[PATCH 2/4] dma-buf: Add dma_buf_try_get()

[Wei Lin Guay <wguay@fb.com>]

From: Jason Gunthorpe <jgg@nvidia.com>

Summary:
Used to increment the refcount of the dma buf's struct file, only if the
refcount is not zero. Useful to allow the struct file's lifetime to
control the lifetime of the dmabuf while still letting the driver to keep
track of created dmabufs.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Wei Lin Guay <wguay@meta.com>
Reviewed-by: Dag Moxnes <dagmoxnes@meta.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Nic Viljoen <nviljoen@meta.com>
---
 include/linux/dma-buf.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 36216d28d8bd..9854578afecd 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -614,6 +614,19 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags);
 struct dma_buf *dma_buf_get(int fd);
 void dma_buf_put(struct dma_buf *dmabuf);

+/**
+ * dma_buf_try_get - try to get a reference on a dmabuf
+ * @dmabuf - the dmabuf to get
+ *
+ * Returns true if a reference was successfully obtained. The caller must
+ * interlock with the dmabuf's release function in some way, such as RCU, to
+ * ensure that this is not called on freed memory.
+ */
+static inline bool dma_buf_try_get(struct dma_buf *dmabuf)
+{
+	return get_file_rcu(&dmabuf->file);
+}
+
 struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
 					enum dma_data_direction);
 void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
--
2.43.5