[PATCH v9 11/15] vb2: add in-fence support to QBUF

Ezequiel Garcia
2018-05-04T20:08:25Z

From: Gustavo Padovan <gustavo.padovan@collabora.com>

Receive in-fence from userspace and add support for waiting on them
before queueing the buffer to the driver. Buffers can't be queued to the
driver before its fences signal. And a buffer can't be queued to the driver
out of the order they were queued from userspace. That means that even if
its fence signals it must wait for all other buffers, ahead of it in the queue,
to signal first.

If the fence for some buffer fails we do not queue it to the driver,
instead we mark it as error and wait until the previous buffer is done
to notify userspace of the error. We wait here to deliver the buffers back
to userspace in order.

v12: fixed dvb_vb2.c usage of vb2_core_qbuf.

v11: - minor doc/comments fixes (Hans Verkuil)
- reviewed the in-fence path at __fill_v4l2_buffer()

v10: - rename fence to in_fence in many places
- handle fences signalling with error better (Hans Verkuil)

v9: - improve comments and docs (Hans Verkuil)
- fix unlocking of vb->fence_cb_lock on vb2_core_qbuf (Hans Verkuil)
- move in-fences code that was in the out-fences patch here (Alex)

v8: - improve comments about fences with errors

v7: - get rid of the fence array stuff for ordering and just use
get_num_buffers_ready() (Hans)
- fix issue of queuing the buffer twice (Hans)
- avoid the dma_fence_wait() in core_qbuf() (Alex)
- merge preparation commit in

v6: - With fences always keep the order userspace queues the buffers.
- Protect in_fence manipulation with a lock (Brian Starkey)
- check if fences have the same context before adding a fence array
- Fix last_fence ref unbalance in __set_in_fence() (Brian Starkey)
- Clean up fence if __set_in_fence() fails (Brian Starkey)
- treat -EINVAL from dma_fence_add_callback() (Brian Starkey)

v5: - use fence_array to keep buffers ordered in vb2 core when
needed (Brian Starkey)
- keep backward compat on the reserved2 field (Brian Starkey)
- protect fence callback removal with lock (Brian Starkey)

v4: - Add a comment about dma_fence_add_callback() not returning a
error (Hans)
- Call dma_fence_put(vb->in_fence) if fence signaled (Hans)
- select SYNC_FILE under config VIDEOBUF2_CORE (Hans)
- Move dma_fence_is_signaled() check to __enqueue_in_driver() (Hans)
- Remove list_for_each_entry() in __vb2_core_qbuf() (Hans)
- Remove if (vb->state != VB2_BUF_STATE_QUEUED) from
vb2_start_streaming() (Hans)
- set IN_FENCE flags on __fill_v4l2_buffer (Hans)
- Queue buffers to the driver as soon as they are ready (Hans)
- call fill_user_buffer() after queuing the buffer (Hans)
- add err: label to clean up fence
- add dma_fence_wait() before calling vb2_start_streaming()

v3: - document fence parameter
- remove ternary if at vb2_qbuf() return (Mauro)
- do not change if conditions behaviour (Mauro)

v2: - fix vb2_queue_or_prepare_buf() ret check
- remove check for VB2_MEMORY_DMABUF only (Javier)
- check num of ready buffers to start streaming
- when queueing, start from the first ready buffer
- handle queue cancel

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
---
drivers/media/common/videobuf2/videobuf2-core.c | 197 ++++++++++++++++++++----
drivers/media/common/videobuf2/videobuf2-v4l2.c | 34 +++-
drivers/media/dvb-core/dvb_vb2.c | 2 +-
drivers/media/v4l2-core/Kconfig | 33 ++++
include/media/videobuf2-core.h | 14 +-
5 files changed, 249 insertions(+), 31 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index 6b8e083893ad..996b99497a98 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -352,6 +352,7 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
vb->index = q->num_buffers + buffer;
vb->type = q->type;
vb->memory = memory;
+ spin_lock_init(&vb->fence_cb_lock);
for (plane = 0; plane < num_planes; ++plane) {
vb->planes[plane].length = plane_sizes[plane];
vb->planes[plane].min_length = plane_sizes[plane];
@@ -905,20 +906,12 @@ void *vb2_plane_cookie(struct vb2_buffer *vb, unsigned int plane_no)
}
EXPORT_SYMBOL_GPL(vb2_plane_cookie);

-void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
+static void vb2_process_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
{
struct vb2_queue *q = vb->vb2_queue;
unsigned long flags;
unsigned int plane;

