On Tue, 15 Sep 2020 08:14:24 +0200
Philippe Mathieu-Daudé <phi...@redhat.com> wrote:
> Hi Matthew,
>
> On 9/15/20 12:29 AM, Matthew Rosato 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 <mjros...@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);
> > + if (hdr == NULL || avail == NULL) {
>
> If you expect the caller to use avail=NULL, then why
> return false when there is available information?
I agree; if the purpose of this function is to check if limiting is in
place and only optionally return the actual limit, we should return
true for hdr != NULL and avail == NULL.
>
> > + return false;
> > + }
> > +
> > + cap = (void *) hdr;
> > + *avail = cap->avail;
> > + return true;
> > +}
> > +
> > static int vfio_setup_region_sparse_mmaps(VFIORegion *region,
> > struct vfio_region_info *info)
> > {
(...)
