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Re: [Xen-devel] simple backend, frontend

To: Keir Fraser <keir.fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] simple backend, frontend
From: Deepak Manohar <mjdeepak@xxxxxxxxx>
Date: Wed, 17 Nov 2004 13:27:33 -0500
Cc: mark.williamson@xxxxxxxxxxxx, andrew.warfield@xxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxxx
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Reply-to: Deepak Manohar <mjdeepak@xxxxxxxxx>
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  Writing a custom backend driver...... can a custom backend driver be
a module in the linux kernel or does it have to be built in?

 write now the backend and front end are very simple.

 a user level program establishes a shared event channel using -
libxc.  this part is complete.

this is the plan for the next part but need some info: 

i manually plan to install the module passing the eventchannel port.
as a command line argument to the module. but i need to know if a
linux kernel module can access the xen api such as



On Sun, 14 Nov 2004 15:42:44 +0000, Keir Fraser
<keir.fraser@xxxxxxxxxxxx> wrote:
> > Hi,
> >
> >  Sorry I seem to be stuck and asking similar questions.
> >
> > > > linux-2.6.9-xen-sparse/arch/xen/kernel/evtchn.c
> > >
> > > That's the one in kernel users will call into.
> >
> >  That file does not contain any code to create event channels.
> >
> >
> >  Do I have to write some code in Xen tht uses xen/common/event_channel.c 
> > creates
> > an event channel on init. And then pass the port returned to some
> > other program which passes it to the other domain?
> The 'old' model for creating event channels was that xend would create
> them and pass each domain the id of its end. So no creation code
> needed in XenLinux.
> The 'new' model (in which one domain creates an unbound port that the
> other end then connects to) is rather recent and so no drivers in
> XenLinux use it, so there's no code to steal. :-)
> evtchn.c is all about receipt and demux of events. You should create
> your own code to create an unbound port, then you should use
> bind_evtchn_to_irq() to get yourself a Linux IRQ number that you can
> then get interrupts for by using 'request_irq()'.
> If you're implementing a user-space driver then you won't want to bind
> into the Linux IRQ subsystem -- instead you would open /dev/xen/evtchn,
> bind to your event-channel port, then read() or poll() your file
> descriptor.  Currently only one process can have /dev/xen/evtchn open
> at any time, but I know of at least two patches to fix this, so I
> guess one of these ought to be checked in to the tree!
> So, yes, in short, you have to write the bit of code that you describe
> in your email. :-)
>  -- Keir

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