[PATCH] Support of /dev/video read with USB camera devices

[PATCH] Support of /dev/video read with USB camera devices

[Hugues Fruchet]

Currently, read() call from /dev/video entry of an USB camera is
returning invalid argument error.
This is quite common for userspace application to read compressed data such as
JPEG from /dev/video then redirect those data to a multimedia player or any
other compressed format consumer, see [1].

There was a tentative of implementation in the past [2] but it was prior to
switch on vb2 helpers usage inside uvc.
Now that vb2 is in place, we can implement read support using vb2_read()
helper.

Tested with Logitech HD Webcam C525 using v4l2-ctl to configure camera
then GStreamer player to play stream:
$> v4l2-ctl -d /dev/video0 --set-fmt-video=width=640,height=480,pixelformat=MJPG
$> gst-play-1.0 /dev/video0

[1]
  http://credentiality2.blogspot.com/2010/04/v4l2-example.html?_sm_au_=ikcQHNZZFn2Rqft5
  https://stackoverrun.com/fr/q/4215615
  https://stackoverflow.com/questions/36297390/read-function-for-webcam-device-in-v4l2-fails-with-invalid-argument
  https://stackoverflow.com/questions/31058571/reading-camera-input-from-dev-video0-in-python-or-c

[2] https://www.mail-archive.com/linux-uvc-devel@lists.berlios.de/msg01258.html

Hugues Fruchet (1):
  media: uvcvideo: Read support

 drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++-
 drivers/media/usb/uvc/uvc_v4l2.c  | 11 ++++++++---
 drivers/media/usb/uvc/uvcvideo.h  |  2 ++
 3 files changed, 24 insertions(+), 4 deletions(-)

-- 
2.7.4

[PATCH] media: uvcvideo: Read support

[Hugues Fruchet]

Add support of read() call from userspace by implementing
uvc_v4l2_read() with vb2_read() helper.

Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
---
 drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++-
 drivers/media/usb/uvc/uvc_v4l2.c  | 11 ++++++++---
 drivers/media/usb/uvc/uvcvideo.h  |  2 ++
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
index 682698e..0c8a0a8 100644
--- a/drivers/media/usb/uvc/uvc_queue.c
+++ b/drivers/media/usb/uvc/uvc_queue.c
@@ -227,7 +227,7 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
 	int ret;
 
 	queue->queue.type = type;
-	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
+	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
 	queue->queue.drv_priv = queue;
 	queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
 	queue->queue.mem_ops = &vb2_vmalloc_memops;
@@ -361,6 +361,19 @@ int uvc_queue_streamoff(struct uvc_video_queue *queue, enum v4l2_buf_type type)
 	return ret;
 }
 
+ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
+		       char __user *buf, size_t count, loff_t *ppos)
+{
+	ssize_t ret;
+
+	mutex_lock(&queue->mutex);
+	ret = vb2_read(&queue->queue, buf, count, ppos,
+		       file->f_flags & O_NONBLOCK);
+	mutex_unlock(&queue->mutex);
+
+	return ret;
+}
+
 int uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
 {
 	return vb2_mmap(&queue->queue, vma);
diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index 84be596..3866832 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -594,7 +594,8 @@ static int uvc_ioctl_querycap(struct file *file, void *fh,
 	strscpy(cap->driver, "uvcvideo", sizeof(cap->driver));
 	strscpy(cap->card, vdev->name, sizeof(cap->card));
 	usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap->bus_info));
-	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING
+	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING |
+			    V4L2_CAP_READWRITE
 			  | chain->caps;
 
 	return 0;
@@ -1434,8 +1435,12 @@ static long uvc_v4l2_compat_ioctl32(struct file *file,
 static ssize_t uvc_v4l2_read(struct file *file, char __user *data,
 		    size_t count, loff_t *ppos)
 {
-	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read: not implemented.\n");
-	return -EINVAL;
+	struct uvc_fh *handle = file->private_data;
+	struct uvc_streaming *stream = handle->stream;
+
+	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read\n");
+
+	return uvc_queue_read(&stream->queue, file, data, count, ppos);
 }
 
 static int uvc_v4l2_mmap(struct file *file, struct vm_area_struct *vma)
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index c7c1baa..5d0515c 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -766,6 +766,8 @@ struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
 					 struct uvc_buffer *buf);
 struct uvc_buffer *uvc_queue_get_current_buffer(struct uvc_video_queue *queue);
 void uvc_queue_buffer_release(struct uvc_buffer *buf);
+ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
+		       char __user *buf, size_t count, loff_t *ppos);
 int uvc_queue_mmap(struct uvc_video_queue *queue,
 		   struct vm_area_struct *vma);
 __poll_t uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,
-- 
2.7.4

