[PATCHSET v3 next 0/4] Extend cancelation support

[Jens Axboe <axboe@kernel.dk>]

Hi,

We currently only support looking up and canceling requests based on
the user_data of the original request. Sometimes it can be useful to
instead key off the fd used in the original request, eg if a socket
goes away.

Patch 1 is just a cleanup spotted while doing this, 2 is a prep patch,
patch 3 adds support for IORING_ASYNC_CANCEL_ALL, and finally patch 4
adds support for IORING_ASYNC_CANCEL_FD.

If IORING_ASYNC_CANCEL_ALL is set, all requests matching the given
criteria are canceled. Return value is number of requests canceled,
and 0 if none were found, or any error encountered canceling requests.

If IORING_ASYNC_CANCEL_FD is set, requests matching sqe->fd are
canceled rather than matching on sqe->addr for user_data.

v3:
- Fixup issues with CANCEL_ALL
- Combine two prep patches, and extent io_cancel_data propagation
  further.
- Get rid of buggy task_work running, we don't need it anymore.

-- 
Jens Axboe