I want to create an RTDM driver that uses a thread (rtdm_task_t) to perform
a cyclic job. Although it's possible to start this thread (using
rtdm_task_init) from the module_init code, I'm unsure of how I should
terminate this thread.
I seem to have several options:
1. Just kill the thread with rtdm_task_destroy. This means that the thread
should never block, except on rtdm_task_wait_period, or else it might be
terminated on the blocking instruction and leave the hardware in an unknown
state.
2. Use a stop variable, along with a semaphore to ensure that the thread has
stopped. E.g.:
volatile int stop_requested = 0;
rtdm_sem_t sem;
void the_thread(void *cookie)
{
while (!stop_requested) {
/* Blocking may occur, due to calls to e.g. rtdm_read */
rtdm_task_wait_period();
}
do_some_cleaning_up();
rtdm_sem_up(&sem); /* Release the pending module_exit */
}
void __exit module_exit()
{
stop_requested = 1;
rtdm sem_down(&sem);
rtdm_sem_destroy(&sem);
rtdm_task_destroy(&task);
rtdm_unregister();
}
However, this means I would issue a blocking call in Linux kernel context.
To me, it seems that the whole Linux thread would be suspended, but I just
tried this and it fails (segfault on sem_down and unusable system). Another
question is if I still need to clean up (destroy) a task that has run to
completion ?
3. Unload the module, set a variable as the one above (stop_requested) and
leave the unregistering to the exiting thread. This seems ugly to me, and I
also think that it would crash, as the Linux kernel will remove the program
(including the thread code) from memory.
So, in short, how do I wait in the module_exit ?
Jeroen.
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