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How to store the latest image without modifying videobuf-core.c


I am developing a driver for a camera. As an example I am using the vivi driver (2.6.28) and the first major difference between my ISR and thread_tick() is that my driver will always attempt to store the latest image, even if nobody is waiting for a new image. 

In my driver, when all queued buffers are used any new images will be stored in the oldest frame which has already been captured (state == VIDEOBUF_DONE) and here is where my problems start. (If this is wrong, what shall I do to always keep the latest captured image?)

In the function videobuf_dqbuf in videobuf-core.c, if a new image is returned by stream_next_buffer and the ISR kicks in before videobuf_dqbuf can set buf->state to VIDEOBUF_IDLE, my driver will modify the image presented to userspace and that is not acceptable. 

The only solution I can find is to use the spinlock in videobuf_queue when the userspace application is requesting a new image (DQBUF/poll) to check for a new image and set some flag indicating that the buffer can't be overwritten by the ISR. However, this approach would require changes to videobuf-core.c and that doesn't seem right. Can someone please give me some guidance on this? 


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