Re: [Xen-devel] [new PV device]

[Vincenzo Maffione <v.maffione@xxxxxxxxx>]

2014-04-14 23:46 GMT+02:00 Wei Liu <wei.liu2@xxxxxxxxxx>:
> On Mon, Apr 14, 2014 at 05:45:00PM +0200, Vincenzo Maffione wrote:
>> Hi,
>>    I would like to design a new paravirtual device for Xen PV guests
>> (under Linux),
>> for research purposes.
>> This device should be a "simplification" of netfront/netback in that
>> the interface
>> with the domU/dom0 O.S. is not the normal TCP/IP stack, but something way
>> simpler (however, this is not so important w.r.t. my question).
>>
>> Looking at the netback code
>>      linux:drivers/net/xen-netback/xenbus.c
>> I've run into some "hotplug scripts" support code.
>> The netfront code, on the other hand, has no hotplug-related code.
>>
>> I don't really understand what is the purpose of this hotplug support
>> (Is it something
>> related to the vif-* scripts?), but I'm wondering whether I can get
>
> Yes, you're right.
>
>> rid of this code for my
>> "simplified" device.
>>
>
> Of course you can, if you don't need user space event handling or don't
> mind doing some tedious configurations by hand.
>
>> It would be enough for me to be able to do the following:
>>   1) manually load my backend driver kernel module in Dom0
>>   2) manually load my frontend driver kernel module in DomU
>>   3) being able to use my device (think as I have userspace access to
>> the device through a character device).
>> I don't want/need any configuration scripts in Dom0 nor DomU (no sw
>> bridges or routing
>> tables to configure).  Just plain simple Dom0 <==> DomU buffer exchange.
>>
>> Is it possibile to achieve this without any "hotplug code"? Or do I need some
>
> Yes, that's possible.
>
> You can have a look at other Xen PV drivers as well. Probably Xen PV
> framebuffer can be a good starting point.
>
> Xen wiki also has some general information on PV driver.
>
> Wei.

Thank you.
So Xen is really a minimal hypervisor, if adding a new device doesn't
require modifications in the hypervisor itself (but only some new
kernel modules for the domains). Great!

I'm not able to find the framebuffer backend in the linux kernel. Is
it somewhere else?

-- 
Vincenzo Maffione

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