Re: [PATCH] media: uvcvideo: Read support

[Hans Verkuil]

On 3/4/19 1:35 PM, Hugues Fruchet wrote:
> Add support of read() call from userspace by implementing
> uvc_v4l2_read() with vb2_read() helper.
> 
> Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
> ---
>  drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++-
>  drivers/media/usb/uvc/uvc_v4l2.c  | 11 ++++++++---
>  drivers/media/usb/uvc/uvcvideo.h  |  2 ++
>  3 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
> index 682698e..0c8a0a8 100644
> --- a/drivers/media/usb/uvc/uvc_queue.c
> +++ b/drivers/media/usb/uvc/uvc_queue.c
> @@ -227,7 +227,7 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
>  	int ret;
>  
>  	queue->queue.type = type;
> -	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
> +	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
>  	queue->queue.drv_priv = queue;
>  	queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
>  	queue->queue.mem_ops = &vb2_vmalloc_memops;
> @@ -361,6 +361,19 @@ int uvc_queue_streamoff(struct uvc_video_queue *queue, enum v4l2_buf_type type)
>  	return ret;
>  }
>  
> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> +		       char __user *buf, size_t count, loff_t *ppos)
> +{
> +	ssize_t ret;
> +
> +	mutex_lock(&queue->mutex);
> +	ret = vb2_read(&queue->queue, buf, count, ppos,
> +		       file->f_flags & O_NONBLOCK);
> +	mutex_unlock(&queue->mutex);
> +
> +	return ret;
> +}
> +
>  int uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
>  {
>  	return vb2_mmap(&queue->queue, vma);
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 84be596..3866832 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -594,7 +594,8 @@ static int uvc_ioctl_querycap(struct file *file, void *fh,
>  	strscpy(cap->driver, "uvcvideo", sizeof(cap->driver));
>  	strscpy(cap->card, vdev->name, sizeof(cap->card));
>  	usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap->bus_info));
> -	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING
> +	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING |
> +			    V4L2_CAP_READWRITE
>  			  | chain->caps;

device_caps for VIDEO_CAPTURE should also get V4L2_CAP_READWRITE. See uvc_register_video_device().

Regards,

	Hans

>  
>  	return 0;
> @@ -1434,8 +1435,12 @@ static long uvc_v4l2_compat_ioctl32(struct file *file,
>  static ssize_t uvc_v4l2_read(struct file *file, char __user *data,
>  		    size_t count, loff_t *ppos)
>  {
> -	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read: not implemented.\n");
> -	return -EINVAL;
> +	struct uvc_fh *handle = file->private_data;
> +	struct uvc_streaming *stream = handle->stream;
> +
> +	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read\n");
> +
> +	return uvc_queue_read(&stream->queue, file, data, count, ppos);
>  }
>  
>  static int uvc_v4l2_mmap(struct file *file, struct vm_area_struct *vma)
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index c7c1baa..5d0515c 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -766,6 +766,8 @@ struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
>  					 struct uvc_buffer *buf);
>  struct uvc_buffer *uvc_queue_get_current_buffer(struct uvc_video_queue *queue);
>  void uvc_queue_buffer_release(struct uvc_buffer *buf);
> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> +		       char __user *buf, size_t count, loff_t *ppos);
>  int uvc_queue_mmap(struct uvc_video_queue *queue,
>  		   struct vm_area_struct *vma);
>  __poll_t uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,
> 

Re: [PATCH] media: uvcvideo: Read support

[Hans Verkuil]

