io_uring IO interface

Here's v2 of the io_uring interface. See the v1 posting for some more info:

https://lore.kernel.org/linux-block/20190108165645.19311-...

The data structures changed, to improve the symmetry of the submission
and completion side. The io_uring_iocb is now io_uring_sqe, but it
otherwise remains the same as before. Ditto on the completion side,
where io_uring_event is now io_uring_cqe.

I've updated the fio io_uring test app, and the io_uring engine. The
liburing git repo has also been adapted to the various changes since the
v1 posting. As a reminder, the liburing git repo contains some helpers
for doing IO without having to muck with the ring directly, setting up
an io_uring context, etc. Clone that here:

git://git.kernel.dk/liburing

In terms of usage, there's also a small test app here:

http://git.kernel.dk/cgit/fio/plain/t/io_uring.c

and the liburing repo has a few test apps in test/ as well.

Patches are aginst 5.0-rc1, but can also be found here:

git://git.kernel.dk/linux-block io_uring

Changes since v1:

- Fail IORING_OP_{READ,WRITE}_FIXED if not configured
- Fix ctx drop ref issue on failure to close ring_fd when sq thread/wq
  are in use
- Move to separate Kconfig entry (CONFIG_IO_URING)
- Add SPDX headers
- Drop gcc ism of zero sized arrays
- Rename io_uring_iocb -> io_uring_sqe
- Rename io_uring_event -> io_uring_cqe
- Drop needless io_event_ring and io_iocb_ring structures
- Drop ctx->max_reqs, use ->sq_entries
- Drop unused ->ring_lock
- Drop io_ring_ctx slab cache
- Fix state batched kiocb alloc failure to put ctx
- Fix missing write ordering barrier when filling in the cqe
- Drop io_req_init()
- Various renames
- Fix a few lines that were too long
- Address other minor review comments
- Fix IORING_SETUP_SQPOLL being set without IORING_SETUP_SQTHREAD
- Drop IORING_SETUP_FIXEDBUFS, iovecs being non-NULL is enough
- Fix error handling free of ctx in setup path
- Change standard read/write commands to be iov based READV/WRITEV
- Pass in struct sqe_submit instead of separate sqe/index everywhere
- Fix reap of polled events on fops->release()
- Lock uring for sq thread polling
- Don't grab ->completion_lock for polled IO cqe filling
- Fix ev_flags vs flags typo
- Consolidate parts of the io_ring_ctx alignment

 Documentation/filesystems/vfs.txt      |    3 +
 arch/x86/entry/syscalls/syscall_64.tbl |    2 +
 block/bio.c                            |   59 +-
 fs/Makefile                            |    1 +
 fs/block_dev.c                         |   19 +-
 fs/file.c                              |   15 +-
 fs/file_table.c                        |    9 +-
 fs/gfs2/file.c                         |    2 +
 fs/io_uring.c                          | 1890 ++++++++++++++++++++++++
 fs/iomap.c                             |   48 +-
 fs/xfs/xfs_file.c                      |    1 +
 include/linux/bio.h                    |   14 +
 include/linux/blk_types.h              |    1 +
 include/linux/file.h                   |    2 +
 include/linux/fs.h                     |    6 +-
 include/linux/iomap.h                  |    1 +
 include/linux/syscalls.h               |    5 +
 include/uapi/linux/io_uring.h          |  114 ++
 init/Kconfig                           |    8 +
 kernel/sys_ni.c                        |    2 +
 20 files changed, 2163 insertions(+), 39 deletions(-)

-- 
Jens Axboe