- if (WARN_ON(vb->state != VB2_BUF_STATE_ACTIVE))
- return;
-
- if (WARN_ON(state != VB2_BUF_STATE_DONE &&
- state != VB2_BUF_STATE_ERROR &&
- state != VB2_BUF_STATE_QUEUED &&
- state != VB2_BUF_STATE_REQUEUEING))
- state = VB2_BUF_STATE_ERROR;

#ifdef CONFIG_VIDEO_ADV_DEBUG
/*
@@ -935,6 +928,9 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
call_void_memop(vb, finish, vb->planes[plane].mem_priv);

spin_lock_irqsave(&q->done_lock, flags);
+ if (vb->state == VB2_BUF_STATE_ACTIVE)
+ atomic_dec(&q->owned_by_drv_count);
+
if (state == VB2_BUF_STATE_QUEUED ||
state == VB2_BUF_STATE_REQUEUEING) {
vb->state = VB2_BUF_STATE_QUEUED;
@@ -943,7 +939,7 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
list_add_tail(&vb->done_entry, &q->done_list);
vb->state = state;
}
- atomic_dec(&q->owned_by_drv_count);
+
spin_unlock_irqrestore(&q->done_lock, flags);

trace_vb2_buf_done(q, vb);
@@ -960,6 +956,36 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
wake_up(&q->done_wq);
break;
}
+
+}
+
+void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
+{
+ if (WARN_ON(vb->state != VB2_BUF_STATE_ACTIVE))
+ return;
+
+ if (WARN_ON(state != VB2_BUF_STATE_DONE &&
+ state != VB2_BUF_STATE_ERROR &&
+ state != VB2_BUF_STATE_QUEUED &&
+ state != VB2_BUF_STATE_REQUEUEING))
+ state = VB2_BUF_STATE_ERROR;
+
+ vb2_process_buffer_done(vb, state);
+
+ /*
+ * Check if there is any buffer with error in the next position of the queue,
+ * buffers whose in-fence signaled with error are not queued to the driver
+ * and kept on the queue until the buffer before them is done, so to not
+ * deliver buffers back to userspace in the wrong order. Here we process
+ * any existing buffers with errors and wake up userspace.
+ */
+ for (;;) {
+ vb = list_next_entry(vb, queued_entry);
+ if (!vb || vb->state != VB2_BUF_STATE_ERROR)
+ break;
+
+ vb2_process_buffer_done(vb, VB2_BUF_STATE_ERROR);
+ }
}
EXPORT_SYMBOL_GPL(vb2_buffer_done);

@@ -1244,6 +1270,9 @@ static void __enqueue_in_driver(struct vb2_buffer *vb)
{
struct vb2_queue *q = vb->vb2_queue;

+ if (vb->in_fence && !dma_fence_is_signaled(vb->in_fence))
+ return;
+
vb->state = VB2_BUF_STATE_ACTIVE;
atomic_inc(&q->owned_by_drv_count);

@@ -1295,6 +1324,24 @@ static int __buf_prepare(struct vb2_buffer *vb, const void *pb)
return 0;
}

+static int __get_num_ready_buffers(struct vb2_queue *q)
+{
+ struct vb2_buffer *vb;
+ int ready_count = 0;
+ unsigned long flags;
+
+ /* count num of buffers ready in front of the queued_list */
+ list_for_each_entry(vb, &q->queued_list, queued_entry) {
+ spin_lock_irqsave(&vb->fence_cb_lock, flags);
+ if (vb->in_fence && !dma_fence_is_signaled(vb->in_fence))
+ break;
+ ready_count++;
+ spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
+ }
+
+ return ready_count;
+}
+
int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb)
{
struct vb2_buffer *vb;
@@ -1383,9 +1430,43 @@ static int vb2_start_streaming(struct vb2_queue *q)
return ret;
}