On 3/4/19 1:35 PM, Hugues Fruchet wrote:
> Add support of read() call from userspace by implementing
> uvc_v4l2_read() with vb2_read() helper.
> 
> Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
> ---
>  drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++-
>  drivers/media/usb/uvc/uvc_v4l2.c  | 11 ++++++++---
>  drivers/media/usb/uvc/uvcvideo.h  |  2 ++
>  3 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
> index 682698e..0c8a0a8 100644
> --- a/drivers/media/usb/uvc/uvc_queue.c
> +++ b/drivers/media/usb/uvc/uvc_queue.c
> @@ -227,7 +227,7 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
>  	int ret;
>  
>  	queue->queue.type = type;
> -	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
> +	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
>  	queue->queue.drv_priv = queue;
>  	queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
>  	queue->queue.mem_ops = &vb2_vmalloc_memops;
> @@ -361,6 +361,19 @@ int uvc_queue_streamoff(struct uvc_video_queue *queue, enum v4l2_buf_type type)
>  	return ret;
>  }
>  
> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> +		       char __user *buf, size_t count, loff_t *ppos)
> +{
> +	ssize_t ret;
> +
> +	mutex_lock(&queue->mutex);
> +	ret = vb2_read(&queue->queue, buf, count, ppos,
> +		       file->f_flags & O_NONBLOCK);
> +	mutex_unlock(&queue->mutex);

This is now used for both video capture and metadata capture. I don't think it
makes sense to support this for metadata capture, so you should test for that.

Regards,

	Hans

> +
> +	return ret;
> +}
> +
>  int uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
>  {
>  	return vb2_mmap(&queue->queue, vma);
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 84be596..3866832 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -594,7 +594,8 @@ static int uvc_ioctl_querycap(struct file *file, void *fh,
>  	strscpy(cap->driver, "uvcvideo", sizeof(cap->driver));
>  	strscpy(cap->card, vdev->name, sizeof(cap->card));
>  	usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap->bus_info));
> -	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING
> +	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING |
> +			    V4L2_CAP_READWRITE
>  			  | chain->caps;
>  
>  	return 0;
> @@ -1434,8 +1435,12 @@ static long uvc_v4l2_compat_ioctl32(struct file *file,
>  static ssize_t uvc_v4l2_read(struct file *file, char __user *data,
>  		    size_t count, loff_t *ppos)
>  {
> -	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read: not implemented.\n");
> -	return -EINVAL;
> +	struct uvc_fh *handle = file->private_data;
> +	struct uvc_streaming *stream = handle->stream;
> +
> +	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read\n");
> +
> +	return uvc_queue_read(&stream->queue, file, data, count, ppos);
>  }
>  
>  static int uvc_v4l2_mmap(struct file *file, struct vm_area_struct *vma)
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index c7c1baa..5d0515c 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -766,6 +766,8 @@ struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
>  					 struct uvc_buffer *buf);
>  struct uvc_buffer *uvc_queue_get_current_buffer(struct uvc_video_queue *queue);
>  void uvc_queue_buffer_release(struct uvc_buffer *buf);
> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> +		       char __user *buf, size_t count, loff_t *ppos);
>  int uvc_queue_mmap(struct uvc_video_queue *queue,
>  		   struct vm_area_struct *vma);
>  __poll_t uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,
> 

Re: [PATCH] media: uvcvideo: Read support

[Kieran Bingham]

Hi Hughes,

On 04/03/2019 12:35, Hugues Fruchet wrote:
> Add support of read() call from userspace by implementing
> uvc_v4l2_read() with vb2_read() helper.

Just thinking out loud,

This opens up UVC devices to read raw full frame images through this
interface as well.

Due to the UVC protocol, there is /already/ a full memcpy to get these
images out of the URB packets, so using a read() interface would be
another full frame copy.

I can perhaps see the usecase for reading compressed data through this
interface - but full frames don't seem appropriate. (not impossible of
course, just is it reasonable?)

If this is to be enabled, should it be enabled for compressed formats
only? or would that complicate matters?

