linux-kernel - Re: [PATCH 3/3] io_uring: add splice(2) support

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Date:   Tue, 21 Jan 2020 19:03:33 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:     Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 3/3] io_uring: add splice(2) support

On 1/21/20 5:05 PM, Pavel Begunkov wrote:
> @@ -373,6 +374,15 @@ struct io_rw {
>  	u64				len;
>  };
>  
> +struct io_splice {
> +	struct file			*file_in;
> +	struct file			*file_out;
> +	loff_t __user			*off_in;
> +	loff_t __user			*off_out;
> +	u64				len;
> +	unsigned int			flags;
> +};
> +
>  struct io_connect {
>  	struct file			*file;
>  	struct sockaddr __user		*addr;

Probably just make that len u32 as per previous email.

> @@ -719,6 +730,11 @@ static const struct io_op_def io_op_defs[] = {
>  		.needs_file		= 1,
>  		.fd_non_neg		= 1,
>  	},
> +	[IORING_OP_SPLICE] = {
> +		.needs_file		= 1,
> +		.hash_reg_file		= 1,
> +		.unbound_nonreg_file	= 1,
> +	}
>  };
>  
>  static void io_wq_submit_work(struct io_wq_work **workptr);

I probably want to queue up a reservation for the EPOLL_CTL that I
haven't included yet, but which has been tested. But that's easily
manageable, so no biggy on my end.

> +static bool io_splice_punt(struct file *file)
> +{
> +	if (get_pipe_info(file))
> +		return false;
> +	if (!io_file_supports_async(file))
> +		return true;
> +	return !(file->f_mode & O_NONBLOCK);
> +}
> +
> +static int io_splice(struct io_kiocb *req, struct io_kiocb **nxt,
> +		     bool force_nonblock)
> +{
> +	struct io_splice* sp = &req->splice;
> +	struct file *in = sp->file_in;
> +	struct file *out = sp->file_out;
> +	unsigned int flags = sp->flags;
> +	long ret;
> +
> +	if (force_nonblock) {
> +		if (io_splice_punt(in) || io_splice_punt(out)) {
> +			req->flags |= REQ_F_MUST_PUNT;
> +			return -EAGAIN;
> +		}
> +		flags |= SPLICE_F_NONBLOCK;
> +	}
> +
> +	ret = do_splice(in, sp->off_in, out, sp->off_out, sp->len, flags);
> +	if (force_nonblock && ret == -EAGAIN)
> +		return -EAGAIN;
> +
> +	io_put_file(req->ctx, out, (flags & IOSQE_SPLICE_FIXED_OUT));
> +	io_cqring_add_event(req, ret);
> +	if (ret != sp->len)
> +		req_set_fail_links(req);
> +	io_put_req_find_next(req, nxt);
> +	return 0;
> +}

This looks good. And this is why the put_file() needs to take separate
arguments...

> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 57d05cc5e271..f234b13e7ed3 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -23,8 +23,14 @@ struct io_uring_sqe {
>  		__u64	off;	/* offset into file */
>  		__u64	addr2;
>  	};
> -	__u64	addr;		/* pointer to buffer or iovecs */
> -	__u32	len;		/* buffer size or number of iovecs */
> +	union {
> +		__u64	addr;		/* pointer to buffer or iovecs */
> +		__u64	off_out;
> +	};
> +	union {
> +		__u32	len;	/* buffer size or number of iovecs */
> +		__s32	fd_out;
> +	};
>  	union {
>  		__kernel_rwf_t	rw_flags;
>  		__u32		fsync_flags;
> @@ -37,10 +43,12 @@ struct io_uring_sqe {
>  		__u32		open_flags;
>  		__u32		statx_flags;
>  		__u32		fadvise_advice;
> +		__u32		splice_flags;
>  	};
>  	__u64	user_data;	/* data to be passed back at completion time */
>  	union {
>  		__u16	buf_index;	/* index into fixed buffers, if used */
> +		__u64	splice_len;
>  		__u64	__pad2[3];
>  	};
>  };

Not a huge fan of this, also mean splice can't ever used fixed buffers.
Hmm...

> @@ -67,6 +75,9 @@ enum {
>  /* always go async */
>  #define IOSQE_ASYNC		(1U << IOSQE_ASYNC_BIT)
>  
> +/* op custom flags */
> +#define IOSQE_SPLICE_FIXED_OUT	(1U << 16)
> +

I don't think it's unreasonable to say that if you specify
IOSQE_FIXED_FILE, then both are fixed. If not, then none of them are.
What do you think?

-- 
Jens Axboe