[PATCH v3 0/4] dma-buf/sync_file: rework fences on struct sync_file

[PATCH v3 0/4] dma-buf/sync_file: rework fences on struct sync_file

[Gustavo Padovan]

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

Hi all,

This patchset improves fence support on Sync File. The basic idea
is to have only sync_file->fence and store all fences there, either as
normal fences or fence_arrays. That way we can remove some potential
duplication when using fence_array with sync_file: the duplication of the array
of fences and the duplication of fence_add_callback() for all fences.

Now when creating a new sync_file during the merge process sync_file_set_fence()
will set sync_file->fence based on the number of fences for that sync_file. If
there is more than one fence a fence_array is created. One important advantage
approach is that we only add one fence callback now, no matter how many fences
there are in a sync_file - the individual callbacks are added by fence_array.

This patchset also adds sync_file_get_fence() to retrieve fence from a sync_file
file descriptor.

Please review! Thanks!

        Gustavo

---
Changes sunce PATCH v2 (Coments from Chris Wilson)
 - fix checkpatch warnings
 - use fence_get() to set the fence directly

Changes since PATCH v1 (Comments from Chris Wilson)
 - use sizeof(*fence) to reallocate array
 - fix typo in comments
 - protect num_fences sum against overflows
 - use array->base instead of casting the to struct fence
 - remove ternary if from ops comparison in fence_is_array()
 - add EXPORT_SYMBOL(fence_array_ops)

Changes since RFC v2 (Comments from Chris Wilson and Christian König):
 - struct sync_file lost status member in favor of fence_is_signaled()
 - drop use of fence_array_teardown()
 - use sizeof(*fence) to allocate only an array on fence pointers

Changes since RFC v1 (Comments from Chris Wilson and Christian König):
 - Not using fence_ops anymore.
 - fence_is_array() was created to differentiate fence from fence_array
 - fence_array_teardown() is now exported and used under fence_is_array()
 - struct sync_file lost num_fences member

Gustavo Padovan (4):
  dma-buf/fence-array: add fence_is_array()
  dma-buf/sync_file: rework fence storage in struct file
  dma-buf/sync_file: add sync_file_get_fence()
  Documentation: add doc for sync_file_get_fence()


Gustavo Padovan (4):
  dma-buf/fence-array: add fence_is_array()
  dma-buf/sync_file: rework fence storage in struct file
  dma-buf/sync_file: add sync_file_get_fence()
  Documentation: add doc for sync_file_get_fence()

 Documentation/sync_file.txt          |  15 +++
 drivers/dma-buf/fence-array.c        |   1 +
 drivers/dma-buf/sync_file.c          | 192 ++++++++++++++++++++++++-----------
 drivers/staging/android/sync_debug.c |  12 ++-
 include/linux/fence-array.h          |  10 ++
 include/linux/sync_file.h            |  18 ++--
 6 files changed, 174 insertions(+), 74 deletions(-)

-- 
2.5.5

[PATCH v3 1/4] dma-buf/fence-array: add fence_is_array()

[Gustavo Padovan]

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

Add helper to check if fence is array.

v2: Comments from Chris Wilson
	- remove ternary if from ops comparison
	- add EXPORT_SYMBOL(fence_array_ops)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/dma-buf/fence-array.c |  1 +
 include/linux/fence-array.h   | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/drivers/dma-buf/fence-array.c b/drivers/dma-buf/fence-array.c
index a8731c8..ee50022 100644
--- a/drivers/dma-buf/fence-array.c
+++ b/drivers/dma-buf/fence-array.c
@@ -99,6 +99,7 @@ const struct fence_ops fence_array_ops = {
 	.wait = fence_default_wait,
 	.release = fence_array_release,
 };
+EXPORT_SYMBOL(fence_array_ops);
 
 /**
  * fence_array_create - Create a custom fence array
diff --git a/include/linux/fence-array.h b/include/linux/fence-array.h
index 86baaa4..a44794e 100644
--- a/include/linux/fence-array.h
+++ b/include/linux/fence-array.h
@@ -52,6 +52,16 @@ struct fence_array {
 extern const struct fence_ops fence_array_ops;
 
