Re: [PATCH 10/13] iomap: use a function pointer for dio submits

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Aug 02, 2019 at 05:00:45PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> This helps filesystems to perform tasks on the bio while
> submitting for I/O. Since btrfs requires the position
> we are working on, pass pos to iomap_dio_submit_bio()

What /does/ btrfs_submit_direct do, anyway?  Looks like it's a custom
submission function that ... does something related to setting
checksums?  And, uh, RAID?

> The correct place for submit_io() is not page_ops. Would it
> better to rename the structure to something like iomap_io_ops
> or put it directly under struct iomap?

Seeing as the ->iomap_begin handler knows if the requested op is a
buffered write or a direct write, what if we just declare a union of
ops?

e.g.

struct iomap_page_ops;
struct iomap_directio_ops;

struct iomap {
	<usual stuff>
	union {
		const struct iomap_page_ops *page_ops;
		const struct iomap_directio_ops *directio_ops;
	};
};

--D

> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> ---
>  fs/iomap/direct-io.c  | 16 +++++++++++-----
>  include/linux/iomap.h |  1 +
>  2 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 5279029c7a3c..a802e66bf11f 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -59,7 +59,7 @@ int iomap_dio_iopoll(struct kiocb *kiocb, bool spin)
>  EXPORT_SYMBOL_GPL(iomap_dio_iopoll);
>  
>  static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
> -		struct bio *bio)
> +		struct bio *bio, loff_t pos)
>  {
>  	atomic_inc(&dio->ref);
>  
> @@ -67,7 +67,13 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
>  		bio_set_polled(bio, dio->iocb);
>  
>  	dio->submit.last_queue = bdev_get_queue(iomap->bdev);
> -	dio->submit.cookie = submit_bio(bio);
> +	if (iomap->page_ops && iomap->page_ops->submit_io) {
> +		iomap->page_ops->submit_io(bio, file_inode(dio->iocb->ki_filp),
> +				pos);
> +		dio->submit.cookie = BLK_QC_T_NONE;
> +	} else {
> +		dio->submit.cookie = submit_bio(bio);
> +	}
>  }
>  
>  static ssize_t iomap_dio_complete(struct iomap_dio *dio)
> @@ -195,7 +201,7 @@ iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
>  	get_page(page);
>  	__bio_add_page(bio, page, len, 0);
>  	bio_set_op_attrs(bio, REQ_OP_WRITE, flags);
> -	iomap_dio_submit_bio(dio, iomap, bio);
> +	iomap_dio_submit_bio(dio, iomap, bio, pos);
>  }
>  
>  static loff_t
> @@ -301,11 +307,11 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>  		iov_iter_advance(dio->submit.iter, n);
>  
>  		dio->size += n;
> -		pos += n;
>  		copied += n;
>  
>  		nr_pages = iov_iter_npages(&iter, BIO_MAX_PAGES);
> -		iomap_dio_submit_bio(dio, iomap, bio);
> +		iomap_dio_submit_bio(dio, iomap, bio, pos);
> +		pos += n;
>  	} while (nr_pages);
>  
>  	/*
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 5b2055e8ca8a..6617e4b6fb6d 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -92,6 +92,7 @@ struct iomap_page_ops {
>  			struct iomap *iomap);
>  	void (*page_done)(struct inode *inode, loff_t pos, unsigned copied,
>  			struct page *page, struct iomap *iomap);
> +	dio_submit_t 		*submit_io;
>  };
>  
>  /*
> -- 
> 2.16.4
>