Writing to eventfd from kernel module

Question

I have created an eventfd instance in a userspace program using eventfd(). Is there a way in which I can pass some reference (a pointer to its struct or pid+fd pair) to this

Answer 1

Consult the kernel source here:

http://lxr.free-electrons.com/source/fs/eventfd.c

Basically, send your userspace file descriptor, as produced by eventfd(), to your module via ioctl() or some other path. From the kernel, call eventfd_ctx_fdget() to get an eventfd context, then eventfd_signal() on the resulting context. Don't forget eventfd_ctx_put() when you're done with the context.