Re: [PATCH v2 1/3] vfio: Find DMA available capability

[Matthew Rosato]

On 9/15/20 6:33 AM, Cornelia Huck wrote:
> On Mon, 14 Sep 2020 18:29:28 -0400
> Matthew Rosato <mjrosato@linux.ibm.com> wrote:
>
> > The underlying host may be limiting the number of outstanding DMA
> > requests for type 1 IOMMU.  Add helper functions to check for the
> > DMA available capability and retrieve the current number of DMA
> > mappings allowed.
> >
> > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> > ---
> >   hw/vfio/common.c              | 37 +++++++++++++++++++++++++++++++++++++
> >   include/hw/vfio/vfio-common.h |  2 ++
> >   2 files changed, 39 insertions(+)
>
> (...)
>
> > +bool vfio_get_info_dma_avail(struct vfio_iommu_type1_info *info,
> > +                             unsigned int *avail)
> > +{
> > +    struct vfio_info_cap_header *hdr;
> > +    struct vfio_iommu_type1_info_dma_avail *cap;
> > +
> > +    /* If the capability cannot be found, assume no DMA limiting */
> > +    hdr = vfio_get_iommu_type1_info_cap(info,
> > +                                        VFIO_IOMMU_TYPE1_INFO_DMA_AVAIL);
>
> ...don't you need a headers sync first to get the new definitions?

You are right of course, though the associated header change is not yet 
merged in the kernel so it's a bit flaky.  But bottom line:  yes, we 
need a header sync first, I'll include one in v3.

> (...)