Re: [PATCH 3/6] xfs: refactor extended attribute buffer pointer functions

[Brian Foster <bfoster@redhat.com>]

On Wed, Jun 26, 2019 at 01:46:52PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Replace the open-coded attribute buffer pointer calculations with helper
> functions to make it more obvious what we're doing with our freeform
> memory allocation w.r.t. either storing xattr values or computing btree
> block free space.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/scrub/attr.c |   15 +++++-------
>  fs/xfs/scrub/attr.h |   65 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 72 insertions(+), 8 deletions(-)
>  create mode 100644 fs/xfs/scrub/attr.h
> 
> 
...
> diff --git a/fs/xfs/scrub/attr.h b/fs/xfs/scrub/attr.h
> new file mode 100644
> index 000000000000..88bb5e29c60c
> --- /dev/null
> +++ b/fs/xfs/scrub/attr.h
> @@ -0,0 +1,65 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * Copyright (C) 2019 Oracle.  All Rights Reserved.
> + * Author: Darrick J. Wong <darrick.wong@oracle.com>
> + */
> +#ifndef __XFS_SCRUB_ATTR_H__
> +#define __XFS_SCRUB_ATTR_H__
> +
> +/*
> + * Temporary storage for online scrub and repair of extended attributes.
> + */
> +struct xchk_xattr_buf {
> +	/*
> +	 * Memory buffer -- either used for extracting attr values while
> +	 * walking the attributes; or for computing attr block bitmaps when
> +	 * checking the attribute tree.
> +	 *
> +	 * Each bitmap contains enough bits to track every byte in an attr
> +	 * block (rounded up to the size of an unsigned long).  The attr block
> +	 * used space bitmap starts at the beginning of the buffer; the free
> +	 * space bitmap follows immediately after; and we have a third buffer
> +	 * for storing intermediate bitmap results.
> +	 */
> +	uint8_t			buf[0];
> +};
> +
> +/* A place to store attribute values. */
> +static inline uint8_t *
> +xchk_xattr_valuebuf(
> +	struct xfs_scrub	*sc)
> +{
> +	struct xchk_xattr_buf	*ab = sc->buf;
> +

I was a little confused by this at first because it seemed unnecessary
to inject the structure in this type conversion from a void pointer. I
see that the next patch adds another field, however, so this looks fine:

Reviewed-by: Brian Foster <bfoster@redhat.com>

> +	return ab->buf;
> +}
> +
> +/* A bitmap of space usage computed by walking an attr leaf block. */
> +static inline unsigned long *
> +xchk_xattr_usedmap(
> +	struct xfs_scrub	*sc)
> +{
> +	struct xchk_xattr_buf	*ab = sc->buf;
> +
> +	return (unsigned long *)ab->buf;
> +}
> +
> +/* A bitmap of free space computed by walking attr leaf block free info. */
> +static inline unsigned long *
> +xchk_xattr_freemap(
> +	struct xfs_scrub	*sc)
> +{
> +	return xchk_xattr_usedmap(sc) +
> +			BITS_TO_LONGS(sc->mp->m_attr_geo->blksize);
> +}
> +
> +/* A bitmap used to hold temporary results. */
> +static inline unsigned long *
> +xchk_xattr_dstmap(
> +	struct xfs_scrub	*sc)
> +{
> +	return xchk_xattr_freemap(sc) +
> +			BITS_TO_LONGS(sc->mp->m_attr_geo->blksize);
> +}
> +
> +#endif	/* __XFS_SCRUB_ATTR_H__ */
>