Re: [PATCH v7 4/5] iomap: Add a page_prepare callback

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

On Tue, Apr 30, 2019 at 12:09:33AM +0200, Andreas Gruenbacher wrote:
> Move the page_done callback into a separate iomap_page_ops structure and
> add a page_prepare calback to be called before the next page is written
> to.  In gfs2, we'll want to start a transaction in page_prepare and end
> it in page_done.  Other filesystems that implement data journaling will
> require the same kind of mechanism.
> 
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Jan Kara <jack@suse.cz>

Looks fine, assuming you've done the appropriate QA/testing on the gfs2
side. :)

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/gfs2/bmap.c        | 15 ++++++++++-----
>  fs/iomap.c            | 36 ++++++++++++++++++++++++++----------
>  include/linux/iomap.h | 22 +++++++++++++++++-----
>  3 files changed, 53 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
> index 5da4ca9041c0..aa014725f84a 100644
> --- a/fs/gfs2/bmap.c
> +++ b/fs/gfs2/bmap.c
> @@ -991,15 +991,20 @@ static void gfs2_write_unlock(struct inode *inode)
>  	gfs2_glock_dq_uninit(&ip->i_gh);
>  }
>  
> -static void gfs2_iomap_journaled_page_done(struct inode *inode, loff_t pos,
> -				unsigned copied, struct page *page,
> -				struct iomap *iomap)
> +static void gfs2_iomap_page_done(struct inode *inode, loff_t pos,
> +				 unsigned copied, struct page *page,
> +				 struct iomap *iomap)
>  {
>  	struct gfs2_inode *ip = GFS2_I(inode);
>  
> -	gfs2_page_add_databufs(ip, page, offset_in_page(pos), copied);
> +	if (page)
> +		gfs2_page_add_databufs(ip, page, offset_in_page(pos), copied);
>  }
>  
> +static const struct iomap_page_ops gfs2_iomap_page_ops = {
> +	.page_done = gfs2_iomap_page_done,
> +};
> +
>  static int gfs2_iomap_begin_write(struct inode *inode, loff_t pos,
>  				  loff_t length, unsigned flags,
>  				  struct iomap *iomap,
> @@ -1077,7 +1082,7 @@ static int gfs2_iomap_begin_write(struct inode *inode, loff_t pos,
>  		}
>  	}
>  	if (!gfs2_is_stuffed(ip) && gfs2_is_jdata(ip))
> -		iomap->page_done = gfs2_iomap_journaled_page_done;
> +		iomap->page_ops = &gfs2_iomap_page_ops;
>  	return 0;
>  
>  out_trans_end:
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 62e3461704ce..a3ffc83134ee 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -665,6 +665,7 @@ static int
>  iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
>  		struct page **pagep, struct iomap *iomap)
>  {
> +	const struct iomap_page_ops *page_ops = iomap->page_ops;
>  	pgoff_t index = pos >> PAGE_SHIFT;
>  	struct page *page;
>  	int status = 0;
> @@ -674,9 +675,17 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
>  	if (fatal_signal_pending(current))
>  		return -EINTR;
>  
> +	if (page_ops && page_ops->page_prepare) {
> +		status = page_ops->page_prepare(inode, pos, len, iomap);
> +		if (status)
> +			return status;
> +	}
> +
>  	page = grab_cache_page_write_begin(inode->i_mapping, index, flags);
> -	if (!page)
> -		return -ENOMEM;
> +	if (!page) {
> +		status = -ENOMEM;
> +		goto out_no_page;
> +	}
>  
>  	if (iomap->type == IOMAP_INLINE)
>  		iomap_read_inline_data(inode, page, iomap);
> @@ -684,15 +693,21 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
>  		status = __block_write_begin_int(page, pos, len, NULL, iomap);
>  	else
>  		status = __iomap_write_begin(inode, pos, len, page, iomap);
> -	if (unlikely(status)) {
> -		unlock_page(page);
> -		put_page(page);
> -		page = NULL;
>  
> -		iomap_write_failed(inode, pos, len);
> -	}
> +	if (unlikely(status))
> +		goto out_unlock;
>  
>  	*pagep = page;
> +	return 0;
> +
> +out_unlock:
> +	unlock_page(page);
> +	put_page(page);
> +	iomap_write_failed(inode, pos, len);
> +
> +out_no_page:
> +	if (page_ops && page_ops->page_done)
> +		page_ops->page_done(inode, pos, 0, NULL, iomap);
>  	return status;
>  }
>  
> @@ -766,6 +781,7 @@ static int
>  iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
>  		unsigned copied, struct page *page, struct iomap *iomap)
>  {
> +	const struct iomap_page_ops *page_ops = iomap->page_ops;
>  	int ret;
>  
>  	if (iomap->type == IOMAP_INLINE) {
> @@ -778,8 +794,8 @@ iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
>  	}
>  
>  	__generic_write_end(inode, pos, ret, page);
> -	if (iomap->page_done)
> -		iomap->page_done(inode, pos, copied, page, iomap);
> +	if (page_ops && page_ops->page_done)
> +		page_ops->page_done(inode, pos, copied, page, iomap);
>  	put_page(page);
>  
>  	if (ret < len)
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 0fefb5455bda..2103b94cb1bf 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -53,6 +53,8 @@ struct vm_fault;
>   */
>  #define IOMAP_NULL_ADDR -1ULL	/* addr is not valid */
>  
> +struct iomap_page_ops;
> +
>  struct iomap {
>  	u64			addr; /* disk offset of mapping, bytes */
>  	loff_t			offset;	/* file offset of mapping, bytes */
> @@ -63,12 +65,22 @@ struct iomap {
>  	struct dax_device	*dax_dev; /* dax_dev for dax operations */
>  	void			*inline_data;
>  	void			*private; /* filesystem private */
> +	const struct iomap_page_ops *page_ops;
> +};
>  
> -	/*
> -	 * Called when finished processing a page in the mapping returned in
> -	 * this iomap.  At least for now this is only supported in the buffered
> -	 * write path.
> -	 */
> +/*
> + * When a filesystem sets page_ops in an iomap mapping it returns, page_prepare
> + * and page_done will be called for each page written to.  This only applies to
> + * buffered writes as unbuffered writes will not typically have pages
> + * associated with them.
> + *
> + * When page_prepare succeeds, page_done will always be called to do any
> + * cleanup work necessary.  In that page_done call, @page will be NULL if the
> + * associated page could not be obtained.
> + */
> +struct iomap_page_ops {
> +	int (*page_prepare)(struct inode *inode, loff_t pos, unsigned len,
> +			struct iomap *iomap);
>  	void (*page_done)(struct inode *inode, loff_t pos, unsigned copied,
>  			struct page *page, struct iomap *iomap);
>  };
> -- 
> 2.20.1
>