-int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
+static void vb2_qbuf_fence_cb(struct dma_fence *f, struct dma_fence_cb *cb)
+{
+ struct vb2_buffer *vb = container_of(cb, struct vb2_buffer, fence_cb);
+ struct vb2_queue *q = vb->vb2_queue;
+ unsigned long flags;
+
+ spin_lock_irqsave(&vb->fence_cb_lock, flags);
+ /*
+ * If the fence signals with an error we mark the buffer as such
+ * and avoid using it by setting it to VB2_BUF_STATE_ERROR and
+ * not queueing it to the driver. However we can't notify the error
+ * to userspace right now because, at the time this callback run, QBUF
+ * has returned already.
+ * So we delay that to DQBUF time. See comments in vb2_buffer_done()
+ * as well.
+ */
+ if (vb->in_fence->error)
+ vb->state = VB2_BUF_STATE_ERROR;
+
+ dma_fence_put(vb->in_fence);
+ vb->in_fence = NULL;
+
+ if (vb->state == VB2_BUF_STATE_ERROR) {
+ spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
+ return;
+ }
+
+ if (q->start_streaming_called)
+ __enqueue_in_driver(vb);
+ spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
+}
+
+int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
+ struct dma_fence *in_fence)
{
struct vb2_buffer *vb;
+ unsigned long flags;
int ret;

vb = q->bufs[index];
@@ -1394,16 +1475,18 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
case VB2_BUF_STATE_DEQUEUED:
ret = __buf_prepare(vb, pb);
if (ret)
- return ret;
+ goto err;
break;
case VB2_BUF_STATE_PREPARED:
break;
case VB2_BUF_STATE_PREPARING:
dprintk(1, "buffer still being prepared\n");
- return -EINVAL;
+ ret = -EINVAL;
+ goto err;
default:
dprintk(1, "invalid buffer state %d\n", vb->state);
- return -EINVAL;
+ ret = -EINVAL;
+ goto err;
}

/*
@@ -1414,6 +1497,7 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
q->queued_count++;
q->waiting_for_buffers = false;
vb->state = VB2_BUF_STATE_QUEUED;
+ vb->in_fence = in_fence;

if (pb)
call_void_bufop(q, copy_timestamp, vb, pb);
@@ -1421,15 +1505,40 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
trace_vb2_qbuf(q, vb);

/*
- * If already streaming, give the buffer to driver for processing.
- * If not, the buffer will be given to driver on next streamon.
+ * For explicit synchronization: If the fence didn't signal
+ * yet we setup a callback to queue the buffer once the fence
+ * signals and then return successfully. But if the fence
+ * already signaled we lose the reference we held and queue the
+ * buffer to the driver.
*/
- if (q->start_streaming_called)
- __enqueue_in_driver(vb);
+ spin_lock_irqsave(&vb->fence_cb_lock, flags);
+ if (vb->in_fence) {
+ ret = dma_fence_add_callback(vb->in_fence, &vb->fence_cb,
+ vb2_qbuf_fence_cb);
+ /* is the fence signaled? */
+ if (ret == -ENOENT) {
+ dma_fence_put(vb->in_fence);
+ vb->in_fence = NULL;
+ } else if (ret) {
+ goto unlock;
+ }
+ }

- /* Fill buffer information for the userspace */
- if (pb)
- call_void_bufop(q, fill_user_buffer, vb, pb);
+ /*
+ * If already streaming and there is no fence to wait on
+ * give the buffer to driver for processing.
+ */
+ if (q->start_streaming_called) {
+ struct vb2_buffer *b;
+
+ list_for_each_entry(b, &q->queued_list, queued_entry) {
+ if (b->state != VB2_BUF_STATE_QUEUED)
+ continue;
+ if (b->in_fence)
+ break;
+ __enqueue_in_driver(b);
+ }
+ }

/*
* If streamon has been called, and we haven't yet called
@@ -1438,14 +1547,36 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
* then we can finally call start_streaming().
*/
if (q->streaming && !q->start_streaming_called &&
- q->queued_count >= q->min_buffers_needed) {
+ __get_num_ready_buffers(q) >= q->min_buffers_needed) {
ret = vb2_start_streaming(q);
if (ret)
- return ret;
+ goto unlock;
}

+ spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
+
+ /* Fill buffer information for the userspace */
+ if (pb)
+ call_void_bufop(q, fill_user_buffer, vb, pb);
+
dprintk(2, "qbuf of buffer %d succeeded\n", vb->index);
return 0;
+
+unlock:
+ spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
+
+err:
+ /* Fill buffer information for the userspace */
+ if (pb)
+ call_void_bufop(q, fill_user_buffer, vb, pb);
+
+ if (vb->in_fence) {
+ dma_fence_put(vb->in_fence);
+ vb->in_fence = NULL;
+ }
+
+ return ret;
+
}
EXPORT_SYMBOL_GPL(vb2_core_qbuf);

