[PATCH V4 00/17] io_uring/ublk: add IORING_OP_FUSED_CMD

[Ming Lei]

Hello Jens,

Add IORING_OP_FUSED_CMD, it is one special URING_CMD, which has to
be SQE128. The 1st SQE(master) is one 64byte URING_CMD, and the 2nd
64byte SQE(slave) is another normal 64byte OP. For any OP which needs
to support slave OP, io_issue_defs[op].fused_slave needs to be set as 1,
and its ->issue() can retrieve/import buffer from master request's
fused_cmd_kbuf. The slave OP is actually submitted from kernel, part of
this idea is from Xiaoguang's ublk ebpf patchset, but this patchset
submits slave OP just like normal OP issued from userspace, that said,
SQE order is kept, and batching handling is done too.

Please see detailed design in commit log of the 2th patch, and one big
point is how to handle buffer ownership.

With this way, it is easy to support zero copy for ublk/fuse device.

Basically userspace can specify any sub-buffer of the ublk block request
buffer from the fused command just by setting 'offset/len'
in the slave SQE for running slave OP. This way is flexible to implement
io mapping: mirror, stripped, ...

The 4th & 5th patches enable fused slave support for the following OPs:

	OP_READ/OP_WRITE
	OP_SEND/OP_RECV/OP_SEND_ZC

The other ublk patches cleans ublk driver and implement fused command
for supporting zero copy.

Follows userspace code, which supports 128byte SQE fused command only:

https://github.com/ming1/ubdsrv/tree/fused-cmd-zc-v2

All three(loop, nbd and qcow2) ublk targets have supported zero copy by passing:

	ublk add -t [loop|nbd|qcow2] -z .... 

Basic fs mount/kernel building and builtin test are done, and also not
observe regression on xfstest test over ublk-loop with zero copy.

Also add liburing test case for covering fused command based on miniublk
of blktest(supports 64byte normal SQE only)

https://github.com/ming1/liburing/commits/fused_cmd_miniublk

Performance improvement is obvious on memory bandwidth related workloads,
such as, 1~2X improvement on 64K/512K BS IO test on loop with ramfs backing file.
ublk-null shows 5X IOPS improvement on big BS test when the copy is avoided.

Please review and consider for v6.4.

V4:
	- improve APIs naming(patch 1 ~ 4)
	- improve documents and commit log(patch 2)
	- add buffer direction bit to opdef, suggested by Jens(patch 2)
	- add ublk zero copy document for cover: technical requirements(most related with
	buffer lifetime), and explains why splice isn't good and how fused command solves it(patch 17)
	- fix sparse warning(patch 7)
	- supports 64byte SQE fused command(patch 3)

V3:
	- fix build warning reported by kernel test robot
	- drop patch for checking fused flags on existed drivers with
	  ->uring_command(), which isn't necessary, since we do not do that
      when adding new ioctl or uring command
    - inline io_init_rq() for core code, so just export io_init_slave_req
	- return result of failed slave request unconditionally since REQ_F_CQE_SKIP
	will be cleared
	- pass xfstest over ublk-loop

V2:
	- don't resue io_mapped_ubuf (io_uring)
	- remove REQ_F_FUSED_MASTER_BIT (io_uring)
	- fix compile warning (io_uring)
	- rebase on v6.3-rc1 (io_uring)
	- grabbing io request reference when handling fused command 
	- simplify ublk_copy_user_pages() by iov iterator
	- add read()/write() for userspace to read/write ublk io buffer, so
	that some corner cases(read zero, passthrough request(report zones)) can
	be handled easily in case of zero copy; this way also helps to switch to
	zero copy completely
	- misc cleanup


Ming Lei (17):
  io_uring: increase io_kiocb->flags into 64bit
  io_uring: add IORING_OP_FUSED_CMD
  io_uring: support normal SQE for fused command
  io_uring: support OP_READ/OP_WRITE for fused slave request
  io_uring: support OP_SEND_ZC/OP_RECV for fused slave request
  block: ublk_drv: mark device as LIVE before adding disk
  block: ublk_drv: add common exit handling
  block: ublk_drv: don't consider flush request in map/unmap io
  block: ublk_drv: add two helpers to clean up map/unmap request
  block: ublk_drv: clean up several helpers
  block: ublk_drv: cleanup 'struct ublk_map_data'
  block: ublk_drv: cleanup ublk_copy_user_pages
  block: ublk_drv: grab request reference when the request is handled by
    userspace
  block: ublk_drv: support to copy any part of request pages
  block: ublk_drv: add read()/write() support for ublk char device
  block: ublk_drv: don't check buffer in case of zero copy
  block: ublk_drv: apply io_uring FUSED_CMD for supporting zero copy

 Documentation/block/ublk.rst   | 126 ++++++-
 drivers/block/ublk_drv.c       | 605 ++++++++++++++++++++++++++-------
 include/linux/io_uring.h       |  49 ++-
 include/linux/io_uring_types.h |  80 +++--
 include/uapi/linux/io_uring.h  |   9 +-
 include/uapi/linux/ublk_cmd.h  |  37 +-
 io_uring/Makefile              |   2 +-
 io_uring/fused_cmd.c           | 259 ++++++++++++++
 io_uring/fused_cmd.h           |  11 +
 io_uring/io_uring.c            |  50 ++-
 io_uring/io_uring.h            |   4 +
 io_uring/net.c                 |  30 +-
 io_uring/opdef.c               |  22 ++
 io_uring/opdef.h               |   7 +
 io_uring/rw.c                  |  20 ++
 15 files changed, 1132 insertions(+), 179 deletions(-)
 create mode 100644 io_uring/fused_cmd.c
 create mode 100644 io_uring/fused_cmd.h

-- 
2.39.2