Re: [Xen-devel] [PATCH] libxl: Don't insert PCI device into xenstore for HVM guests

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, May 29, 2015 at 08:59:45AM +0100, Ross Lagerwall wrote:
> When doing passthrough of a PCI device for an HVM guest, don't insert
> the device into xenstore, otherwise pciback attempts to use it which
> conflicts with QEMU.

How does it conflict?
> 
> This manifests itself such that the first time a device is passed to a
> domain, it succeeds. Subsequent attempts fail unless the device is
> unbound from pciback or the machine rebooted.

Can you be more specific please? What are the issues? Why does it
fail?

There are certain things that pciback does to "prepare" an PCI device
which QEMU also does. Some of them - such as saving the configuration
registers (And then restoring them after the device has been detached) -
is something that QEMU does not do.

> 
> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> ---
>  tools/libxl/libxl_pci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
> index e0743f8..2552889 100644
> --- a/tools/libxl/libxl_pci.c
> +++ b/tools/libxl/libxl_pci.c
> @@ -994,7 +994,7 @@ out:
>          }
>      }
>  
> -    if (!starting)
> +    if (!starting && type == LIBXL_DOMAIN_TYPE_PV)
>          rc = libxl__device_pci_add_xenstore(gc, domid, pcidev, starting);
>      else
>          rc = 0;
> -- 
> 2.1.0
> 
> 
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