Re: [PATCH v2 5/7] vfio: Use new interfaces for MSI/MSI-X enablement

Alex Williamson
2014-01-08T13:45:53Z

On Wed, 2014-01-08 at 08:57 +0100, Alexander Gordeev wrote:
> Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
> ---
> drivers/vfio/pci/vfio_pci_intrs.c | 8 ++++----
> 1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> index 641bc87..66d1746 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -482,15 +482,15 @@ static int vfio_msi_enable(struct vfio_pci_device *vdev, int nvec, bool msix)
> for (i = 0; i < nvec; i++)
> vdev->msix[i].entry = i;
>
> - ret = pci_enable_msix(pdev, vdev->msix, nvec);
> - if (ret) {
> + ret = pci_enable_msix_range(pdev, vdev->msix, nvec, nvec);
> + if (ret < 0) {
> kfree(vdev->msix);
> kfree(vdev->ctx);
> return ret;
> }
> } else {
> - ret = pci_enable_msi_block(pdev, nvec);
> - if (ret) {
> + ret = pci_enable_msi_range(pdev, nvec, nvec);
> + if (ret < 0) {
> kfree(vdev->ctx);
> return ret;
> }

Based on your description, this is a user visible API change. We now
return success so long as we allocated at least a single vector and the
user has no way to know that they didn't get all the vectors they
requested. That's unacceptable, userspace expects the old API - setup
the requested vectors or setup none and tell me how many to retry with.
To maintain the same API exposed to userspace, I'd think we need
something like:

if (ret != nvec) {
if (ret > 0)
pci_disable...
kfree(...
kfree(...
return ret;
}

Thanks,
Alex