--
Regards

Kieran


> Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
> ---
>  drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++-
>  drivers/media/usb/uvc/uvc_v4l2.c  | 11 ++++++++---
>  drivers/media/usb/uvc/uvcvideo.h  |  2 ++
>  3 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
> index 682698e..0c8a0a8 100644
> --- a/drivers/media/usb/uvc/uvc_queue.c
> +++ b/drivers/media/usb/uvc/uvc_queue.c
> @@ -227,7 +227,7 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
>  	int ret;
>  
>  	queue->queue.type = type;
> -	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
> +	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
>  	queue->queue.drv_priv = queue;
>  	queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
>  	queue->queue.mem_ops = &vb2_vmalloc_memops;
> @@ -361,6 +361,19 @@ int uvc_queue_streamoff(struct uvc_video_queue *queue, enum v4l2_buf_type type)
>  	return ret;
>  }
>  
> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> +		       char __user *buf, size_t count, loff_t *ppos)
> +{
> +	ssize_t ret;
> +
> +	mutex_lock(&queue->mutex);
> +	ret = vb2_read(&queue->queue, buf, count, ppos,
> +		       file->f_flags & O_NONBLOCK);
> +	mutex_unlock(&queue->mutex);
> +
> +	return ret;
> +}
> +
>  int uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
>  {
>  	return vb2_mmap(&queue->queue, vma);
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 84be596..3866832 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -594,7 +594,8 @@ static int uvc_ioctl_querycap(struct file *file, void *fh,
>  	strscpy(cap->driver, "uvcvideo", sizeof(cap->driver));
>  	strscpy(cap->card, vdev->name, sizeof(cap->card));
>  	usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap->bus_info));
> -	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING
> +	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING |
> +			    V4L2_CAP_READWRITE
>  			  | chain->caps;
>  
>  	return 0;
> @@ -1434,8 +1435,12 @@ static long uvc_v4l2_compat_ioctl32(struct file *file,
>  static ssize_t uvc_v4l2_read(struct file *file, char __user *data,
>  		    size_t count, loff_t *ppos)
>  {
> -	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read: not implemented.\n");
> -	return -EINVAL;
> +	struct uvc_fh *handle = file->private_data;
> +	struct uvc_streaming *stream = handle->stream;
> +
> +	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read\n");
> +
> +	return uvc_queue_read(&stream->queue, file, data, count, ppos);
>  }
>  
>  static int uvc_v4l2_mmap(struct file *file, struct vm_area_struct *vma)
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index c7c1baa..5d0515c 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -766,6 +766,8 @@ struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
>  					 struct uvc_buffer *buf);
>  struct uvc_buffer *uvc_queue_get_current_buffer(struct uvc_video_queue *queue);
>  void uvc_queue_buffer_release(struct uvc_buffer *buf);
> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> +		       char __user *buf, size_t count, loff_t *ppos);
>  int uvc_queue_mmap(struct uvc_video_queue *queue,
>  		   struct vm_area_struct *vma);
>  __poll_t uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,
> 


-- 
Regards
--
Kieran

Re: [PATCH] media: uvcvideo: Read support

[Laurent Pinchart]

Hello,

On Mon, Mar 04, 2019 at 03:36:32PM +0000, Kieran Bingham wrote:
> On 04/03/2019 12:35, Hugues Fruchet wrote:
> > Add support of read() call from userspace by implementing
> > uvc_v4l2_read() with vb2_read() helper.
> 
> Just thinking out loud,
> 
> This opens up UVC devices to read raw full frame images through this
> interface as well.
> 
> Due to the UVC protocol, there is /already/ a full memcpy to get these
> images out of the URB packets, so using a read() interface would be
> another full frame copy.
> 
> I can perhaps see the usecase for reading compressed data through this
> interface - but full frames don't seem appropriate. (not impossible of
> course, just is it reasonable?)
> 
> If this is to be enabled, should it be enabled for compressed formats
> only? or would that complicate matters?

