Re: [PATCH 13/44] splice: stop abusing iov_iter_advance() to flush a pipe

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2022-06-22 at 05:15 +0100, Al Viro wrote:
> Use pipe_discard_from() explicitly in generic_file_read_iter(); don't bother
> with rather non-obvious use of iov_iter_advance() in there.
> 
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
>  fs/splice.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/splice.c b/fs/splice.c
> index 047b79db8eb5..6645b30ec990 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -301,11 +301,9 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
>  {
>  	struct iov_iter to;
>  	struct kiocb kiocb;
> -	unsigned int i_head;
>  	int ret;
>  
>  	iov_iter_pipe(&to, READ, pipe, len);
> -	i_head = to.head;
>  	init_sync_kiocb(&kiocb, in);
>  	kiocb.ki_pos = *ppos;
>  	ret = call_read_iter(in, &kiocb, &to);
> @@ -313,9 +311,8 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
>  		*ppos = kiocb.ki_pos;
>  		file_accessed(in);
>  	} else if (ret < 0) {
> -		to.head = i_head;
> -		to.iov_offset = 0;
> -		iov_iter_advance(&to, 0); /* to free what was emitted */
> +		/* free what was emitted */
> +		pipe_discard_from(pipe, to.start_head);
>  		/*
>  		 * callers of ->splice_read() expect -EAGAIN on
>  		 * "can't put anything in there", rather than -EFAULT.

Reviewed-by: Jeff Layton <jlayton@kernel.org>