 /**
+ * fence_is_array - check if a fence is from the array subsclass
+ *
+ * Return true if it is a fence_array and false otherwise.
+ */
+static inline bool fence_is_array(struct fence *fence)
+{
+	return fence->ops == &fence_array_ops;
+}
+
+/**
  * to_fence_array - cast a fence to a fence_array
  * @fence: fence to cast to a fence_array
  *
-- 
2.5.5

Re: [PATCH v3 1/4] dma-buf/fence-array: add fence_is_array()

[Christian König]

Am 05.07.2016 um 01:57 schrieb Gustavo Padovan:
> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
>
> Add helper to check if fence is array.
>
> v2: Comments from Chris Wilson
> 	- remove ternary if from ops comparison
> 	- add EXPORT_SYMBOL(fence_array_ops)
>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

For this patch Reviewed-by: Christian König <christian.koenig@amd.com>.

I'm not deep enough into the sync file code to fully judge, but the 
remaining patches look good to me as well.

So for patch #2-#4 Acked-by: Christian König <christian.koenig@amd.com>.

Regards,
Christian.

> ---
>   drivers/dma-buf/fence-array.c |  1 +
>   include/linux/fence-array.h   | 10 ++++++++++
>   2 files changed, 11 insertions(+)
>
> diff --git a/drivers/dma-buf/fence-array.c b/drivers/dma-buf/fence-array.c
> index a8731c8..ee50022 100644
> --- a/drivers/dma-buf/fence-array.c
> +++ b/drivers/dma-buf/fence-array.c
> @@ -99,6 +99,7 @@ const struct fence_ops fence_array_ops = {
>   	.wait = fence_default_wait,
>   	.release = fence_array_release,
>   };
> +EXPORT_SYMBOL(fence_array_ops);
>   
>   /**
>    * fence_array_create - Create a custom fence array
> diff --git a/include/linux/fence-array.h b/include/linux/fence-array.h
> index 86baaa4..a44794e 100644
> --- a/include/linux/fence-array.h
> +++ b/include/linux/fence-array.h
> @@ -52,6 +52,16 @@ struct fence_array {
>   extern const struct fence_ops fence_array_ops;
>   
>   /**
> + * fence_is_array - check if a fence is from the array subsclass
> + *
> + * Return true if it is a fence_array and false otherwise.
> + */
> +static inline bool fence_is_array(struct fence *fence)
> +{
> +	return fence->ops == &fence_array_ops;
> +}
> +
> +/**
>    * to_fence_array - cast a fence to a fence_array
>    * @fence: fence to cast to a fence_array
>    *

[PATCH v3 2/4] dma-buf/sync_file: rework fence storage in struct file

[Gustavo Padovan]

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

Create sync_file->fence to abstract the type of fence we are using for
each sync_file. If only one fence is present we use a normal struct fence
but if there is more fences to be added to the sync_file a fence_array
is created.

This change cleans up sync_file a bit. We don't need to have sync_file_cb
array anymore. Instead, as we always have  one fence, only one fence
callback is registered per sync_file.

v4: fixes checkpatch warnings

v4: Comments from Chris Wilson
	- use sizeof(*fence) to reallocate array
	- fix typo in comments
	- protect num_fences sum against overflows
	- use array->base instead of casting the to struct fence

v3: Comments from Chris Wilson and Christian König
	- struct sync_file lost status member in favor of fence_is_signaled()
	- drop use of fence_array_teardown()
	- use sizeof(*fence) to allocate only an array on fence pointers

v2: Comments from Chris Wilson and Christian König
	- Not using fence_ops anymore
	- fence_is_array() was created to differentiate fence from fence_array
	- fence_array_teardown() is now exported and used under fence_is_array()
	- struct sync_file lost num_fences member

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/dma-buf/sync_file.c          | 169 +++++++++++++++++++++++------------
 drivers/staging/android/sync_debug.c |  12 ++-
 include/linux/sync_file.h            |  17 ++--
 3 files changed, 124 insertions(+), 74 deletions(-)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 9aaa608..a223f48 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -28,11 +28,11 @@
 
 static const struct file_operations sync_file_fops;
 
