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Re: passing data to kernel driver from a file.

On Mon, 9 Oct 2006, sanjay yaragatti wrote:

Hi,

Hi, please don't cross-post to multiple lists. If you don't get an answer from one list after a few days it's OK to resend your question to another. It's not OK to spam both at the same time like this.

I have written a kernel resident driver.I need to pass
some data to the driver which is stored in a file.How
can this be accomplised.Came to know that file
operations are not supported in kernel.Read about the
UserClient but still not clear.Please suggest me how
to pass  data to the driver.

OK, here we go again. File access in the kernel is discouraged (as I have learnt the hard way :). Even if you are accessing it through a UserClient it still imports userland dependencies into the kernel.

So the first question is: why? What are the contents of this file? Is it like a firmware blob that gets loaded once and discarded, or is it a settings file? Something else? Also: when? At boot time or later?

Note that if you're trying to access a resource file within your kext's directory, then I believe that there are even cases where it won't be available (e.g. when netbooted) so you need to worry about that too.

If the file you want is just a firmware blob, then a good way around loading a file is to have a kext in your plugins directory with the blob compiled-in. That way you stay within the kext system and it can even be unloaded when you're done with it.

If however the file is a settings file you will need to go the UserClient route. I have done this before and now have a daemon plus a kext that provides access to files through a nice C++ class. It can even return a .plist file as an OSDictionary. You're welcome to use it or just study it and write your own if you prefer.

Thanks in Advance.. 

No worries.

{P^/
John


(You can find that daemon+kext in my CVS repository, instructions to access it are under 'Development' here: <http://www.defyne.org/dvb/>. Check out Driver/UDMUtils/UDMResourceFile.hpp for the interface. The drivers package on that site installs it all for you if you don't want to build it yourself.)
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 >passing data to kernel driver from a file. (From: sanjay yaragatti <email@hidden>)



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