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Re: [Xen-devel] [RFC] [0/4] User-space grants for Console and XenStore

To: Keir Fraser <keir@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC] [0/4] User-space grants for Console and XenStore
From: Derek Murray <Derek.Murray@xxxxxxxxxxxx>
Date: Wed, 2 May 2007 15:38:55 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, xense-devel@xxxxxxxxxxxxxxxxxxx, John Levon <levon@xxxxxxxxxxxxxxxxx>
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On 2 May 2007, at 13:46, Keir Fraser wrote:

It should be easy to support the old way and choose dynamically at run time. We should somehow tag the values passed to or stored in xenstore explicitly
as being grant-refs, at the very least.

At present, I don't store the grant-refs in xenstore, because they are constant (always 0 for xenstore, 1 for the console). I suppose I can see an argument where two different tool stacks are used with different conventions, but the same console and xenstore daemons are used. The tricky part is getting the grant references out of the domain builder without changing the interface to xc_linux_build(). Would it be reasonable to assume that the current versions of xend and libxc are consistent, and therefore the fixed grant references could be written into xenstore (from constants in the Python code) at the same time as the console and xenstore mfns are?

I would like to continue to avoid dependence on particular dom0 kernel
features, so new tool stack on old kernel (with no gnttab driver) should
really continue to work.

This should be quite simple: if the call to xc_gnttab_open() fails, it could set a flag which determines the method to be used. All that needs to be done in the mean time is to add stub functions to xc_solaris.c - I'll do that.



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