how is register_(buffer|file) supposed to work?

[Glauber Costa <glauber@scylladb.com>]

Hi,

I am trying to experiment with the interface for registering files and buffers.

(almost) Every time I call io_uring_register with those opcodes, my
application hangs.

It's easy to see the reason. I am blocking here:

                mutex_unlock(&ctx->uring_lock);
                ret = wait_for_completion_interruptible(&ctx->completions[0]);
                mutex_lock(&ctx->uring_lock);

Am I right in my understanding that this is waiting for everything
that was submitted to complete? Some things in my ring may never
complete: for instance one may be polling for file descriptors that
may never really become ready.

This sounds a bit too restrictive to me. Is this really the intended
use of the interface?