Is it possible to follow a rebooted domain (with a different ID)?

Is it possible to follow a rebooted domain (with a different ID)?

[Razvan Cojocaru]

Hello,

I have an application, running in dom0 userspace, that receives 
mem_events about a domU HVM guest. At some point, the HVM guest (a 
Windows machine) restarts, at which point I need to shut down my 
userspace application, find it's new ID (with 'xm list'), then re-start 
my application passing the new ID as a parameter.

What I'd like to be able to do is to automatically follow the domain 
after it has started again. Is it possible to do this from dom0 
userspace (using libxc), and if it is, how?

A related question is this: is it possible to get notifications from 
userspace about a new domU that's just been started (regardless of 
whether it's a reboot of a previously watched domU or not)?

Thanks,
Razvan Cojocaru

Re: Is it possible to follow a rebooted domain (with a different ID)?

[Ian Campbell]

On Mon, 2013-01-07 at 10:48 +0000, Razvan Cojocaru wrote:
> Hello,
> 
> I have an application, running in dom0 userspace, that receives 
> mem_events about a domU HVM guest. At some point, the HVM guest (a 
> Windows machine) restarts, at which point I need to shut down my 
> userspace application, find it's new ID (with 'xm list'), then re-start 
> my application passing the new ID as a parameter.
> 
> What I'd like to be able to do is to automatically follow the domain 
> after it has started again. Is it possible to do this from dom0 
> userspace (using libxc), and if it is, how?
> 
> A related question is this: is it possible to get notifications from 
> userspace about a new domU that's just been started (regardless of 
> whether it's a reboot of a previously watched domU or not)?

I don't think this can be done using just libxc.

xenstore fires @introduceDomain and @releaseDomain pseudo-watches when
domains come and go. They don't tell you which so you would need to
track the domain you are interested in yourself (libxl has some helpers
for this sort of thing I think).

I'm not sure how to map from the old domid to the new one other than by
following the name or uuid.

Ian.

Re: Is it possible to follow a rebooted domain (with a different ID)?

[Mats Petersson]

On 07/01/13 10:48, Razvan Cojocaru wrote:
> Hello,
>
> I have an application, running in dom0 userspace, that receives
> mem_events about a domU HVM guest. At some point, the HVM guest (a
> Windows machine) restarts, at which point I need to shut down my
> userspace application, find it's new ID (with 'xm list'), then re-start
> my application passing the new ID as a parameter.
>
> What I'd like to be able to do is to automatically follow the domain
> after it has started again. Is it possible to do this from dom0
> userspace (using libxc), and if it is, how?
Xenstore will keep track of the name of the domain, which has to be 
unique, so you should be able to "find" your domain again by looking for 
its name. I've just reinstalled everything on my test-box, so I can't 
look at exactly where the name is stored [I don't have any VM's on 
there!], but I think you can figure it out yourself with a bit of 
"xenstore-ls".
>
> A related question is this: is it possible to get notifications from
> userspace about a new domU that's just been started (regardless of
> whether it's a reboot of a previously watched domU or not)?
You can have a xenstore watch for that.

I was looking at some code that does that the other day in xenconsoled 
[it watches for "new domain appearing"]. Have a look at 
xen/tools/console/daemon/io.c (I think!)

--
Mats
>
> Thanks,
> Razvan Cojocaru
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
>
>

Re: Is it possible to follow a rebooted domain (with a different ID)?

[Razvan Cojocaru]

> Xenstore will keep track of the name of the domain, which has to be
> unique, so you should be able to "find" your domain again by looking for
> its name. I've just reinstalled everything on my test-box, so I can't
> look at exactly where the name is stored [I don't have any VM's on
> there!], but I think you can figure it out yourself with a bit of
> "xenstore-ls".
> [...]
>> A related question is this: is it possible to get notifications from
>> userspace about a new domU that's just been started (regardless of
>> whether it's a reboot of a previously watched domU or not)?
> You can have a xenstore watch for that.
>
> I was looking at some code that does that the other day in xenconsoled
> [it watches for "new domain appearing"]. Have a look at
> xen/tools/console/daemon/io.c (I think!)

Thank you for all the replies, I appreciate your help! I'll look those up.

Thanks,
Razvan Cojocaru