[RFC 0/8] io_uring: buffer registration enhancements

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

Hi Jens,

This RFC 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

- readv/writev with fixed buffers	IOSQE_FIXED_BUFFER

- buffer registration sharing		IORING_SETUP_SHARE_BUF
					IORING_SETUP_ATTACH_BUF

Patches 1,2 modularize existing buffer registration code.

Patch 3 generalizes fixed_file functionality to fixed_rsrc.

Patch 4 applies fixed_rsrc functionality for fixed buffers support.

Patch 5 generalizes files_update functionality to rsrc_update.

Patch 6 implements buffer registration update, and introduces
IORING_REGISTER_BUFFERS_UPDATE and IORING_OP_BUFFERS_UPDATE, consistent
with file registration update.

Patch 7 implements readv/writev support with fixed buffers, and introduces
IOSQE_FIXED_BUFFER, consistent with fixed files.

Patch 8 implements buffer sharing among multiple rings; it works as
follows based on previous conversations:

- 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.

TBD

- I think I have to add IORING_UNREGISTER_BUFFERS to
  io_register_op_must_quiesce() but wanted to confirm.

- IORING_OP_SHUTDOWN has been removed but still in liburing, not sure why.
  I wanted to verify before removing that functionality.

I have used liburing file-{register,update} tests as models for
buffer-{register,update}, and it seems to work ok.

Bijan Mottahedeh (8):
  io_uring: modularize io_sqe_buffer_register
  io_uring: modularize io_sqe_buffers_register
  io_uring: generalize fixed file functionality
  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 readv/writev with fixed buffers
  io_uring: support buffer registration sharing

 fs/io_uring.c                 | 1021 ++++++++++++++++++++++++++++++++---------
 include/uapi/linux/io_uring.h |   15 +-
 2 files changed, 807 insertions(+), 229 deletions(-)

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1.8.3.1