Re: [Xen-devel] simple backend, frontend

[Georgios Portokalidis <georgios.portokalidis@xxxxxxxxx>]

I have actually written some code for xen & xend allowing you to
request the creation of an event channel and share a memory page. It's
still work in progress, but it works fine. No crashes, very simple
communication scheme.

It's not in the repository, since i don't have access to it yet. But
I'm working with Rolf in IRC, so i guess it will eventually get there.

The only possible problem i believe is the
ctrl_if_register_receiver(). I think you can only register a single
receiver for each control message type per domain. So even with a
generic shared channel mechanism you will be able to use it just from
a single driver/module.

George P.

On Wed, 17 Nov 2004 21:59:04 +0000, Keir Fraser
<keir.fraser@xxxxxxxxxxxx> wrote:
> > Hi,
> >
> >   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.
> 
> If you mean that the user-level program creates the event channel, I
> would recommend not doing that. Instead, your frontend should
> allocate an unbound port that the backend can then connect to (or vice
> versa). i.e., frontend does EVTCHNOP_alloc_unbound.
> 
> I guess if you are using an existing front-end then this doesn't make
> sense as you need to go along with the existing protocol. However,
> both blkif and netif protocols will change to the new evtchn creation
> model in the near future.
> 
> > 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
> > "bind_evtchn_to_irq".
> 
> As Bin says, some functions will need EXPORT_SYMBOL(). Bin checked in
> EXPORT_SYMBOL(bind_evtchn_to_irq) earlier today.
> 
>  -- Keir
> 
> 
> 
> > thanks.
> >
> >
> > Deepak
> >
> >
> >
> >
> > 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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