volodya@xxxxxxxxxxxxxx wrote:
The major difference is in increased flexibility and stability of
kernel-user space interface.
On the application side:
* ability to utilize advanced driver features without explicit
knowledge of their behaviour
* wider compatibility without the need for recompile
On the kernel side:
* elimination of interfaced specific headers
On the driver side:
* be compatible with a wide range of applications
* introduce support for new features without the need to modify
kernel interfaces
The last point is the very important in my opinion. For example, in
current specification, v4l2 has no support for TV-out in graphics cards.
It has no support for setting complex parameters like gamma tables.
Using memory-mapped buffers requires device specific ioctls.
TV-out _is_ supported. Complex parameters are supported through
ennumeratable controls.
The goal is to create an interface that does not rely on structures
defined in kernel headers for communication.
Possibly a good idea, but memory protection and buffer overrun
protection can often be a problem in these implementations.
(I also doubt that an interface this complex would ever make it into the
kernel.)
It is not very complex. It is much simpler than software modem driver,
for example.
The software modem is a _bad_ example. The interface to the modem is
still very simple.
Ultimately these questions are best answered with a sample implementation.
Would you have any other concerns/suggestions ?
Not really. Streaming capture will need to be reworked, and the
"general" control structure will have to be limmited to make non
hardware specific apps possible.
-justin