-static struct sync_file *sync_file_alloc(int size)
+static struct sync_file *sync_file_alloc(void)
 {
 	struct sync_file *sync_file;
 
-	sync_file = kzalloc(size, GFP_KERNEL);
+	sync_file = kzalloc(sizeof(*sync_file), GFP_KERNEL);
 	if (!sync_file)
 		return NULL;
 
@@ -45,6 +45,8 @@ static struct sync_file *sync_file_alloc(int size)
 
 	init_waitqueue_head(&sync_file->wq);
 
+	INIT_LIST_HEAD(&sync_file->cb.node);
+
 	return sync_file;
 
 err:
@@ -54,14 +56,11 @@ err:
 
 static void fence_check_cb_func(struct fence *f, struct fence_cb *cb)
 {
-	struct sync_file_cb *check;
 	struct sync_file *sync_file;
 
-	check = container_of(cb, struct sync_file_cb, cb);
-	sync_file = check->sync_file;
+	sync_file = container_of(cb, struct sync_file, cb);
 
-	if (atomic_dec_and_test(&sync_file->status))
-		wake_up_all(&sync_file->wq);
+	wake_up_all(&sync_file->wq);
 }
 
 /**
@@ -76,22 +75,18 @@ struct sync_file *sync_file_create(struct fence *fence)
 {
 	struct sync_file *sync_file;
 
-	sync_file = sync_file_alloc(offsetof(struct sync_file, cbs[1]));
+	sync_file = sync_file_alloc();
 	if (!sync_file)
 		return NULL;
 
-	sync_file->num_fences = 1;
-	atomic_set(&sync_file->status, 1);
+	sync_file->fence = fence;
+
 	snprintf(sync_file->name, sizeof(sync_file->name), "%s-%s%llu-%d",
 		 fence->ops->get_driver_name(fence),
 		 fence->ops->get_timeline_name(fence), fence->context,
 		 fence->seqno);
 
-	sync_file->cbs[0].fence = fence;
-	sync_file->cbs[0].sync_file = sync_file;
-	if (fence_add_callback(fence, &sync_file->cbs[0].cb,
-			       fence_check_cb_func))
-		atomic_dec(&sync_file->status);
+	fence_add_callback(fence, &sync_file->cb, fence_check_cb_func);
 
 	return sync_file;
 }
@@ -121,14 +116,49 @@ err:
 	return NULL;
 }
 
-static void sync_file_add_pt(struct sync_file *sync_file, int *i,
-			     struct fence *fence)
+static int sync_file_set_fence(struct sync_file *sync_file,
+			       struct fence **fences, int num_fences)
+{
+	struct fence_array *array;
+
+	/*
+	 * The reference for the fences in the new sync_file and held
+	 * in add_fence() during the merge procedure, so for num_fences == 1
+	 * we already own a new reference to the fence. For num_fence > 1
+	 * we own the reference of the fence_array creation.
+	 */
+	if (num_fences == 1) {
+		sync_file->fence = fences[0];
+	} else {
+		array = fence_array_create(num_fences, fences,
+					   fence_context_alloc(1), 1, false);
+		if (!array)
+			return -ENOMEM;
+
+		sync_file->fence = &array->base;
+	}
+
+	return 0;
+}
+
+static struct fence **get_fences(struct sync_file *sync_file, int *num_fences)
 {
-	sync_file->cbs[*i].fence = fence;
-	sync_file->cbs[*i].sync_file = sync_file;
+	if (fence_is_array(sync_file->fence)) {
+		struct fence_array *array = to_fence_array(sync_file->fence);
 
-	if (!fence_add_callback(fence, &sync_file->cbs[*i].cb,
-				fence_check_cb_func)) {
+		*num_fences = array->num_fences;
+		return array->fences;
+	}
+
+	*num_fences = 1;
+	return &sync_file->fence;
+}
+
+static void add_fence(struct fence **fences, int *i, struct fence *fence)
+{
+	fences[*i] = fence;
+
+	if (!fence_is_signaled(fence)) {
 		fence_get(fence);
 		(*i)++;
 	}
@@ -147,16 +177,24 @@ static void sync_file_add_pt(struct sync_file *sync_file, int *i,
 static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 					 struct sync_file *b)
 {
-	int num_fences = a->num_fences + b->num_fences;
 	struct sync_file *sync_file;
-	int i, i_a, i_b;
-	unsigned long size = offsetof(struct sync_file, cbs[num_fences]);
+	struct fence **fences, **nfences, **a_fences, **b_fences;
+	int i, i_a, i_b, num_fences, a_num_fences, b_num_fences;
 
