[RFC PATCH 4/7] vfio: selftests: Add vfio_pci_dmabuf_create() helper

[David Matlack <dmatlack@google.com>]

Add vfio_pci_dmabuf_create() and __vfio_pci_dmabuf_create() to export a
VFIO PCI region range as a dma-buf fd via VFIO_DEVICE_FEATURE_DMA_BUF,
and preserve -errno on failure in vfio_device_feature_ioctl().

Native iommufd maps device MMIO BARs for peer-to-peer DMA via dma-buf
file descriptors rather than VM_PFNMAP virtual addresses.

Signed-off-by: David Matlack <dmatlack@google.com>
---
 .../lib/include/libvfio/vfio_pci_device.h     |  5 +++
 .../selftests/vfio/lib/vfio_pci_device.c      | 33 +++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h b/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h
index 19d458adba1a..fd130f680a2d 100644
--- a/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h
+++ b/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h
@@ -172,6 +172,11 @@ static inline bool vfio_pci_device_match(struct vfio_pci_device *device,
 bool vfio_pci_find_mem_bar(struct vfio_pci_device *device, u64 min_size,
 			   struct vfio_pci_mem_bar *mem_bar);
 
+int __vfio_pci_dmabuf_create(struct vfio_pci_device *device, u32 region_index,
+			     u64 offset, u64 length, u32 open_flags);
+int vfio_pci_dmabuf_create(struct vfio_pci_device *device, u32 region_index,
+			   u64 offset, u64 length, u32 open_flags);
+
 const char *vfio_pci_get_cdev_path(const char *bdf);
 
 void vfio_pci_group_setup(struct vfio_pci_device *device, const char *bdf);
diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
index 9840463594ab..eca6eb13d7f0 100644
--- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
+++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
@@ -153,11 +153,44 @@ static int vfio_device_feature_ioctl(int fd, u32 flags, void *data,
 	feature->flags = flags;
 
 	ret = ioctl(fd, VFIO_DEVICE_FEATURE, feature);
+	if (ret < 0)
+		ret = -errno;
 	free(feature);
 
 	return ret;
 }
 
+int __vfio_pci_dmabuf_create(struct vfio_pci_device *device, u32 region_index,
+			     u64 offset, u64 length, u32 open_flags)
+{
+	u8 buf[sizeof(struct vfio_device_feature_dma_buf) +
+	       sizeof(struct vfio_region_dma_range)] = {};
+	struct vfio_device_feature_dma_buf *dma_buf = (void *)buf;
+
+	dma_buf->region_index = region_index;
+	dma_buf->open_flags = open_flags;
+	dma_buf->nr_ranges = 1;
+	dma_buf->dma_ranges[0].offset = offset;
+	dma_buf->dma_ranges[0].length = length;
+
+	return vfio_device_feature_ioctl(device->fd,
+					 VFIO_DEVICE_FEATURE_GET |
+					 VFIO_DEVICE_FEATURE_DMA_BUF,
+					 buf, sizeof(buf));
+}
+
+int vfio_pci_dmabuf_create(struct vfio_pci_device *device, u32 region_index,
+			   u64 offset, u64 length, u32 open_flags)
+{
+	int fd;
+
+	fd = __vfio_pci_dmabuf_create(device, region_index, offset, length,
+				      open_flags);
+	VFIO_ASSERT_GE(fd, 0, "VFIO_DEVICE_FEATURE_DMA_BUF failed: %d\n", fd);
+
+	return fd;
+}
+
 static void vfio_device_feature_set(int fd, u16 feature, void *data, size_t data_size)
 {
 	u32 flags = VFIO_DEVICE_FEATURE_SET | feature;
-- 
2.56.0.567.gdb80ae8cd5-goog