[libvirt] [PATCH] qemu: Fix mdev checking for VFIO support

[Daniel P. Berrange]

On Wed, Apr 12, 2017 at 12:26:35PM +0200, Erik Skultety wrote:
> Commit a4a39d90 added a check that checks for VFIO support with mediated
> devices. The problem is that the hostdev preparing functions behave like
> a fallthrough if device of that specific type doesn't exist. However,
> the check for VFIO support was independent of the existence of a mdev
> device which caused the guest to fail to start with any device to be
> directly assigned if VFIO was disabled/unavailable in the kernel.
> The proposed change first ensures that it makes sense to check for VFIO
> support in the first place, and only then performs the VFIO support check
> itself.
> 
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1441291
> 
> Signed-off-by: Erik Skultety <eskultet at redhat.com>
> ---
>  src/qemu/qemu_hostdev.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/src/qemu/qemu_hostdev.c b/src/qemu/qemu_hostdev.c
> index 685bf5b59..9b5504832 100644
> --- a/src/qemu/qemu_hostdev.c
> +++ b/src/qemu/qemu_hostdev.c
> @@ -330,11 +330,19 @@ qemuHostdevPrepareMediatedDevices(virQEMUDriverPtr driver,
>                                    int nhostdevs)
>  {
>      virHostdevManagerPtr hostdev_mgr = driver->hostdevMgr;
> +    bool supportsVFIO = qemuHostdevHostSupportsPassthroughVFIO();
> +    size_t i;
>  
> -    if (!qemuHostdevHostSupportsPassthroughVFIO()) {
> -        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> -                       _("host doesn't support VFIO PCI interface"));
> -        return -1;
> +    for (i = 0; i < nhostdevs; i++) {
> +        if (hostdevs[i]->mode == VIR_DOMAIN_HOSTDEV_MODE_SUBSYS &&
> +            hostdevs[i]->source.subsys.type == VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_MDEV) {
> +            if (!supportsVFIO) {
> +                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                               _("host doesn't support VFIO PCI interface"));

BTW, I'd suggest changing that message to

  "Mediated host device assignment requires VFIO support"

to make it clear what feature usage is triggering the error

> +                return -1;
> +            }
> +            break;
> +        }
>      }
>  
>      return virHostdevPrepareMediatedDevices(hostdev_mgr, QEMU_DRIVER_NAME,

ACK,

Regards,
Daniel
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