Hi Stephan, I'm no expert this is what I think: > 1. What event awakes the process? Has the driver any way to control it? The kernel code executing on behalf of the process is usually waiting for some resource to become available, we sleep because we can't return from the middle and have to wait till we get the resource. For example, consider a write operation being done on a page belonging to a file -by 2 processes. They both can't write to the same page at the same time, so what happens is the kernel locks the first page on behalf of say process 1 and copies data into it, updates its flags and whatever. Now while this is going on, when the other process tries to lock the same page, it will be put to sleep (and added to a wait queue) till the lock is available. You usually don't want to return till you have this resource available. So during this kind of lock, the process is put on a wait queue and when the lock is free, any processes on this queue are woken up. There is usually some sort of a wait queue for each event/resource and on completion of a certain event, processes from these lists are woken up. > 2. Would a timer (kernel timer) do the same? I mean instead calling "schedule()" just > setup and start a timer which will trigger the same driver function until the device > service is completed. You usually don't want to return once you need the resource, so I don't think a timer would work, but maybe someone else can give a better explanation about this. Hope this helps, -Joel -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