@@ -1656,6 +1787,8 @@ EXPORT_SYMBOL_GPL(vb2_core_dqbuf);
static void __vb2_queue_cancel(struct vb2_queue *q)
{
unsigned int i;
+ struct vb2_buffer *vb;
+ unsigned long flags;

/*
* Tell driver to stop all transactions and release all queued
@@ -1686,6 +1819,16 @@ static void __vb2_queue_cancel(struct vb2_queue *q)
q->queued_count = 0;
q->error = 0;

+ list_for_each_entry(vb, &q->queued_list, queued_entry) {
+ spin_lock_irqsave(&vb->fence_cb_lock, flags);
+ if (vb->in_fence) {
+ dma_fence_remove_callback(vb->in_fence, &vb->fence_cb);
+ dma_fence_put(vb->in_fence);
+ vb->in_fence = NULL;
+ }
+ spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
+ }
+
/*
* Remove all buffers from videobuf's list...
*/
@@ -1756,7 +1899,7 @@ int vb2_core_streamon(struct vb2_queue *q, unsigned int type)
* Tell driver to start streaming provided sufficient buffers
* are available.
*/
- if (q->queued_count >= q->min_buffers_needed) {
+ if (__get_num_ready_buffers(q) >= q->min_buffers_needed) {
ret = v4l_vb2q_enable_media_source(q);
if (ret)
return ret;
@@ -2278,7 +2421,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
* Queue all buffers.
*/
for (i = 0; i < q->num_buffers; i++) {
- ret = vb2_core_qbuf(q, i, NULL);
+ ret = vb2_core_qbuf(q, i, NULL, NULL);
if (ret)
goto err_reqbufs;
fileio->bufs[i].queued = 1;
@@ -2457,7 +2600,7 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_

if (copy_timestamp)
b->timestamp = ktime_get_ns();
- ret = vb2_core_qbuf(q, index, NULL);
+ ret = vb2_core_qbuf(q, index, NULL, NULL);
dprintk(5, "vb2_dbuf result: %d\n", ret);
if (ret)
return ret;
@@ -2560,7 +2703,7 @@ static int vb2_thread(void *data)
if (copy_timestamp)
vb->timestamp = ktime_get_ns();
if (!threadio->stop)
- ret = vb2_core_qbuf(q, vb->index, NULL);
+ ret = vb2_core_qbuf(q, vb->index, NULL, NULL);
call_void_qop(q, wait_prepare, q);
if (ret || threadio->stop)
break;
diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index b1c0fa2b0b88..74d7062e5285 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -23,6 +23,7 @@
#include <linux/sched.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
+#include <linux/sync_file.h>

#include <media/v4l2-dev.h>
#include <media/v4l2-fh.h>
@@ -178,6 +179,17 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b,
return -EINVAL;
}

+ if ((b->fence_fd != 0 && b->fence_fd != -1) &&
+ !(b->flags & V4L2_BUF_FLAG_IN_FENCE)) {
+ dprintk(1, "%s: fence_fd set without IN_FENCE flag\n", opname);
+ return -EINVAL;
+ }
+
+ if (b->fence_fd < 0 && (b->flags & V4L2_BUF_FLAG_IN_FENCE)) {
+ dprintk(1, "%s: IN_FENCE flag set but no fence_fd\n", opname);
+ return -EINVAL;
+ }
+
return __verify_planes_array(q->bufs[b->index], b);
}

@@ -203,9 +215,14 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, void *pb)
b->timestamp = ns_to_timeval(vb->timestamp);
b->timecode = vbuf->timecode;
b->sequence = vbuf->sequence;
- b->fence_fd = 0;
b->reserved = 0;

+ b->fence_fd = 0;
+ if (vb->in_fence)
+ b->flags |= V4L2_BUF_FLAG_IN_FENCE;
+ else
+ b->flags &= ~V4L2_BUF_FLAG_IN_FENCE;
+
if (q->is_multiplanar) {
/*
* Fill in plane-related data if userspace provided an array
@@ -562,6 +579,7 @@ EXPORT_SYMBOL_GPL(vb2_create_bufs);

int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
{
+ struct dma_fence *in_fence = NULL;
int ret;

if (vb2_fileio_is_active(q)) {
@@ -570,7 +588,19 @@ int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
}

