Handle for events?

Handle for events?

[Srujan D. Kotikela]

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Hi,

I am trying to send events from DomU to the Dom0. I have established an
event channel. I used to xc_evtchn_notify() to send an event. But I am not
sure how to check if the event has been sent. Through source browsing I
found an event handler for xensource. Is there no generic handler for event
channels?

--
Srujan D. Kotikela

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Re: Handle for events?

[Jeremy Fitzhardinge]

 On 09/28/2010 09:46 PM, Srujan D. Kotikela wrote:
> Hi,
>
> I am trying to send events from DomU to the Dom0. I have established
> an event channel. I used to xc_evtchn_notify() to send an event. But I
> am not sure how to check if the event has been sent. Through source
> browsing I found an event handler for xensource. Is there no generic
> handler for event channels?

/dev/xen/evtchn allows a usermode program to wait for specific event
channels.

    J

Re: Handle for events?

[Srujan D. Kotikela]

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I called the xc_evtchn_notify(). But I see no message/notification in
/dev/xen/evtchn (in either DomU or Dom0). I did a little research and found
there might be problem with my xen-evtchn module. However it is statically
compiled into my kernel and i can see the following contents in /proc/xen

ls /proc/xen/
balloon  capabilities  privcmd    xenbus    xsd_kva  xsd_port

For now I just  want to send and event and acknowledge it (later application
will be built on top of this).

--
Srujan D. Kotikela


On Wed, Sep 29, 2010 at 11:08 AM, Jeremy Fitzhardinge <jeremy@goop.org>wrote:

>  On 09/28/2010 09:46 PM, Srujan D. Kotikela wrote:
> > Hi,
> >
> > I am trying to send events from DomU to the Dom0. I have established
> > an event channel. I used to xc_evtchn_notify() to send an event. But I
> > am not sure how to check if the event has been sent. Through source
> > browsing I found an event handler for xensource. Is there no generic
> > handler for event channels?
>
> /dev/xen/evtchn allows a usermode program to wait for specific event
> channels.
>
>    J
>

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Re: Handle for events?

[Jeremy Fitzhardinge]

 On 09/29/2010 09:27 AM, Srujan D. Kotikela wrote:
> I called the xc_evtchn_notify(). But I see no message/notification in
> /dev/xen/evtchn (in either DomU or Dom0). I did a little research and
> found there might be problem with my xen-evtchn module. However it is
> statically compiled into my kernel and i can see the following
> contents in /proc/xen
>
> ls /proc/xen/
> balloon  capabilities  privcmd    xenbus    xsd_kva  xsd_port

/proc/xen is not the same as /dev/xen

    J

Re: Handle for events?

[Srujan D. Kotikela]

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Sorry,

But from what I read I may not get notifications on /dev/xen/evtchn if my
xen-evtchn module is not functioning. However if it is statically compiled
it wont be found as a module. I can confirm it's working by checking if
there are directories in my /proc/xen

correct me if I am wrong.

I am calling notify() and I am getting a return value 0 but no notification
mesages in /dev/xen/evtchn

--
Srujan D. Kotikela


On Wed, Sep 29, 2010 at 11:29 AM, Jeremy Fitzhardinge <jeremy@goop.org>wrote:

>  On 09/29/2010 09:27 AM, Srujan D. Kotikela wrote:
> > I called the xc_evtchn_notify(). But I see no message/notification in
> > /dev/xen/evtchn (in either DomU or Dom0). I did a little research and
> > found there might be problem with my xen-evtchn module. However it is
> > statically compiled into my kernel and i can see the following
> > contents in /proc/xen
> >
> > ls /proc/xen/
> > balloon  capabilities  privcmd    xenbus    xsd_kva  xsd_port
>
> /proc/xen is not the same as /dev/xen
>
>    J
>

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Re: Handle for events?

[Jeremy Fitzhardinge]

 On 09/29/2010 09:34 AM, Srujan D. Kotikela wrote:
> Sorry,
>
> But from what I read I may not get notifications on /dev/xen/evtchn if
> my xen-evtchn module is not functioning. However if it is statically
> compiled it wont be found as a module. I can confirm it's working by
> checking if there are directories in my /proc/xen
>
> correct me if I am wrong.

/proc/xen is irrelevant to xen-evtchn; you would not expect to see any
changes in /proc/xen as a result of xen-evtchn being present or absent.

>
> I am calling notify() and I am getting a return value 0 but no
> notification mesages in /dev/xen/evtchn

You should look carefully at the existing examples of how to use that
device to see where you're going wrong.

    J

Re: Handle for events?

[Srujan D. Kotikela]

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Hi Jeremy,

I was going through the code in mini-os. The hypervisor_callback, which
handles all the events, is defined in the x86_64.S file. In xen sources I
see xen/arch/x86/x86_64/entry.S with no such callback function.

>From what I read in the Xen Definitive guide, There is a single handler for
all events (hypervisor_callback) which in turn should call individual
handlers, which are registered before hand, for each event. I have few
questions regarding this:

1. Is there a default event handler for Dom0 kernel (like
hypervisor_callback in mini-os). If so, what is the function to register
event handlers for specific port/channel (I tried searching the code and
couldn't find any)?

