RE: [Xen-devel] Re: [PATCH] Support swap a page from user spacetools -- Was RE: [RFC][PATCH] Basic support for page offline

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Keir Fraser <mailto:keir.fraser@xxxxxxxxxxxxx> wrote:
> On 20/03/2009 10:13, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:
> 
>>> Even this may not work. Old grants will reference the old page. Subsequent
>>> attempts by a backend to map the grant will fail. And the resulting failed
>>> I/Os will probably make the frontend driver throw a fit. Getting this
>>> working with suspend-cancel seems pretty tricky.
>> 
>> If there is grant map for it, I think we will fail since the reference is
>> not 1 when XENMEM_exchange. 
>> 
>> Or do you mean there is a reference in grant table but is not mapped still?
>> Will the refrence count be added when a page is granted? I'm not quite sure
>> about this, but I think that will be same to original XENMEM_exchange. If
>> yes, we may have to update the grant information?
> 
> Reference counts are not adjusted until a grant is mapped. So
> I'm talking
> about grants which have been written by the domU, passed to the backend
> driver, but not yet used. Those will be screwed.

Got it. 

> 
> Anyway, see my email just now, which suggests you map the guest's grant
> table into your toolstack code, and you can go check for
> existing grants
> yourself. As I say there -- if you do that I don't think you need worry
> about atomicity of the copy. 

Are there any method for user space to get the grant table information?

> 
> -- Keir
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