[RFC v2 00/11] Add dmabuf read/write via io_uring

[Pavel Begunkov <asml.silence@gmail.com>]

Picking up the work on supporting dmabuf in the read/write path. There
are two main changes. First, it doesn't pass a dma addresss directly by
rather wraps it into an opaque structure, which is extended and
understood by the target driver.

The second big change is support for dynamic attachments, which added a
good part of complexity (see Patch 5). I kept the main machinery in nvme
at first, but move_notify can ask to kill the dma mapping asynchronously,
and any new IO would need to wait during submission, thus it was moved
to blk-mq. That also introduced an extra callback layer b/w driver and
blk-mq.

There are some rough corners, and I'm not perfectly happy about the
complexity and layering. For v3 I'll try to move the waiting up in the
stack to io_uring wrapped into library helpers.

For now, I'm interested what is the best way to test move_notify? And
how dma_resv_reserve_fences() errors should be handled in move_notify?

The uapi didn't change, after registration it looks like a normal
io_uring registered buffer and can be used as such. Only non-vectored
fixed reads/writes are allowed. Pseudo code:

// registration
reg_buf_idx = 0;
io_uring_update_buffer(ring, reg_buf_idx, { dma_buf_fd, file_fd });

// request creation
io_uring_prep_read_fixed(sqe, file_fd, buffer_offset,
                         buffer_size, file_offset, reg_buf_idx);

And as previously, a good bunch of code was taken from Keith's series [1].

liburing based example:

git: https://github.com/isilence/liburing.git dmabuf-rw
link: https://github.com/isilence/liburing/tree/dmabuf-rw

[1] https://lore.kernel.org/io-uring/20220805162444.3985535-1-kbusch@fb.com/

Pavel Begunkov (11):
  file: add callback for pre-mapping dmabuf
  iov_iter: introduce iter type for pre-registered dma
  block: move around bio flagging helpers
  block: introduce dma token backed bio type
  block: add infra to handle dmabuf tokens
  nvme-pci: add support for dmabuf reggistration
  nvme-pci: implement dma_token backed requests
  io_uring/rsrc: add imu flags
  io_uring/rsrc: extended reg buffer registration
  io_uring/rsrc: add dmabuf-backed buffer registeration
  io_uring/rsrc: implement dmabuf regbuf import

 block/Makefile                   |   1 +
 block/bdev.c                     |  14 ++
 block/bio.c                      |  21 +++
 block/blk-merge.c                |  23 +++
 block/blk-mq-dma-token.c         | 236 +++++++++++++++++++++++++++++++
 block/blk-mq.c                   |  20 +++
 block/blk.h                      |   3 +-
 block/fops.c                     |   3 +
 drivers/nvme/host/pci.c          | 217 ++++++++++++++++++++++++++++
 include/linux/bio.h              |  49 ++++---
 include/linux/blk-mq-dma-token.h |  60 ++++++++
 include/linux/blk-mq.h           |  21 +++
 include/linux/blk_types.h        |   8 +-
 include/linux/blkdev.h           |   3 +
 include/linux/dma_token.h        |  35 +++++
 include/linux/fs.h               |   4 +
 include/linux/uio.h              |  10 ++
 include/uapi/linux/io_uring.h    |  13 +-
 io_uring/rsrc.c                  | 201 +++++++++++++++++++++++---
 io_uring/rsrc.h                  |  23 ++-
 io_uring/rw.c                    |   7 +-
 lib/iov_iter.c                   |  30 +++-
 22 files changed, 948 insertions(+), 54 deletions(-)
 create mode 100644 block/blk-mq-dma-token.c
 create mode 100644 include/linux/blk-mq-dma-token.h
 create mode 100644 include/linux/dma_token.h

-- 
2.52.0