Re: [PATCH for-next v12 02/12] io_uring: introduce fixed buffer support for io_uring_cmd

[Jens Axboe <axboe@kernel.dk>]

On 9/30/22 12:27 AM, Anuj Gupta wrote:
> Add IORING_URING_CMD_FIXED flag that is to be used for sending io_uring
> command with previously registered buffers. User-space passes the buffer
> index in sqe->buf_index, same as done in read/write variants that uses
> fixed buffers.
> 
> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> ---
>  include/linux/io_uring.h      |  2 +-
>  include/uapi/linux/io_uring.h |  9 +++++++++
>  io_uring/uring_cmd.c          | 18 +++++++++++++++++-
>  3 files changed, 27 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
> index 1dbf51115c30..e10c5cc81082 100644
> --- a/include/linux/io_uring.h
> +++ b/include/linux/io_uring.h
> @@ -28,7 +28,7 @@ struct io_uring_cmd {
>  		void *cookie;
>  	};
>  	u32		cmd_op;
> -	u32		pad;
> +	u32		flags;
>  	u8		pdu[32]; /* available inline for free use */
>  };
>  
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 92f29d9505a6..ab7458033ee3 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -56,6 +56,7 @@ struct io_uring_sqe {
>  		__u32		hardlink_flags;
>  		__u32		xattr_flags;
>  		__u32		msg_ring_flags;
> +		__u32		uring_cmd_flags;
>  	};
>  	__u64	user_data;	/* data to be passed back at completion time */
>  	/* pack this to avoid bogus arm OABI complaints */
> @@ -219,6 +220,14 @@ enum io_uring_op {
>  	IORING_OP_LAST,
>  };
>  
> +/*
> + * sqe->uring_cmd_flags
> + * IORING_URING_CMD_FIXED	use registered buffer; pass thig flag
> + *				along with setting sqe->buf_index.
> + */
> +#define IORING_URING_CMD_FIXED	(1U << 0)
> +
> +
>  /*
>   * sqe->fsync_flags
>   */
> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> index 6a6d69523d75..05e8ad8cef87 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -4,6 +4,7 @@
>  #include <linux/file.h>
>  #include <linux/io_uring.h>
>  #include <linux/security.h>
> +#include <linux/nospec.h>
>  
>  #include <uapi/linux/io_uring.h>
>  
> @@ -77,7 +78,22 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  {
>  	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
>  
> -	if (sqe->rw_flags || sqe->__pad1)
> +	if (sqe->__pad1)
> +		return -EINVAL;
> +
> +	ioucmd->flags = READ_ONCE(sqe->uring_cmd_flags);
> +	if (ioucmd->flags & IORING_URING_CMD_FIXED) {
> +		struct io_ring_ctx *ctx = req->ctx;
> +		u16 index;
> +
> +		req->buf_index = READ_ONCE(sqe->buf_index);
> +		if (unlikely(req->buf_index >= ctx->nr_user_bufs))
> +			return -EFAULT;
> +		index = array_index_nospec(req->buf_index, ctx->nr_user_bufs);
> +		req->imu = ctx->user_bufs[index];
> +		io_req_set_rsrc_node(req, ctx, 0);
> +	}
> +	if (ioucmd->flags & ~IORING_URING_CMD_FIXED)
>  		return -EINVAL;

Not that it _really_ matters, but why isn't this check the first thing
that is done after reading the flags? No need to respin, I can just move
it myself.

-- 
Jens Axboe