accessing files, devices, in kernel modules

hi there!

I have just started studying the linux kernel, version 2.6. i read some
manuals, howtos, have already made some really simple modules, but when
I tried to do a little more complex work, I stumbled across some
dificulties.
well, what I want to is a kernel module that opens a regular file,
writes something to it, and closes it. easy, isn't it? I also thought
that ;)

but then I tried making a simple open over the file, but the module
complains it can't find the symbols open, close and write. Is there
anything unusual I must do to work with files in the kernel? none of
the manuals I read mentioned how to open and do some I/O over it.

now, to my real problem: I must record some sound, and then play it!
since in LInux everything is a file, I'm able to do it by means of
/dev/dsp. that's why I asked abou t how to work with regular files. but
I don't know if this way of accessing devices hold for modules. and I
can't open that file!

I looked at /proc/kallsyms, and open is there. I don't have a clue why
the module complains it couldn't find the open.

thanks for any help you could provide, and sorry for such noob question

.

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