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Re: [Xen-devel] capturing SIGKILL in DomU

To: "Srujan D. Kotikela" <ksrujandas@xxxxxxxxx>
Subject: Re: [Xen-devel] capturing SIGKILL in DomU
From: Michal Novotny <minovotn@xxxxxxxxxx>
Date: Tue, 05 Oct 2010 15:22:50 +0200
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Hi Srujan,

I'm not that familiar with event channels themselves however I was thinking about using xenstore. You can modify the device model (qemu-dm) to be watching some entry in the xenstore and the communication could be both way since if you establish a xenstore watch in both Dom0 and DomU you could intercept the changes on both sides.

If you would like to use interrupts instead you may have to modify the HVMLoader source codes at tools/firmware/hvmloader of the user-space stack but I think using the xenstore could do the job since this is how it's working with PV drivers AFAIK since PV drivers themselves implement xenbus to connect to host's xenstore facility.

Hope this helps!


On 10/05/2010 03:14 PM, Srujan D. Kotikela wrote:
Hi Michal,

I have no special interest in SIGKILL. All I want to do is notify Dom0 about an event in DomU (I don't need to pass any data). I am trying to indicate events by signals or interrupts. It means, if a "particular" interrupt has occurred in DomU, the Dom0 should be notified. Is there any other way of doing the same other than using event channels?

I am successful in establishing the event channel. But I am not quite sure how to send a notification that an event occurred in DomU to Dom0. Any pointers for the same would be appreciated.

Srujan D. Kotikela

On Tue, Oct 5, 2010 at 3:36 AM, Michal Novotny <minovotn@xxxxxxxxxx <mailto:minovotn@xxxxxxxxxx>> wrote:

    Hi Srujan,
    what about adding a signal handler to qemu-dm in the
    tools/ioemu-dir of the user-space tools? Using the signal() API?
    Nevertheless why would you like to catch SIGKILL? This one (as can
    be seen using included program source and killing it using kill -9
    pid or kill -SIGKILL pid) is not being caught at all nevertheless
    most of the other signals can be caught.

    This is the source of the example mentioned:
    #include <stdio.h>
    #include <signal.h>
    #include <stdlib.h>

    void sig_handler(int sig) {
       fprintf(stderr, "Signal %d caught.\n", sig);

    int main()
       signal(SIGINT, sig_handler);
       signal(SIGKILL, sig_handler);

       return 0;

    When I did try SIGINT (Ctrl + C or kill -2 pid) it caught the
    signal well but when I did try kill -9 pid (or kill -SIGKILL pid
    respectively) it was not working at all since it killed the
    process instead of going to the signal handler. When you need to
    catch signals like interruption signal (Ctrl + C one) this will
    work fine.


    On 10/04/2010 09:03 PM, Srujan D. Kotikela wrote:


        I am trying to capture SIGKILL through event channel.

        On my Dom0, the following process is running (remaining code
        in attachment).

           int main(void){

               int ret, dom, remote_dom;

               //initialize domains

               //create the event channel
               ret = create_channel(dom, remote_dom);

               if (0 == ret) {
                   printf("\n Event Channel established successfully \n");
               } else {
                   return -1;    //EVENT_CHANNEL_CREATION_FAILED

               //wait 20 seconds for an event to occur in DomU

               //close the opened interfaces

               return 0;


        While this process is running; I killed a process in DomU
        using `*kill SIGKILL pid*`

        How can I capture this event (occured in DomU) at the Dom0. I
        watched /dev/xen/evtchn, but no notification.

        Srujan D. Kotikela

        Xen-devel mailing list

-- Michal Novotny<minovotn@xxxxxxxxxx <mailto:minovotn@xxxxxxxxxx>>, RHCE
    Virtualization Team (xen userspace), Red Hat

Michal Novotny<minovotn@xxxxxxxxxx>, RHCE
Virtualization Team (xen userspace), Red Hat

Xen-devel mailing list

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