> >From a practial point of view though a high performance bttv application
> (unless there ever is V4L async IO read) is going to want to use the
> mmap interface, and so maybe read trade-offs should be selected in favor
> of fuctionality/ease of use rather than performance - i.e. dma to bounce
> buffer and provide non-blocking read and partial read if useful.
I agree. If you care about performance, you likely need multiple
buffers and the mmap() interface anyway. And partial reads are useful
for scripting: "cat /dev/video0 > frame.raw".
Should we to separate frames then? With EOF maybe?
> One problem is that as things stand for some drivers read() is the only
> supported interface so needs to be as efficient as possible.
Do such drivers exist? Is partial read a issue for them? If they
use kernel buffers anyway for some reason (decompress video data from
usb for example), copy_to_user in many small instead of one big chunk
is no big deal.
Gerd
--
Gerd Knorr <[EMAIL PROTECTED]> -- SuSE Labs, Au�enstelle Berlin
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