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

From: Matthew Rosato
Subject: Re: [PATCH v2 1/3] vfio: Find DMA available capability
Date: Tue, 15 Sep 2020 09:57:03 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0

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.


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