From: Hans Verkuil <hans.verkuil@xxxxxxxxx>
Commit 88e268702bfba78448abd20a31129458707383aa ("vb2: Improve file I/O
emulation to handle buffers in any order") broke read/write support if
the size of the buffer being read/written is less than the size of the
image.
When the commit was tested originally I used qv4l2, which calls read()
with exactly the size of the image. But if you try 'cat /dev/video0'
then it will fail and typically hang after reading two buffers.
This patch fixes the behavior by adding a new cur_index field that
contains the index of the field currently being filled/read, or it
is num_buffers in which case a new buffer needs to be dequeued.
The old index field has been renamed to initial_index in order to be
a bit more descriptive.
This has been tested with both read and write.
Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
Tested-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
Cc: Andy Walls <awalls@xxxxxxxxxxxxxxxx>
---
drivers/media/v4l2-core/videobuf2-core.c | 46 +++++++++++++++++++++++++++-----
1 file changed, 40 insertions(+), 6 deletions(-)
diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index a127925..f1a2857c 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -2251,6 +2251,22 @@ struct vb2_fileio_buf {
/**
* struct vb2_fileio_data - queue context used by file io emulator
*
+ * @cur_index: the index of the buffer currently being read from or
+ * written to. If equal to q->num_buffers then a new buffer
+ * must be dequeued.
+ * @initial_index: in the read() case all buffers are queued up immediately
+ * in __vb2_init_fileio() and __vb2_perform_fileio() just cycles
+ * buffers. However, in the write() case no buffers are initially
+ * queued, instead whenever a buffer is full it is queued up by
+ * __vb2_perform_fileio(). Only once all available buffers have
+ * been queued up will __vb2_perform_fileio() start to dequeue
+ * buffers. This means that initially __vb2_perform_fileio()
+ * needs to know what buffer index to use when it is queuing up
+ * the buffers for the first time. That initial index is stored
+ * in this field. Once it is equal to q->num_buffers all
+ * available buffers have been queued and __vb2_perform_fileio()
+ * should start the normal dequeue/queue cycle.
+ *
* vb2 provides a compatibility layer and emulator of file io (read and
* write) calls on top of streaming API. For proper operation it required
* this structure to save the driver state between each call of the read
@@ -2260,7 +2276,8 @@ struct vb2_fileio_data {
struct v4l2_requestbuffers req;
struct v4l2_buffer b;
struct vb2_fileio_buf bufs[VIDEO_MAX_FRAME];
- unsigned int index;
+ unsigned int cur_index;
+ unsigned int initial_index;
unsigned int q_count;
unsigned int dq_count;
unsigned int flags;
@@ -2360,7 +2377,12 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
goto err_reqbufs;
fileio->bufs[i].queued = 1;
}
- fileio->index = q->num_buffers;
+ /*
+ * All buffers have been queued, so mark that by setting
+ * initial_index to q->num_buffers
+ */
+ fileio->initial_index = q->num_buffers;
+ fileio->cur_index = q->num_buffers;
}
/*
@@ -2439,7 +2461,7 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
/*
* Check if we need to dequeue the buffer.
*/
- index = fileio->index;
+ index = fileio->cur_index;
if (index >= q->num_buffers) {
/*
* Call vb2_dqbuf to get buffer back.
@@ -2453,7 +2475,7 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
return ret;
fileio->dq_count += 1;
- index = fileio->b.index;
+ fileio->cur_index = index = fileio->b.index;
buf = &fileio->bufs[index];
/*
@@ -2529,8 +2551,20 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
buf->queued = 1;
buf->size = vb2_plane_size(q->bufs[index], 0);
fileio->q_count += 1;
- if (fileio->index < q->num_buffers)
- fileio->index++;
+ /*
+ * If we are queuing up buffers for the first time, then
+ * increase initial_index by one.
+ */
+ if (fileio->initial_index < q->num_buffers)
+ fileio->initial_index++;
+ /*
+ * The next buffer to use is either a buffer that's going to be
+ * queued for the first time (initial_index < q->num_buffers)
+ * or it is equal to q->num_buffers, meaning that the next
+ * time we need to dequeue a buffer since we've now queued up
+ * all the 'first time' buffers.
+ */
+ fileio->cur_index = fileio->initial_index;
}
/*
--
1.9.rc1
--
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