[v4,0/4] open/accept directly into io_uring fixed file table

Message

Pavel Begunkov Aug. 25, 2021, 11:25 a.m. UTC

Add an optional feature to open/accept directly into io_uring's fixed
file table bypassing the normal file table. Same behaviour if as the
snippet below, but in one operation:

sqe = io_uring_[open|accept]_prep();
io_uring_submit(sqe);
// ... once we get a CQE back
io_uring_register_files_update(uring_idx, (fd = cqe->res));
close((fd = cqe->res));

The idea is old, and was brough up and implemented a year ago by
Josh Triplett, though haven't sought the light.

The behaviour is controlled by setting sqe->file_index, where 0 implies
the old behaviour using normal file tables. If non-zero value is
specified, then it will behave as described and place the file into a
fixed file slot sqe->file_index - 1. A file table should be already
created, the slot should be valid and empty, otherwise the operation
will fail.

note: IOSQE_FIXED_FILE can't be used as a mode switch, because accept
takes a file, and it already uses the flag with a different meaning.

v2, since RFC:
 - added attribution
 - updated descriptions
 - rebased

v3:
 - EBADF if slot is already used (Josh Triplett)
 - alias index with splice_fd_in (Josh Triplett)
 - fix a bound check bug

v4:
 - separate u32 fields to internally store indexes (Jens, Josh)

Pavel Begunkov (4):
  net: add accept helper not installing fd
  io_uring: openat directly into fixed fd table
  io_uring: hand code io_accept() fd installing
  io_uring: accept directly into fixed file table

 fs/io_uring.c                 | 115 +++++++++++++++++++++++++++++-----
 include/linux/socket.h        |   3 +
 include/uapi/linux/io_uring.h |   5 +-
 net/socket.c                  |  71 +++++++++++----------
 4 files changed, 143 insertions(+), 51 deletions(-)

Comments

Jens Axboe Aug. 25, 2021, 3 p.m. UTC | #1

On 8/25/21 5:25 AM, Pavel Begunkov wrote:
> Add an optional feature to open/accept directly into io_uring's fixed
> file table bypassing the normal file table. Same behaviour if as the
> snippet below, but in one operation:
> 
> sqe = io_uring_[open|accept]_prep();
> io_uring_submit(sqe);
> // ... once we get a CQE back
> io_uring_register_files_update(uring_idx, (fd = cqe->res));
> close((fd = cqe->res));
> 
> The idea is old, and was brough up and implemented a year ago by
> Josh Triplett, though haven't sought the light.
> 
> The behaviour is controlled by setting sqe->file_index, where 0 implies
> the old behaviour using normal file tables. If non-zero value is
> specified, then it will behave as described and place the file into a
> fixed file slot sqe->file_index - 1. A file table should be already
> created, the slot should be valid and empty, otherwise the operation
> will fail.
> 
> note: IOSQE_FIXED_FILE can't be used as a mode switch, because accept
> takes a file, and it already uses the flag with a different meaning.

Updated the tree and picked you davem's ack as well.