[vlc-devel] [PATCH 2/2] add V4L2 video_output module

Francois Cartegnie fcvlcdev at free.fr
Tue Jan 17 20:50:54 CET 2012

Le 17/01/2012 19:10, Rémi Denis-Courmont a écrit :
>> By same result I meant "not working".
>> It ends up the same way as doing many writes to the device. I have no
>> clue on this.
>> The writev() code was correct as I verified it on the yuv output module.
> If the driver is buggy, complain to linux-media. Or then, it should be 
> documented by V4L2 that writev() is not allowed. But that would be peculiar.

The linux driver documentation says writev() is emulated with write()
when the driver doesn't support vectored I/O. Which looks exactly like
the behaviour I see.

The v4l2_file_operations struct doesn't make reference to vectored I/O.

And this has been confirmed on #V4L
"vectored I/O only works with the read() method. for non-MPEG hardware,
the mmap() and userptr methods offer better performances"


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