Re: [Xen-devel] two questions about xen on arm

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 1 Nov 2013, Ian Campbell wrote:
> > > > > > > 2, xen kernel config   
> > > > > > > i am confuse about what does "CONFIG XEN" mean. it  will check 
> > > > > > > the  
> > > kernel    
> > > > >   
> > > > > > > features for dom0 and domU kernel(mix XEN_BANDEND and 
> > > > > > > XXX_FRONTEND)   
> > > > > > > should we define XEN_DOM0 and XEN_DOMU configs respectively?    
> > > > >   
> > > > > I'm not sure what you mean, but yes, if you want to run Xen you 
> > > > > should  
> > > > > enable the relevant CONFIG options, including CONFIG_XEN and I think  
> > > > > CONFIG_XEN_DOM0.  
> > > > i mean when i select the CONFIG_XEN in kernel config, both XEN_BACKEND 
> > > > and 
> > > > XEN_xxx_FRONTEND will be selected.  
> > > > i think backend and frontend should not select at the same time, isn't 
> > > > it?  
> > >  
> > > I think (but I'm not sure) that these are just umbrella options which 
> > > don't add any code themselves but just make the other more specific e.g. 
> > > netback) options. 
> > it is compiled into kernel, but it might be no harm?
> 
> If you don't boot under Xen then none of the code will be (should be!)
> active. If you are booting under Xen then I think it is expected?

Right, having both the backends and the frontends compiled in should
cause no troubles.
If you are really concerned about the size of the kernel it might make
sense to disable the backends or the frontends depending on whether you
are running linux in dom0 or another domU.


> > CONFIG_XEN_BACKEND will select xenbus_probe_backend.c and
> > xenbus_dev_backend.c, xenbus_probe_backend.c will register the
> > "xen-backend" bus. is it unused until the xen backend device
> > registered? 

It is unused until xenbus_backend_init and later xenbus_probe_backend
are called.


> > and xenbus_backend_init(xenbus_dev_backend.c) will fail if it
> > is not the initial domain.

Yep, but the failure in that case is normal and expected.


> > > In any case, I think anyone enabling CONFIG_XEN would expect to get the 
> > > rest of the Xen stuff by default. Or at least a basic working subset. 
> > yes, i think so.

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