functions in a single module

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HI,

   I have 6 functions in a single module, some of those are netfilter hook
functions, others read/write etc functions for a char device, both type of
functions work closely.Plus, I have a couple of timer expiry functions
within my module.  My doubt is : can functions within a single module
pre-empt each other, i use kenel 2.4.20-8, on a uniprocessor system.

My read/write char device functions are used by a user level process, the
char device is used as a control interface between the module and the user
space process. So the user space process sets certain variables using
write() on the char device fd. The netfilter hook functions that reside in
the same module, use these variables(ones set in the char device driver's
write() function ). So as the write function(write()) writes to these
shared variable, can a packet come in and the netfilter hook function be
called, i.e basically the hook function pre-empts the write() function?
Also, what happens when a timer expires, its expiry callback function is
called immediately while write() is in progress, or what exactly happens.

And if they can/do pre-empt each other then what would be the best strategy
to protect these shared variables.

thanks
Amit

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