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System call and preemption...


I want to do the following changes to write() system call...

sys_write()
{
  if (some_condition)
       reschedule the process at a later time (preempt)
   else
     do whatever write does
}

The problem is when I'm checking the condition, I'm in kernel mode, so how do I preempt the process that called write. Also, how do I access the instruction pointer (eip for x86) so that I decrement it to what it was before calling write ? I am trying to decrement the eip because, when the process is rescheduled it should issue write again (and not the "next" instruction).

Is there some other/better way of handling this ?

TIA,
-siddharth

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