Re: [PATCH v2 3/6] iomap: modify ->end_io() calling convention

[Matthew Bobrowski <mbobrowski@mbobrowski.org>]

+ CC: linux-xfs@vger.kernel.org

On Mon, Sep 09, 2019 at 09:19:31AM +1000, Matthew Bobrowski wrote:
> This patch modifies the calling convention for the iomap ->end_io()
> callback. Rather than passing either dio->error or dio->size as the
> 'size' argument, we instead pass both dio->error and dio->size values
> separately.
> 
> In the instance that an error occurred during a write, we currently
> cannot determine whether any blocks have been allocated beyond the
> current EOF and data has subsequently been written to these blocks
> within the ->end_io() callback. As a result, we cannot judge whether
> we should take the truncate failed write path. Having both dio->error
> and dio->size will allow us to perform such checks within this
> callback.
> 
> Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>

Please note, this patch is now part of the recent end_io improvements
posted through by Christoph, and can be found here:
https://git.kernel.org/pub/scm/fs/xfs/xfs-linux.git/commit/?h=iomap-5.4-merge&id=db10bd824bc0353702231f1294b58903cb66bac7.

> ---
>  fs/iomap/direct-io.c  | 9 +++------
>  fs/xfs/xfs_file.c     | 8 +++++---
>  include/linux/iomap.h | 4 ++--
>  3 files changed, 10 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 10517cea9682..2ccf1c6460d4 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -77,13 +77,10 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
>  	loff_t offset = iocb->ki_pos;
>  	ssize_t ret;
>  
> -	if (dio->end_io) {
> -		ret = dio->end_io(iocb,
> -				dio->error ? dio->error : dio->size,
> -				dio->flags);
> -	} else {
> +	if (dio->end_io)
> +		ret = dio->end_io(iocb, dio->size, dio->error, dio->flags);
> +	else
>  		ret = dio->error;
> -	}
>  
>  	if (likely(!ret)) {
>  		ret = dio->size;
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 28101bbc0b78..d49759008c54 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -369,21 +369,23 @@ static int
>  xfs_dio_write_end_io(
>  	struct kiocb		*iocb,
>  	ssize_t			size,
> +	int                     error,
>  	unsigned		flags)
>  {
>  	struct inode		*inode = file_inode(iocb->ki_filp);
>  	struct xfs_inode	*ip = XFS_I(inode);
>  	loff_t			offset = iocb->ki_pos;
>  	unsigned int		nofs_flag;
> -	int			error = 0;
>  
>  	trace_xfs_end_io_direct_write(ip, offset, size);
>  
>  	if (XFS_FORCED_SHUTDOWN(ip->i_mount))
>  		return -EIO;
>  
> -	if (size <= 0)
> -		return size;
> +	if (error)
> +		return error;
> +	if (!size)
> +		return 0;
>  
>  	/*
>  	 * Capture amount written on completion as we can't reliably account
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index bc499ceae392..d983cdcf2e72 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -188,8 +188,8 @@ sector_t iomap_bmap(struct address_space *mapping, sector_t bno,
>   */
>  #define IOMAP_DIO_UNWRITTEN	(1 << 0)	/* covers unwritten extent(s) */
>  #define IOMAP_DIO_COW		(1 << 1)	/* covers COW extent(s) */
> -typedef int (iomap_dio_end_io_t)(struct kiocb *iocb, ssize_t ret,
> -		unsigned flags);
> +typedef int (iomap_dio_end_io_t)(struct kiocb *iocb, ssize_t size,
> +				 int error, unsigned int flags);
>  ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  		const struct iomap_ops *ops, iomap_dio_end_io_t end_io);
>  int iomap_dio_iopoll(struct kiocb *kiocb, bool spin);
> -- 
> 2.20.1
>