ret = vb2_queue_or_prepare_buf(q, b, "qbuf");
- return ret ? ret : vb2_core_qbuf(q, b->index, b);
+ if (ret)
+ return ret;
+
+ if (b->flags & V4L2_BUF_FLAG_IN_FENCE) {
+ in_fence = sync_file_get_fence(b->fence_fd);
+ if (!in_fence) {
+ dprintk(1, "failed to get in-fence from fd %d\n",
+ b->fence_fd);
+ return -EINVAL;
+ }
+ }
+
+ return vb2_core_qbuf(q, b->index, b, in_fence);
}
EXPORT_SYMBOL_GPL(vb2_qbuf);

diff --git a/drivers/media/dvb-core/dvb_vb2.c b/drivers/media/dvb-core/dvb_vb2.c
index b811adf88afa..7da53f10db1a 100644
--- a/drivers/media/dvb-core/dvb_vb2.c
+++ b/drivers/media/dvb-core/dvb_vb2.c
@@ -385,7 +385,7 @@ int dvb_vb2_qbuf(struct dvb_vb2_ctx *ctx, struct dmx_buffer *b)
{
int ret;

- ret = vb2_core_qbuf(&ctx->vb_q, b->index, b);
+ ret = vb2_core_qbuf(&ctx->vb_q, b->index, b, NULL);
if (ret) {
dprintk(1, "[%s] index=%d errno=%d\n", ctx->name,
b->index, ret);
diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
index 8e37e7c5e0f7..79dfb5dfd1fc 100644
--- a/drivers/media/v4l2-core/Kconfig
+++ b/drivers/media/v4l2-core/Kconfig
@@ -80,3 +80,36 @@ config VIDEOBUF_DMA_CONTIG
config VIDEOBUF_DVB
tristate
select VIDEOBUF_GEN
+
+# Used by drivers that need Videobuf2 modules
+config VIDEOBUF2_CORE
+ select DMA_SHARED_BUFFER
+ select SYNC_FILE
+ tristate
+
+config VIDEOBUF2_MEMOPS
+ tristate
+ select FRAME_VECTOR
+
+config VIDEOBUF2_DMA_CONTIG
+ tristate
+ depends on HAS_DMA
+ select VIDEOBUF2_CORE
+ select VIDEOBUF2_MEMOPS
+ select DMA_SHARED_BUFFER
+
+config VIDEOBUF2_VMALLOC
+ tristate
+ select VIDEOBUF2_CORE
+ select VIDEOBUF2_MEMOPS
+ select DMA_SHARED_BUFFER
+
+config VIDEOBUF2_DMA_SG
+ tristate
+ depends on HAS_DMA
+ select VIDEOBUF2_CORE
+ select VIDEOBUF2_MEMOPS
+
+config VIDEOBUF2_DVB
+ tristate
+ select VIDEOBUF2_CORE
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 364e4cb41b10..28ce8f66882e 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -17,6 +17,7 @@
#include <linux/poll.h>
#include <linux/dma-buf.h>
#include <linux/bitops.h>
+#include <linux/dma-fence.h>

#define VB2_MAX_FRAME (32)
#define VB2_MAX_PLANES (8)
@@ -255,12 +256,21 @@ struct vb2_buffer {
* done_entry: entry on the list that stores all buffers ready
* to be dequeued to userspace
* vb2_plane: per-plane information; do not change
+ * in_fence: fence received from vb2 client to wait on before
+ * using the buffer (queueing to the driver)
+ * fence_cb: fence callback information
+ * fence_cb_lock: protect callback signal/remove
*/
enum vb2_buffer_state state;

struct vb2_plane planes[VB2_MAX_PLANES];
struct list_head queued_entry;
struct list_head done_entry;
+
+ struct dma_fence *in_fence;
+ struct dma_fence_cb fence_cb;
+ spinlock_t fence_cb_lock;
+
#ifdef CONFIG_VIDEO_ADV_DEBUG
/*
* Counters for how often these buffer-related ops are
@@ -773,6 +783,7 @@ int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb);
* @index: id number of the buffer
* @pb: buffer structure passed from userspace to
* v4l2_ioctl_ops->vidioc_qbuf handler in driver
+ * @in_fence: in-fence to wait on before queueing the buffer
*
* Videobuf2 core helper to implement VIDIOC_QBUF() operation. It is called
* internally by VB2 by an API-specific handler, like ``videobuf2-v4l2.h``.
@@ -787,7 +798,8 @@ int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb);
*
* Return: returns zero on success; an error code otherwise.
*/
-int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb);
+int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
+ struct dma_fence *in_fence);

/**
* vb2_core_dqbuf() - Dequeue a buffer to the userspace
--
2.16.3