I've repeatedly refused read() support in uvcvideo for this reason, and
also because read() doesn't carry framing information very well. It's
just not a good API for capturing video frames from a webcam, and so far
I haven't heard a compeling reason why it should be enabled. I thus
haven't changed my mind :-)

> > Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
> > ---
> >  drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++-
> >  drivers/media/usb/uvc/uvc_v4l2.c  | 11 ++++++++---
> >  drivers/media/usb/uvc/uvcvideo.h  |  2 ++
> >  3 files changed, 24 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
> > index 682698e..0c8a0a8 100644
> > --- a/drivers/media/usb/uvc/uvc_queue.c
> > +++ b/drivers/media/usb/uvc/uvc_queue.c
> > @@ -227,7 +227,7 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
> >  	int ret;
> >  
> >  	queue->queue.type = type;
> > -	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
> > +	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
> >  	queue->queue.drv_priv = queue;
> >  	queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
> >  	queue->queue.mem_ops = &vb2_vmalloc_memops;
> > @@ -361,6 +361,19 @@ int uvc_queue_streamoff(struct uvc_video_queue *queue, enum v4l2_buf_type type)
> >  	return ret;
> >  }
> >  
> > +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> > +		       char __user *buf, size_t count, loff_t *ppos)
> > +{
> > +	ssize_t ret;
> > +
> > +	mutex_lock(&queue->mutex);
> > +	ret = vb2_read(&queue->queue, buf, count, ppos,
> > +		       file->f_flags & O_NONBLOCK);
> > +	mutex_unlock(&queue->mutex);
> > +
> > +	return ret;
> > +}
> > +
> >  int uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
> >  {
> >  	return vb2_mmap(&queue->queue, vma);
> > diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> > index 84be596..3866832 100644
> > --- a/drivers/media/usb/uvc/uvc_v4l2.c
> > +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> > @@ -594,7 +594,8 @@ static int uvc_ioctl_querycap(struct file *file, void *fh,
> >  	strscpy(cap->driver, "uvcvideo", sizeof(cap->driver));
> >  	strscpy(cap->card, vdev->name, sizeof(cap->card));
> >  	usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap->bus_info));
> > -	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING
> > +	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING |
> > +			    V4L2_CAP_READWRITE
> >  			  | chain->caps;
> >  
> >  	return 0;
> > @@ -1434,8 +1435,12 @@ static long uvc_v4l2_compat_ioctl32(struct file *file,
> >  static ssize_t uvc_v4l2_read(struct file *file, char __user *data,
> >  		    size_t count, loff_t *ppos)
> >  {
> > -	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read: not implemented.\n");
> > -	return -EINVAL;
> > +	struct uvc_fh *handle = file->private_data;
> > +	struct uvc_streaming *stream = handle->stream;
> > +
> > +	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read\n");
> > +
> > +	return uvc_queue_read(&stream->queue, file, data, count, ppos);
> >  }
> >  
> >  static int uvc_v4l2_mmap(struct file *file, struct vm_area_struct *vma)
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index c7c1baa..5d0515c 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -766,6 +766,8 @@ struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
> >  					 struct uvc_buffer *buf);
> >  struct uvc_buffer *uvc_queue_get_current_buffer(struct uvc_video_queue *queue);
> >  void uvc_queue_buffer_release(struct uvc_buffer *buf);
> > +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> > +		       char __user *buf, size_t count, loff_t *ppos);
> >  int uvc_queue_mmap(struct uvc_video_queue *queue,
> >  		   struct vm_area_struct *vma);
> >  __poll_t uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,

-- 
Regards,

Laurent Pinchart

Re: [PATCH] media: uvcvideo: Read support

[Hugues FRUCHET]

Hi Kieran, Laurent,

On 3/4/19 4:44 PM, Laurent Pinchart wrote:
> Hello,
> 
> On Mon, Mar 04, 2019 at 03:36:32PM +0000, Kieran Bingham wrote:
>> On 04/03/2019 12:35, Hugues Fruchet wrote:
>>> Add support of read() call from userspace by implementing
>>> uvc_v4l2_read() with vb2_read() helper.
>>
>> Just thinking out loud,
>>
>> This opens up UVC devices to read raw full frame images through this
>> interface as well.
>>
>> Due to the UVC protocol, there is /already/ a full memcpy to get these
>> images out of the URB packets, so using a read() interface would be
>> another full frame copy.
>>
>> I can perhaps see the usecase for reading compressed data through this
>> interface - but full frames don't seem appropriate. (not impossible of
>> course, just is it reasonable?)
>>
>> If this is to be enabled, should it be enabled for compressed formats
>> only? or would that complicate matters?
> 
> I've repeatedly refused read() support in uvcvideo for this reason, and
> also because read() doesn't carry framing information very well. It's
> just not a good API for capturing video frames from a webcam, and so far
> I haven't heard a compeling reason why it should be enabled. I thus
> haven't changed my mind :-)
> 

