You have to use synchronization techniques like semaphores or spinlocks.
Hi,
I am writing a driver.
I need to make my functions re-entrant, how do I go about writing my functions to make them so ?
Yes I believe so but I don't remember. You have to look at it :)I will have a hash function there, which maintains a list of structures, like the list_head structure(a standard eature of linux kernel) is there any such standard thing given even for hash tables ?
Also, though my system is not SMP, but still if I want to use spinlocks, whats the starting point to read and know about them. A user space process writes the value of a variable to the driver, and the driver has to check this value before doing anything, so I believe this is right place for a spinlock right ?, I dont want one part of the driver to read this variable while it is being updated. Or, do I not need a spin lock because everything would be sequential ? I am not very clear about this.
You should use semaphores instead of spinlocks. Like this : down(sem) CRITICAL SECTION up(sem) The critical is the read or write operation.
You have effectively to protect the reading or the writing of the variable. In this case, I thinl you can't use semaphores. You will have to use spinlocks. You cant't use semaphores in tasklet or interrupt handler. And your hook function will be called inside a tasklet or interrupt handler, right ?Actually my driver would have a char device driver portion and netfilter hook functions, a user level process would write to the char device, and the netfilter hook functions wld read this variable to find whats to be done when they catch packets. So in this scenario would spin locks be needed ?
So you can use spinlocks.
The main rules for spinlocks and semaphores are :
_ Don't hold a spinlock when a function which can sleep is called
_ Don't use semaphorse in a non process context (tasklet,bh,interrupt handler)
_ The spinlocks shouldn't be use if the critiical section is too big
a very good link for locking functions : http://csworks.com:10080/linux/kernel-locking/book1.html
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