Hi Luca,

> According to the V4L2 API, the prot argument of the mmap()
> system call must be set to PROT_READ | PROT_WRITE by the caller
> (whetever is the direction of data exchange):
>
> http://www.linuxtv.org/downloads/video4linux/API/V4L2_API/spec-single/v4l2.
>html#FUNC-MMAP
>
> The UVC driver should enforce this requirement by  checking  the memory
> flags and returning the -EACCESS error code to the caller, in case of
> missing flags.

Thanks for pointing this out. Out of curiosity, do you have any idea why 
PROT_WRITE is required for video acquisition mappings ? Without PROT_WRITE, 
user space applications can't write to the buffer. I haven't been able to 
find any other implication.

Best regards,

Laurent Pinchart
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