[PATCH RFC v6 00/16] fuse: fuse-over-io-uring

[Bernd Schubert <bschubert@ddn.com>]

[Still marked as RFC as I need to run tests on this version
and need to review myself. The design should be complete now.]

This adds support for uring communication between kernel and
userspace daemon using opcode the IORING_OP_URING_CMD. The basic
approach was taken from ublk.

Motivation for these patches is all to increase fuse performance,
by:
- Reducing kernel/userspace context switches
    - Part of that is given by the ring ring - handling multiple 
      requests on either side of kernel/userspace without the need
      to switch per request
    - Part of that is FUSE_URING_REQ_COMMIT_AND_FETCH, i.e. submitting 
      the result of a request and fetching the next fuse request
      in one step. In contrary to legacy read/write to /dev/fuse
- Core and numa affinity - one ring per core, which allows to
  avoid cpu core context switches

A more detailed motivation description can be found in the
introction of previous patch series
https://lore.kernel.org/r/20241016-fuse-uring-for-6-10-rfc4-v4-0-9739c753666e@ddn.com
That description also includes benchmark results with RFCv1.
Performance with the current series needs to be tested, but will
be lower, as several optimization patches are missing, like
wake-up on the same core. These optimizations will be submitted
after merging the main changes.

The corresponding libfuse patches are on my uring branch, but needs
cleanup for submission - that will be done once the kernel design
will not change anymore
https://github.com/bsbernd/libfuse/tree/uring

Testing with that libfuse branch is possible by running something
like:

example/passthrough_hp -o allow_other --debug-fuse --nopassthrough \
--uring  --uring-q-depth=128 /scratch/source /scratch/dest

With the --debug-fuse option one should see CQE in the request type,
if requests are received via io-uring:

cqe unique: 4, opcode: GETATTR (3), nodeid: 1, insize: 16, pid: 7060
    unique: 4, result=104

Without the --uring option "cqe" is replaced by the default "dev"

dev unique: 4, opcode: GETATTR (3), nodeid: 1, insize: 56, pid: 7117
   unique: 4, success, outsize: 120

Future work
- different payload sizes per ring
- zero copy

Signed-off-by: Bernd Schubert <bschubert@ddn.com>
---
Changes in v6:
- Update to linux-6.12
- Use 'struct fuse_iqueue_ops' and redirect fiq->ops once
  the ring is ready.
- Fix return code from fuse_uring_copy_from_ring on
  copy_from_user failure (Dan Carpenter / kernel test robot)
- Avoid list iteration in fuse_uring_cancel (Joanne)
- Simplified struct fuse_ring_req_header
	- Adds a new 'struct struct fuse_ring_ent_in_out'
- Fix assigning ring->queues[qid] in fuse_uring_create_queue,
  it was too early, resulting in races
- Add back 'FRRS_INVALID = 0' to ensure ring-ent states always
  have a value > 0
- Avoid assigning struct io_uring_cmd *cmd->pdu multiple times,
  once on settings up IO_URING_F_CANCEL is sufficient for sending
  the request as well.
- Link to v5: https://lore.kernel.org/r/20241107-fuse-uring-for-6-10-rfc4-v5-0-e8660a991499@ddn.com

Changes in v5:
- Main focus in v5 is the separation of headers from payload,
  which required to introduce 'struct fuse_zero_in'.
- Addressed several teardown issues, that were a regression in v4.
- Fixed "BUG: sleeping function called" due to allocation while
  holding a lock reported by David Wei
- Fix function comment reported by kernel test rebot
- Fix set but unused variabled reported by test robot
- Link to v4: https://lore.kernel.org/r/20241016-fuse-uring-for-6-10-rfc4-v4-0-9739c753666e@ddn.com

Changes in v4:
- Removal of ioctls, all configuration is done dynamically
  on the arrival of FUSE_URING_REQ_FETCH
- ring entries are not (and cannot be without config ioctls)
  allocated as array of the ring/queue - removal of the tag
  variable. Finding ring entries on FUSE_URING_REQ_COMMIT_AND_FETCH
  is more cumbersome now and needs an almost unused 
  struct fuse_pqueue per fuse_ring_queue and uses the unique
  id of fuse requests.
- No device clones needed for to workaroung hanging mounts
  on fuse-server/daemon termination, handled by IO_URING_F_CANCEL
- Removal of sync/async ring entry types
- Addressed some of Joannes comments, but probably not all
- Only very basic tests run for v3, as more updates should follow quickly.

Changes in v3
- Removed the __wake_on_current_cpu optimization (for now
  as that needs to go through another subsystem/tree) ,
  removing it means a significant performance drop)
- Removed MMAP (Miklos)
- Switched to two IOCTLs, instead of one ioctl that had a field
  for subcommands (ring and queue config) (Miklos)
- The ring entry state is a single state and not a bitmask anymore
  (Josef)
- Addressed several other comments from Josef (I need to go over
  the RFCv2 review again, I'm not sure if everything is addressed
  already)

- Link to v3: https://lore.kernel.org/r/20240901-b4-fuse-uring-rfcv3-without-mmap-v3-0-9207f7391444@ddn.com
- Link to v2: https://lore.kernel.org/all/20240529-fuse-uring-for-6-9-rfc2-out-v1-0-d149476b1d65@ddn.com/
- Link to v1: https://lore.kernel.org/r/20240529-fuse-uring-for-6-9-rfc2-out-v1-0-d149476b1d65@ddn.com

---
Bernd Schubert (15):
      fuse: rename to fuse_dev_end_requests and make non-static
      fuse: Move fuse_get_dev to header file
      fuse: Move request bits
      fuse: Add fuse-io-uring design documentation
      fuse: make args->in_args[0] to be always the header
      fuse: {uring} Handle SQEs - register commands
      fuse: Make fuse_copy non static
      fuse: Add fuse-io-uring handling into fuse_copy
      fuse: {uring} Add uring sqe commit and fetch support
      fuse: {uring} Handle teardown of ring entries
      fuse: {uring} Allow to queue fg requests through io-uring
      fuse: {uring} Allow to queue to the ring
      fuse: {uring} Handle IO_URING_F_TASK_DEAD
      fuse: {io-uring} Prevent mount point hang on fuse-server termination
      fuse: enable fuse-over-io-uring

Pavel Begunkov (1):
      io_uring/cmd: let cmds to know about dying task

 Documentation/filesystems/fuse-io-uring.rst |  101 ++
 fs/fuse/Kconfig                             |   12 +
 fs/fuse/Makefile                            |    1 +
 fs/fuse/dax.c                               |   13 +-
 fs/fuse/dev.c                               |  139 +--
 fs/fuse/dev_uring.c                         | 1339 +++++++++++++++++++++++++++
 fs/fuse/dev_uring_i.h                       |  201 ++++
 fs/fuse/dir.c                               |   41 +-
 fs/fuse/fuse_dev_i.h                        |   69 ++
 fs/fuse/fuse_i.h                            |   21 +
 fs/fuse/inode.c                             |    5 +-
 fs/fuse/xattr.c                             |    9 +-
 include/linux/io_uring_types.h              |    1 +
 include/uapi/linux/fuse.h                   |   57 ++
 io_uring/uring_cmd.c                        |    6 +-
 15 files changed, 1939 insertions(+), 76 deletions(-)
---
base-commit: 3022e9d00ebec31ed435ae0844e3f235dba998a9
change-id: 20241015-fuse-uring-for-6-10-rfc4-61d0fc6851f8

Best regards,
-- 
Bernd Schubert <bschubert@ddn.com>