[RFC PATCH 7/8] vb2: add thread support

Hans Verkuil
2013-11-21T15:22:47Z

From: Hans Verkuil <hans.verkuil@cisco.com>

In order to implement vb2 DVB or ALSA support you need to be able to start
a kernel thread that queues and dequeues buffers, calling a callback
function for every captured/displayed buffer. This patch adds support for
that.

It's based on drivers/media/v4l2-core/videobuf-dvb.c, but with all the DVB
specific stuff stripped out, thus making it much more generic.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
---
drivers/media/v4l2-core/videobuf2-core.c | 134 +++++++++++++++++++++++++++++++
include/media/videobuf2-core.h | 28 +++++++
2 files changed, 162 insertions(+)

diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 7d1498f..66cd81d 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -6,6 +6,9 @@
* Author: Pawel Osciak <pawel@osciak.com>
* Marek Szyprowski <m.szyprowski@samsung.com>
*
+ * The vb2_thread implementation was based on code from videobuf-dvb.c:
+ * (c) 2004 Gerd Knorr <kraxel@bytesex.org> [SUSE Labs]
+ *
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation.
@@ -18,6 +21,8 @@
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/sched.h>
+#include <linux/freezer.h>
+#include <linux/kthread.h>

#include <media/v4l2-dev.h>
#include <media/v4l2-fh.h>
@@ -2500,6 +2505,135 @@ size_t vb2_write(struct vb2_queue *q, const char __user *data, size_t count,
}
EXPORT_SYMBOL_GPL(vb2_write);

+struct vb2_threadio_data {
+ struct task_struct *thread;
+ vb2_thread_fnc fnc;
+ void *priv;
+ bool stop;
+};
+
+static int vb2_thread(void *data)
+{
+ struct vb2_queue *q = data;
+ struct vb2_threadio_data *threadio = q->threadio;
+ struct vb2_fileio_data *fileio = q->fileio;
+ int prequeue = 0;
+ int index = 0;
+ int ret = 0;
+
+ if (V4L2_TYPE_IS_OUTPUT(q->type))
+ prequeue = q->num_buffers;
+
+ set_freezable();
+
+ for (;;) {
+ struct vb2_buffer *vb;
+
+ /*
+ * Call vb2_dqbuf to get buffer back.
+ */
+ memset(&fileio->b, 0, sizeof(fileio->b));
+ fileio->b.type = q->type;
+ fileio->b.memory = q->memory;
+ if (prequeue) {
+ fileio->b.index = index++;
+ prequeue--;
+ } else {
+ call_qop(q, wait_finish, q);
+ ret = vb2_internal_dqbuf(q, &fileio->b, 0);
+ call_qop(q, wait_prepare, q);
+ dprintk(5, "file io: vb2_dqbuf result: %d\n", ret);
+ }
+ if (threadio->stop)
+ break;
+ if (ret)
+ break;
+ try_to_freeze();
+
+ vb = q->bufs[fileio->b.index];
+ if (!(fileio->b.flags & V4L2_BUF_FLAG_ERROR))
+ ret = threadio->fnc(vb, threadio->priv);
+ if (ret)
+ break;
+ call_qop(q, wait_finish, q);
+ ret = vb2_internal_qbuf(q, &fileio->b);
+ call_qop(q, wait_prepare, q);
+ if (ret)
+ break;
+ }
+
+ /* Hmm, linux becomes *very* unhappy without this ... */
+ while (!kthread_should_stop()) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule();
+ }
+ return 0;
+}
+
+int vb2_thread_start(struct vb2_queue *q, vb2_thread_fnc fnc, void *priv,
+ const char *thread_name)
+{
+ struct vb2_threadio_data *threadio;
+ int ret = 0;
+
+ if (q->threadio)
+ return -EBUSY;
+ if (vb2_is_busy(q))
+ return -EBUSY;
+ if (WARN_ON(q->fileio))
+ return -EBUSY;
+
+ threadio = kzalloc(sizeof(*threadio), GFP_KERNEL);
+ if (threadio == NULL)
+ return -ENOMEM;
+ threadio->fnc = fnc;
+ threadio->priv = priv;
+
+ ret = __vb2_init_fileio(q, !V4L2_TYPE_IS_OUTPUT(q->type));
+ dprintk(3, "file io: vb2_init_fileio result: %d\n", ret);
+ if (ret)
+ goto nomem;
+ q->threadio = threadio;
+ threadio->thread = kthread_run(vb2_thread, q, "vb2-%s", thread_name);
+ if (IS_ERR(threadio->thread)) {
+ ret = PTR_ERR(threadio->thread);
+ threadio->thread = NULL;
+ goto nothread;
+ }
+ return 0;
+
+nothread:
+ __vb2_cleanup_fileio(q);
+nomem:
+ kfree(threadio);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(vb2_thread_start);
+
+int vb2_thread_stop(struct vb2_queue *q)
+{
+ struct vb2_threadio_data *threadio = q->threadio;
+ struct vb2_fileio_data *fileio = q->fileio;
+ int err;
+
+ if (threadio == NULL)
+ return 0;
+ call_qop(q, wait_finish, q);
+ threadio->stop = true;
+ vb2_internal_streamoff(q, q->type);
+ call_qop(q, wait_prepare, q);
+ q->fileio = NULL;
+ fileio->req.count = 0;
+ vb2_reqbufs(q, &fileio->req);
+ kfree(fileio);
+ err = kthread_stop(threadio->thread);
+ threadio->thread = NULL;
+ kfree(threadio);
+ q->fileio = NULL;
+ q->threadio = NULL;
+ return err;
+}
+EXPORT_SYMBOL_GPL(vb2_thread_stop);

