Re: [PATCH v9 06/12] vfio_pci: Update vfio_pci to use vfio_info_add_capability()

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 25 Oct 2016 02:52:39 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> On 10/21/2016 12:54 AM, Alex Williamson wrote:
> > On Tue, 18 Oct 2016 02:52:06 +0530
> > Kirti Wankhede <kwankhede@nvidia.com> wrote:
> >   
> >> Update msix_sparse_mmap_cap() to use vfio_info_add_capability()
> >> Update region type capability to use vfio_info_add_capability()
> >> Can't split this commit for MSIx and region_type cap since there is a
> >> common code which need to be updated for both the cases.
> >>
> >> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> >> Signed-off-by: Neo Jia <cjia@nvidia.com>
> >> Change-Id: I52bb28c7875a6da5a79ddad1843e6088aff58a45
> >> ---
> >>  drivers/vfio/pci/vfio_pci.c | 72 +++++++++++++++++----------------------------
> >>  1 file changed, 27 insertions(+), 45 deletions(-)
> >>
> >> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> >> index d624a527777f..1ec0565b48ea 100644
> >> --- a/drivers/vfio/pci/vfio_pci.c
> >> +++ b/drivers/vfio/pci/vfio_pci.c
> >> @@ -556,12 +556,12 @@ static int vfio_pci_for_each_slot_or_bus(struct pci_dev *pdev,
> >>  }
> >>  
> >>  static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev,
> >> +				struct vfio_region_info *info,
> >>  				struct vfio_info_cap *caps)
> >>  {
> >> -	struct vfio_info_cap_header *header;
> >>  	struct vfio_region_info_cap_sparse_mmap *sparse;
> >>  	size_t end, size;
> >> -	int nr_areas = 2, i = 0;
> >> +	int nr_areas = 2, i = 0, ret;
> >>  
> >>  	end = pci_resource_len(vdev->pdev, vdev->msix_bar);
> >>  
> >> @@ -572,13 +572,10 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev,
> >>  
> >>  	size = sizeof(*sparse) + (nr_areas * sizeof(*sparse->areas));
> >>  
> >> -	header = vfio_info_cap_add(caps, size,
> >> -				   VFIO_REGION_INFO_CAP_SPARSE_MMAP, 1);
> >> -	if (IS_ERR(header))
> >> -		return PTR_ERR(header);
> >> +	sparse = kzalloc(size, GFP_KERNEL);
> >> +	if (!sparse)
> >> +		return -ENOMEM;
> >>  
> >> -	sparse = container_of(header,
> >> -			      struct vfio_region_info_cap_sparse_mmap, header);
> >>  	sparse->nr_areas = nr_areas;
> >>  
> >>  	if (vdev->msix_offset & PAGE_MASK) {
> >> @@ -594,26 +591,11 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev,
> >>  		i++;
> >>  	}
> >>  
> >> -	return 0;
> >> -}
> >> -
> >> -static int region_type_cap(struct vfio_pci_device *vdev,
> >> -			   struct vfio_info_cap *caps,
> >> -			   unsigned int type, unsigned int subtype)
> >> -{
> >> -	struct vfio_info_cap_header *header;
> >> -	struct vfio_region_info_cap_type *cap;
> >> -
> >> -	header = vfio_info_cap_add(caps, sizeof(*cap),
> >> -				   VFIO_REGION_INFO_CAP_TYPE, 1);
> >> -	if (IS_ERR(header))
> >> -		return PTR_ERR(header);
> >> +	ret = vfio_info_add_capability(info, caps,
> >> +				      VFIO_REGION_INFO_CAP_SPARSE_MMAP, sparse);
> >> +	kfree(sparse);
> >>  
> >> -	cap = container_of(header, struct vfio_region_info_cap_type, header);
> >> -	cap->type = type;
> >> -	cap->subtype = subtype;
> >> -
> >> -	return 0;
> >> +	return ret;
> >>  }
> >>  
> >>  int vfio_pci_register_dev_region(struct vfio_pci_device *vdev,
> >> @@ -704,7 +686,8 @@ static long vfio_pci_ioctl(void *device_data,
> >>  			if (vdev->bar_mmap_supported[info.index]) {
> >>  				info.flags |= VFIO_REGION_INFO_FLAG_MMAP;
> >>  				if (info.index == vdev->msix_bar) {
> >> -					ret = msix_sparse_mmap_cap(vdev, &caps);
> >> +					ret = msix_sparse_mmap_cap(vdev, &info,
> >> +								   &caps);
> >>  					if (ret)
> >>  						return ret;
> >>  				}
> >> @@ -752,6 +735,9 @@ static long vfio_pci_ioctl(void *device_data,
> >>  
> >>  			break;
> >>  		default:
> >> +		{
> >> +			struct vfio_region_info_cap_type cap_type;
> >> +
> >>  			if (info.index >=
> >>  			    VFIO_PCI_NUM_REGIONS + vdev->num_regions)
> >>  				return -EINVAL;
> >> @@ -762,27 +748,23 @@ static long vfio_pci_ioctl(void *device_data,
> >>  			info.size = vdev->region[i].size;
> >>  			info.flags = vdev->region[i].flags;
> >>  
> >> -			ret = region_type_cap(vdev, &caps,
> >> -					      vdev->region[i].type,
> >> -					      vdev->region[i].subtype);
> >> +			cap_type.type = vdev->region[i].type;
> >> +			cap_type.subtype = vdev->region[i].subtype;
> >> +
> >> +			ret = vfio_info_add_capability(&info, &caps,
> >> +						      VFIO_REGION_INFO_CAP_TYPE,
> >> +						      &cap_type);
> >>  			if (ret)
> >>  				return ret;
> >> +
> >> +		}
> >>  		}
> >>  
> >> -		if (caps.size) {
> >> -			info.flags |= VFIO_REGION_INFO_FLAG_CAPS;
> >> -			if (info.argsz < sizeof(info) + caps.size) {
> >> -				info.argsz = sizeof(info) + caps.size;
> >> -				info.cap_offset = 0;
> >> -			} else {
> >> -				vfio_info_cap_shift(&caps, sizeof(info));
> >> -				if (copy_to_user((void __user *)arg +
> >> -						  sizeof(info), caps.buf,
> >> -						  caps.size)) {
> >> -					kfree(caps.buf);
> >> -					return -EFAULT;
> >> -				}
> >> -				info.cap_offset = sizeof(info);  
> > 
> > I prefer the case above, I'm fine with breaking out helpers to build a
> > buffer containing the capability chain, but I would rather have the
> > caller manage placing that back into the return structure.  That also
> > allows the helper to be independent of the structure we're operating
> > on, it could be a region_info, irq_info, device_info, etc.  It only
> > needs to know the layout of the capability type we're trying to add,
> > not the info structure itself.  Thanks,
> >   
> 
> The capability feature is for region_info (VFIO_REGION_INFO_FLAG_CAPS),
> then structure we are operating couldn't be irq_info or device_info, right?

My point was that I prefer the caller managing region_info.flags and
region_info.cap_offset, the helper only managing creating the
capability chain within the buffer.  There is a namespace conflict for
the various capabilities though, each foo_info has their own space,
which can conflict, which make make a common helper impractical.
Thanks,

Alex