On Thu, Apr 06, 2023 at 09:57:05AM -0700, Breno Leitao wrote:
> Currently uring CMD operation relies on having large SQEs, but future
> operations might want to use normal SQE.
>
> The io_uring_cmd currently only saves the payload (cmd) part of the SQE,
> but, for commands that use normal SQE size, it might be necessary to
> access the initial SQE fields outside of the payload/cmd block. So,
> saves the whole SQE other than just the pdu.
>
> This changes slighlty how the io_uring_cmd works, since the cmd
> structures and callbacks are not opaque to io_uring anymore. I.e, the
> callbacks can look at the SQE entries, not only, in the cmd structure.
>
> The main advantage is that we don't need to create custom structures for
> simple commands.
>
> Suggested-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
> Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
> ---
...
> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> index 2e4c483075d3..9648134ccae1 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -63,14 +63,15 @@ EXPORT_SYMBOL_GPL(io_uring_cmd_done);
> int io_uring_cmd_prep_async(struct io_kiocb *req)
> {
> struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
> - size_t cmd_size;
> + size_t size = sizeof(struct io_uring_sqe);
>
> BUILD_BUG_ON(uring_cmd_pdu_size(0) != 16);
> BUILD_BUG_ON(uring_cmd_pdu_size(1) != 80);
>
> - cmd_size = uring_cmd_pdu_size(req->ctx->flags & IORING_SETUP_SQE128);
> + if (req->ctx->flags & IORING_SETUP_SQE128)
> + size <<= 1;
>
> - memcpy(req->async_data, ioucmd->cmd, cmd_size);
> + memcpy(req->async_data, ioucmd->sqe, size);
The copy will make some fields of sqe become READ TWICE, and driver may see
different sqe field value compared with the one observed in io_init_req().
Can this kind of inconsistency cause trouble to driver?
If it isn't one problem, this patch looks fine.
But I guess any access on cmd->sqe in driver may have to be careful for dealing
with potential post-sqe-update.
Thanks,
Ming