/*
* The following functions are not part of the vb2 core API, but are helper
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 2d88897..5f6347a 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -20,6 +20,7 @@

struct vb2_alloc_ctx;
struct vb2_fileio_data;
+struct vb2_threadio_data;

/**
* struct vb2_mem_ops - memory handling/memory allocator operations
@@ -328,6 +329,7 @@ struct v4l2_fh;
* buffers queued. If set, then retry calling start_streaming when
* queuing a new buffer.
* @fileio: file io emulator internal data, used only if emulator is active
+ * @threadio: thread io internal data, used only if thread is active
*/
struct vb2_queue {
enum v4l2_buf_type type;
@@ -362,6 +364,7 @@ struct vb2_queue {
unsigned int retry_start_streaming:1;

struct vb2_fileio_data *fileio;
+ struct vb2_threadio_data *threadio;
};

void *vb2_plane_vaddr(struct vb2_buffer *vb, unsigned int plane_no);
@@ -400,6 +403,31 @@ size_t vb2_read(struct vb2_queue *q, char __user *data, size_t count,
loff_t *ppos, int nonblock);
size_t vb2_write(struct vb2_queue *q, const char __user *data, size_t count,
loff_t *ppos, int nonblock);
+/**
+ * vb2_thread_fnc - callback function for use with vb2_thread
+ *
+ * This is called whenever a buffer is dequeued in the thread.
+ */
+typedef int (*vb2_thread_fnc)(struct vb2_buffer *vb, void *priv);
+
+/**
+ * vb2_thread_start() - start a thread for the given queue.
+ * @q: videobuf queue
+ * @fnc: callback function
+ * @priv: priv pointer passed to the callback function
+ * @thread_name:the name of the thread. This will be prefixed with "vb2-".
+ *
+ * This starts a thread that will queue and dequeue until an error occurs
+ * or @vb2_thread_stop is called.
+ */
+int vb2_thread_start(struct vb2_queue *q, vb2_thread_fnc fnc, void *priv,
+ const char *thread_name);
+
+/**
+ * vb2_thread_stop() - stop the thread for the given queue.
+ * @q: videobuf queue
+ */
+int vb2_thread_stop(struct vb2_queue *q);

/**
* vb2_is_streaming() - return streaming status of the queue
--
1.8.4.3