[RFC PATCH 0/4] Read/Write with meta buffer

[Kanchan Joshi <joshi.k@samsung.com>]

This patchset is aimed at getting the feedback on a new io_uring
interface that userspace can use to exchange meta buffer along with
read/write.

Two new opcodes for that: IORING_OP_READ_META and IORING_OP_WRITE_META.
The leftover space in the SQE is used to send meta buffer pointer
and its length. Patch #2 for this.

The interface is supported for block direct IO. Patch #4 for this.
Other two are prep patches.

It has been tried not to touch the hot read/write path, as much as
possible. Performance for non-meta IO is same after the patches [2].
There is some code in the cold path (worker-based async)
though.

Moderately tested by modifying the fio [1] to use this interface
(only for NVMe block devices)

[1] https://github.com/OpenMPDK/fio/tree/feat/test-meta

[2]
without this:

taskset -c 2,5 t/io_uring -b512 -d128 -c32 -s32 -p1 -F1 -B1 -n2 -r4 /dev/nvme0n1 /dev/nvme1n1
submitter=1, tid=2453, file=/dev/nvme1n1, node=-1
submitter=0, tid=2452, file=/dev/nvme0n1, node=-1
polled=1, fixedbufs=1, register_files=1, buffered=0, QD=128
Engine=io_uring, sq_ring=128, cq_ring=128
IOPS=10.02M, BW=4.89GiB/s, IOS/call=31/31
IOPS=10.04M, BW=4.90GiB/s, IOS/call=31/31

With this:
taskset -c 2,5 t/io_uring -b512 -d128 -c32 -s32 -p1 -F1 -B1 -n2 -r4 /dev/nvme0n1 /dev/nvme1n1
submitter=1, tid=2453, file=/dev/nvme1n1, node=-1
submitter=0, tid=2452, file=/dev/nvme0n1, node=-1
polled=1, fixedbufs=1, register_files=1, buffered=0, QD=128
Engine=io_uring, sq_ring=128, cq_ring=128
IOPS=10.02M, BW=4.89GiB/s, IOS/call=31/31
IOPS=10.04M, BW=4.90GiB/s, IOS/call=31/31

Anuj Gupta (3):
  io_uring/rw: Get rid of flags field in struct io_rw
  io_uring/rw: support read/write with metadata
  block: modify bio_integrity_map_user to accept iov_iter as argument

Kanchan Joshi (1):
  block: add support to pass the meta buffer

 block/bio-integrity.c         |  27 ++++++---
 block/fops.c                  |   9 +++
 block/t10-pi.c                |   6 ++
 drivers/nvme/host/ioctl.c     |  11 +++-
 include/linux/bio.h           |  13 +++-
 include/linux/fs.h            |   1 +
 include/uapi/linux/io_uring.h |   6 ++
 io_uring/io_uring.c           |   2 +
 io_uring/opdef.c              |  29 +++++++++
 io_uring/rw.c                 | 108 +++++++++++++++++++++++++++++-----
 io_uring/rw.h                 |   8 +++
 11 files changed, 193 insertions(+), 27 deletions(-)


base-commit: 6f0974eccbf78baead1735722c4f1ee3eb9422cd
-- 
2.25.1