Waiting / Blocking in a Linux Driver Part 4

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In the last article, we discussed the usage of wait queues in Linux kernel. We saw the variants of wait_event(). Just for completeness, we will discuss how the wait queues are implemented internally. First step is the creation and initialization of wait queue entry. This is done as below:


Next step is to add the wait queue entry to the queue and set the process state. Both of these things are being done by a single function declared below:

prepare_to_wait(wait_queue_head_t *wq_head, wait_queue_t *wq, int state);

After this, we schedule out the process by invoking the schedule() API. Once we are done with waiting, next step is to clean up with the API below:

finish_wait(wait_queue_head_t *wq_head, wait_queue_t *wq);

All the above are available from:

#include <linux/wait.h>

One more point worth noting is that the condition has to be tested manually as was done in our earlier article.

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