On Wed, Oct 20, 2021 at 10:49:07AM -0600, Jens Axboe wrote:

It's not used for anything, and we're wasting time passing in zeroes
where we could just ignore it instead. Update all ki_complete users in
the kernel to drop that last argument.

The exception is the USB gadget code, which passes in non-zero. But
since nobody every looks at ret2, it's still pointless.

Yes, the USB gadget passes non-zero, and aio passes that on to
userspace.  So this is an ABI change.  Does it actually matter?
I don't know, but you could CC the relevant maintainers and list
to try to figure that out.