xfs: refactor extended attribute buffer pointer functions

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

fs/xfs/scrub/attr.c

@@ -18,7 +18,7 @@
 #include "scrub/scrub.h"
 #include "scrub/common.h"
 #include "scrub/dabtree.h"
-
+#include "scrub/attr.h"
 
 /* Set us up to scrub an inode's extended attributes. */
 int
@@ -101,7 +101,7 @@ xchk_xattr_listent(
 	args.namelen = namelen;
 	args.hashval = xfs_da_hashname(args.name, args.namelen);
 	args.trans = context->tp;
-	args.value = sx->sc->buf;
+	args.value = xchk_xattr_valuebuf(sx->sc);
 	args.valuelen = XATTR_SIZE_MAX;
 
 	error = xfs_attr_get_ilocked(context->dp, &args);
@@ -160,13 +160,12 @@ xchk_xattr_check_freemap(
 	unsigned long			*map,
 	struct xfs_attr3_icleaf_hdr	*leafhdr)
 {
-	unsigned long			*freemap;
-	unsigned long			*dstmap;
+	unsigned long			*freemap = xchk_xattr_freemap(sc);
+	unsigned long			*dstmap = xchk_xattr_dstmap(sc);
 	unsigned int			mapsize = sc->mp->m_attr_geo->blksize;
 	int				i;
 
 	/* Construct bitmap of freemap contents. */
-	freemap = (unsigned long *)sc->buf + BITS_TO_LONGS(mapsize);
 	bitmap_zero(freemap, mapsize);
 	for (i = 0; i < XFS_ATTR_LEAF_MAPSIZE; i++) {
 		if (!xchk_xattr_set_map(sc, freemap,
@@ -176,7 +175,6 @@ xchk_xattr_check_freemap(
 	}
 
 	/* Look for bits that are set in freemap and are marked in use. */
-	dstmap = freemap + BITS_TO_LONGS(mapsize);
 	return bitmap_and(dstmap, freemap, map, mapsize) == 0;
 }
 
@@ -191,13 +189,13 @@ xchk_xattr_entry(
 	char				*buf_end,
 	struct xfs_attr_leafblock	*leaf,
 	struct xfs_attr3_icleaf_hdr	*leafhdr,
-	unsigned long			*usedmap,
 	struct xfs_attr_leaf_entry	*ent,
 	int				idx,
 	unsigned int			*usedbytes,
 	__u32				*last_hashval)
 {
 	struct xfs_mount		*mp = ds->state->mp;
+	unsigned long			*usedmap = xchk_xattr_usedmap(ds->sc);
 	char				*name_end;
 	struct xfs_attr_leaf_name_local	*lentry;
 	struct xfs_attr_leaf_name_remote *rentry;
@@ -257,7 +255,7 @@ xchk_xattr_block(
 	struct xfs_attr_leafblock	*leaf = bp->b_addr;
 	struct xfs_attr_leaf_entry	*ent;
 	struct xfs_attr_leaf_entry	*entries;
-	unsigned long			*usedmap = ds->sc->buf;
+	unsigned long			*usedmap = xchk_xattr_usedmap(ds->sc);
 	char				*buf_end;
 	size_t				off;
 	__u32				last_hashval = 0;
@@ -314,7 +312,7 @@ xchk_xattr_block(
 
 		/* Check the entry and nameval. */
 		xchk_xattr_entry(ds, level, buf_end, leaf, &leafhdr,
-				usedmap, ent, i, &usedbytes, &last_hashval);
+				ent, i, &usedbytes, &last_hashval);
 
 		if (ds->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
 			goto out;

fs/xfs/scrub/attr.h

+/* 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;
+
+	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__ */