[libcamera-devel] [PATCH] cam: Limit file write to payload size

[Kieran Bingham]

On 24/08/2020 23:53, Laurent Pinchart wrote:
> On Tue, Aug 25, 2020 at 12:04:11AM +0200, Niklas Söderlund wrote:
>> On 2020-08-24 10:32:24 +0100, Kieran Bingham wrote:
>>> On 22/08/2020 14:40, Laurent Pinchart wrote:
>>>> The payload size in a captured framebuffer is usually equal to the
>>>> buffer size. However, for compressed formats, the payload may be
>>>> smaller Only write the payload when capturing to a file.
>>>>
>>>> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
>>>> ---
>>>>  src/cam/buffer_writer.cpp | 12 ++++++++++--
>>>>  1 file changed, 10 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/src/cam/buffer_writer.cpp b/src/cam/buffer_writer.cpp
>>>> index c5a5eb46224a..6305958924a4 100644
>>>> --- a/src/cam/buffer_writer.cpp
>>>> +++ b/src/cam/buffer_writer.cpp
>>>> @@ -64,9 +64,17 @@ int BufferWriter::write(FrameBuffer *buffer, const std::string &streamName)
>>>>  	if (fd == -1)
>>>>  		return -errno;
>>>>  
>>>> -	for (const FrameBuffer::Plane &plane : buffer->planes()) {
>>>> +	for (unsigned int i = 0; i < buffer->planes().size(); ++i) {
>>>> +		const FrameBuffer::Plane &plane = buffer->planes()[i];
>>>> +		const FrameMetadata::Plane &meta = buffer->metadata().planes[i];
>>>> +
>>>>  		void *data = mappedBuffers_[plane.fd.fd()].first;
>>>> -		unsigned int length = plane.length;
>>>> +		unsigned int length = std::min(meta.bytesused, plane.length);
>>>> +
>>>> +		if (length < meta.bytesused)
>>>> +			std::cerr << "payload size " << meta.bytesused
>>>> +				  << " smaller than plane size " << plane.length
>>>> +				  << std::endl;
>>>
>>> Is the cerr necessary? If saving out an MJPEG stream from an MJPEG UVC
>>> camera - this would print every frame...
>>
>> Now I'm confused :-)
>>
>> Would not the cerr only print if length is set to plane.length while 
>> meta.bytesused is larger? I read this as plane.length being the buffer's 
>> max allocated size while if the cerr triggers the driver is reporitng 
>> that more then the max size is used as bytesused is larger then the 
>> plane?
> 
> The check is correct, but the message isn't. And the check could
> actually be be made clearer.
> 
> 		if (meta.bytesused > plane.length)
> 			std::cerr << "payload size " << meta.bytesused
> 				  << " larger than plane size " << plane.length
> 				  << std::endl;


Ahh, now that would be a lot easier to parse.

+1

--
Kieran


> 
>>> Which is however the use case that makes me believe this patch is useful...
>>>
>>> So with that considered either way,
>>>
>>> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
>>>
>>>>  
>>>>  		ret = ::write(fd, data, length);
>>>>  		if (ret < 0) {
>>>>
> 

-- 
Regards
--
Kieran