Hello Guys, This patch extends io_uring/splice by adding two flags(SPLICE_F_DIRECT & SPLICE_F_READ_TO_READ) for supporting ublk zero copy, and fuse could benefit from the change too. - SPLICE_F_DIRECT is for using do_splice_direct() to support zero copy - SPLICE_F_READ_TO_READ is for supporting ublk READ zero copy, the plain splice can support WRITE zero copy by: splice(ublkc_fd, ublkc_pos, pipe_wr_fd, NULL, len, flags) splice(pipe_rd_fd, NULL, backing_fd, backing_off, len, flags) but can't support READ zc. Extend splice to allow to splice from the 1st ->splice_read()(producer) to the 2nd ->splice_read()(consumer), then READ request pages reference can be transferred to backing IO code path. The initial idea is suggested by Miklos Szeredi & Stefan Hajnoczi. The patchset has been verified basically by ublk builtin tests(loop/008, loop/009, generic/003), and basic mount, git clone, kernel building, umount tests on ublk-loop[1] which is created by 'ublk add -t loop -f $backing -z'. The next step is to allow io_uring to run do_splice_direct*() in async style like normal async RW instead of offloading to iowq context, so that top performance can be reached, and that depends on current work. Any comments are welcome. [1] https://github.com/ming1/ubdsrv/commits/splice-zc Ming Lei (4): io_uring/splice: support do_splice_direct fs/splice: add helper of splice_dismiss_pipe() io_uring/splice: support splice from ->splice_read to ->splice_read ublk_drv: support splice based read/write zero copy drivers/block/ublk_drv.c | 151 +++++++++++++++++++++++++- fs/read_write.c | 5 +- fs/splice.c | 193 +++++++++++++++++++++++++++++----- include/linux/fs.h | 2 + include/linux/pipe_fs_i.h | 9 ++ include/linux/splice.h | 14 +++ include/uapi/linux/ublk_cmd.h | 34 +++++- io_uring/splice.c | 16 ++- 8 files changed, 392 insertions(+), 32 deletions(-) -- 2.31.1
