On Wed, Mar 11, 2020 at 12:20 PM David Stevens stevensd@chromium.org wrote:

This change adds a new dma-buf operation that allows dma-bufs to be used by virtio drivers to share exported objects. The new operation allows the importing driver to query the exporting driver for the UUID which identifies the underlying exported object.

Signed-off-by: David Stevens stevensd@chromium.org

Adding Tomasz Figa, I've discussed this with him at elce last year I think. Just to make sure.

Bunch of things: - obviously we need the users of this in a few drivers, can't really review anything stand-alone - adding very specific ops to the generic interface is rather awkward, eventually everyone wants that and we end up in a mess. I think the best solution here would be if we create a struct virtio_dma_buf which subclasses dma-buf, add a (hopefully safe) runtime upcasting functions, and then a virtio_dma_buf_get_uuid() function. Just storing the uuid should be doable (assuming this doesn't change during the lifetime of the buffer), so no need for a callback. - for the runtime upcasting the usual approach is to check the ->ops pointer. Which means that would need to be the same for all virtio dma_bufs, which might get a bit awkward. But I'd really prefer we not add allocator specific stuff like this to dma-buf. -Daniel

---

drivers/dma-buf/dma-buf.c | 12 ++++++++++++ include/linux/dma-buf.h | 18 ++++++++++++++++++ 2 files changed, 30 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index d4097856c86b..fa5210ba6aaa 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -1158,6 +1158,18 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr) } EXPORT_SYMBOL_GPL(dma_buf_vunmap);

+int dma_buf_get_uuid(struct dma_buf *dmabuf, uuid_t *uuid) +{

•   if (WARN_ON(!dmabuf) || !uuid)
  

•           return -EINVAL;
  

•   if (!dmabuf->ops->get_uuid)
  

•           return -ENODEV;
  

•   return dmabuf->ops->get_uuid(dmabuf, uuid);
  

+} +EXPORT_SYMBOL_GPL(dma_buf_get_uuid);

#ifdef CONFIG_DEBUG_FS static int dma_buf_debug_show(struct seq_file *s, void *unused) { diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index abf5459a5b9d..00758523597d 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -251,6 +251,21 @@ struct dma_buf_ops {

    void *(*vmap)(struct dma_buf *);
    void (*vunmap)(struct dma_buf *, void *vaddr);

•   /**
  

•    * @get_uuid
  

•    *
  

•    * This is called by dma_buf_get_uuid to get the UUID which identifies
  

•    * the buffer to virtio devices.
  

•    *
  

•    * This callback is optional.
  

•    *
  

•    * Returns:
  

•    *
  

•    * 0 on success or a negative error code on failure. On success uuid
  

•    * will be populated with the buffer's UUID.
  

•    */
  

•   int (*get_uuid)(struct dma_buf *dmabuf, uuid_t *uuid);
  

};

/** @@ -444,4 +459,7 @@ int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *, unsigned long); void *dma_buf_vmap(struct dma_buf *); void dma_buf_vunmap(struct dma_buf *, void *vaddr);

+int dma_buf_get_uuid(struct dma_buf *dmabuf, uuid_t *uuid);

#endif /* __DMA_BUF_H__ */

2.25.1.481.gfbce0eb801-goog