Re: [PATCH 2/5] iomap: add per-iomap_iter private data

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, May 04, 2022 at 09:23:39AM -0700, Christoph Hellwig wrote:
> Allow the file system to keep state for all iterations.  For now only
> wire it up for direct I/O as there is an immediate need for it there.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/iomap/direct-io.c  | 8 ++++++++
>  include/linux/iomap.h | 1 +
>  2 files changed, 9 insertions(+)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 15929690d89e3..355abe2eacc6a 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -520,6 +520,14 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  	dio->submit.waiter = current;
>  	dio->submit.poll_bio = NULL;
>  
> +	/*
> +	 * Transfer the private data that was passed by the caller to the
> +	 * iomap_iter, and clear it in the iocb, as iocb->private will be
> +	 * used for polled bio completion later.
> +	 */
> +	iomi.private = iocb->private;
> +	WRITE_ONCE(iocb->private, NULL);

Do we need to transfer it back after the bio completes?  Or is it a
feature that iocb->private changes to the bio?

--D

> +
>  	if (iov_iter_rw(iter) == READ) {
>  		if (iomi.pos >= dio->i_size)
>  			goto out_free_dio;
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index a5483020dad41..109c055865f73 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -188,6 +188,7 @@ struct iomap_iter {
>  	unsigned flags;
>  	struct iomap iomap;
>  	struct iomap srcmap;
> +	void *private;
>  };
>  
>  int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops);
> -- 
> 2.30.2
>