On Sat, Oct 26, 2024 at 3:13 AM Keith Busch <kbusch@xxxxxxxx> wrote:
>
> From: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
>
> With F_SET_RW_HINT fcntl, user can set a hint on the file inode, and
> all the subsequent writes on the file pass that hint value down. This
> can be limiting for block device as all the writes will be tagged with
> only one lifetime hint value. Concurrent writes (with different hint
> values) are hard to manage. Per-IO hinting solves that problem.
>
> Allow userspace to pass additional metadata in the SQE.
>
> __u16 write_hint;
>
> If the hint is provided, filesystems may optionally use it. A filesytem
> may ignore this field if it does not support per-io hints, or if the
> value is invalid for its backing storage. Just like the inode hints,
> requesting values that are not supported by the hardware are not an
> error.
>
> Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
> Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
> Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx>
> ---
> include/uapi/linux/io_uring.h | 4 ++++
> io_uring/rw.c | 3 ++-
> 2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 60b9c98595faf..8cdcc461d464c 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -92,6 +92,10 @@ struct io_uring_sqe {
> __u16 addr_len;
> __u16 __pad3[1];
> };
> + struct {
> + __u16 write_hint;
> + __u16 __pad4[1];
> + };
> };
> union {
> struct {
> diff --git a/io_uring/rw.c b/io_uring/rw.c
> index 8080ffd6d5712..5a1231bfecc3a 100644
> --- a/io_uring/rw.c
> +++ b/io_uring/rw.c
> @@ -279,7 +279,8 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
> rw->kiocb.ki_ioprio = get_current_ioprio();
> }
> rw->kiocb.dio_complete = NULL;
> -
> + if (ddir == ITER_SOURCE)
> + rw->kiocb.ki_write_hint = READ_ONCE(sqe->write_hint);
> rw->addr = READ_ONCE(sqe->addr);
> rw->len = READ_ONCE(sqe->len);
> rw->flags = READ_ONCE(sqe->rw_flags);
> --
> 2.43.5
>
Since this patch adds a couple of new fields, it makes sense to add
BUILD_BUG_ON() checks in io_uring_init for these fields to assert the
layout of struct io_uring_sqe. And probably a zero check for pad4 in
io_prep_rw.
--
Anuj Gupta
