[Xen-devel] Re: [Xen-users] Blktap in mainline kernel 3.x

[David Della Vecchia <ddv@xxxxxxxxxxxxxxxx>]

I've had it running for about a month now with no issues, i've got 35 beta tester domU's on the box and everything seems to be going swimmingly.

A few things to keep in mind:

For some reason the debian xen packages do not have pv-grub so you need to acquire that elsewhere, it doesn't need to be built on your system though, i downloaded mine from a forum post somewhere (i used to download the xen source and compile from scratch to get it). 

This next one isn't so much a dom0 problem as a domU one but for some reason debian squeeze (stable) guests are not capable of saving and restoring their state. On restore the console and/or network devices will be locked/frozen. I was able to get it to kinda work by custom compiling a 3.0.4 kernel but even then it was not reliable; however the centos domU's are able to save/restore flawlessly. This was all on the wheezy dom0.

The xen packages in debian, and this might be the default for xen4.1+ now, expect you to setup your own bridge, the network-bridge line of the xend-config.sxp will be commented out or just not there at all. I put it back in, I let the script the handle the bridging since it works fine for my needs; that and my attempts to manually create a bridge following the xen instructions always fail for some reason. 

Stuff gets put into /usr/lib/xen-4.1 instead of /usr/lib/xen so i had to update a lot of my scripts and config files when i switched to debian. 

Also as far as i can tell, wheezy uses the stock 3.0.0-1 kernel for xen so no custom kernel required like in squeeze with its 2.6.32-5-xen (its my understanding this is the pvops option?). 

As far as hvm guests go, as long as you use the hvmloader from the package you'll be fine, if you custom compile xen there's a good chance your hvmloader will be corrupted, it has something to do with the newer version of gcc, though this may have been fixed in 4.1.2. 

Hope that helps,

David

On Wed, Nov 2, 2011 at 12:44 PM, Steven Wilcoxon <stevew@xxxxxxxxx> wrote:

I've been thinking of doing a Wheezy install myself. How stable does it feel to you?

S.W.

On 11/2/2011 10:26 AM, David Della Vecchia wrote:

I run a debian wheezy (testing) dom0 and it's 3.0.1 kernel does not have blktap(2) as you said however I did install the blktap dkms and was able to get the kernel module installed and running yet still domU's with blktap devices would just hang on boot with no error messages ever. I even tried recompiling the kernel and statically linking the blktap driver but it was the same results as using it modularized.

Sorry i can't help but to confirm your issue. I was also unable to get blktap working in centos6 with the 2.6 kernel. I use lvm-backed domU's but it would be nice to be able to store the swap or something locally with a tap: instead of file: 

Thanks,

DDV

On Wed, Nov 2, 2011 at 7:14 AM, João Paulo <jtpaulo@xxxxxxxxxxxx> wrote:

Hi guys,

I am using blktap for implementing a custom disk device for XEN DomUs. I was using a previous version of Ubuntu that I need to upgrade to version 11.10.  If i understood correctly, the blktap kernel module is not present in the mainline kernel 3.x. So my questions are:

Can I get blktap/blktap2 working on ubuntu 11.10? If yes, can you point me the procedure?

I saw that project Kronos is aiming at a blktap dkms module for debian/ubuntu http://blog.xen.org/index.php/2011/07/22/project-kronos/ . However, i tried it in a AMD64 bit distribution and the module was deployed correctly but blktap is still not working.

Is there any other linux distro, or alternative better than Ubuntu 11.10 for my objectives?

Finally, is there a better alternative for implementing custom I/O disk drivers for VMs instead of the blktap mechanism? I have not looked deeply to HVM-XEN and Qemu, would this solution be less painful?

Thanks for your help,

Kind Regards,

João Paulo
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