more POLL... fun

[Al Viro]

On Fri, Dec 04, 2015 at 10:16:50AM +0100, Arnd Bergmann wrote:

> I don't remember why we put in fasync support, but I have checked the libspe
> implementation and found that it doesn't use it (not a big surprise there).
> It always uses epoll() to get notifications from spufs, and based on your
> explanation I assume everything else (there may have been one or two users
> that used the low-level interfaces rather than libspe) did too.

OK...  So should we just rip ->{mfc,ibox,wbox}_fasync out, along with all
three kill_fasync() and ->fasync() instances in there?  We obviously need to
leave spufs_{mfc,ibox,wbox}_callback() in place for the sake of those
wake_up_all(&ctx->{mfc,ibox,wbox}_wq); in them...

I mean, fasync in there obviously never been used at all - it never delivered
a single SIGIO, and the first user to try would get the BUG_ON() in fcntl.c
instead.  Since nobody complained in more than 10 years...