[POC RFC 0/3] splice(2) support for io_uring

Pavel Begunkov
2020-01-22T00:06:11Z

It works well for basic cases, but there is still work to be done. E.g.
it misses @hash_reg_file checks for the second (output) file. Anyway,
there are some questions I want to discuss:

- why sqe->len is __u32? Splice uses size_t, and I think it's better
to have something wider (e.g. u64) for fututre use. That's the story
behind added sqe->splice_len.

- it requires 2 fds, and it's painful. Currently file managing is done
by common path (e.g. io_req_set_file(), __io_req_aux_free()). I'm
thinking to make each opcode function handle file grabbing/putting
themself with some helpers, as it's done in the patch for splice's
out-file.
1. Opcode handler knows, whether it have/needs a file, and thus
doesn't need extra checks done in common path.
2. It will be more consistent with splice.
Objections? Ideas?

- do we need offset pointers with fallback to file->f_pos? Or is it
enough to have offset value. Jens, I remember you added the first
option somewhere, could you tell the reasoning?

Pavel Begunkov (3):
splice: make do_splice public
io_uring: add interface for getting files
io_uring: add splice(2) support

fs/io_uring.c | 152 ++++++++++++++++++++++++++++------
fs/splice.c | 6 +-
include/linux/splice.h | 3 +
include/uapi/linux/io_uring.h | 16 +++-
4 files changed, 147 insertions(+), 30 deletions(-)

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