2. If no default handler exists how are the handlers for xen_console and
xen_store events or any other events setup?

3. Is the ./xen/arch/x86/x86_64/entry.S analogous to
./extras/mini-os/arch/x86/x86_64.S? I mean If I have to write event handler,
should I edit entry.S?

--
Srujan D. Kotikela



On Wed, Sep 29, 2010 at 12:16 PM, Jeremy Fitzhardinge <jeremy@goop.org>wrote:

>  On 09/29/2010 09:34 AM, Srujan D. Kotikela wrote:
> > Sorry,
> >
> > But from what I read I may not get notifications on /dev/xen/evtchn if
> > my xen-evtchn module is not functioning. However if it is statically
> > compiled it wont be found as a module. I can confirm it's working by
> > checking if there are directories in my /proc/xen
> >
> > correct me if I am wrong.
>
> /proc/xen is irrelevant to xen-evtchn; you would not expect to see any
> changes in /proc/xen as a result of xen-evtchn being present or absent.
>
> >
> > I am calling notify() and I am getting a return value 0 but no
> > notification mesages in /dev/xen/evtchn
>
> You should look carefully at the existing examples of how to use that
> device to see where you're going wrong.
>
>    J
>

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Re: Handle for events?

[Srujan D. Kotikela]

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Hi jeremy,

I have looked into the events.c

The function *bind_evtchn_to_irqhandler(*(int evtchn, irq_handler_t
handler, unsigned long irqflags, *const char *devname, void *dev_id) *looks
the most appropriate for me. However, I wouldn't have any device name or
Id. So I am not sure how I can use it to set up the handler.

I am looking to setup a very light weight communication mechanism from DomU
to Dom0. The application in DomU will raise a hypercall. The hypercall
handler will send an event to Dom0. This communication setup is just to
notify an *event* to Dom0 excluding the DomU kernel.

I am facing 2 roadblocks for this setup.
 - How to install an event handler for the event channel (between Dom0 and
hypervisor).
 - How can I send an event to Dom0. The only function I found was
*xc_evtchn_notify()
*But AFAIK this function or the
            *event_channel_op send* are to be done by from a domain (through
port). So how can I trigger/send an event from hypervisor to Dom0.

Finally, does establishing an event channel (using xc_evtchn_open) guarantee
an event channel between Dom0 and hypervisor? Or is there any specific
function for the same.

Thanks and regards,
Srujan D. Kotikela


On Tue, Oct 12, 2010 at 12:57 PM, Jeremy Fitzhardinge <jeremy@goop.org>wrote:

>  On 10/08/2010 09:10 AM, Srujan D. Kotikela wrote:
> > From what I read in the Xen Definitive guide, There is a single
> > handler for all events (hypervisor_callback) which in turn should call
> > individual handlers, which are registered before hand, for each event.
> > I have few questions regarding this:
> >
> > 1. Is there a default event handler for Dom0 kernel (like
> > hypervisor_callback in mini-os). If so, what is the function to
> > register event handlers for specific port/channel (I tried searching
> > the code and couldn't find any)?
>
> Yes, xen_do_hypervisor_callback in kernel/entry_64.S.  Events are mapped
> to the Linux IRQ subsystem, so registering for an event channel requires
> mapping it to an irq, then registering an irq as normal.  The code to
> implement it is in drivers/xen/events.c.
>
>
> >
> > 2. If no default handler exists how are the handlers for xen_console
> > and xen_store events or any other events setup?
>
> The events are bound to irqs, and the irq handler deals with the
> events.  You can see the registrations in /proc/interrupts.
>
> >
> > 3. Is the ./xen/arch/x86/x86_64/entry.S analogous to
> > ./extras/mini-os/arch/x86/x86_64.S? I mean If I have to write event
> > handler, should I edit entry.S?
>
> That looks like a path into the source for Xen (the hypervisor) itself.
> Xen doesn't need an event upcall entrypoint because it is initiating all
> the upcalls.
>
>    J
>
> >
> > --
> > Srujan D. Kotikela
> >
> >
> > On Wed, Sep 29, 2010 at 12:16 PM, Jeremy Fitzhardinge <jeremy@goop.org
> > <mailto:jeremy@goop.org>> wrote:
> >
> >      On 09/29/2010 09:34 AM, Srujan D. Kotikela wrote:
> >     > Sorry,
> >     >
> >     > But from what I read I may not get notifications on
> >     /dev/xen/evtchn if
> >     > my xen-evtchn module is not functioning. However if it is
> statically
> >     > compiled it wont be found as a module. I can confirm it's working
> by
> >     > checking if there are directories in my /proc/xen
> >     >
> >     > correct me if I am wrong.
> >
> >     /proc/xen is irrelevant to xen-evtchn; you would not expect to see
> any
> >     changes in /proc/xen as a result of xen-evtchn being present or
> >     absent.
> >
> >     >
> >     > I am calling notify() and I am getting a return value 0 but no
> >     > notification mesages in /dev/xen/evtchn
> >
> >     You should look carefully at the existing examples of how to use that
> >     device to see where you're going wrong.
> >
> >        J
> >
> >
>
>

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