-	sync_file = sync_file_alloc(size);
+	sync_file = sync_file_alloc();
 	if (!sync_file)
 		return NULL;
 
-	atomic_set(&sync_file->status, num_fences);
+	a_fences = get_fences(a, &a_num_fences);
+	b_fences = get_fences(b, &b_num_fences);
+	if (a_num_fences > INT_MAX - b_num_fences)
+		return NULL;
+
+	num_fences = a_num_fences + b_num_fences;
+
+	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
+	if (!fences)
+		goto err;
 
 	/*
 	 * Assume sync_file a and b are both ordered and have no
@@ -165,55 +203,68 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 	 * If a sync_file can only be created with sync_file_merge
 	 * and sync_file_create, this is a reasonable assumption.
 	 */
-	for (i = i_a = i_b = 0; i_a < a->num_fences && i_b < b->num_fences; ) {
-		struct fence *pt_a = a->cbs[i_a].fence;
-		struct fence *pt_b = b->cbs[i_b].fence;
+	for (i = i_a = i_b = 0; i_a < a_num_fences && i_b < b_num_fences; ) {
+		struct fence *pt_a = a_fences[i_a];
+		struct fence *pt_b = b_fences[i_b];
 
 		if (pt_a->context < pt_b->context) {
-			sync_file_add_pt(sync_file, &i, pt_a);
+			add_fence(fences, &i, pt_a);
 
 			i_a++;
 		} else if (pt_a->context > pt_b->context) {
-			sync_file_add_pt(sync_file, &i, pt_b);
+			add_fence(fences, &i, pt_b);
 
 			i_b++;
 		} else {
 			if (pt_a->seqno - pt_b->seqno <= INT_MAX)
-				sync_file_add_pt(sync_file, &i, pt_a);
+				add_fence(fences, &i, pt_a);
 			else
-				sync_file_add_pt(sync_file, &i, pt_b);
+				add_fence(fences, &i, pt_b);
 
 			i_a++;
 			i_b++;
 		}
 	}
 
-	for (; i_a < a->num_fences; i_a++)
-		sync_file_add_pt(sync_file, &i, a->cbs[i_a].fence);
+	for (; i_a < a_num_fences; i_a++)
+		add_fence(fences, &i, a_fences[i_a]);
+
+	for (; i_b < b_num_fences; i_b++)
+		add_fence(fences, &i, b_fences[i_b]);
+
+	if (num_fences > i) {
+		nfences = krealloc(fences, i * sizeof(*fences),
+				  GFP_KERNEL);
+		if (!nfences)
+			goto err;
 
-	for (; i_b < b->num_fences; i_b++)
-		sync_file_add_pt(sync_file, &i, b->cbs[i_b].fence);
+		fences = nfences;
+	}
+
+	if (sync_file_set_fence(sync_file, fences, i) < 0) {
+		kfree(fences);
+		goto err;
+	}
 
-	if (num_fences > i)
-		atomic_sub(num_fences - i, &sync_file->status);
-	sync_file->num_fences = i;
+	fence_add_callback(sync_file->fence, &sync_file->cb,
+			   fence_check_cb_func);
 
 	strlcpy(sync_file->name, name, sizeof(sync_file->name));
 	return sync_file;
+
+err:
+	fput(sync_file->file);
+	return NULL;
+
 }
 
 static void sync_file_free(struct kref *kref)
 {
 	struct sync_file *sync_file = container_of(kref, struct sync_file,
 						     kref);
-	int i;
-
-	for (i = 0; i < sync_file->num_fences; ++i) {
-		fence_remove_callback(sync_file->cbs[i].fence,
-				      &sync_file->cbs[i].cb);
-		fence_put(sync_file->cbs[i].fence);
-	}
 
