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Re: Questions about the device driver framework

From: Vittore Scolari
Subject: Re: Questions about the device driver framework
Date: Sat, 22 Jan 2005 00:22:11 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040804

Daniel Wagner wrote:

Why there is the need for a virtual driver?

The ddf should not have knowlegde about the OS which is using it.  So
the real driver can't implement OS dependent code.

Can't deva, which is OS dependent, trust access to drivers?

It could but that would serialize all access through deva ->
bottleneck.  As soon the real driver trusts a virtual driver they can
communicate without the help of deva.

Yes, but i don't understand why deva would be a bottleneck. If the ddf would be a library on top of deva (better if there would be a deva for each driver) then deva could be thin and really fast.

Also this would make ddf easier to port on different (l4?)-os. You would just write a replacement for deva, no need for a virtual driver for every os.

Of course, the more ddf is portable, the more it is difficult to implement it efficently. There must be libraries for replacement of:
- c standard functions
- memory menagement (also for mapping buffers from users)
- security (p.e. entropy)
- trust
- drivers interfaces

And all this libraries (that we can call deva) shouldn't rely on os-dependant facilities, because there could be not.

Having deva as a library can also give a fast way to use os resources if they exists.


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