[PATCH 6/7] drm/vgem: import support

[Ben Widawsky]

dma-buf import support. The function definitely needs some cleanup.

When reading through this code, there are 3 cases to consider:
1. vgem exporter, vgem importer, same fd
2. vgem exporter, vgem importer, different fd
3. X expoter, vgem importer - not yet tested

See the comments in the code for detailed explanation.

Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Dave Airlie <airlied at redhat.com>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/vgem/vgem_dma_buf.c |  120 +++++++++++++++++++++++++++++++++++
 1 files changed, 120 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/vgem/vgem_dma_buf.c b/drivers/gpu/drm/vgem/vgem_dma_buf.c
index eca9445..92c1823 100644
--- a/drivers/gpu/drm/vgem/vgem_dma_buf.c
+++ b/drivers/gpu/drm/vgem/vgem_dma_buf.c
@@ -120,9 +120,129 @@ out_fd:
 	return 0;
 }
 
+/*
+ * Convert a dma-buf fd to a drm object handle, creating new object/handle as
+ * needed.
+ *
+ * There are 2 "interesting" cases we have to consider. The other, less interesting
+ * case is when importer == exporter, and drm_files are the same.
+ * vgem exporter
+ *   The original exporter may or may not still hold a reference to the
+ *   object by the time we reach here. Once we get a dma_buf reference though
+ *   we know the original object cannot go away. Next we grab the prime mutex
+ *   to prevent our lists from being screwed up from under us. We should next
+ *   find the object in our global dma_buf hash. To make everything cool
+ *   though we need to
+ *     create a handle for the importer
+ *     add the handle to the per file list
+ *     drop the dma_buf reference
+ *       the object can't go away due to us owning a file handle for it.
+ *   In the end there should be 2 handle references, and 1 dma-buf reference.
+ *
+ * other exporter
+ *   This case is very similar to the previous one. The primary difference is we
+ *   do not want to drop the dma_buf reference since we know nothing about the
+ *   reference counting from the exporter. So instead, we hold the dma_buf
+ *   reference, but can drop the object reference. In the end of this case there
+ *   should be 1 handle reference, and 1 dma-buf reference.
+ */
 int vgem_prime_to_handle(struct drm_device *dev,
 			 struct drm_file *file, int prime_fd,
 			 uint32_t *handle)
 {
+	struct drm_vgem_file_private *file_priv = file->driver_priv;
+	struct drm_vgem_gem_object *vobj = NULL;
+	struct drm_gem_object *obj = NULL;
+	struct dma_buf *dma_buf;
+	struct dma_buf_attachment *attach = NULL;
+	struct sg_table *sg = NULL;
+	bool drop_dma_buf_ref = false;
+	int ret;
+
+	dma_buf = dma_buf_get(prime_fd);
+	if (IS_ERR(dma_buf))
+		return PTR_ERR(dma_buf);
+
+	mutex_lock(&dev->prime_mutex);
+	/* First check that we don't dup on this file */
+	ret = drm_prime_lookup_fd_handle_mapping(&file_priv->prime, dma_buf,
+						 handle);
+	if (ret == 0) {
+		DRM_DEBUG_PRIME("file_priv has an object for this dma_buf\n");
+		dma_buf_put(dma_buf);
+		mutex_unlock(&dev->prime_mutex);
+		return 0;
+	}
+
+	/* Now check if we've already created/imported this object */
+	ret = drm_prime_lookup_obj(dev, dma_buf, &obj);
+	if (ret == 0 && obj != NULL) {
+		DRM_DEBUG_PRIME("driver has an object for this dma_buf\n");
+		drop_dma_buf_ref = true;
+		vobj = to_vgem_bo(obj);
+		goto handle_create;
+	}
+
+	DRM_DEBUG_PRIME("Creating a new object for dma_buf\n");
+
+	attach = dma_buf_attach(dma_buf, dev->dev);
+	if (IS_ERR(attach)) {
+		ret = PTR_ERR(attach);
+		goto fail_put;
+	}
+
+	sg = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
+	if (IS_ERR(sg)) {
+		ret = PTR_ERR(sg);
+		goto fail_detach;
+	}
+
+	vobj = kzalloc(sizeof(*vobj), GFP_KERNEL);
+	if (vobj == NULL) {
+		ret = -ENOMEM;
+		goto fail_unmap;
+	}
+
+	/* As a result of this mmap will not work -yet- */
+	ret = drm_gem_private_object_init(dev, &vobj->base, dma_buf->size);
+	if (ret) {
+		kfree(vobj);
+		ret = -ENOMEM;
+		goto fail_unmap;
+	}
+
+	obj = &vobj->base;
+
+handle_create:
+	ret = drm_gem_handle_create(file, obj, handle);
+	if (ret)
+		return ret;
+
+	ret = drm_prime_insert_fd_handle_mapping(&file_priv->prime,
+						 dma_buf, *handle);
+	if (ret)
+		goto fail_handle;
+
+	mutex_unlock(&dev->prime_mutex);
+
+	if (drop_dma_buf_ref) {
+		/* This should mean we found this in the global hash */
+		dma_buf_put(dma_buf);
+	} else {
+		/* Handle holds the reference for the object we created */
+		drm_gem_object_unreference(obj);
+	}
+	return 0;
+
+fail_handle:
+	drm_gem_object_handle_unreference_unlocked(obj);
+fail_unmap:
+	dma_buf_unmap_attachment(attach, sg);
+fail_detach:
+	dma_buf_detach(dma_buf, attach);
+fail_put:
+	dma_buf_put(dma_buf);
+	mutex_unlock(&dev->prime_mutex);
+
 	return 0;
 }
-- 
1.7.9.1