+	fence_remove_callback(sync_file->fence, &sync_file->cb);
+	fence_put(sync_file->fence);
 	kfree(sync_file);
 }
 
@@ -232,9 +283,9 @@ static unsigned int sync_file_poll(struct file *file, poll_table *wait)
 
 	poll_wait(file, &sync_file->wq, wait);
 
-	status = atomic_read(&sync_file->status);
+	status = fence_is_signaled(sync_file->fence);
 
-	if (!status)
+	if (status)
 		return POLLIN;
 	if (status < 0)
 		return POLLERR;
@@ -315,8 +366,9 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 {
 	struct sync_file_info info;
 	struct sync_fence_info *fence_info = NULL;
+	struct fence **fences;
 	__u32 size;
-	int ret, i;
+	int num_fences, ret, i;
 
 	if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
 		return -EFAULT;
@@ -324,6 +376,8 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	if (info.flags || info.pad)
 		return -EINVAL;
 
+	fences = get_fences(sync_file, &num_fences);
+
 	/*
 	 * Passing num_fences = 0 means that userspace doesn't want to
 	 * retrieve any sync_fence_info. If num_fences = 0 we skip filling
@@ -333,16 +387,16 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	if (!info.num_fences)
 		goto no_fences;
 
-	if (info.num_fences < sync_file->num_fences)
+	if (info.num_fences < num_fences)
 		return -EINVAL;
 
-	size = sync_file->num_fences * sizeof(*fence_info);
+	size = num_fences * sizeof(*fence_info);
 	fence_info = kzalloc(size, GFP_KERNEL);
 	if (!fence_info)
 		return -ENOMEM;
 
-	for (i = 0; i < sync_file->num_fences; ++i)
-		sync_fill_fence_info(sync_file->cbs[i].fence, &fence_info[i]);
+	for (i = 0; i < num_fences; i++)
+		sync_fill_fence_info(fences[i], &fence_info[i]);
 
 	if (copy_to_user(u64_to_user_ptr(info.sync_fence_info), fence_info,
 			 size)) {
@@ -352,11 +406,8 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 
 no_fences:
 	strlcpy(info.name, sync_file->name, sizeof(info.name));
-	info.status = atomic_read(&sync_file->status);
-	if (info.status >= 0)
-		info.status = !info.status;
-
-	info.num_fences = sync_file->num_fences;
+	info.status = fence_is_signaled(sync_file->fence);
+	info.num_fences = num_fences;
 
 	if (copy_to_user((void __user *)arg, &info, sizeof(info)))
 		ret = -EFAULT;
diff --git a/drivers/staging/android/sync_debug.c b/drivers/staging/android/sync_debug.c
index 5f57499..e07958c 100644
--- a/drivers/staging/android/sync_debug.c
+++ b/drivers/staging/android/sync_debug.c
@@ -159,10 +159,16 @@ static void sync_print_sync_file(struct seq_file *s,
 	int i;
 
 	seq_printf(s, "[%p] %s: %s\n", sync_file, sync_file->name,
-		   sync_status_str(atomic_read(&sync_file->status)));
+		   sync_status_str(!fence_is_signaled(sync_file->fence)));
 
-	for (i = 0; i < sync_file->num_fences; ++i)
-		sync_print_fence(s, sync_file->cbs[i].fence, true);
+	if (fence_is_array(sync_file->fence)) {
+		struct fence_array *array = to_fence_array(sync_file->fence);
+
+		for (i = 0; i < array->num_fences; ++i)
+			sync_print_fence(s, array->fences[i], true);
+	} else {
+		sync_print_fence(s, sync_file->fence, true);
+	}
 }
 
 static int sync_debugfs_show(struct seq_file *s, void *unused)
diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
index c6ffe8b..2efc5ec 100644
--- a/include/linux/sync_file.h
+++ b/include/linux/sync_file.h
@@ -19,12 +19,7 @@
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/fence.h>
-
-struct sync_file_cb {
-	struct fence_cb cb;
-	struct fence *fence;
-	struct sync_file *sync_file;
-};
+#include <linux/fence-array.h>
 
