Re: [Xen-users] DomU fails to reboot with storage driver domain

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Wei Liu writes ("Re: [Xen-users] DomU fails to reboot with storage driver 
domain"):
> On Fri, Apr 01, 2016 at 01:04:42PM +0200, Roger Pau Monné wrote:
> > TBH, I don't see an easy way to solve this, I've thought about fetching 
> > the "backend" node from the xenstore frontend path of each device, but 
> > that's not safe since the guest can modify those entries.
> > 
> Interrogating frontend  is not entirely unsafe because we can validate
> that path before reading from it. There is also a backend-id field that
> we can use if that make validation easier -- no need to parse a frontend
> provided string.
> 
> Another fix is to fetch all backend domain name / domid from JSON, then
> fetch all xenstore backend entries. This is safe because JSON is not
> controlled by guest. This might require adding locks to multiple APIs,
> but luckily that wouldn't change their semantics.
>
> Ian, do you have better ideas?

Either of these two approaches sound good.

I'm not sure why using the JSON domid would need any additional
locking.  The code here already has the JSON in its hand, doesn't it ?
But using the domain _name_ rather than the domid is wrong, and I
think the JSON might have only the name.

I think the xenstore approach is probably better.  I think it may be
best to use (with checking) the frontend's backend path, since ideally
we would find the corresponding device entry directly.

But I am happy with whatever is most convenient.

I think we should fix this for 4.7 and the fix is a bugfix so OK to go
in after the freeze.

Ian.

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