[Libvir] PATCH: Fix xen unified driver open logic

[Daniel Veillard]

On Mon, Mar 10, 2008 at 07:09:36PM +0000, Daniel P. Berrange wrote:
> When adding PolicyKit support we disabled the proxy driver, but did not
> correctly fix up the Xen unified driver. The result is that it is still
> trying to run the proxy setuid helper which doesn't exist and thus it fails
> the open operation before the remote driver gets the opportunity to process
> the URI. I attempted to fix this by just disabling the proxy driver in the
> unified driver, but came to the conclusion the logic of the current code is
> just not flexible enough for what we need to be able todo  these days.
> 
> THe core problem is the 'for(;;)' loop iterating over the drivers - it
> already has several special cases in the loop body to skip drivers, or
> ignore errors and adding more special cases is making my mind hurt trying
> to trace the logic.
> 
> So I have removed the loop, and encode the desired logic explicitly. The
> diff a little unpleasant to read, so to summarize the logic is thus:
> 
>  - If root only, try open the hypervisor driver
>          -> Failure to open is fatal, do not try other drivers

  hum, I'm not 100% sure of that, an old libvirt version might still be
able to work though xend in face of an hypervisor change it can't handle,
we had the problem for example with 0.4.0 on xen-3.2, there was side effects
but it was basically working without hypervisor access...

>  - Try to open the XenD driver
>       - If XenD suceeds
>           -> If XenD < 3.0.4, then open the XM driver for inactive domains
>           -> Try to open the XS driver
>                    => Failure to open is fatal if root
>       - Else XenD fails
>           ->.If proxy is compiled in, try to open proxy
>                 => Failure to open is fatal
> 
> 
> This should result in one of the following combinations of drivers being
> activated:
> 
>  root: (HV + XenD + XS)
>  root: (HV + XenD + XS + XM)

  root: (XenD + XS [+XM]) should still be allowed IMHO,

>  non-root: (XenD)
>  non-root: (XenD + XS)
>  non-root: (proxy)
> 
> If non-root, and the proxy is not compiled in, we'll hand off to the remote
> driver. Any other scenario will result in an explicit fail.

  okay except for the exception I sugegst to add back,

Daniel

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