For sure read() is not optimal, but is very common and pretty simple to 
use from userspace as explained in the cover letter with some examples.

Moreover, read() is enabled by many (all ?) camera interfaces:

drivers/media/platform/pxa_camera.c:	.read		= vb2_fop_read,
drivers/media/platform/atmel/atmel-isi.c:	.read	= vb2_fop_read,
drivers/media/platform/rcar-vin/rcar-v4l2.c:	.read	= vb2_fop_read,
drivers/media/platform/stm32/stm32-dcmi.c:	.read	= vb2_fop_read,
drivers/media/platform/vivid/vivid-core.c:	.read   = vb2_fop_read,
drivers/media/platform/vimc/vimc-capture.c:	.read   = vb2_fop_read,
drivers/media/platform/marvell-ccic/mcam-core.c:.read   = vb2_fop_read,
drivers/media/platform/qcom/camss/camss-video.c:.read	= vb2_fop_read,

on my setup, this leads to have /dev/video0 (mapped on DCMI camera 
interface) supporting JPEG streaming through read() while /dev/video1 
(mapped on Hercule USB camera) fails with "invalid argument" error...


>>> Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
>>> ---
>>>   drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++-
>>>   drivers/media/usb/uvc/uvc_v4l2.c  | 11 ++++++++---
>>>   drivers/media/usb/uvc/uvcvideo.h  |  2 ++
>>>   3 files changed, 24 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
>>> index 682698e..0c8a0a8 100644
>>> --- a/drivers/media/usb/uvc/uvc_queue.c
>>> +++ b/drivers/media/usb/uvc/uvc_queue.c
>>> @@ -227,7 +227,7 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
>>>   	int ret;
>>>   
>>>   	queue->queue.type = type;
>>> -	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
>>> +	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
>>>   	queue->queue.drv_priv = queue;
>>>   	queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
>>>   	queue->queue.mem_ops = &vb2_vmalloc_memops;
>>> @@ -361,6 +361,19 @@ int uvc_queue_streamoff(struct uvc_video_queue *queue, enum v4l2_buf_type type)
>>>   	return ret;
>>>   }
>>>   
>>> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
>>> +		       char __user *buf, size_t count, loff_t *ppos)
>>> +{
>>> +	ssize_t ret;
>>> +
>>> +	mutex_lock(&queue->mutex);
>>> +	ret = vb2_read(&queue->queue, buf, count, ppos,
>>> +		       file->f_flags & O_NONBLOCK);
>>> +	mutex_unlock(&queue->mutex);
>>> +
>>> +	return ret;
>>> +}
>>> +
>>>   int uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
>>>   {
>>>   	return vb2_mmap(&queue->queue, vma);
>>> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
>>> index 84be596..3866832 100644
>>> --- a/drivers/media/usb/uvc/uvc_v4l2.c
>>> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
>>> @@ -594,7 +594,8 @@ static int uvc_ioctl_querycap(struct file *file, void *fh,
>>>   	strscpy(cap->driver, "uvcvideo", sizeof(cap->driver));
>>>   	strscpy(cap->card, vdev->name, sizeof(cap->card));
>>>   	usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap->bus_info));
>>> -	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING
>>> +	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING |
>>> +			    V4L2_CAP_READWRITE
>>>   			  | chain->caps;
>>>   
>>>   	return 0;
>>> @@ -1434,8 +1435,12 @@ static long uvc_v4l2_compat_ioctl32(struct file *file,
>>>   static ssize_t uvc_v4l2_read(struct file *file, char __user *data,
>>>   		    size_t count, loff_t *ppos)
>>>   {
>>> -	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read: not implemented.\n");
>>> -	return -EINVAL;
>>> +	struct uvc_fh *handle = file->private_data;
>>> +	struct uvc_streaming *stream = handle->stream;
>>> +
>>> +	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read\n");
>>> +
>>> +	return uvc_queue_read(&stream->queue, file, data, count, ppos);
>>>   }
>>>   
>>>   static int uvc_v4l2_mmap(struct file *file, struct vm_area_struct *vma)
>>> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
>>> index c7c1baa..5d0515c 100644
>>> --- a/drivers/media/usb/uvc/uvcvideo.h
>>> +++ b/drivers/media/usb/uvc/uvcvideo.h
>>> @@ -766,6 +766,8 @@ struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
>>>   					 struct uvc_buffer *buf);
>>>   struct uvc_buffer *uvc_queue_get_current_buffer(struct uvc_video_queue *queue);
>>>   void uvc_queue_buffer_release(struct uvc_buffer *buf);
>>> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
>>> +		       char __user *buf, size_t count, loff_t *ppos);
>>>   int uvc_queue_mmap(struct uvc_video_queue *queue,
>>>   		   struct vm_area_struct *vma);
>>>   __poll_t uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,
> 

