>   <currentMemory unit='KiB'>524288</currentMemory>
>   <vcpu placement='static'>1</vcpu>
>   <os>
>     <type>linux</type>
>     <kernel>/xen/boot/vmlinuz-3.9.9</kernel>
>     <initrd>/xen/boot/initramfs-3.9.9.img</initrd>
>     <cmdline>root=/dev/xvda selinux=0</cmdline>
>   </os>
>   <clock offset='utc' adjustment='reset'/>
>   <on_poweroff>destroy</on_poweroff>
>   <on_reboot>restart</on_reboot>
>   <on_crash>destroy</on_crash>
>   <devices>
>     <disk type='file' device='disk'>
>       <source 
> file='/xen/data/fed10f30-077d-4d2a-87aa-ccc76c290426/fed10f30-077d-4d2a-87aa-ccc76c290426.img'/>
>       <driver name="tap2" type="raw" />

Is this disk image raw file? You can probably get better performance by
using blkback driver.

>       <target dev='xvda' bus='xen'/>
>     </disk>
>     <interface type='bridge'>
>       <mac address='00:16:3e:24:bd:8d'/>
>       <source bridge='virbr0'/>
>       <ip address='10.0.1.123'/>
>       <script path='/etc/xen/scripts/vif-bridge'/>
>     </interface>
>     <console type='pty'>
>       <target type='xen' port='0'/>
>     </console>
>   </devices>
> </domain>
>  
> I believe loading blktap2 kernel module can solve this problem which I can't 
> find it from major repository(CentOS repo, epel, etc..). Ubuntu and Debian 
> have blktap-dkms package, is there no such package like blktap-dkms for 
> CentOS? Already looked into xen source and found out tools/blktap2 directory 
> but it doesn't contain kernel module. 
> 

Those are out-of-tree patches packaged by XAPI team.

Wei.

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