[PATCH v6 0/5] io_uring: buffer registration enhancements

[Bijan Mottahedeh <bijan.mottahedeh@oracle.com>]

v6:

- address v5 comments
- rebase on Pavel's rsrc generalization changes
- see also TBD section below

v5:

- call io_get_fixed_rsrc_ref for buffers
- make percpu_ref_release names consistent
- rebase on for-5.12/io_uring
- see also TBD section below

v4:

- address v3 comments (TBD REGISTER_BUFFERS)
- rebase

v3:

- batch file->rsrc renames into a signle patch when possible
- fix other review changes from v2
- fix checkpatch warnings

v2:

- drop readv/writev with fixed buffers patch
- handle ref_nodes both both files/buffers with a single ref_list
- make file/buffer handling more unified

This patchset implements a set of enhancements to buffer registration
consistent with existing file registration functionality:

- buffer registration updates		IORING_REGISTER_BUFFERS_UPDATE
					IORING_OP_BUFFERS_UPDATE

- buffer registration sharing		IORING_SETUP_SHARE_BUF
					IORING_SETUP_ATTACH_BUF

Patch 1 calls io_get_fixed_rsrc_ref() for buffers as well as files.

Patch 2 applies fixed_rsrc functionality for fixed buffers support.

Patch 3 generalize files_update functionality to rsrc_update.

Patch 4 implements buffer registration update, and introduces
IORING_REGISTER_BUFFERS_UPDATE and IORING_OP_BUFFERS_UPDATE, consistent
with file registration update.

Patch 5 implements buffer sharing among multiple rings; it works as follows:

- A new ring, A,  is setup. Since no buffers have been registered, the
  registered buffer state is an empty set, Z. That's different from the
  NULL state in current implementation.

- Ring B is setup, attaching to Ring A. It's also attaching to it's
  buffer registrations, now we have two references to the same empty
  set, Z.

- Ring A registers buffers into set Z, which is no longer empty.

- Ring B sees this immediately, since it's already sharing that set.

Testing

I have used liburing file-{register,update} tests as models for
buffer-{register,update,share}, tests and they run ok. Liburing test/self
fails but seems unrelated to these changes.

TBD

- Need a patch from Pavel to address a race between fixed IO from async
context and buffer unregister, or force buffer registration ops to do
full quiesce.

Bijan Mottahedeh (5):
  io_uring: call io_get_fixed_rsrc_ref for buffers
  io_uring: implement fixed buffers registration similar to fixed files
  io_uring: generalize files_update functionlity to rsrc_update
  io_uring: support buffer registration updates
  io_uring: support buffer registration sharing

 fs/io_uring.c                 | 448 +++++++++++++++++++++++++++++++++++++-----
 include/uapi/linux/io_uring.h |   4 +
 2 files changed, 403 insertions(+), 49 deletions(-)

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1.8.3.1