Best regards,
Hugues.

Re: [PATCH] media: uvcvideo: Read support

[Laurent Pinchart]

Hi Hugues,

On Tue, Mar 05, 2019 at 10:24:15AM +0000, Hugues FRUCHET wrote:
> On 3/4/19 4:44 PM, Laurent Pinchart wrote:
> > On Mon, Mar 04, 2019 at 03:36:32PM +0000, Kieran Bingham wrote:
> >> On 04/03/2019 12:35, Hugues Fruchet wrote:
> >>> Add support of read() call from userspace by implementing
> >>> uvc_v4l2_read() with vb2_read() helper.
> >>
> >> Just thinking out loud,
> >>
> >> This opens up UVC devices to read raw full frame images through this
> >> interface as well.
> >>
> >> Due to the UVC protocol, there is /already/ a full memcpy to get these
> >> images out of the URB packets, so using a read() interface would be
> >> another full frame copy.
> >>
> >> I can perhaps see the usecase for reading compressed data through this
> >> interface - but full frames don't seem appropriate. (not impossible of
> >> course, just is it reasonable?)
> >>
> >> If this is to be enabled, should it be enabled for compressed formats
> >> only? or would that complicate matters?
> > 
> > I've repeatedly refused read() support in uvcvideo for this reason, and
> > also because read() doesn't carry framing information very well. It's
> > just not a good API for capturing video frames from a webcam, and so far
> > I haven't heard a compeling reason why it should be enabled. I thus
> > haven't changed my mind :-)
> 
> For sure read() is not optimal, but is very common and pretty simple to 
> use from userspace as explained in the cover letter with some examples.
> 
> Moreover, read() is enabled by many (all ?) camera interfaces:
> 
> drivers/media/platform/pxa_camera.c:	.read		= vb2_fop_read,
> drivers/media/platform/atmel/atmel-isi.c:	.read	= vb2_fop_read,
> drivers/media/platform/rcar-vin/rcar-v4l2.c:	.read	= vb2_fop_read,
> drivers/media/platform/stm32/stm32-dcmi.c:	.read	= vb2_fop_read,
> drivers/media/platform/vivid/vivid-core.c:	.read   = vb2_fop_read,
> drivers/media/platform/vimc/vimc-capture.c:	.read   = vb2_fop_read,
> drivers/media/platform/marvell-ccic/mcam-core.c:.read   = vb2_fop_read,
> drivers/media/platform/qcom/camss/camss-video.c:.read	= vb2_fop_read,

Cargo-cult doesn't mean we have to repear the same mistakes everywhere
:-)

> on my setup, this leads to have /dev/video0 (mapped on DCMI camera 
> interface) supporting JPEG streaming through read() while /dev/video1 
> (mapped on Hercule USB camera) fails with "invalid argument" error...

Let's not encourage applications to use inefficient interfaces, when
using streaming I/O wouldn't be that more difficult. I'd argue that
supporting read() in the above drivers is part of the problem, not of
the solution.

