[PATCHSET v4 next 0/5] 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, patch 4 adds support
for IORING_ASYNC_CANCEL_FD, and patch 5 adds support for matching
any request (useful with CANCEL_ALL).

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.

If IORING_ASYNC_CANCEL_ANY is set, all requests are matched vs using
the fd or user_data key.

There's some support in the below liburing branch:

https://git.kernel.dk/cgit/liburing/log/?h=cancel-fd-all

which also has various test cases.

v4:
- Minor cleanups
- Rebase on current tree
- Add IORING_ASYNC_CANCEL_ANY

-- 
Jens Axboe