Re: [PATCH 3/8] fs: add file_operations->uring_cmd()

[Christoph Hellwig <hch@lst.de>]

On Wed, Mar 17, 2021 at 04:10:22PM -0600, Jens Axboe wrote:
> This is a file private handler, similar to ioctls but hopefully a lot
> more sane and useful.

I really hate defining the interface in terms of io_uring.  This really
is nothing but an async ioctl.

> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index ec8f3ddf4a6a..009abc668987 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1884,6 +1884,15 @@ struct dir_context {
>  #define REMAP_FILE_ADVISORY		(REMAP_FILE_CAN_SHORTEN)
>  
>  struct iov_iter;
> +struct io_uring_cmd;
> +
> +/*
> + * f_op->uring_cmd() issue flags
> + */
> +enum io_uring_cmd_flags {
> +	IO_URING_F_NONBLOCK		= 1,
> +	IO_URING_F_COMPLETE_DEFER	= 2,
> +};

I'm a little worried about exposing a complete io_uring specific
concept like IO_URING_F_COMPLETE_DEFER to random drivers.  This
needs to be better encapsulated.

>  struct file_operations {
>  	struct module *owner;
> @@ -1925,6 +1934,8 @@ struct file_operations {
>  				   struct file *file_out, loff_t pos_out,
>  				   loff_t len, unsigned int remap_flags);
>  	int (*fadvise)(struct file *, loff_t, loff_t, int);
> +
> +	int (*uring_cmd)(struct io_uring_cmd *, enum io_uring_cmd_flags);

As of this patch io_uring_cmd is still a private structure.  In general
I'm not sure this patch makes much sense on its own either.