> >>> Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
> >>> ---
> >>>   drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++-
> >>>   drivers/media/usb/uvc/uvc_v4l2.c  | 11 ++++++++---
> >>>   drivers/media/usb/uvc/uvcvideo.h  |  2 ++
> >>>   3 files changed, 24 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
> >>> index 682698e..0c8a0a8 100644
> >>> --- a/drivers/media/usb/uvc/uvc_queue.c
> >>> +++ b/drivers/media/usb/uvc/uvc_queue.c
> >>> @@ -227,7 +227,7 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
> >>>   	int ret;
> >>>   
> >>>   	queue->queue.type = type;
> >>> -	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR;
> >>> +	queue->queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
> >>>   	queue->queue.drv_priv = queue;
> >>>   	queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
> >>>   	queue->queue.mem_ops = &vb2_vmalloc_memops;
> >>> @@ -361,6 +361,19 @@ int uvc_queue_streamoff(struct uvc_video_queue *queue, enum v4l2_buf_type type)
> >>>   	return ret;
> >>>   }
> >>>   
> >>> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> >>> +		       char __user *buf, size_t count, loff_t *ppos)
> >>> +{
> >>> +	ssize_t ret;
> >>> +
> >>> +	mutex_lock(&queue->mutex);
> >>> +	ret = vb2_read(&queue->queue, buf, count, ppos,
> >>> +		       file->f_flags & O_NONBLOCK);
> >>> +	mutex_unlock(&queue->mutex);
> >>> +
> >>> +	return ret;
> >>> +}
> >>> +
> >>>   int uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
> >>>   {
> >>>   	return vb2_mmap(&queue->queue, vma);
> >>> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> >>> index 84be596..3866832 100644
> >>> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> >>> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> >>> @@ -594,7 +594,8 @@ static int uvc_ioctl_querycap(struct file *file, void *fh,
> >>>   	strscpy(cap->driver, "uvcvideo", sizeof(cap->driver));
> >>>   	strscpy(cap->card, vdev->name, sizeof(cap->card));
> >>>   	usb_make_path(stream->dev->udev, cap->bus_info, sizeof(cap->bus_info));
> >>> -	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING
> >>> +	cap->capabilities = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_STREAMING |
> >>> +			    V4L2_CAP_READWRITE
> >>>   			  | chain->caps;
> >>>   
> >>>   	return 0;
> >>> @@ -1434,8 +1435,12 @@ static long uvc_v4l2_compat_ioctl32(struct file *file,
> >>>   static ssize_t uvc_v4l2_read(struct file *file, char __user *data,
> >>>   		    size_t count, loff_t *ppos)
> >>>   {
> >>> -	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read: not implemented.\n");
> >>> -	return -EINVAL;
> >>> +	struct uvc_fh *handle = file->private_data;
> >>> +	struct uvc_streaming *stream = handle->stream;
> >>> +
> >>> +	uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_read\n");
> >>> +
> >>> +	return uvc_queue_read(&stream->queue, file, data, count, ppos);
> >>>   }
> >>>   
> >>>   static int uvc_v4l2_mmap(struct file *file, struct vm_area_struct *vma)
> >>> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> >>> index c7c1baa..5d0515c 100644
> >>> --- a/drivers/media/usb/uvc/uvcvideo.h
> >>> +++ b/drivers/media/usb/uvc/uvcvideo.h
> >>> @@ -766,6 +766,8 @@ struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
> >>>   					 struct uvc_buffer *buf);
> >>>   struct uvc_buffer *uvc_queue_get_current_buffer(struct uvc_video_queue *queue);
> >>>   void uvc_queue_buffer_release(struct uvc_buffer *buf);
> >>> +ssize_t uvc_queue_read(struct uvc_video_queue *queue, struct file *file,
> >>> +		       char __user *buf, size_t count, loff_t *ppos);
> >>>   int uvc_queue_mmap(struct uvc_video_queue *queue,
> >>>   		   struct vm_area_struct *vma);
> >>>   __poll_t uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,

-- 
Regards,

Laurent Pinchart