 /**
  * struct sync_file - sync file to export to the userspace
@@ -32,10 +27,9 @@ struct sync_file_cb {
  * @kref:		reference count on fence.
  * @name:		name of sync_file.  Useful for debugging
  * @sync_file_list:	membership in global file list
- * @num_fences:		number of sync_pts in the fence
  * @wq:			wait queue for fence signaling
- * @status:		0: signaled, >0:active, <0: error
- * @cbs:		sync_pts callback information
+ * @fence:		fence with the fences in the sync_file
+ * @cb:			fence callback information
  */
 struct sync_file {
 	struct file		*file;
@@ -44,12 +38,11 @@ struct sync_file {
 #ifdef CONFIG_DEBUG_FS
 	struct list_head	sync_file_list;
 #endif
-	int num_fences;
 
 	wait_queue_head_t	wq;
-	atomic_t		status;
 
-	struct sync_file_cb	cbs[];
+	struct fence		*fence;
+	struct fence_cb cb;
 };
 
 struct sync_file *sync_file_create(struct fence *fence);
-- 
2.5.5

[PATCH v3 3/4] dma-buf/sync_file: add sync_file_get_fence()

[Gustavo Padovan]

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

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

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

v3:
	- Adapt to use fput() directly
	- rename to sync_file_get_fence() as we always return one fence

v4: Adapt to use fence_array

v5: set fence through fence_get()

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/dma-buf/sync_file.c | 23 +++++++++++++++++++++++
 include/linux/sync_file.h   |  1 +
 2 files changed, 24 insertions(+)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index a223f48..61a687c 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -116,6 +116,29 @@ err:
 	return NULL;
 }
 
+/**
+ * sync_file_get_fence - get the fence related to the sync_file fd
+ * @fd:		sync_file fd to get the fence from
+ *
+ * Ensures @fd references a valid sync_file and returns a fence that
+ * represents all fence in the sync_file. On error NULL is returned.
+ */
+struct fence *sync_file_get_fence(int fd)
+{
+	struct sync_file *sync_file;
+	struct fence *fence;
+
+	sync_file = sync_file_fdget(fd);
+	if (!sync_file)
+		return NULL;
+
+	fence = fence_get(sync_file->fence);
+	fput(sync_file->file);
+
+	return fence;
+}
+EXPORT_SYMBOL(sync_file_get_fence);
+
 static int sync_file_set_fence(struct sync_file *sync_file,
 			       struct fence **fences, int num_fences)
 {
diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
index 2efc5ec..f7de5a0 100644
--- a/include/linux/sync_file.h
+++ b/include/linux/sync_file.h
@@ -46,5 +46,6 @@ struct sync_file {
 };
 
 struct sync_file *sync_file_create(struct fence *fence);
+struct fence *sync_file_get_fence(int fd);
 
 #endif /* _LINUX_SYNC_H */
-- 
2.5.5

[PATCH v3 4/4] Documentation: add doc for sync_file_get_fence()

[Gustavo Padovan]

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

Document the new function added to sync_file.c

v2: Adapt to fence_array

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 Documentation/sync_file.txt | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Documentation/sync_file.txt b/Documentation/sync_file.txt
index e8e2eba..ae2dbad1 100644
--- a/Documentation/sync_file.txt
+++ b/Documentation/sync_file.txt
@@ -64,6 +64,21 @@ The sync_file fd now can be sent to userspace.
 If the creation process fail, or the sync_file needs to be released by any
 other reason fput(sync_file->file) should be used.
 
+Receiving Sync Files from Userspace
+-----------------------------------
+
+When userspace needs to send an in-fence to the driver it pass file descriptor
+of the Sync File to the kernel. The kernel then can retrieve the fences
+from it.
+
+Interface:
+	struct fence *sync_file_get_fence(int fd);
+
+
+The function return a struct fence pointer referencing the fence(s) in the Sync
+File.
+
+
 References:
 [1] struct sync_file in include/linux/sync_file.h
 [2] All interfaces mentioned above defined in include/linux/sync_file.h
-- 
2.5.5