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

[Nikolay Borisov <nborisov@suse.com>]

On 4.05.22 г. 19:23 ч., 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);

nit: Why use WRITE_ONCE here? Generaly when it's used it will suggest to 
the reader something funny is going on with accessing that variable 
without holding a particular lock?

> +
>   	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);