[PATCH v3 0/8] io_uring: add kernel-managed buffer rings

[Joanne Koong <joannelkoong@gmail.com>]

Currently, io_uring buffer rings require the application to allocate and
manage the backing buffers. This series introduces buffer rings where the
kernel allocates and manages the buffers on behalf of the application. From
the uapi side, this goes through the pbuf ring interface, through the
IOU_PBUF_RING_KERNEL_MANAGED flag.

There was a long discussion with Pavel on v1 [1] regarding the design. The
alternatives were to have the buffers allocated and registered through a
memory region or through the registered buffers interface and have fuse
implement ring buffer logic internally outside of io-uring. However, because
the buffers need to be contiguous for DMA and some high-performance fuse
servers may need non-fuse io-uring requests to use the buffer ring directly,
v3 keeps the design.

This is split out from the fuse-over-io_uring series in [2], which needs the
kernel to own and manage buffers shared between the fuse server and the
kernel. The link to the fuse tree that uses the commits in this series is in
[3].

This series is on top of the for-7.1/io_uring branch in Jens' io-uring
tree (commit ee1d7dc33990). The corresponding liburing changes are in [4] and
will be submitted after the changes in this patchset have landed.

Thanks,
Joanne

[1] https://lore.kernel.org/linux-fsdevel/20260210002852.1394504-1-joannelkoong@gmail.com/T/#t
[2] https://lore.kernel.org/linux-fsdevel/20260116233044.1532965-1-joannelkoong@gmail.com/
[3] https://github.com/joannekoong/linux/commits/fuse_zero_copy_for_v3/
[4] https://github.com/joannekoong/liburing/commits/pbuf_kernel_managed/

Changelog
---------
Changes from v1 -> v3:
* Incorporate Jens' feedback, including fixing wraparound int promotion bug
* uapi: merge kmbuf into pbuf interface/apis as IOU_PBUF_RING_KERNEL_MANAGED
  flag (Pavel)
v1: https://lore.kernel.org/linux-fsdevel/20260210002852.1394504-1-joannelkoong@gmail.com/T/#t

Changes since [1]:
* add "if (bl)" check for recycling API (Bernd)
* check mul overflow, use GFP_USER, use PTR as return type (Christoph)
* fix bl->ring leak (me)

Joanne Koong (8):
  io_uring/kbuf: add support for kernel-managed buffer rings
  io_uring/kbuf: support kernel-managed buffer rings in buffer selection
  io_uring/kbuf: add buffer ring pinning/unpinning
  io_uring/kbuf: return buffer id in buffer selection
  io_uring/kbuf: add recycling for kernel managed buffer rings
  io_uring/kbuf: add io_uring_is_kmbuf_ring()
  io_uring/kbuf: export io_ring_buffer_select()
  io_uring/cmd: set selected buffer index in __io_uring_cmd_done()

 include/linux/io_uring/cmd.h   |  53 ++++++-
 include/linux/io_uring_types.h |  10 +-
 include/uapi/linux/io_uring.h  |  16 ++-
 io_uring/kbuf.c                | 250 +++++++++++++++++++++++++++++----
 io_uring/kbuf.h                |  11 +-
 io_uring/memmap.c              | 111 +++++++++++++++
 io_uring/memmap.h              |   4 +
 io_uring/uring_cmd.c           |   6 +-
 8 files changed, 427 insertions(+), 34 deletions(-)

-- 
2.47.3