Interaction between user and kernel space

[Thomas Petazzoni <thomas.petazzoni@xxxxxxxx>]

Hello,

Recently, Linus committed a patch from Alan Cox that removes the 
controversial decompressors of the PWC module from the kernel. The 
commit log [1] suggests to reimplement the decompression code in userspace.

I'm wondering how this could work. Webcam drivers are supposed to offer 
to userspace a V4L-compatible API, in order to work with programs such 
as xawtv or gnomemeeting. If the decompression code is not made in 
kernel space, how can the kernel offer a V4L-compatible API for the PWC 
webcams ? Having a library called by the user programs doesn't seem to 
be an option, because it would require an adaptation of all user 
programs, adaptation which would specific to a particular webcam type.

Should the compressed frame be sent to a userspace daemon which 
decompress it and then sends it back to the kernel, which could offer a 
V4L-compatible API ? Isn't it a bit overkilled ?

I just wanted your opinion and ideas about this subject, just for 
curiosity. I'm not saying I will try to do the horrible reverse 
engineering stuff, I just want to understand how it _could_ work.

Thanks !

Thomas

[1] 
http://www.kernel.org/git/gitweb.cgi?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=88c1834633341bbb94e315433067496338bff4ad
--
Thomas Petazzoni
thomas.petazzoni@xxxxxxxx

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