[RFC v2 3/8] dma-buf/sync_file: add sync_file_fences_get()

[Gustavo Padovan <gustavo@padovan.org>]

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Creates a function that given an sync file descriptor returns a
fence_collection containing all fences in the sync_file.

If there is only one fence in the sync_file this fence itself is returned,
however if there is more than one, a fence_collection fence is returned.

v2: Comments by Daniel Vetter
	- Adapt to new version of fence_collection_init()
	- Hold a reference for the fence we return

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 drivers/dma-buf/sync_file.c | 60 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/sync_file.h   |  3 +++
 2 files changed, 63 insertions(+)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 40ee098..5dd76c0 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -23,6 +23,7 @@
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <linux/anon_inodes.h>
+#include <linux/fence-collection.h>
 #include <linux/sync_file.h>
 #include <uapi/linux/sync_file.h>
 
@@ -147,6 +148,62 @@ void sync_file_install(struct sync_file *sync_file, int fd)
 }
 EXPORT_SYMBOL(sync_file_install);
 
+/**
+ * sync_file_fences_get - get the fence(s) related to the sync_file fd
+ * @fd:		sync_file fd to get the fence(s) from
+ *
+ * Ensures @fd references a valid sync_file and returns a fence that
+ * represents all fence in the sync_file.
+ *
+ * If there is only one fence in the sync_file, this fence is returned.
+ * If there is more than one, a fence_collection containing all fences
+ * is created and its base fence object is returned.
+ * On both cases a reference to the returned fence is held. On error
+ * NULL is returned.
+ */
+struct fence *sync_file_fences_get(int fd)
+{
+	struct sync_file *sync_file;
+	struct fence_collection *collection;
+	struct fence_collection_cb *cb;
+	int i;
+
+	sync_file = sync_file_fdget(fd);
+	if (!sync_file)
+		return NULL;
+
+	if (sync_file->num_fences == 1) {
+		struct fence *fence = sync_file->cbs[0].fence;
+
+		fence_get(fence);
+		sync_file_put(sync_file);
+		return fence;
+	}
+
+	cb = kcalloc(sync_file->num_fences, sizeof(*cb), GFP_KERNEL);
+	if (!cb) {
+		sync_file_put(sync_file);
+		return NULL;
+	}
+
+	for (i = 0 ; i < sync_file->num_fences ; i++)
+		cb[i].fence = sync_file->cbs[i].fence;
+
+	collection = fence_collection_create(sync_file->num_fences, cb);
+	if (!collection) {
+		kfree(cb);
+		sync_file_put(sync_file);
+		return NULL;
+	}
+
+	sync_file->collection = collection;
+	fence_get(&collection->base);
+	sync_file_put(sync_file);
+
+	return &collection->base;
+}
+EXPORT_SYMBOL(sync_file_fences_get);
+
 static void sync_file_add_pt(struct sync_file *sync_file, int *i,
 			     struct fence *fence)
 {
@@ -234,6 +291,9 @@ static void sync_file_free(struct kref *kref)
 						     kref);
 	int i;
 
+	if (sync_file->collection)
+		fence_put(&sync_file->collection->base);
+
 	for (i = 0; i < sync_file->num_fences; ++i) {
 		fence_remove_callback(sync_file->cbs[i].fence,
 				      &sync_file->cbs[i].cb);
diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
index 900fa0c..3eb3aad 100644
--- a/include/linux/sync_file.h
+++ b/include/linux/sync_file.h
@@ -35,6 +35,7 @@ struct sync_file_cb {
  * @num_fences:		number of sync_pts in the fence
  * @wq:			wait queue for fence signaling
  * @status:		0: signaled, >0:active, <0: error
+ * @collection:		collection with the fences in the sync_file
  * @cbs:		sync_pts callback information
  */
 struct sync_file {
@@ -49,6 +50,7 @@ struct sync_file {
 	wait_queue_head_t	wq;
 	atomic_t		status;
 
+	struct fence_collection *collection;
 	struct sync_file_cb	cbs[];
 };
 
@@ -59,4 +61,5 @@ void sync_file_install(struct sync_file *sync_file, int fd);
 struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 				  struct sync_file *b);
 
+struct fence *sync_file_fences_get(int fd);
 #endif /* _LINUX_SYNC_H */
-- 
2.5.5