Waiting for long running ioctl on a non-blocking file descriptor

Question

Take a serial port. A serial port can call ioctl with TIOCMIWAIT to wait for a signal change. However if the serial port is open as non-blocking, how does one use something like select, poll or epoll to break out of an event-loop when a signal line like CTS changes? Lets assume that the serial port is also used heavily for reading and writing. Spawning another thread seems like a bad option.

On Windows, OVERLAPPED IO solves this problem perfectly.

I am interested in the specific case listed above but also how to approach writing device drivers that need to pass an interrupt to user space.

As far as I can tell, such a mechanism does not exist. I have spent quite a while looking for one. I'm on the verge of designing and documenting a `TIOCMNOTIFY` call which registers interest for later notification via `poll`() et.al. Though I've no idea how to argue that into Linux kernel... :/ — LeoNerd, Jul 02 '19 at 15:24

score 0 · Answer 1 · answered Aug 05 '18 at 08:45

0

I think you may want to look at using pselect(). It's the same as select() but it also allows you to set a signal mask. An example of how to use pselect can be found in the top answer here:

catching signals while reading from pipe with select()

answered Aug 05 '18 at 08:45

hermit

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Does not really help since what signal will be generated by the ioctl? – doron Aug 05 '18 at 11:05

Waiting for long running ioctl on a non-blocking file descriptor

1 Answers1