Re: [PATCH RFC] io_uring: support ioctl

[Pavel Begunkov <asml.silence@gmail.com>]

On 02/11/2020 07:44, Hao Xu wrote:
> Async ioctl is necessary for some scenarios like nonblocking
> single-threaded model

Once I fell for it myself, see Jann explained why that's a bad idea.
https://lore.kernel.org/io-uring/CAG48ez0N_b+kjbddhHe+BUvSnOSvpm1vdfQ9cv+cgTLuCMXqug@mail.gmail.com/

> 
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
> I've written corresponding liburing tests for this feature. Currently
> just a simple test for BLKGETSIZE operation. I'll release it later soon
> when it gets better.
> 
>  fs/io_uring.c                 | 56 +++++++++++++++++++++++++++++++++++++++++++
>  fs/ioctl.c                    |  4 ++--
>  include/linux/fs.h            |  3 ++-
>  include/uapi/linux/io_uring.h |  1 +
>  4 files changed, 61 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index b42dfa0243bf..c8ab6b6d2d70 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -539,6 +539,13 @@ struct io_statx {
>  	struct statx __user		*buffer;
>  };
>  
> +struct io_ioctl {
> +	struct file			*file;
> +	unsigned int                    fd;
> +	unsigned int                    cmd;
> +	unsigned long                   arg;
> +};
> +
>  struct io_completion {
>  	struct file			*file;
>  	struct list_head		list;
> @@ -665,6 +672,7 @@ struct io_kiocb {
>  		struct io_splice	splice;
>  		struct io_provide_buf	pbuf;
>  		struct io_statx		statx;
> +		struct io_ioctl         ioctl;
>  		/* use only after cleaning per-op data, see io_clean_op() */
>  		struct io_completion	compl;
>  	};
> @@ -932,6 +940,10 @@ struct io_op_def {
>  		.hash_reg_file		= 1,
>  		.unbound_nonreg_file	= 1,
>  	},
> +	[IORING_OP_IOCTL] = {
> +		.needs_file             = 1,
> +		.work_flags             = IO_WQ_WORK_MM | IO_WQ_WORK_FILES
> +	},
>  };
>  
>  enum io_mem_account {
> @@ -4819,6 +4831,45 @@ static int io_connect(struct io_kiocb *req, bool force_nonblock,
>  }
>  #endif /* CONFIG_NET */
>  
> +static int io_ioctl_prep(struct io_kiocb *req,
> +			 const struct io_uring_sqe *sqe)
> +{
> +	if (sqe->ioprio || sqe->buf_index || sqe->rw_flags)
> +		return -EINVAL;
> +	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
> +		return -EINVAL;
> +
> +	req->ioctl.fd = READ_ONCE(sqe->fd);
> +	req->ioctl.cmd = READ_ONCE(sqe->len);
> +	req->ioctl.arg = READ_ONCE(sqe->addr);
> +	return 0;
> +}
> +
> +static int io_ioctl(struct io_kiocb *req, bool force_nonblock)
> +{
> +	int ret;
> +
> +	if (force_nonblock)
> +		return -EAGAIN;
> +
> +	if (!req->file)
> +		return -EBADF;
> +
> +	ret = security_file_ioctl(req->file, req->ioctl.cmd, req->ioctl.arg);
> +	if (ret)
> +		goto out;
> +
> +	ret = do_vfs_ioctl(req->file, req->ioctl.fd, req->ioctl.cmd, req->ioctl.arg);
> +	if (ret == -ENOIOCTLCMD)
> +		ret = vfs_ioctl(req->file, req->ioctl.cmd, req->ioctl.arg);
> +
> +out:
> +	if (ret)
> +		req_set_fail_links(req);
> +	io_req_complete(req, ret);
> +	return 0;
> +}
> +
>  struct io_poll_table {
>  	struct poll_table_struct pt;
>  	struct io_kiocb *req;
> @@ -5742,6 +5793,8 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  		return io_remove_buffers_prep(req, sqe);
>  	case IORING_OP_TEE:
>  		return io_tee_prep(req, sqe);
> +	case IORING_OP_IOCTL:
> +		return io_ioctl_prep(req, sqe);
>  	}
>  
>  	printk_once(KERN_WARNING "io_uring: unhandled opcode %d\n",
> @@ -5985,6 +6038,9 @@ static int io_issue_sqe(struct io_kiocb *req, bool force_nonblock,
>  	case IORING_OP_TEE:
>  		ret = io_tee(req, force_nonblock);
>  		break;
> +	case IORING_OP_IOCTL:
> +		ret = io_ioctl(req, force_nonblock);
> +		break;
>  	default:
>  		ret = -EINVAL;
>  		break;
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 4e6cc0a7d69c..4ff2eb0d8ee0 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -664,8 +664,8 @@ static int ioctl_file_dedupe_range(struct file *file,
>   * When you add any new common ioctls to the switches above and below,
>   * please ensure they have compatible arguments in compat mode.
>   */
> -static int do_vfs_ioctl(struct file *filp, unsigned int fd,
> -			unsigned int cmd, unsigned long arg)
> +int do_vfs_ioctl(struct file *filp, unsigned int fd,
> +		unsigned int cmd, unsigned long arg)
>  {
>  	void __user *argp = (void __user *)arg;
>  	struct inode *inode = file_inode(filp);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 0bd126418bb6..ad62aa6f6136 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1732,7 +1732,8 @@ int vfs_mkobj(struct dentry *, umode_t,
>  int vfs_utimes(const struct path *path, struct timespec64 *times);
>  
>  extern long vfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
> -
> +extern int do_vfs_ioctl(struct file *filp, unsigned int fd,
> +			unsigned int cmd, unsigned long arg);
>  #ifdef CONFIG_COMPAT
>  extern long compat_ptr_ioctl(struct file *file, unsigned int cmd,
>  					unsigned long arg);
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 98d8e06dea22..4919b4e94c12 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -132,6 +132,7 @@ enum {
>  	IORING_OP_PROVIDE_BUFFERS,
>  	IORING_OP_REMOVE_BUFFERS,
>  	IORING_OP_TEE,
> +	IORING_OP_IOCTL,
>  
>  	/* this goes last, obviously */
>  	IORING_OP_LAST,
> 

-- 
Pavel Begunkov